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CONTENTS
Director's Corner USBPO Topical Group Highlights Z.S. Hartwig, H.S. Barnard, R.C. Lanza, et al.
ITPA Update Schedule of Burning Plasma Events Contact and Contribution Information
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.
Director's Corner
by C.M. Greenfield
ITER Council holds its 12th meeting in Tokyo
The ITER Council, the governing body of ITER, held its twelfth meeting (IC-12) on June 19 and 20 in Tokyo, Japan. The Council was briefed about progress in construction at the ITER site, which has picked up considerably in recent months (see eNews 72, May 31, 2013). They also heard about progress in manufacturing critical components and supporting systems. This includes more than 420 tons of niobium-tin strand that has been produced for the toroidal field coils, and another 133 tons of niobium-titanium strand for the poloidal field coils. They also heard reports on steps being taken to recover some of the delay in reaching first plasma.
In the last eNews, I reported on two major upcoming design decisions, to start ITER with tungsten divertor targets and to include internal coils for ELM control in the ITER baseline design. These decisions are expected to be taken at the IC-13 meeting in November. Among the six charges to the STAC (Science and Technology Advisory Committee) issued at IC-12 were studies of each of these systems.
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The governing board of the ITER project reunites delegates from the seven ITER Members – China, the European Union, India, Japan, Korea, Russia and the United States. (Photo ©ITER Organization). |
US Burning Plasma Organization update
As I reported last month, we are in the process of selecting new leadership for five of our topical groups (Energetic Particles, Fusion Engineering Science, Operations and Control, Pedestal and Divertor/SOL, and Plasma-Wave Interactions) as the terms of their leaders expire this summer. Many good suggestions were made by members of these topical groups. The selection process is continuing; we anticipate having the new leadership in place in August.
Webinars
The USBPO has resumed our series of webinars with a report on Recent Activities in the ITPA Energetic Particle Physics Topical Group given by Eric Fredrickson on June 12. It was very well attended, and we are currently making arrangements for a report from another ITPA Topical Group in the near future. Watch for an announcement with more information and instructions for participation, arriving soon in your in-box.
Plans for APS-DPP conference
For the sixth straight year, the US Burning Plasma Organization is organizing a contributed oral session on Research in Support of ITER at the 55th Annual Meeting of the Division of Plasma Physics, which will take place in Denver, Colorado, on November 11-15. We had a very strong response to our request for suggestions, with 27 proposals being made for the 15 available slots. We have informed the authors of all 27 proposals of whether they were selected for this session. Abstracts not included in the USBPO session can still be submitted to the conference, but they will be placed in other sessions by the Program Committee. All authors should be aware of the deadline for submission of abstracts via the conference website, which is 5:00 PM Eastern Daylight Time on July 12. Those selected for this oral session should indicate “Research in Support of ITER” in the placement requests box. Any researchers with ITER-related presentations may if they wish indicate “ITER poster session”, helping the sorters to group these posters.
The USBPO is also organizing a Town Meeting on ITER, tentatively scheduled for Thursday evening (November 14) in the Sheraton Denver Downtown Hotel. I believe we will have a compelling program focusing on some timely issues for ITER.
USBPO Topical Group Highlights
[The BPO Diagnostics Topical Group facilitates US efforts in developing advanced measurement techniques for existing and future magnetic fusion devices (leaders are David Brower and Matt Reinke). This month's Research Highlight by Z.S. Hartwig, et al., describes initial results from deuterium retention measurements following wall-conditioning operations in the Alcator C-Mod tokamak. The authors describe a diagnostic system that employs a particle beam to induce nuclear reactions along the surface of the molybdenum plasma facing tiles, coupled with a sensitive set of neutron/gamma detectors that quantify the reaction products. This diagnostic is capable of characterizing wall conditions following each tokamak shot, thereby providing unique capability compared to alternate techniques that require extracting tiles from the device. -Ed.]
First measurements of deuterium retention using Accelerator-based In-situ Materials Surveillance (AIMS) on the Alcator C-Mod tokamak
Z.S. Hartwig1, H.S. Barnard1, R.C. Lanza1, B.N. Sorbom1, P.W. Stahle2, D.G. Whyte1, and the Alcator C-Mod Team
1 MIT Plasma Science and Fusion Center, Cambridge MA 02139, USA
2 MIT Department of Nuclear Science and Engineering, Cambridge MA 02139, USA
We present the first in-situ, time-resolved measurements of deuterium retention for plasma-facing components (PFC) in a magnetic fusion device [1]. The measurements were made using accelerator-based in-situ materials science (AIMS), a novel diagnostic technique that is being developed on the Alcator C-Mod tokamak at MIT's Plasma Science and Fusion Center. The implementation of AIMS on C-Mod is shown in Figure 1.
