Category Archives: Physics

The Next Phase in the Hunt for New Superheavy Elements is About to Start

Background

On 24 January 2016, I posted the article, “Where in the Periodic Table Will We Put Element 119?”, which reviews the development of the modern periodic table of chemical elements since it was first formulated in 1869 by Russian chemist Dimitri Mendeleev, through the completion of Period 7 with the naming element 118 in 2016.  You can read this post here:

https://lynceans.org/all-posts/where-in-the-periodic-table-will-we-put-element-119/

2019 is the 150thanniversary of Dimitri Mendeleev’s periodic table of elements.  To commemorate this anniversary, the United Nations General Assembly and the United Nations Educational, Scientific and Cultural organization (UNESCO) have proclaimed 2019 as the International Year of the Periodic Table of Chemical Elements (IYPT). You’ll find more information on the IYPT here:

https://www.iypt2019.org

A brief animated “visualization” entitled “Setting the Table,”created by J. Yeston, N. Desai and E. Wang, provides a good overview of the history and configuration of the periodic table.  Check it out here:

http://vis.sciencemag.org/periodic-table/

The prospects for extending the periodic table beyond element 118 (into a new Period 8) is discussed in a short 2018 video from Science Magazine entitled “Where does the periodic table end?,”which you can view here:

https://www.sciencemag.org/news/2019/02/where-does-periodic-table-end?utm_campaign=news_weekly_2019-02-01&et_rid=215579562&et_cid=2632608

The next phase in the hunt for new superheavy elements is about to start in Russia 

Flerov Laboratory of Nuclear Reactions (FLNR) Joint Institute for Nuclear Research (JINR) in Dubna is the leading laboratory in Russia, and perhaps the world, in the search for superheavy elements.  The FLNR website is here:

http://flerovlab.jinr.ru/flnr/she_factory_no.html

FLNR is the home of several accelerators and other experimental setups for nuclear research, including the U400 accelerator, which has been the laboratory’s basic tool for the synthesis of new elements since being placed in operation in 1979.  You can take a virtual tour of U400 on the FLNR website.  

On 30 May 2012 the International Union of Pure and Applied Chemistry (IUPAC) honored the work done by FLNR when it approved the name Flerovium (Fl) for superheavy element 114.

Yuri Oganessian, the Scientific Leader of FLNR, has contributed greatly to extending the periodic table through the synthesis of new superheavy elements.  On 30 November 2016, IUPAC recognized his personal contributions by naming superheavy element 118 after him:  Oganesson (Og). 

Yuri Oganessian.  Source:  MAX AGUILERA HELLWEG / WWW.SCIENCEMAG.ORG
2017 Armenian postage stamp honoring Yuri Oganessian.  Source: FLNR JINR

FLNR has built a new $60 million accelerator facility, dubbed the Superheavy Element Factory (SHEF), which is expected to be capable of synthesizing elements beyond 118.  The SHEF building and the DC-280 cyclotron that will be used to synthesize superheavy elements are shown in the photos below.

The SHEF building, 14 Nov 2016. Source:  FLNR JINR
The completed DC-280 cyclotron, 26 December 2018.  Source:  FLNR JINR

The 2016 paper, “Status and perspectives of the Dubna superheavy element factory,”by S. Dmitriev, M. Itkis and Y. Oganessian, presents an overview of the DC-280 cyclotron design, including the following diagram showing the general arrangement of the major components.

Arrangement of the major components of the DC-280 cyclotron.  

You can read this 2016 paper here:

http://inspirehep.net/record/1502737/files/epjconf-NS160-08001.pdf

For insights into the processes for synthesizing superheavy elements, I recommend that you view the following March 2018 video in which FLNR Director Sergey Dmitriev describes the design of SHEF and the planned process of synthesizing superheavy elements 119 and 120.  This is a rather long (23 min) video, but I think it will be worth your time.

On 26 December 2018, the DC-280 cyclotron produced its first beam of accelerated heavy ions.  The hunt for new superheavy elements using DC-280 is scheduled to begin in the spring of 2019.

A good overview of FLNR, as it prepares to put its Superheavy Element Factory into operation, is available in the article by Sam Kean, entitled “A storied Russian lab is trying to push the periodic table past its limits—and uncover exotic new elements,” which was posted on 30 January 2019 on the Science Magazine website. You’ll find this article at the following link:

https://www.sciencemag.org/news/2019/01/storied-russian-lab-trying-push-periodic-table-past-its-limits-and-uncover-exotic-new?utm_campaign=news_weekly_2019-02-01&et_rid=215579562&et_cid=2632608

The next few years may yield exciting new discoveries of the first members of Period 8 of the periodic table.  I think Dimitri Mendeleev would be impressed.

Additional reading:

75th Anniversary of the Kurchatov Institute

The I. V. Kurchatov Institute of Atomic Energy in Moscow was founded 75 years ago, in 1943, and is named for its founder, Soviet nuclear physicist Igor Vasilyevich Kurchatov.  Until 1955, the Institute was a secret organization known only as “Laboratory No. 2 of the USSR Academy of Sciences.”  The initial focus of the Institute was the development of nuclear weapons.

Kurchatov Institute 75thanniversary on Russian commemorative postage stamp. https://en.wikipedia.org/

I. V. Kurchatov and the team of scientists and engineers at the Institute led or supported many important historical Soviet nuclear milestones, including: 

  • 25 December 1946: USSR’s F-1 (Physics-1) reactor achieved initial criticality at Kurchatov Institute.  This was the 1st reactor built and operated outside the US.
  • 10 June 1948: USSR’s 1st plutonium production reactor achieved initial criticality (Unit A at Chelyabinak-65). The reactor was designed under the leadership of N. A. Dollezhal.
  • 29 August 1949: USSR’s 1st nuclear device, First Lightning [aka RDS-1, Izdeliye 501 (device 501) and Joe 1], was detonated at the Semipalatinsk test site in what is now Kazakhstan.  This was the 1st nuclear test other than by the US.
  • 27 June 1954: World’s 1st nuclear power plant, AM-1 (aka APS-1), was commissioned and connected to the electrical grid, delivering power in Obninsk.  AM-1 was designed under the leadership of N. A. Dollezhal.
  • 22 November 1955: USSR’s 1st thermonuclear device (RDS-37, a two-stage device) was detonated at the Semipalatinsk test site.  This also was the world’s 1stair-dropped thermonuclear device.
  • 5 December 1957: USSR’s 1st nuclear-powered icebreaker, Lenin, was launched.  This also was the world’s 1st nuclear-powered surface ship.
  • 4 July 1958: USSR’s 1st  nuclear-powered submarine, Project 627 SSN K-3, Leninskiy Komsomol, made its 1st underway on nuclear power.
  • 1958: World’s 1st Tokamak, T-1, initial operation at Kurchatov Institute.
I. V. Kurchatov and F-1 reactor on Russian commemorative postage stamp. Source:  Wikimedia Commons

I. V. Kurchatov served as the Institute’s director until his death in 1960 and was awarded Hero of Socialist Labor three times and Order of Lenin five times during his lifetime.

