News and Events


U.S. Burning Plasma Organization eNews
November 30, 2014 (Issue 90)

 

USBPO Mission Statement: Advance the scientific understanding of burning plasmas and ensure the greatest benefit from a burning plasma experiment by coordinating relevant U.S. fusion research with broad community participation.

 

CONTENTS

Announcements  
Director’s Corner
C.M. Greenfield
Research Highlight
T.G. Jenkins and D.N. Smithe
3D Modeling of RF Antennas, Sheaths, and Slow Waves in Time Domain
ITPA Update
Schedule of Burning Plasma Events
Image of the Month
Fusion on Film
Contact and Contribution Information

Announcements

Job Posting: Associate Research Physicist (Postdoc)

The Princeton Plasma Physics Laboratory (PPPL) seeks to fill a research physicist position at the DIII-D National Facility in San Diego. The successful candidate will be required to spend significant time (~4 months total a year) on-site at the EAST tokamak facility in Hefei, China, with the remainder of the time in San Diego at the DIII-D National Fusion Facility. This will be part of a coordinated effort on these two devices aimed at optimizing long pulse steady-state performance, particularly exploiting high bootstrap driven current as a means of sustaining the plasma current. Since a large part of the bootstrap current originates from the pedestal, the work will necessarily focus on validating and improving pedestal and bootstrap current models. As such, an important responsibility will be integrating existing pedestal models within the TRANSP transport analysis code, and assembling tools to prepare the necessary kinetic profiles and other inputs needed for TRANSP for EAST. The successful candidate will then be expected to exploit these capabilities to optimize pedestal performance in steady-state solutions. This will include time-dependent analysis of heat, momentum and particles of both existing steady-state scenario plasmas, as well as promising future directions such as the exploitation of a recently discovered path to achieving very high pedestal pressures in the so-called Super H-mode regime.

Applicants should have a strong experimental background, familiarity with running sophisticated modeling codes, and possess a Ph.D. in plasma physics or a similar field.

Interested applicants should submit letters of recommendation to Dr. Wayne Solomon at wsolomon@pppl.gov.

Apply online at jobs.princeton.edu, Requisition number: 1400701


Director’s Corner

by C.M. Greenfield

ITER News

The Fifteenth meeting of the ITER Council was held at ITER Headquarters this month. The highlight of the meeting was the Council’s nomination of Bernard Bigot as the next Director General of ITER. Bigot, currently the chairman of the French Alternative Energies and Atomic Energy Commission, CEA, has a long history of leadership positions within the French scientific community, and has been the “High Commissioner for the implementation of the ITER Project in France” since 2006. He is expected to assume his new duties in 2015 following formalization of the appointment in accordance with the ITER Agreement. We look forward to continuing to work closely with the ITER Organization under Mr. Bigot’s leadership. The Council also took note of developments at the ITER site since their last meeting in June. During that time, the B2 slab (that will support the tokamak complex) was completed, and the next step in construction, pouring of the walls, was begun.

USBPO News

During the recent APS–DPP Conference, the US Burning Plasma Organization organized the annual contributed Research in Support of ITER session. As usual, the session was very well attended, with about 150 people in the audience. Those of you who expressed disappointment at the lack of an evening ITER Town Meeting should be pleased to know that we plan to organize both a contributed oral session and the Town Meeting at next year’s conference in Savannah, Georgia.

Jon Menard (PPPL) has been serving as Chair of the USBPO Council since summer, 2012, with a term that was scheduled to end this past summer. He graciously agreed to continue his term through APS to allow Vice Chair Mark Koepke (WVU) to complete his responsibilities for the recent FESAC Strategic Planning Panel and as APS–DPP Chair. At a recent USBPO Council meeting Mark Koepke assumed the chairmanship, with Chuck Kessel (PPPL) taking over as Vice Chair. I would like to thank Jon, Mark, and Chuck for their willingness to take on these responsibilities.

Both the Disruptions (chaired by Val Izzo and Bob Granetz) and ITER Modes of Participation (chaired by Rajesh Maingi) Task Groups remain quite active. The Disruption TG web page on the BPO web site has been significantly expanded and updated, and records of Task Group meetings are now available on the Forum. Group members were active in the 2014 National Campaign, and in a Theory workshop held at PPPL. The work of the Maingi TG is nearing completion. A draft report was completed, posted, presented as a web seminar and was discussed at a recent Council meeting.