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Figure 1: Solid model showing the AIMS diagnostic installed on the Alcator C-Mod tokamak. The RFQ accelerator (color: cyan) beamline connects to a radial diagnostic port; three different beam trajectories (colors: yellow, orange, red) demonstrate magnetic steering to PFC surfaces on the inner wall using the toroidal field coils (color: copper). The small neutron and gamma detectors (color: green) are just barely visible in the cutaway of the reentrant tube. |
Magnetically confined plasmas and their boundary materials form a dynamically coupled physical system known as plasma-wall interactions (PWI). PWI issues, such as the erosion/redeposition of PFC material, the evolution of PFC surface isotope composition, and fusion fuel retention present significant plasma physics and materials science challenges. These challenges will be particularly important in future long-pulse or steady-state burning plasma devices, where the combination of increased plasma run time and elevated heat flux to surfaces will cause substantial - and presently uncertain - modifications to both the materials and the confined plasma.
Achieving an integrated understanding of plasma physics and materials science in magnetic fusion devices, however, has been severely hindered by an asymmetry in scientific diagnosis. While many mature techniques are routinely employed to characterize the confined plasma, the few existing in-situ materials diagnostics have been extremely limited in access and capability. Ex-situ techniques, such as the offsite analysis of materials with ion beams [2,3], and specialized linear plasma devices for PWI studies [4,5], which attempt to replicate the conditions of heat and particle flux to surfaces, have significantly advanced PWI science. However, ex-situ studies provide “archaelogical” information integrated over an entire run campaign, and linear plasma devices cannot replicate important features of the fusion device, such as the magnet topologies that can be critical for particle transport near material surfaces.
To close this diagnostic gap, AIMS can now provide time-resolved measurements of PFC surface composition over a large surface area, without the resource intensive need to remove PFCs for ex-situ analysis. AIMS uses a compact (~1 meter), high-current (~1 milliamp) radio-frequency quadrupole accelerator to inject ~1 MeV deuterons into the C-Mod vacuum vessel through a radial diagnostic port. We control the tokamak's toroidal and vertical magnetic fields - in between plasma shots - to steer the deuterons to PFC surfaces, where they induce high-Q nuclear reactions with low-Z isotopes in the first ~10 microns of material. Analysis of the induced gamma and neutron energy spectra provides quantitative reconstruction of PFC surface conditions. This nondestructive, in-situ technique achieves PFC surface composition measurements with plasma shot-to-shot time resolution, 1 micron depth resolution, and 1 centimeter spatial resolution over large PFC areas. A depiction of the AIMS process is shown in Figure 2.
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Figure 2: Depiction of the principles of Accelerator-based In-situ Materials Surveillance. (1) A compact, high-current radiofrequency quadrupole accelerator injects 0.9 MeV deuterons into the vacuum vessel. (2) In between shots, the tokamak magnetic fields steer the beam to PFC surfaces of interest. (3) Deuterons induce high-Q nuclear reactions in the first ~10 microns of the PFC surface. (4) Energy spectroscopy of ~MeV neutrons and gammas provides for quantitative surface analysis. |
Two types of nuclear reactions are of particular interest for AIMS:
(1) X(d,p)Y* ￫ Y + γ | (2) X(d,n)Y |
In Type 1 reactions, the bombarding deuterons (d) react with low-Z isotopes (X) to produce a gamma ray. Because the gamma ray results from an isomeric transition of the excited nucleus Y*, the discrete gamma energy uniquely identifies the isotope for quantification. These reactions are used in AIMS, for example, to identify and quantify the concentration of boron and oxygen on the PFC surface. In Type 2 reactions, the bombarding deuterons produce an outgoing neutron, which also carries energy information that can be used for isotope quantification. Type 2 reactions are used in AIMS principally to diagnose deuterium retention in PFCs via the well known 2H(d,n)3He fusion reaction.