After I. V. Kurchatov’s death in 1960, the noted academician Anatoly P. Aleksandrov was appointed as the director of the Institute and continued in that role until 1989.  Aleksandrov already had a key role at the Institute, having been appointed by Stalin in September 1952 as the scientific supervisor for developing the USSR’s first nuclear-powered submarine and its nuclear power unit.

A. P. Aleksandrov and OK-150 reactor on Russian commemorative postage stamp. Source:  Wikimedia Commons

Until 1991, the Soviet Ministry of Atomic Energy oversaw the administration of Kurchatov Institute.  After the formation of the Russian Federation at the end of 1991, the Institute became a State Scientific Center reporting directly to the Russian Government.  Today, the President of Kurchatov Institute is appointed by the Russian Prime Minister, based on recommendations from Rosatom (the Russian State Energy Corporation), which was formed in 2007.

You’ll find a comprehensive history of Kurchatov Institute in a 2013 (70thanniversary) special issue of the Russian version of Scientific American magazine, which you can download here:

 https://sciam.ru/download_issues/7/47.pdf

The evolution of Kurchatov Institute capabilities from its initial roles on the Soviet nuclear weapons program is shown in the following diagram.

Source: Special issue 2013, www.scientificrussia.ru

Modern roles for Kurchatov Institute are shown in the following graphic.

Source: Special issue 2013, www.scientificrussia.ru

In the past 75 years, the Kurchatov Institute has performed many major roles in the Soviet / Russian nuclear industry and, with a national security focus, continues to be a driving force in that industry sector.

Now, lets take a look at a few of the pioneering nuclear projects led or supported by Kurchatov Institute:

  • F-1 (Physics-1) reactor
  • Plutonium production reactors
  • Obninsk nuclear power plant AM-1
  • T-1 Tokamak

F-1 (Physics-1) reactor

The F-1 reactor designed by the Kurchatov Institute was a graphite-moderated, air-cooled, natural uranium fueled reactor with a spherical core about 19 feet (5.8 meters) in diameter. F-1 was the first reactor to be built and operated outside of the US.  It was a bit more compact than the first US reactor, the Chicago Pile, CP-1, which had an ellipsoidal core with a maximum diameter of about 24.2 feet (7.4 meters) and a height of 19 feet (5.8 meters).

The F-1 achieved initial criticality on 25 December 1946 and initially was operated at a power level of 10 watts.  Later, F-1 was able to operate at a maximum power level of 24 kW to support a wide range of research activities. In a 2006 report on the reactor’s 60thanniversary by RT News (www.rt.com), Oleg Vorontsov, Deputy Chief of the Nuclear Security Department reported, “Layers of lead as they are heated by uranium literally make F1 a self-controlling nuclear reactor. And the process inside is called – the safe-developing chain reaction of uranium depletion. If the temperature rises to 70 degrees Celsius (158° Fahrenheit), it slows down by its own! So it simply won’t let itself get out of control.” 

F-1 was never refueled prior to its permanent shutdown in November 2016, after 70 years of operation.

Top of the F-1 reactor core. Source: http://nuclearweaponarchive.org/
F-1 reactor facility cross-section diagram.  The F-1 reactor is the igloo-shaped structure located in the open pit.  Source: http://nuclearweaponarchive.org/
Graphite stacks of the F-1 reactor.  Source: Kurchatov Institute

Plutonium production reactors

The first generation of Soviet plutonium production reactors were graphite-moderated, natural uranium fueled reactors designed under the leadership of N.A. Dollezhal while he was at the Institute of Chemical Machinery in Moscow.  The Kurchatov Institute had a support role in the development of these reactors.The five early production reactors at Chelyabinsk-65 (later known as the Mayak Production Association) operated with a once-through primary cooling water system that discharged into open water ponds.

Simplified cross-section of a Russian graphite-moderated, water-cooled plutonium production reactor.  Source: PNL-9982

Four of the five later graphite-moderated production reactors at Tomsk had closed primary cooling systems that enabled them to also generate electric power and provide district heating (hot water) for the surrounding region.  You’ll find a good synopsis of the Soviet plutonium production reactors in the 2011 paper by Anatoli Diakov, “The History of Plutonium Production in Russia,” here:  

http://scienceandglobalsecurity.org/archive/sgs19diakov.pdf

Additional details on the design of the production reactors is contained in the 1994 Pacific Northwest Laboratory report PNL-9982, “Summary of Near-term Options for Russian Plutonium Production Reactors,” by Newman, Gesh, Love and Harms.  This report is available on the OSTI website here:   

https://www.osti.gov/servlets/purl/10173950

Obninsk nuclear power plant AM-1 (Atom Mirny or “Peaceful Atom”)

AM-1 nuclear power plant exterior view.  Source:  tass.ru
Panoramic view of the AM-1 power plant control room.  Source: www.chistoprudov.ru via https://reactor.space/news_en/

Obninsk was the site of the world’s first nuclear power plant (NPP).  This NPP had a single graphite-moderated, water-cooled reactor fueled with low-enriched uranium fuel. The reactor had a maximum power rating of 30 MWt.  AM-1 was designed by N.A. Dollezhal and the Research and Development Institute of Power Engineering (RDIPE / NIKIET) in Moscow, as an evolution of an earlier Dollezhal design of a small graphite-moderated reactor for ship propulsion.  The Kurchatov Institute had a support role in the development of AM-1.

The basic AM-1 reactor layout is shown in the following diagram.

Source: Directory of Nuclear Reactors, Vol. IV, Power Reactors, International Atomic Energy Agency, 1962

The closed-loop primary cooling system delivered heat via steam generators to the secondary-side steam system, which drove a steam turbine generator that delivered 5 MWe (net) to the external power grid.   Following is a basic process flow diagram for the reactor cooling loops.

Source: Directory of Nuclear Reactors, Vol. IV, Power Reactors, International Atomic Energy Agency, 1962

Construction on AM-1 broke ground on 31 December 1950 at the Physics and Power Engineering Institute (PEI) in Obninsk, about 110 km southwest of Moscow.  Other early milestone dates were:

  • Initial criticality:  5 May 1954
  • Commissioning and first grid connection:  26 June 1954
  • Commercial operation:  30 November 1954

In addition to its power generation role, AM-1 had 17 test loops installed in the reactor to support a variety of experimental studies. After 48 years of operation, AM-1 was permanently shutdown on 28 April 2002.