With all of the meetings held during the last quarter of the calendar year it is difficult to find time for web seminars. However, as we exit the “meeting season” we are planning on several upcoming seminars. Please watch your email for news on these.

Happy Holidays

On behalf of the entire leadership of the US Burning Plasma Organization, I would like to wish you and your families a happy holiday season.


Research Highlight

Plasma-wave Interactions Topical Group, Leaders: D. Green and R. Pinsker

Coupling radio-frequency (RF) power in the ion-cyclotron range of frequencies to tokamak plasmas is complicated by the parasitic loss of power in the plasma edge, as well as the production of impurities resulting from the RF driven sheath voltages on plasma facing components. The work highlighted here shows the first simulations where the 3D geometry of the launching antenna is captured, the RF rectified sheath potential is resolved, and the possibility of slow-wave generation at the antenna is included. Ultimately, such simulations will help improve our ability to reliably couple RF power on ITER.

3D Modeling of RF Antennas, Sheaths, and Slow Waves in Time Domain

T.G. Jenkins and D.N. Smithe
Tech-X Corporation, 5621 Arapahoe Avenue, Boulder, CO 80303, USA

Plasma sheaths play important roles in magnetic fusion experiments, especially in the delivery of radio-frequency (RF) power. As RF antennas heat the plasma in fusion experiments, rectified sheath formation on antenna surfaces can result in large sheath potentials. Ions accelerating through the sheath may then strike antenna surfaces with sufficient energy to sputter high-Z impurities back toward the reactor core, contaminating the fusion reaction and giving rise to radiative cooling [1]. The sheath dynamics also open up parasitic-loss channels into which antenna-delivered power may be deposited in the edge plasma, rather than in the core as desired. Realistic numerical modeling of sheath formation and evolution in fusion experiments can augment experimental understanding of these harmful effects, and can aid in the development of impurity-mitigation strategies. Such modeling efforts are, however, challenged by the non-linear dependence of the rectified sheath potential on the local electric field strength and power, and the fast timescales and small spatial scales (micrometers) of the sheath relative to the temporal and spatial scales of plasma waves launched by the RF antennas. The nontrivial geometry of antenna structures on which sheaths form also introduces three-dimensional complexity, with surfaces ranging from fully normal to fully parallel to the magnetic field.

Finite-difference time-domain (FDTD) simulation tools offer unique capability for modeling of RF antennas in fusion experiments. They are based on advanced cut-cell techniques [2] which enable detailed, accurate representations of experimental antenna hardware on the computational grid. Time-centered, locally implicit models for plasma current evolution [3] then capture plasma dispersion effects arising from antenna operation (e.g. wave propagation, cutoffs, resonances, and mode conversion), and allow these behaviors to be modeled on timescales long relative to the electron gyro-period and plasma frequency. In addition, a newly developed method for incorporating the physics of the RF-rectified sheath [4] into macroscopic boundary conditions [5] now permits self-consistent, nonlinear computations of the evolving sheath potential (without the need to resolve sheath space and time scales) on the antenna surfaces. Implementations of the FDTD and sheath algorithms [6] have also been shown to scale well up to hundreds of thousands of processors on Titan, the Cray XK7 supercomputer at Oak Ridge National Laboratory. Collectively, these capabilities enable us to carry out realistic 3D simulations of antenna operation and sheath formation in existing experiments.

We have performed simulations on a quarter of the ITER ion cyclotron range of frequency (ICRF) antenna, including RF sheath potential, and can model the effect of the magnetic field alignment relative to the antenna components (in particular, the lack of sheath formation when surfaces are aligned). Figure 1 shows positive and negative contours of RF sheath potential superposed atop the antenna structure, in cases of aligned fields (Btoroidal only — left) and unaligned fields (Btoroidal and Bpoloidal — right). Sheath potential formation at the antenna surface is much more prominent on the Faraday shields in the unaligned case on the right, and circulation patterns of high and low sheath potentials also form around the outer antenna housing (the negative-potential green region at the right of the right plot moves clockwise around the antenna housing, together with positive-potential regions not visible in the plot; the full animation is available at http://youtu.be/sYLJw3NDS9s. Higher sputtering yields are expected when antennas and fields are misaligned, due to the increase in overall antenna surface area with these high sheath potentials.