As proof-of-principle, we present a series of time-resolved AIMS measurements of deuterium retention in Figure 3. These measurements were made during dedicated AIMS experiments on C-Mod during the end of the FY12 run campaign. The purpose of the experiments was to measure the relative change in deuterium concentration at a single PFC location in response to a variety of controlled wall-perturbing events, such as boronization (BZN), electron cyclotron discharge cleaning (ECDC), and glow discharge cleaning (GDC). The measurement location was fixed approximately 10 cm below the midplane on the central column PFCs. Two statistically significant changes in retained deuterium concentration are evident from the data shown in Figure 3: the first from boronization and the second from discharge cleanings.
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| Figure 3: The first time-resolved measurements of deuterium retention produced by AIMS for a single location on the inner wall PFCs. The relative strength of the deuterium signal shows significant and expected changes in response to dedicated boronizations and plasma discharge cleanings. |
During each of the two 4 hour boronizations, a spatially localized ion cyclotron resonance frequency (ICRF) layer was used to ionize ambient deuterated diborane gas, depositing boron and deuterium on the first wall as ions and recombined neutrals. In the first boronization, the resonance layer was swept across the major radius of C-Mod, resulting in only small increase in deuterium content. In the second boronization, the resonance layer was held as close to the inner wall measurement location as possible, leading to strongly enhanced deuterium deposition at the measurement site. Then, over the course of 24 hours, a series of electron cyclotron and glow discharge cleanings were used to clean the PFC surfaces with low temperature plasmas, with measurements showing a significant reduction in the retained deuteron on the inner wall PFC surfaces.
Although these results and others not included are preliminary, we believe that they demonstrate three key capabilities of the AIMS technique: first, using magnetic steering to perform localized PFC surface composition measurements over a large PFC surface area; second, achieving sufficient detector signal in an adverse detection environment; and third, performing time-resolved measurements on the order of plasma shot and wall conditioning time scales. Ultimately, we believe the successful demonstration of AIMS on Alcator C-Mod promises a new generation of diagnostics capable of comprehensively exploring the physics of plasma-wall interactions, one of the critical challenges to the success of magnetic fusion energy.
Work supported by U.S DOE Grant DE-FG02-94ER54235 and Cooperative Agreement DE-FC02-99ER54512
References
- Z.S. Hartwig, H.S. Barnard, R.C. Lanza, B.N. Sorbom, P.W. Stahle, and D.G. Whyte, In preparation for Rev. Sci. Instrum.
- M. Rubel, P. Wienhold, and D. Hildebrandt, Vacuum 70, 423 (2003)
- W.R. Wampler, Nucl. Instr. and Methods B 219-220, 836 (2004)
- H.J.N. van Eck et al, Fus. Eng. and Design 82, 1878 (2007)
- G. M. Wright, submitted to Rev. Sci. Instr., June 2013
ITPA Update
For information on the proposed agenda, see BPO forum link.
| Coordinating Committee | |
| 4th Meeting, ITER Site, France, December 9 - 11, 2013 | |
| Diagnostics Topical Group | |
| 24th Meeting, San Diego, CA, USA, June 4 - 7, 2013 BPO Forum: https://burningplasma.org/forum/index.php?showtopic=1247 | |
| Energetic Particle Physics Topical Group | |
10th Meeting, Culham, UK, April 22 - 25, 2013 | |
| Integrated Operation Scenarios Topical Group | |
| 11th Meeting, Fukuoka, Japan, October 7 - 9, 2013 | |
| MHD, Disruptions & Control Topical Group | |
| 22nd Meeting, Hefei, China, October 8 - 11, 2013 The meeting will cover key MHD stability topics for ITER, including disruptions, disruption mitigation, axisymmetric control, sawteeth, tearing modes, resistive wall modes, error fields, and 3D effects. | |
| Pedestal & Edge Physics Topical Group | |
| 24th Meeting, IPP Garching, Germany, April 22 - 24, 2013 | |
| Scrape-Off-Layer & Divertor Topical Group | |
| 18th Meeting, Hefei, China, March 19 - 22, 2013 | |
| Transport & Confinement Topical Group | |
| 11th Meeting, Fukuoka, Japan, October 7 - 9, 2013 http://www.triam.kyushu-u.ac.jp/QUEST_HP/ITPAMeeting/ Areas to be covered include impurity and particle transport; validation of gyrofluid transport models; momentum transport; transport in the L-mode edge, particularly during the current rise phase of ITER; L-H and H-L transitions; profile stiffness; 3D effects; and the long-term effort to provide a fully validated model of plasma transport for ITER. These areas include topics that have been selected for special reports to the Integrated Operation Scenarios Topical Group. | |
Schedule of Burning Plasma Events
Click here to visit a list of previously concluded events.