You can read more details on AM-1 in the following two articles: “Obninsk: Number One,” by Lev Kotchetkov on the Nuclear Engineering International website here:

 https://www.neimagazine.com/features/featureobninsk-number-one

“Anniversary at Obninsk: The First Commercial Nuclear Power Plant,” by Will Davis on the ANS Nuclear Café website here:

 http://ansnuclearcafe.org/2015/06/24/anniversary-at-obninsk-the-first-commercial-nuclear-power-plant/#sthash.4wTrQueH.vhtfLcPK.dpbs

The AM-1 nuclear power plant design was developed further by NIKIET into the much larger scale RBMK (Reaktor Bolshoy Moshchnosti Kanalnyy, “High Power Channel-type Reactor”) NPPs.  The four reactors at the Chernobyl NPP were RBMK-1000 reactors.

The T-1 Tokamak

Research on plasma confinement is a toroidal magnetic field began in Russia in 1951, leading to the construction of the first experimental toroidal magnetic confinement system, known as a tokamak, at Kurchatov Institute. T-1 began operation in 1958.  

T-1 Tokamak.  Source: https://www.iter.org/sci/BeyondITER

Early operation of T-1 and successive models revealed many problems that limited the plasma confinement capabilities of tokamaks.  Solving these problems led to a better understanding of plasma physics and significant improvements in the design of tokamak machines.  You’ll find a historical overview of early Soviet / Russian work on Tokamaks in a 2010 IAEA paper by V. P. Smirnov, ”Tokamak Foundation in USSR/Russia 1950–1990,” which you can read here:

 https://fire.pppl.gov/nf_50th_5_Smirnov.pdf

The basic tokamak design for magnetic plasma confinement has been widely implemented in many international fusion research machines, winning out over other magnetic confinement concepts, including the Stellarator machine championed in the US by Dr. Lyman Spitzer (see my 30 August 2017 post on Stellarators).  Major international tokamak projects include the Joint European Torus (JET) at the Culham Center for Fusion Energy in Oxfordshire, UK, the Tokamak Fusion Test Reactor (TFTR) at Princeton Plasma Physics Laboratory in the US, the JT-60 at the Japan Atomic Energy Agency’s Naka Fusion Institute, and most recently the International Thermonuclear Experimental Reactor (ITER) being built now at the Saclay Nuclear Center in southern France.


2018 Nobel Prize in Physics

On 2 October 2018, the Royal Swedish Academy of Sciences announced the winners of the 2018 Nobel Prize in Physics. Arthur Ashkin (US) shares this Nobel Prize with Gérard Mourou (France) and Donna Strickland (Canada) for their “groundbreaking inventions in the field of laser physics.”

Arthur Ashkin’s award was “for the optical tweezers and their application to biological systems.” This is a technique developed by Ashkin in the late 1960s (first published in 1970) using laser beam(s) to create a force trap that can be used to physically hold and move microscopic objects (from atoms and molecules to living cells).  The technique now is widely used in studying a variety of biological systems, with applications such as cell sorting and bio-molecular assay.

You’ll find a detailed briefing entitled, “Optical Tweezers – Working Principles and Applications,” here:

http://www.phys.sinica.edu.tw/TIGP-NANO/Course/2008_Fall/classnote/NBP_Optical%20Tweezers_Wen-Tau%20Juan.pdf

Arthur Ashkin. Source: laserfest.org

Arthur Ashkin is a researcher at Bell Laboratories in New Jersey.  At 96, he the oldest person to be awarded a Nobel Prize.

The award to Mourou and Strickland was “for their method of generating high-intensity, ultra-short optical pulses.” They developed a technique in the mid-1980s called “chirped pulse amplification” (CPA) that is used to produce very short duration laser pulses of very high intensity.  CPA is applied today in laser micromachining, surgery, medicine, and in fundamental science studies.

You’ll find a brief tutorial entitled, “Chirped-Pulse Amplification Ultrahigh peak power production from compact short-pulse laser systems,” here:

https://pdfs.semanticscholar.org/1c96/a800faaa341d9719a6ca3fbb7ccff9ff9419.pdf

  Gérard Mourou. Source: American Physical Society (APS).  Donna Strickland. Source: University of Waterloo

Gérard Mourou is the director of the Laboratoire d’Optique Appliquee at the ENSTA ParisTech (École nationale supérieure de techniques avancées).  He was Donna Strickland’s PhD advisor.

Donna Strickland is an associate professor in the Physics and Astronomy Department of the University of Waterloo, Canada (about 90 km west of Toronto).  She is the first female Physics laureate in 55 years. The preceding female Physics laureates were:

  • In 1963, Maria Goeppert-Mayer was recognized for her work on the structure of atomic nuclei (shared with J. Hans D. Jensen and Eugene Wigner).
  • In 1903, Marie Curie was recognized for her pioneering work on nuclear radiation phemomena (shared with Pierre Curie and Henri Becquerel).

You can read the press release from the Royal Swedish Academy of Sciences for the 2018 Nobel Prize in Physics here:

https://www.nobelprize.org/uploads/2018/10/press-physics2018.pdf

Congratulations to the 2018 Nobel Physics laureates!

Return of the Stellarator

Background

Dr. Lyman Spitzer invented the stellarator in 1951 and built several versions of this magnetic plasma confinement machine at Princeton University during the 1950s and 1960s, establishing the world famous Princeton Plasma Physics Laboratory (PPPL) in the process. Dr. Spitzer’s earliest Stellarators were figure-eight devices as shown in the following photo.

Example of an early stellarator at the 1958 Atoms for Peace Conference, Geneva

In these first-generation stellarators, field coils wrapped around the figure-eight vacuum vessel provided the basic plasma confinement field. The physical twist in the stellarator’s structure twisted the internal magnetic confinement field and cancelled the effects of plasma ion drift during each full circuit around the device. You can download Dr. Spitzer’s historic 1958 IAEA conference paper, “The Stellarator Concept,” at the following link:

http://www-naweb.iaea.org/napc/physics/2ndgenconf/data/Proceedings%201958/papers%20Vol32/Paper23_Vol32.pdf

The next generation of stellarators adopted a simpler torus shape and created the twist in the magnetic confinement field with helical field coils outside the vacuum vessel.

While stellarators achieved many important milestones in magnetic confinement, by the late 1960s, the attention of the fusion community was shifting toward a different type of magnetic confinement machine: the tokamak. Since then, this basic design concept has been employed in many of the world’s major fusion devices, including the Alcator-C Mod (MIT, USA), Doublet III-D (DIII-D at General Atomics, USA), Tokamak Fusion Test Reactor (TFTR at PPPL, USA), Joint European Torus (JET, UK), National Spherical Torus Experiment Upgrade (NSTX-U at PPPL, USA) and the International Thermonuclear Experimental Reactor (ITER, France).

Now, almost 50 years later, there is significant renewed interest in stellarators. The newest device, the Wendelstein 7-X stellarator, became operational in 2016. It may help determine if modern technology has succeeded in making the stellarator a more promising path to fusion power than the tokamak.