Figure 1 (left) Figure 1 (right)

Figure 1: Sheath potential contours on a quarter-portion of the ITER ICRF antenna during zero-phase operation. In the left plot, the background magnetic fields are aligned with the Faraday shields of the antenna. When these fields are not aligned, as in the right plot, the overall surface area of antenna components on which sheaths form is considerably increased, which is expected to yield a commensurate increase in sputtering.

Simulations have also served to illustrate a potential power coupling issue, in low edge density scenarios, if the lower hybrid resonance frequency drops below the drive frequency. The lower hybrid frequency is very nearly equal to the ion plasma frequency in the edge region, and thus, if the plasma is “under-dense” in this sense, either naturally, or as a result of the powered antenna changing the edge plasma conditions, the slow wave can propagate in a thin layer between the antenna and the resonance. High resolution simulations (~109 cells) on the Oak Ridge Leadership Computing Facility’s Titan Cray XK7 were used to accurately capture the fine detail of the slow wave’s short wavelength and resonance. The right pane of Figure 2 shows a simulation of Alcator C-Mod’s field-aligned antenna, with an artificially reduced edge density, and widened scrape-off layer, so that several slow wavelengths could be observed. Movies of the slow wave behavior can be viewed at: http://youtu.be/bHs0qUOqA4M?list=UUwksoGsp2BWoMwiTF3tnJkg, http://youtu.be/eoXKjy4TdVw?list=UUwksoGsp2BWoMwiTF3tnJkg.

Continued studies in coming months will include the detailed modeling of power flow during antenna operation, as well as the modeling of sputtering effects and thermal loading induced by the sheath potentials at antenna surfaces.

In summary, increasingly detailed impurity-production studies in realistic geometries are being enabled by the new 3D sheath model. The effective use of this model in high-performance computation is also shedding light on the roles that sheath and slow wave physics play in parasitic loss mechanisms. These maturing FDTD code capabilities afford expanding opportunities for experimental validation studies, and for predictive ITER modeling on broader scales. In such efforts, we are confident that these numerical simulation tools will serve as an additional, and increasingly powerful, resource for augmenting scientific understanding of the physics of RF and its role in the development of economical fusion power production.

Figure 2 (left) Figure 2 (right)

Figure 2: Simulation of the Alcator C-Mod Field Aligned Antenna, in pi-mode. The left plot shows fast wave propagation from the antenna for high edge density. The right plot shows fast and slow waves when edge density is low. If slow waves are present, their field amplitudes can be high, and can contribute to both the amplitude of the RF sheath voltage and to parasitic power losses in the edge plasma.

This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. Funding was provided by the U.S. Department of Energy’s Office of Science (Office of Fusion Energy Sciences) under the SBIR program, Grant DE-SC0009501; the Theory program, Grant DE-FG02-09ER55006; and the SciDAC program, Grant DE-FC02-08ER54953 (Center for Simulation of Wave-Plasma Interactions).

References

[1] S. Wukitch, et al., “Evaluation of Optimized ICRF and LHRF Antennas in Alcator C-Mod”, in Proc. 24th Int. Conf. on Fusion Energy (San Diego, 2012), p. FTP/11, IAEA, Vienna, 2012

[2] S. Dey and R. Mittra, IEEE Microwave and Guided Wave Letters 7, 273 (1997)

[3] D.N. Smithe, Phys. Plasmas 14, 056104 (2007)

[4] D.A. D’Ippolito and J.R. Myra, Phys. Plasmas 13, 102508 (2006)

[5] T.G. Jenkins and D. N. Smithe, “Benchmarking sheath subgrid boundary conditions for macroscopic-scale simulations”, accepted for publication in Plasma Sources Science and Technology

[6] The VSim code, a Tech-X Corporation product, has exhibited excellent performance while making use of over 180,000 cores on Titan.


ITPA Update

More information concerning the ITPA may be found at the Official ITPA Website.

Energetic Particles Topical Group
  The 13th Energetic Particles Topical Group meeting was hosted at Consorzio RFX, Padova (Italy) from October 21–23, 2014. The meeting started with an update on ITER status and high-priority research needs, followed by reports on joint experiments and discussion on new joint experiments. Several presentations were given on specific topics, namely AE stabilization by ECH, ICRF physics and implications on EP dynamics, progress in theory and modeling of EP physics. Recent analyses of TBM effects on EP confinement were presented, suggesting a potential risk for lost fast ions to reach unshielded elements in the divertor region. Status and perspectives for EP diagnostics on ITER were also discussed, focusing on the assessment of charge-exchange-based diagnostics to measure confined fast ions in ITER. A joint session was held with the MHD TG to discuss ITPA publication policies, in preparation for the December 2014 ITPA coordination meeting. — M. Podestà [Information related to this meeting is archived within the BPO EP Forum.]
 