| 2013 | |
| July 1 - 5, EPS Conference on Plasma Physics, Espoo, Finland A satellite conference on Plasma Diagnostics will be held July 6. | |
| September 14 - 16, ICNSP: 23rd International Conference on Numerical Simulation of Plasmas, Beijing, China | |
September 17 - 20, IAEA: 13th TM on Energetic Particles in Magnetic Confinement Systems, | |
| October 1 - 3, IAEA: 7th TM on Electron Cyclotron Resonance Heating Physics and Technology for Large Fusion Devices, Vienna, Austria | |
| October 2-4, 14th International Workshop on H-mode Physics and Transport Barriers, Kyushu University, Fukuoka, Japan | |
| October 7 - 9, ITPA PED Topical Group Meeting, Japan | |
| November 11 - 15, APS DPP Meeting, Denver, United States | |
| November 18 - 20, 18th Workshop on MHD Stability Control, Santa Fe, New Mexico, USA https://fusion.gat.com/conferences/mhd13/ | |
| December 9 - 11, ITPA: 4th CC/CTP Meeting, ITER | |
| December 16 - 20, IAEA: 2nd DEMO Programme Workshop, Vienna, Austria | |
| December 11, 4th CTP Ex Com Meeting, ITER | |
| 2014 NSTX-U commissioning operations begin | 2020 November, First plasma at ITER |
| 2015 First plasma at W7-X | 2027 March, Beginning of full DT-operation at ITER |
| 2019 First plasma at JT-60SA | |
Contact and Contribution Information
This newsletter provides a monthly update on U.S. Burning Plasma Organization activities. Topical Group Highlight articles are selected by the Leader and Deputy Leader of those groups (burningplasma.org/groups.html). ITPA Reports are solicited by the Editor based on recently held meetings. Announcements, Upcoming Burning Plasma Events, and all comments may be sent to the Editor. Suggestions for the Image of the Month may be sent to the Editor. The images should be photos, as opposed to data plots, though combined graphics are welcome. The goal is to highlight U.S. fusion resources through interesting visualizations.
Become a member of the U.S. Burning Plasma Organization by signing up for a topical group:
burningplasma.org/jointopical
Editor: David Pace (pacedc@fusion.gat.com)
Assistant Editor: Amadeo Gonzales (agonzales@austin.utexas.edu)
Image of the Month
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High Energy Computations
Results from a massively parallel, gyrokinetic eigenvalue solver show "twisting" Alfvén eigenmodes (AEs) driven by high-energy beam ions in a DIII-D plasma. This tokamak shot is characterized by frequency sweeping reverse-shear AEs (RSAEs) interacting with toroidal AEs and beta-induced AEs (shown) at the upper and lower ends of the frequency sweep, respectively. The eigenvalue solver is installed in GYRO, which solves the gyrokinetic equations on a fixed, field-aligned continuum grid in toroidal systems. Originally developed for linear and nonlinear studies of microturbulent transport using Eulerian time stepping, GYRO now includes two separate eigenvalue-solving algorithms. It has been successfully applied to thermally-driven mesoscale turbulent transport, cross-scale turbulent couplings (meso-micro and macro-meso), and linear stability across scales. GYRO's eigenvalue solver is well suited for cases with multiple unstable, interacting modes. Numerical results match experimental frequency measurements within a few percent, with qualitative agreement in the eigenfunction structure. The study reveals a sensitive dependence of the RSAE lower sweep limit on the driving energetic particle pressure. For global modes of the type shown, eigenvalues and vectors are determined from a matrix of more than 1.1 million rows, requiring over 50,000 processor cores on the Hopper Cray XE6 supercomputer shown in the photo. The NERSC system Hopper is named in honor of US Navy Rear Admiral Grace Murray Hopper, whose many contributions to computer science include development of the first compiler.
Contributed by E.M. Bass1 and R.E. Waltz2
1 University of California, San Diego, California, 92093
2 General Atomics, San Diego, California, 92186
E.M. Bass and R.E. Waltz, Phys. Plasmas 20, 012508 (2013), http://dx.doi.org/10.1063/1.4773177
D. A. Spong, et al., Phys. Plasmas 19, 082511 (2012), http://link.aip.org/link/doi/10.1063/1.4747505
National Energy Research Scientific Computing (NERSC) Center homepage, http://www.nersc.gov/
GYRO homepage, https://fusion.gat.com/theory/Gyro
Click here to visit a Directory of Other Plasma Events
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