Comparison of Tokamaks and Stellarators

Modern tokamaks and stellarators both implement plasma confinement within a (more or less) toroidal vacuum vessel that operates at very high vacuum conditions, on the order of 10-7 torr. Both types of machines use the combined effects of two or more magnetic fields to create and control helical field lines (HFL) that enable plasma confinement and reduce particle drift in the circulating plasma.

In the following description, the simple “classical” tokamak configuration shown below will be the point of reference.

Source: Hans-Jürgen Hartfuß, Thomas Geist, “Fusion Plasma Diagnostics With mm-Waves: An Introduction”

The main features of a tokamak are summarized below.

  • The vacuum vessel in a modern tokamak typically is an azimuthally-symmetric torus of revolution (donut-shaped), typically with a vertically elongated, D-shaped cross section. Modern “spherical” tokomaks maintain the D-shaped cross section, but minimize the diameter of the hole in the center of the torus.
  • Plasma confinement within the vacuum vessel is accomplished by the combined effects of a toroidal magnetic field and an induced poloidal magnetic field. Together, these fields create the helical field lines for plasma confinement. In the following diagram, the toroidal field is represented by the blue arrow and the poloidal field is represented by the red arrow.

By Dave Burke – Own work, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=1169843

  • The toroidal field (blue) is generated by a set of external toroidal field coils (TFCs) that surround the vacuum vessel.
  • The poloidal field (red) is generated by a strong induced plasma current (Iplasma), on the order of 106 amperes, flowing within the plasma inside the vacuum vessel. An external coil in the center of the tokamak serves as the primary coil of a transformer and the circulating plasma serves as the secondary coil of the transformer. To create the poloidal field, the transformer primary coil is charged at a controlled rate (i.e. to yield the desired rate of flux increase), thereby inducing a current in the plasma and heating the plasma by ohmic heating. When the primary coil reaches maximum flux, current is no longer induced in the plasma and the tokamak “pulse” is over.
  • A pair of vertical field coils (VFC), one above and one below the plane of the torus, provide the ability to radially position the plasma within the vacuum vessel.
  • Divertors inside the vacuum vessel define the maximum extent of the magnetically confined plasma, remove impurities from the edge of the plasma, and help minimize plasma-wall interactions.
  • The high current in the plasma can falter unexpectedly, resulting in a “disruption”, which is a sudden losses of plasma confinement that can unleash magnetic forces powerful enough to damage the machine.
  • A tokamak is mechanically simpler than a stellarator.
  • The physics characteristics of a tokamak typically yield better confinement capabilities than a stellarator.
  • While the “pulse” in a modern tokamak can last several tens of minutes, a pulsed mode of operation may not be suitable for a commercial fusion reactor.
  • Pulsed magnetic and thermal loads create mechanical fatigue issues that must be accommodated in the design of tokamak structures.

The simple “classical” stellarator configuration shown below will be the point of reference for the following discussion.

Source: Hans-Jürgen Hartfuß, Thomas Geist, “Fusion Plasma Diagnostics With mm-Waves: An Introduction”

The main features of a stellarator are summarized below.

  • There are many variants of devices called stellarators, with names such as Torsatron, Heliotron, Heliac, and Helias. All create the plasma confinement field with external magnet systems in various configurations and none depend on the existence of a toroidal plasma current.
  • In the classical stellarator in the above diagram, the plasma confinement field is created by a set of planar (flat) TFCs and external pairs (1, 2 or 3) of twisting helical field coils (HFC) with opposite currents in each conductor in the pair.
  • A stellarator is mechanically more complex and more difficult to manufacture than a tokamak.
  • Stellarators may use a divertor or a simpler “limiter” to define the outer extent of the plasma.
  • While a stellarator has no induced plasma current, other small currents, known as “pressure-driven” or “bootstrap” currents, exist. These small currents do not cause plasma disruptions as may occur in a tokamak, but complicate plasma confinement.
  • A stellarator is intrinsically capable of steady-state operation.
  • For a variety of reasons, a classical stellarator tends to lose energy at a higher rate than a tokamak. Advanced, modular stellarators are making progress in improving confinement performance.

You’ll find more comparative information in the July 2016 paper by Y. XU, “A general comparison between tokamak and stellarator plasmas,” which is available at the following link:

http://ac.els-cdn.com/S2468080X16300322/1-s2.0-S2468080X16300322-main.pdf?_tid=7d9ff748-c680-11e6-9909-00000aacb35d&acdnat=1482216764_912e05c8d6b4957207a2e7ae31c30f03

Modern stellarators

In the last two decades, dramatic improvements in computer power and 3-dimensional modeling capabilities have enabled researchers and designers to accurately model a stellarator’s complex magnetic fields, plasma behavior, and mechanical components (i.e., vacuum vessel, magnet systems and other structures). This has enabled implementation of a “plasma first” design process in which the initial design focus is on optimizing plasma equilibrium based on selected physics conditions. Key goals of this optimization process are to define plasma equilibrium conditions that reduce heat transport and particle loss from the plasma. As you might suspect, there are different technical bases for approaching the plasma optimization process. The stellarator’s magnet systems are designed to produce the confinement field needed for the specified, optimized plasma design.

This class of modern, optimized stellarators is characterized by complex, twisting plasma shapes and non-planar, modular toroidal coils that are individually designed, built and assembled. The net result is a stellarator with significantly better confinement performance that earlier stellarator designs. In this post, we’ll look in more detail at the following three advanced stellarators:

  • Wendelstein 7-AS [Max Planck Institute for Plasma Physics (IPP), Garching, Germany]
  • Helically Symmetric eXperiment (HSX, University of Wisconsin – Madison, USA)
  • Wendelstein 7-X [Max Planck Institute for Plasma Physics (IPP), Griefswald, Germany]

 Wendelstein 7-AS Stellarator (1988 – 2002)

The Wendelstein 7-AS was the first modular, advanced stellarator and was the first stellarator equipped with a divertor. It was used to test and validate basic elements of stellarator optimization.  Basic physical parameters of 7-AS are:

  • Major radius 2 m
  • Minor radius 0.2 m
  • Magnetic field 2.5 – 3 T

The physical layout and scale of the 7-AS machine is shown in the first diagram, below, with more details on the magnet system in the following diagram.

Above & below: Wendelstein 7-AS. Source: Max Planck IPP, I. Weber

The 7-AS operated from 1988 to 2002.   The IPP reported the following results:

  • Demonstrated that the innovative modular magnet coil system can be manufactured to exacting specifications.
  • Demonstrated improved plasma equilibrium and transport behavior because of the improved magnetic field structure.
  • Confirmed the effectiveness of the optimization criteria.
  • Demonstrated the effectiveness of a divertor on a stellarator (a common feature in tokamaks).

You’ll find more details on the 7-AS on the IPP website at the following link:

http://www.ipp.mpg.de/2665443/w7as?page=1

Its successor is the Wendelstein 7-X.