Integrated Operation Scenarios Topical Group
  Highlights of ITPA–IOS meeting held at CEA in Cadarache, France, on October 21–24, 2014.
  The present ITPA—IOS priorities include experimental assessment of the ITER baseline scenario, the assessment of particle and impurity transport on the scenario modeling, and the development of transferable control methods for plasma ramp-up and ramp-down.
  The group discussed experiments and modeling of helium plasmas and comparison with deuterium plasmas. This included: characterization of edge MHD, ELMs and their mitigation, ELM control compatibility with low Te divertor, the power threshold for the L–H transition, pedestal characteristics, determination of the minimum heating power required for sustained type-I ELMy H-mode, and impact of medium- and high-Z impurities.
  There was discussion about the control requirements for the baseline plasma. These included details of plasma initiation (ECH assist, pre-magnetization, etc), vertical stability, position, shape, and X-point formation during the current rise, basic EC control of the current profile and NTMs, RE mitigation, and plasma ramp-down. It is desirable that ITER-like control is implemented on existing machines. DIII-D is contributing with current profile control led by E. Schuster. A new ITPA-IOS activity has been launched to examine procedures for safe ITER plasma termination and will be led by I. Nunes. — F. Poli and C. Holcomb
 
Pedestal and Edge Physics Topical Group
  The ITPA Pedestal and Edge Physics Group met at the ITER Headquarters in Cadarache, France, October 20–22, 2014. One focus of this meeting was a special session concerning the effect of impurities on the H-mode pedestal. This effort aimed at understanding the performance of the pedestal in metal walled machines, which show degradation as compared to carbon-PFC machines. The introduction of Nitrogen restores much of the performance degradation with metal walls, but does not impact carbon-wall machines. A new joint experiment is being proposed to compare the effect of low-Z impurity injection on tokamaks. In addition, there was good progress made on understanding the effects of Magnetic Perturbations on ELM mitigation and suppression from a number of devices. There was also a joint session with the IOS and T&C groups on pedestal confinement and global confinement, as well as Helium experiments. Finally, updates to existing open joint experiments were given, several of which have been brought to closure. — R. Maingi
 
Transport and Confinement Topical Group
  The ITPA Transport and Confinement group met at ITER headquarters in Cadarache over October 20–22nd. The meeting kicked off with a talk from Alberto Loarte, the ITER representative for the TC group, discussing some of ITER’s most pressing open questions in relation to transport. These are:
- Helium operation
- Main ion particle transport and fueling
- W transport in the core, as well as in the pedestal, and its control in stationary phases
- The influence of PFCs and β scaling on plasma confinement
- Access to/exit from H-mode
  As a response to some of these urgent issues a new joint experiment was proposed to investigate main ion particle transport versus fueling in Deuterium as well as Helium plasmas (TC-27). The other topics discussed at this meeting include gyrokinetic and quasi-linear simulations and comparisons to experiments, rotation, the transport short fall (L-mode core-edge transport), and profile stiffness with respect to the heat fluxes. Wednesday morning was spent as a joint session with the Integrated Scenarios and the Pedestal Topical Groups to discuss Helium operations as well as β scaling. The next meeting is proposed to be held March 10–12, 2015 at the Institute for Plasma Research, Ahmedabad, India together with the PEP ITPA. Also, Darren McDonald’s term as chair has come to an end and Paola Mantica will take over as chair with Joydeep Ghosh as deputy. — S. Mordijck

Schedule of Burning Plasma Events

USBPO Public Calendar: View Online or Subscribe

2014
December 20, DEADLINE to register for the Winter School on Turbulence, Magnetic Fields and Self Organization in Laboratory and Astrophysical Plasmas
 
2015
NSTX-U First Plasma —
W7-X First Plasma —
 
January, Due date for report concerning the ten-year strategic plan of the Fusion Energy Sciences division of the US Department of Energy.
 