Helically Symmetric eXperiment (HSX)

HSX is a small modular coil advanced stellarator that began operation in 1999 at the Electrical and Computer Engineering Department at the University of Wisconsin-Madison. HSX basic design parameters are:

  • Major radius 1.2 m
  • Minor radius 0.15 m
  • Magnetic field 1T

The physical arrangement of HSX is shown in the following diagram.

HSX physical configuration. Source: University of Wisconsin – Madison

The HSX was the first stellarator to be optimized to deliver a “quasi-symmetric” magnetic field. While the magnetic field strength is usually a two-dimensional function on the magnetic surfaces traced out by the field lines, quasi-symmetry is achieved by making it one-dimensional in so-called “magnetic coordinates” (Boozer coordinates).

Author Masayuki Yokoyama’s paper, “Quasi-symmetry Concepts in Helical Systems,” provides a description of quasi-symmetry.

“A key point of quasi-symmetry is that the drift trajectories of charged particles depend on the absolute value of the magnetic field (B) expressed in terms of magnetic field coordinates (Boozer coordinates). The plasma can be optimized in terms of the Boozer coordinates instead of the vector components of the field.”

You can read Yokoyama’s complete paper at the following link:

https://www.jstage.jst.go.jp/article/jspf/78/3/78_3_205/_pdf

The HSX main magnetic field is generated by a set of 48 non-planar, modular coils, arranged in four field periods, yielding the twisting flux shape shown below.


HSX plasma configuration. Source: University of Wisconsin – Madison

The HSX team reported that “this is the first demonstration that quasi-symmetry works, and you can actually measure the reduction in transport that you get.”

The home page for this project is at the following link:

http://www.hsx.wisc.edu

You can download a description of the HSX here:

http://www.hsx.wisc.edu/wp-uploads/2016/04/A-helically-symmetric-stellarator-HSX_Almagri_Anderson-DT_Anderson-FSB_Probert_Shohet_Talmadge_1999.pdf

 Wendelstein 7-X Stellarator

The Wendelstein 7-X is a Helias (helical advanced stellarator) and is the first large-scale optimized stellarator; significantly larger than Wendelstein 7-S and HSX. The complete 7-X machine weighs about 750 tons, with about 425 tons operating under cryogenic conditions. The superconducting magnet system is designed for steady-state, high-power operation; nominally 30 minutes of plasma operation at 10 MW power. 7-X basic design parameters are:

  • Major radius 5.5m
  • Minor radius 0.52m
  • Magnetic field 2.5 T (up to 3T)

The IPP home page for this project is here:

http://www.ipp.mpg.de/w7x

The 7-X is drift optimized for improved thermal and fast ion confinement by: (a) implementing quasi-symmetry to reduce transport losses, (b) minimizing plasma currents (Pfirsch-Schluter & bootstrap currents) to improve equilibrium, and (c) designing a large magnetic well in the plasma cross-section to avoid plasma pressure instabilities.

The primary purpose of the Wendelstein 7-X is to investigate the new stellarator’s suitability for extrapolation to a fusion power plant design. The IPP website provides the following clarification:

“It is expected that plasma equilibrium and confinement will be of a quality comparable to that of a tokamak of the same size. But it will avoid the disadvantages of a large current flowing in a tokamak plasma: With plasma discharges lasting up to 30 minutes, Wendelstein 7-X is to demonstrate the essential stellarator property, viz. continuous operation.”

The main assembly of Wendelstein 7-X was completed in 2014. An IPP presentation on the manufacturing and assembly of 7-X is at the following link:

https://www.iter.org/doc/www/content/com/Lists/Stories/Attachments/680/ITER_W7X.pdf

You’ll also find a good video, “Wendelstein 7-X — from concept to reality,” which provides an overview of the design and construction of the 7-X stellarator and the associated research facility, at the following link:

https://www.youtube.com/watch?v=lyqt6u5_sHA

After engineering tests, the first plasma was produced at 7-X on 10 December 2015. A November 2016 article in Nature summarized on the results of initial operation of 7-X.  The article, entitled, “Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000,” confirmed that the 7-X is producing the intended confinement field. This article includes the following 3-D rendering and description of the complex magnetic coil sets that establish the twisting plasma confinement fields in the 7-X.

“Some representative nested magnetic surfaces are shown in different colors in this computer-aided design (CAD) rendering, together with a magnetic field line that lies on the green surface. The coil sets that create the magnetic surfaces are also shown, planar coils in brown, non-planar coils in grey. Some coils are left out of the rendering, allowing for a view of the nested surfaces (left) and a Poincaré section of the shown surfaces (right). Four out of the five external trim coils are shown in yellow. The fifth coil, which is not shown, would appear at the front of the rendering.”

You can read the complete article at the following link:

http://www.nature.com/articles/ncomms13493

A more detailed mechanical view of the 7-X, with a scale (gold) human figure is shown in the following diagram:

Source: IPP presentation, “Stellarators difficult to build? The construction of Wendelstein 7-X”

The large scale of the 7-X vacuum vessel is even more apparent in the following photo.

Source: adapted from IPP by C. Bickel and A. Cuadra/Science

Current status is outlined in a February 2017 presentation by the 7-X team to the Fusion Energy Science Advisory Committee (FESAC), entitled “Recent results and near-term plans for Wendelstein 7-X,” which is available at the following link:

http://www.firefusionpower.org/FESAC_W7-X_Pedersen_02.2017.pdf

Conclusion

So the jury is still out on the ability of advanced stellarators to take the lead over tokamaks in the long, hard journey toward the goal of delivering usable power from a fusion machine. Hopefully, the advanced stellarators will move the fusion community closer to that goal.  No doubt, we still have a very long way to go before fusion power becomes a reality.

For more background information on stellarators:

A summary of Dr. Spitzer’s pioneering work at PPPL is documented in a presentation entitled, “Spitzer’s Pioneering Fusion Work and the Search for Improved Confinement,” which you can download at the following link:

http://w3.pppl.gov/~hammett/refs/2013/Spitzer_100th_Hammett_2013.pdf

There is a good briefing on the basics of stellarator design and operation in the following two documents:

Dudson, B., “Stellarators,” University of York, UK, 6 February 2014 at the following link:

http://www-users.york.ac.uk/~bd512/teaching/media/mcf_lecture_06.pdf

Beidler, C.D., et al., “Stellarator Fusion Reactors – an Overview”, Max-Planck Institute for Plasma Physics, 2001, at the following link:

http://fire.pppl.gov/itc12_wobig_paper.pdf

 

 

 

Preliminary Design of an Experimental World-Circling Spaceship

The title of this post also is the title of the first RAND report, SM-11827, which was issued on 5 May 1946 when Project RAND still was part of the Douglas Aircraft Company. The basic concept for an oxygen-alcohol fueled multi-stage world-circling spaceship is shown below.

Source: RAND

Source: RAND

Now, more than 70 years later, it’s very interesting to read this report to gain an appreciation of the state of the art of rocketry in the U.S. in 1946, which already was benefiting from German experience with the V-2 and other rocket programs during WW II.

RAND offers the following abstract for SM-11827:

“More than eleven years before the orbiting of Sputnik, history’s first artificial space satellite, Project RAND — then active within Douglas Aircraft Company’s Engineering Division — released its first report: Preliminary Design of an Experimental World-Circling Spaceship (SM-11827), May 2, 1946. Interest in the feasibility of space satellites had surfaced somewhat earlier in a Navy proposal for an interservice space program (March 1946). Major General Curtis E. LeMay, then Deputy Chief of the Air Staff for Research and Development, considered space operations to be an extension of air operations. He tasked Project RAND to undertake a feasibility study of its own with a three-week deadline. The resulting report arrived two days before a critical review of the subject with the Navy. The central argument turns on the feasibility of such a space vehicle from an engineering standpoint, but alongside the curves and tabulations are visionary statements, such as that by Louis Ridenour on the significance of satellites to man’s store of knowledge, and that of Francis Clauser on the possibility of man in space. But the most riveting observation, one that deserves an honored place in the Central Premonitions Registry, was made by one of the contributors, Jimmy Lipp (head of Project RAND’s Missile Division), in a follow-on paper nine months later: ‘Since mastery of the elements is a reliable index of material progress, the nation which first makes significant achievements in space travel will be acknowledged as the world leader in both military and scientific techniques. To visualize the impact on the world, one can imagine the consternation and admiration that would be felt here if the United States were to discover suddenly that some other nation had already put up a successful satellite.’”

You can buy the book from several on-line sellers or directly from RAND. However you also can download the complete report for free in three pdf files that you’ll find on the RAND website at the following link:

https://www.rand.org/pubs/special_memoranda/SM11827.html

 

 

First Ever Antimatter Spectroscopy in ALPHA-2

ALPHA-2 is a device at the European particle physics laboratory at CERN, in Meyrin, Switzerland used for collecting and analyzing antimatter, or more specifically, antihydrogen.  A common hydrogen atom is composed of an electron and proton.  In contrast, an  antihydrogen atom is made up of a positron bound to an antiproton.

Screen Shot 2016-12-22 at 4.19.01 PMSource: CERN

The ALPHA-2 project homepage is at the following link:

http://alpha.web.cern.ch

On 16 December 2016, the ALPHA-2 team reported the first ever optical spectroscopic observation of the 1S-2S (ground state – 1st excited state) transition of antihydrogen that had been trapped and excited by a laser.

“This is the first time a spectral line has been observed in antimatter. ……..This first result implies that the 1S-2S transition in hydrogen and antihydrogen are not too different, and the next steps are to measure the transition’s lineshape and increase the precision of the measurement.”

In the ALPHA-2 online news article, “Observation of the 1S-2S Transition in Trapped Antihydrogen Published in Nature,” you will find two short videos explaining how this experiment was conducted:

  • Antihydrogen formation and 1S-2S excitation in ALPHA
  • ALPHA first ever optical spectroscopy of a pure anti atom

These videos describe the process for creating antihydrogen within a magnetic trap (octupole & mirror coils) containing positrons and antiprotons. Selected screenshots from the first video are reproduced below to illustrate the process of creating and exciting antihydrogen and measuring the results.

Alpha2 mirror trap

The potentials along the trap are manipulated to allow the initially separated positron and antiproton populations to combine, interact and form antihydrogen.

Combining positron & antiproton 1Combining positron & antiproton 2Combining positron & antiproton 3

If the magnetic trap is turned off, the antihydrogen atoms will drift into the inner wall of the device and immediately be annihilated, releasing pions that are detected by the “annihilation detectors” surrounding the magnetic trap. This 3-layer detector provides a means for counting antihydrogen atoms.

Detecting antihydrogen

A tuned laser is used to excite the antihydrogen atoms in the magnetic trap from the 1S (ground) state to the 2S (first excited) state. The interaction of the laser with the antihydrogen atoms is determined by counting the number of free antiprotons annihilating after photo ionization (an excited antihydrogen atom loses its positron) and counting all remaining antihydrogen atoms. Two cases were investigated: (1) laser tuned for resonance of the 1S-2S transition, and (2) laser detuned, not at resonance frequency. The observed differences between these two cases confirmed that, “the on-resonance laser light is interacting with the antihydrogen atoms via their 1S-2S transition.”

Exciting antihydrogen

The ALPHA-2 team reported that the accuracy of the current antihydrogen measurement of the 1S-2S transition is about “a few parts in 10 billion” (1010). In comparison, this transition in common hydrogen has been measured to an accuracy of “a few parts in a thousand trillion” (1015).

For more information, see the 19 December 2016 article by Adrian Cho, “Deep probe of antimatter puts Einstein’s special relativity to the test,” which is posted on the Sciencemag.org website at the following link:

http://www.sciencemag.org/news/2016/12/deep-probe-antimatter-puts-einstein-s-special-relativity-test?utm_campaign=news_daily_2016-12-19&et_rid=215579562&et_cid=1062570

 

 

Emergent Gravity Theory Passes its First Test

In 2010, Prof. Erik Verlinde, University of Amsterdam, Delta Institute for Theoretical Physics, published the paper, “The Origin of Gravity and the Laws of Newton.” In this paper, the author concluded:

 “The results of this paper suggest gravity arises as an entropic force, once space and time themselves have emerged. If the gravity and space time can indeed be explained as emergent phenomena, this should have important implications for many areas in which gravity plays a central role. It would be especially interesting to investigate the consequences for cosmology. For instance, the way redshifts arise from entropy gradients could lead to many new insights.

The derivation of the Einstein equations presented in this paper is analogous to previous works, in particular [the 1995 paper by T. Jacobson, ‘Thermodynamics of space-time: The Einstein equation of state.’]. Also other authors have proposed that gravity has an entropic or thermodynamic origin, see for instance [the paper by T. Padmanabhan, ‘Thermodynamical Aspects of Gravity: New insights.’]. But we have added an important element that is new. Instead of only focusing on the equations that govern the gravitational field, we uncovered what is the origin of force and inertia in a context in which space is emerging. We identified a cause, a mechanism, for gravity. It is driven by differences in entropy, in whatever way defined, and a consequence of the statistical averaged random dynamics at the microscopic level. The reason why gravity has to keep track of energies as well as entropy differences is now clear. It has to, because this is what causes motion!”

You can download Prof. Verlinde’s 2010 paper at the following link:

https://arxiv.org/pdf/1001.0785.pdf

On 8 November 2016, Delta Institute announced that Prof. Verlinde had published a new research paper, “Emergent Gravity and the Dark Universe,” expanding on his previous work. You can read this announcement and see a short video by Prof. Verlinde on the Delta Institute website at the following link:

http://www.d-itp.nl/news/list/list/content/folder/press-releases/2016/11/new-theory-of-gravity-might-explain-dark-matter.html

You can download this new paper at the following link:

https://arxiv.org/abs/1611.02269

I found it helpful to start with Section 8, Discussion and Outlook, which is the closest you will find to a layman’s description of the theory.