January 14, DEADLINE for abstract submission to the 7th IAEA Technical Meeting on Theory of Plasma Instabilities
 
January 15, DEADLINE for abstract submission to the 1st European Conference on Plasma Diagnostics
 
February 6–7, 1st BAPSF User Workshop, Los Angeles, CA, United States
 
February 14, DEADLINE for abstract submission to the 12th International Symposium on Fusion Nuclear Technology
 
March 4–6, 7th IAEA Technical Meeting on Theory of Plasma Instabilities, Frascati, Italy
 
March 10–12, ITPA: Joint meeting of the Transport & Confinement and Pedestal & Edge Physics Topical Groups, Ahmedabad, India
 
March 16–27, Joint ICTP–IAEA Advanced School and Workshop on Modern Methods in Plasma Spectroscopy, ICTP — Miramare, Trieste, Italy
 
March 23 – April 3, Winter School on Turbulence, Magnetic Fields and Self Organization in Laboratory and Astrophysical Plasmas, Les Houches, France
 
March 25–27, ITPA: Energetic Particles Topical Group Meeting, ITER Headquarters, France
 
April 14–17, 1st European Conference on Plasma Diagnostics, Frascati, Italy
 
April 14–17, ITPA: MHD Topical Group Meeting, ITER Headquarters, France
 
April 27–29, 21st Topical Conference on Radiofrequency Power in Plasmas, Lake Arrowhead, CA, United States
 
April 28 – May 1, US/EU Transport Task Force Workshop, Salem, MA, United States
 
June 22–26, 42nd EPS Conference on Plasma Physics, Lisbon, Portugal
 
September 14–18, 12th International Symposium on Fusion Nuclear Technology, Jeju Island, South Korea
 
November 16–20, 57th APS Division of Plasma Physics Meeting, Savannah, GA, United States

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Image of the Month

Image of the Month

Fusion On Film

This month’s Image is inspired by the recent increase in depictions of nuclear fusion in popular cinema. As with the movies themselves, artistic license (or outright exaggeration) is taken in the qualification of an item for this list. These fusion references run the gamut from simple requests that one “not shoot the fusion reactor” (Aliens), to cold fusion (The Saint), and even the mining of helium-3 (Moon). In particular, fusion reactors began to appear frequently in large budget movies following the release of Spider-man 21 in 2004. The bar plot shows the production budget2 of movies in which nuclear fusion is referenced. The U.S. budget3 for magnetic fusion energy (MFE) research has its own blockbusters in the form of the American Recovery and Reinvestment Act of 2009 (ARRA), and ITER, which are responsible for the increase seen in the plot of the total MFE budget (green stars). The magnetic fusion budget without the ITER contribution is plotted as the gold stars. A few films with very specific tokamak references are highlighted in the still frames on the right of the Image. The Iron Man franchise utilizes the geometry of the tokamak as its power source for the actual suit, as well as for large installations as shown here. Wall Street: Money Never Sleeps (called Wall St 2 in the Image) is a fictional account of a quest to obtain financial backing for the Fusion Simulation Project4, with one of the documents from that program highlighted in the movie as shown. A mobile tokamak is seen powering a jet in the most recent movie plotted, with the bottom-right image coming from X-Men: Days of Future Past.

Acknowledgements to V. Izzo, M. Reinke, R. Mumgaard, C. Chrystal, J. King, O. Meneghini, and N. Ferraro.

(0) All of the budget values are unadjusted to reflect the actual amount budgeted in each year, and all copyright information is available at the IMDb page for each movie. (1) It is unclear whether the fusion device’s confinement is inertial (with evil robot arms in place of lasers) or magnetic (with evil robot arms suppressing edge instabilities in place of magnetic perturbation coils). (2) As reported by IMDb. (3) As reported by Fusion Power Associates at http://fpa.ucsd.edu/OFESbudget.shtml, with the ITER contribution extracted from N. Sauthoff, “ITER Project Status,” FESAC Meeting, April 9, 2014. (4) This project is presently known as the Fusion Simulation Program.

Contact and Contribution Information

This newsletter provides a monthly update on U.S. Burning Plasma Organization activities. The USBPO operates under the auspices of the U.S. Department of Energy, Fusion Energy Sciences (FES) division. All comments, including suggestions for content, may be sent to the Editor. Correspondence may also be submitted through the USBPO Website Feedback Form.

Become a member of the U.S. Burning Plasma Organization by signing up for a topical group.

Editor: David Pace (pacedc@fusion.gat.com)

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