On the Physics.org website, a short 8 November 2016 article, “New Theory of Gravity Might Explain Dark Matter,” provides a good synopsis of Verlinde’s emergent gravity theory:

“According to Verlinde, gravity is not a fundamental force of nature, but an emergent phenomenon. In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in the very structure of spacetime……

According to Erik Verlinde, there is no need to add a mysterious dark matter particle to the theory……Verlinde shows how his theory of gravity accurately predicts the velocities by which the stars rotate around the center of the Milky Way, as well as the motion of stars inside other galaxies.

One of the ingredients in Verlinde’s theory is an adaptation of the holographic principle, introduced by his tutor Gerard ‘t Hooft (Nobel Prize 1999, Utrecht University) and Leonard Susskind (Stanford University). According to the holographic principle, all the information in the entire universe can be described on a giant imaginary sphere around it. Verlinde now shows that this idea is not quite correct—part of the information in our universe is contained in space itself.

This extra information is required to describe that other dark component of the universe: Dark energy, which is believed to be responsible for the accelerated expansion of the universe. Investigating the effects of this additional information on ordinary matter, Verlinde comes to a stunning conclusion. Whereas ordinary gravity can be encoded using the information on the imaginary sphere around the universe, as he showed in his 2010 work, the result of the additional information in the bulk of space is a force that nicely matches that attributed to dark matter.”

Read the full Physics.org article at the following link:

http://phys.org/news/2016-11-theory-gravity-dark.html#jCp

On 12 December 2016, a team from Leiden Observatory in The Netherlands reported favorable results of the first test of the emergent gravity theory. Their paper, “First Test of Verlinde’s Theory of Emergent Gravity Using Weak Gravitational Lensing Measurements,” was published in the Monthly Notices of the Royal Astronomical Society. The complete paper is available at the following link:

http://mnras.oxfordjournals.org/content/early/2016/12/09/mnras.stw3192

An example of a gravitational lens is shown in the following diagram.

Gravitational-lensing-galaxyApril12_2010-1024x768-e1481555047928 Source: NASA, ESA & L. Calça

As seen from the Earth, the light from the galaxy at the left is bent by the gravitational forces of the galactic cluster in the center, much like light passing though an optical lens.

The Leiden Observatory authors reported:

“We find that the prediction from EG, despite requiring no free parameters, is in good agreement with the observed galaxy-galaxy lensing profiles in four different stellar mass bins. Although this performance is remarkable, this study is only a first step. Further advancements on both the theoretical framework and observational tests of EG are needed before it can be considered a fully developed and solidly tested theory.”

These are exciting times! As noted in the Physics.org article, “We might be standing on the brink of a new scientific revolution that will radically change our views on the very nature of space, time and gravity.”

New Testable Theory on the Flow of Time and the Meaning of Now

Richard A. Muller, a professor of physics at the University of California, Berkeley, and Facility Senior Scientist at Lawrence Berkeley Laboratory, is the author of in intriguing new book entitled, “NOW, the Physics of Time.”

NOW cover page  Source: W. W. Norton & Company

In Now, Muller addresses weaknesses in past theories about the flow of time and the meaning of “now.” He also presents his own revolutionary theory, one that makes testable predictions. He begins by describing the physics building blocks of his theory: relativity, entropy, entanglement, antimatter, and the Big Bang. Muller points out that the standard Big Bang theory explains the ongoing expansion of the universe as the continuous creation of new space. He argues that time is also expanding and that the leading edge of the new time is what we experience as “now.”

You’ll find a better explanation in the UC Berkeley short video, “Why does time advance?: Richard Muller’s new theory,” at the following link:

https://www.youtube.com/watch?v=FYxUzm7gQkY

In the video, Muller explains that his theory would have resulted in a measurable 1 millisecond delay in “chirp” seen in the first gravitational wave signals detected on 11 February 2016 by the Laser Interferometer Gravitational-Wave Observatory (LIGO). LIGO’s current sensitivity precluded seeing the predicted small delay. If LIGO and other and-based gravity wave detector sensitivities are not adequate, a potentially more sensitive space-based gravity wave detection array, eLISA, should be in place in the 2020s to test Muller’s theory.

It’ll be interesting to see if LIGO, any of the other land-based gravity wave detectors, or eLISA will have the needed sensitivity to prove or disprove Muller’s theory.

For more information related to gravity wave detection, see my following posts:

  • 16 December 2015 post, “100th Anniversary of Einstein’s General Theory of Relativity and the Advent of a New Generation of Gravity Wave Detectors ”
  • 11 February 2016 post, “NSF and LIGO Team Announce First Detection of Gravitational Waves”
  • 27 September 2016, “Space-based Gravity Wave Detection System to be Deployed by ESA”

The Universe is Isotropic

The concepts of up and down appear to be relatively local conventions that can be applied at the levels of subatomic particles, planets and galaxies. However, the universe as a whole apparently does not have a preferred direction that would allow the concepts of up and down to be applied at such a grand scale.

A 7 September 2016 article entitled, “It’s official: You’re lost in a directionless universe,” by Adrian Cho, provides an overview of research that demonstrates, with a high level of confidence, that the universe is isotropic. The research was based on data from the Planck space observatory. In this article, Cho notes:

“Now, one team of cosmologists has used the oldest radiation there is, the afterglow of the big bang, or the cosmic microwave background (CMB), to show that the universe is “isotropic,” or the same no matter which way you look: There is no spin axis or any other special direction in space. In fact, they estimate that there is only a one-in-121,000 chance of a preferred direction—the best evidence yet for an isotropic universe. That finding should provide some comfort for cosmologists, whose standard model of the evolution of the universe rests on an assumption of such uniformity.”

The European Space Agency (ESA) developed the Planck space observatory to map the CMB in microwave and infrared frequencies at unprecedented levels of detail. Planck was launched on 14 May 2009 and was placed in a Lissajous orbit around the L2 Lagrange point, which is 1,500,000 km (930,000 miles) directly behind the Earth. L2 is a quiet place, with the Earth shielding Planck from noise from the Sun. The approximate geometry of the Earth-Moon-Sun system and a representative spacecraft trajectory (not Planck, specifically) to the L2 Lagrange point is shown in the following figure.

Lissajous orbit L2Source: Abestrobi / Wikimedia Commons

The Planck space observatory entered service on 3 July 2009. At the end of its service life, Planck departed its valuable position at L2, was placed in a heliocentric orbit, and was deactivated on 23 October 2013. During more than four years in service, Planck performed its CBM mapping mission with much greater resolution than NASA’s Wilkinson Microwave Anisotropy Probe, which operated from 2001 to 2010.

One key result of the Planck mission is the all-sky survey shown below.

Planck_CMB_black_background_fullwidthPlanck all-sky survey. Source; ESA / Planck Collaboration

ESA characterizes this map as follows:

“The CMB is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just 380,000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today.”

The researchers who reported that the universe was isotropic noted that an anisotropic universe would leave telltale patterns in the CMB. However, these researchers found that the actual CMB shows only random noise and no signs of such patterns.

You’ll find more details on the Planck mission and scientific results on the ESA’s website at the following link:

http://www.esa.int/Our_Activities/Space_Science/Planck

You can read Adrian Cho’s article on the Science magazine website at the following link:

http://www.sciencemag.org/news/2016/09/it-s-official-you-re-lost-directionless-universe?utm_source=howtogeek&utm_medium=email&utm_campaign=newsletter

The original research paper, “How Isotropic is the Universe?” by Saadeh, D., et al., was published on 21 September 2016. It is available on the Physical Review Letters website, if you have a subscription, at the following link:

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.117.131302

 

 

Space-based Gravity Wave Detection System to be Deployed by ESA

The first detection of gravitational waves occurred on 14 September 2015 at the land-based Laser Interferometer Gravitational-Wave Observatory (LIGO). Using optical folding techniques, LIGO has an effective baseline of 1,600 km (994 miles). See my 16 December 2015 and 11 February 2016 posts for more information on LIGO and other land-based gravitational wave detectors.

Significantly longer baselines, and theoretically greater sensitivity can be achieved with gravitational wave detectors in space. Generically, such a space-based detector has become known as a Laser Interferometer Space Antenna (LISA). Three projects associated with space-based gravitational wave detection are:

  • LISA (the project name predated the current generic usage of LISA)
  • LISA Pathfinder (a space-based gravitational wave detection technology demonstrator, not a detector)
  • Evolved LISA (eLISA)

These projects are discussed below.

The science being addressed by space-based gravitational wave detectors is discussed in the eLISA white paper, “The Gravitational Universe.” You can download this whitepaper, a 1-page summary, and related gravitational wave science material at the following link:

https://www.elisascience.org/whitepaper/

LISA

The LISA project originally was planned as a joint European Space Agency (ESA) and National Aeronautics & Space Administration (NASA) project to detect gravitational waves using a very long baseline, triangular interferometric array of three spacecraft.

Each spacecraft was to contain a gravitational wave detector sensitive at frequencies between 0.03 mHz and 0.1 Hz and have the capability to precisely measure its distances to the other two spacecraft forming the array. The equilateral triangular array, which was to measure about 5 million km (3.1 million miles) on a side, was expected to be capable of measuring gravitational-wave induced strains in space-time by precisely measuring changes of the separation distance between pairs of test masses in the three spacecraft. In 2011, NASA dropped out of this project because of funding constraints.

LISA Pathfinder

The LISA Pathfinder (LPF) is a single spacecraft intended to validate key technologies for space-based gravitational wave detection. It does not have the capability to detect gravity waves.

This mission was launched by ESA on 3 December 2015 and the spacecraft took station in a Lissajous orbit around the Sun-Earth L1 Lagrange point on 22 January 2016. L1 is directly between the Earth and the Sun, about 1.5 million km (932,000 miles) from Earth. An important characteristic of a Lissajous orbit is that the spacecraft will follow the L1 point without requiring any propulsion. This is important for minimizing external forces on the LISA Pathfinder experiment package. The approximate geometry of the Earth-Moon-Sun system and a representative spacecraft (not LPF, specifically) stationed at the L1 Lagrange point is shown in the following figure.

L1 Lagrange pointSource: Wikimedia Commons

The LISA Pathfinder’s mission is to validate the technologies used to shield two free-floating metal cubes (test masses), which form the core of the experiment package, from all internal and external forces that could contribute to noise in the gravitational wave measurement instruments. The on-board measurement instruments (inertial sensors and a laser interferometer) are designed to measure the relative position and orientation of the test masses, which are 38 cm (15 inches) apart, to an accuracy of less than 0.01 nanometers (10e-11 meters). This measurement accuracy is believed to be adequate for detecting gravitational waves using this technology on ESA’s follow-on mission, eLISA.

The first diagram below is an artist’s impression of the LISA Pathfinder technology package, showing the inertial sensors housing the test masses (gold) and the laser interferometer (middle platform). The second diagram provides a clearer view of the test masses and the laser interferometer.

LPF technology package 1

Source: ESA/ATG medialab, August 2015LPF technology package 2Source: ESA LISA Pathfinder briefing, 7 June 2016

You’ll find more general information in an ESA LISA Pathfinder overview, which you can download from NASA’s LISA website at the following link:

http://lisa.nasa.gov/Documentation/LISA-LPF-RP-0001_v1.1.pdf

LISA Pathfinder was commissioned and ready for scientific work on 1 March 2016. In a 7 June 2016 briefing, ESA reported very favorable performance results from LISA Pathfinder:

  • LPF successfully validated the technologies used in the local (in-spacecraft) instrument package (test masses, inertial sensors and interferometer).
  • LPF interferometer noise was a factor of 100 less than on the ground.
  • The measurement instruments can see femtometer motion of the test masses (LPF goal was picometer).
  • Performance is essentially at the level needed for the follow-on eLISA mission

You can watch this full (1+ hour) ESA briefing at the following link:

http://www.esa.int/Our_Activities/Space_Science/Watch_LISA_Pathfinder_briefing

eLISA

Evolved LISA, or eLISA, is ESA’s modern incarnation of the original LISA program described previously. ESA’s eLISA website home page is at the following link:

https://www.elisascience.org

As shown in the following diagrams, three eLISA spacecraft will form a very long baseline interferometric array that is expected to directly observe gravitational waves from sources anywhere in the universe. In essence, this array will be a low frequency microphone listening for the sounds of gravitational waves as they pass through the array.

eLISA constellation 1Source: ESAeLISA constellation 2Source: ESA

As discussed previously, gravity wave detection depends on the ability to very precisely measure the distance between test masses that are isolated from their environment but subject to the influence of passing gravitational waves. Measuring the relative motion of a pair of test masses is considerably more complex for eLISA than it was for LPF. The relative motion measurements needed for a single leg of the eLISA triangular array are:

  • Test mass 1 to Spacecraft 1
  • Spacecraft 1 to Spacecraft 2
  • Spacecraft 2 to Test Mass 2

This needs to be done for each of the three legs of the array.

LPF validated the technology for making the test mass to spacecraft measurement. Significant development work remains to be done on the spacecraft-to-spacecraft laser system that must take precise measurements at very long distances (5 million km, 3.1 million miles) of the relative motion between each pair of spacecraft.

In the 6 June 2016 LISA Pathfinder briefing, LPF and ESA officials indicated that an eLisa launch date is expected in the 2029 – 2032 time frame. Then it reaches its assigned position in a trailing heliocentric orbit, eLISA will be a remarkable collaborative technical achievement and a new window to our universe.