News and Events


U.S. Burning Plasma Organization eNews
June 30, 2014 (Issue 85)

 

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
Topical Group Research Highlight
A. Bortolon
Mitigation of Alfvénic Activity by 3D Magnetic Perturbations on NSTX
ITPA Update
Schedule of Burning Plasma Events
Image of the Month
T.M. Brewer and R.T. Mumgaard
40 Years of HTPD
Contact and Contribution Information

Announcements

BPO Web Seminar

Fusion Nuclear Science Facility, What is it and What are the Plasma Requirements?

C. Kessel, Princeton Plasma Physics Laboratory

Day and Time: Wednesday, July 2nd, 13:00 EDT, 12:00 CDT, 10:00 PDT

Dr. Kessel is leading Fusion Energy Systems Studies (FESS), a new multi-institutional study group from national laboratories and universities exploring the future of fusion energy systems to identify critical research needs and program directions. FESS is currently studying a potential Fusion Nuclear Science Facility. This web seminar will describe the mission and requirements of such a facility, including areas where physics input is needed.

Connection information is provided through email to members of the USBPO. Interested persons can become a member of the U.S. Burning Plasma Organization by signing up for a topical group.



ITER Opportunity: US ITER Diagnostics WBS Manager

Application Website: Princeton University Jobs (search for Requisition Number 1400278)

The US ITER Diagnostics WBS Manager manages the work needed to fulfill USIPO diagnostic commit- ments and to complete planned activities on cost and schedule. This involves working closely with the Diagnostic Division of the ITER Organization (IO) to develop the US diagnostics, the USIPO, which is responsible for all ITER procurement arrangements, and the diagnostic scientists and engineers in other do- mestic agencies as needed. This also entails managing the activities of a PPPL engineering team designing and procuring port plug components and diagnostic front-end components, and procuring and overseeing services of expert diagnostic teams to provide design support and components for US ITER diagnostics consistent with the requirements (hardware, software, and documentation requirements) specified by the USIPO and the IO.

Responsible for the delivery to ITER of 7 diagnostic systems (Toroidal Interferometer /Polarimeter, Upper Visible/IR Cameras, Motional Stark Effect Diagnostic, Residual Gas Analyzer, Low Field Side Reflectome- ter, Electron Cyclotron Emission Diagnostic, and the Core Imaging X-ray Spectrometer) and 4 port plugs, following completion of the design of these components.



Call for Nominations: USBPO Council

July 8: Email your nomination(s) to Gary Staebler, Nominating Committee Chair

July 21 – July 28: Election by USBPO regular members from a slate of candidates using web-based poll software (to be described in a later email).

August 1: USBPO announces the new Council members, both elected and appointed.

The USBPO seeks nominees to be considered for the USBPO Council. As described in the bylaws, each year two new Council members will be elected by the USBPO regular membership and two will be appointed by the USBPO Director.

The USBPO bylaws define the role of the Council (Bylaws Online):

“The Council represents the U.S. MFE research community in providing oversight of the USBPO activities, and, working with the Directorate, is the primary USBPO element responsible for long-term strategic planning of burning plasma research. The Council is responsible for setting the policies and procedures of the USBPO, including establishing the by-laws governing USBPO operations. It will receive regular reports on USBPO activities from the Director, and will provide feedback and assessment on those activities to the Director regarding progress, issues, priorities, and opportunities. When required, a simple majority vote of the Council shall serve to designate Council approval of a decision. When Council comment and recommendations are required, the Council Chair and/or Vice-Chair will work to convey the sense of the Council to the Director and the OFES.”


Director’s Corner

by C.M. Greenfield

ITER International School

The 7th ITER International School will be held in Aix en Provence, France, during August 25–29, 2014. The theme of this year’s Summer School will be “Highly parallel computing in modeling magnetically confined plasmas for nuclear fusion.” These Schools are primarily designed for graduate students, postdocs, and young researchers. The registration deadline has now closed, but I am happy to announce the winners of the 2014 USBPO scholarships:

Graduate StudentsPost-docs
Evan Michael Davis (MIT) Nathan Howard (MIT)
Noah Reddell (U. Washington) Mark Cianciosa (Auburn)
Jen Sierchio (MIT) Orso Meneghini (GA)
Peter deVietien (Purdue) Ari Le (UCSD)

Congratulations to all! The winners were selected by a committee consisting of François Waelbroeck (chair), Nermin Uckan, and Xianzhu Tang. They had a surprisingly difficult job in selecting eight winners from 32 applications. These scholarships will cover travel costs and registration for the school.

APS–DPP activities

For the sixth time, last year’s APS Division of Plasma Physics annual meeting included a contributed oral session on Research in Support of ITER, which included 15 talks from US and foreign participants. These sessions have become quite popular, and are always well attended. The US Burning Plasma Organization is organizing a similar session for the 56th Annual Meeting of the Division of Plasma Physics, which will take place in New Orleans, Louisiana, on October 27–31. Once again, we have put together what we believe is a collection of compelling talks on research that has been done specifically to address ITER design, operation, or physics issues. These brief talks are “standard” contributed orals: 10 minutes in duration, followed by a 2 minute discussion period. The talks have been selected, but I will delay publishing the list until next month as the speakers are in process of being notified.

We are also considering whether to host a town meeting again this year. More on this next month.

ITER Council Meets

The ITER Council held its fourteenth meeting on June 18–19 at ITER headquarters. Under the chairmanship of Robert Iotti (US), the Council reviewed the progress of ITER construction and manufacturing. The ITER Organization reported on the arrival of components and the Council agreed on necessary changes to meet the challenges of construction and assembly. The Members discussed the current status of their activities and procurements as well as the need to finalize an updated schedule.

Attendees at the IC–14 meeting

Attendees at the IC–14 meeting in June 2014 (Photo © ITER Organization)

FESAC Subpanels

The work of two FESAC (Fusion Energy Sciences Advisory Committee) subcommittees has been underway, and once again, the USBPO is assisting with communication to the community at large. You can find links to each at http://burningplasma.org/. Look for “Non-USBPO Activities.” The two committees are:

• The Subcommittee on Workforce Development, chaired by Hantao Ji. This group has finished its work and its report (http://burningplasma.org/ref/STEM/FESAC-AWDNreport-Koepke-Ji22June2014.pdf) has been accepted by the full FESAC. Their report is available on the USBPO website.

• The Strategic Planning Panel, chaired by Mark Koepke is holding two public meetings. The first, on June 3–5, received community input on a variety of issues relevant to long pulse and discovery science. The second meeting, on July 8–10, will hear from major facilities (US and international), and a variety of topics within burning plasma foundations. Their work is due October 1, and is being done as input for the Fusion Energy Science strategic plan requested by Congress and due in January.

back to top


Topical Group Research Highlight

Research Highlights are selected by the leaders of the BPO Topical Groups on a rotating basis. The BPO Energetic Particles Topical Group works to facilitate U.S. efforts to understand the behavior of energetic particles via improved measurements and computational models for existing and future magnetic fusion devices (leaders are David Pace and Nikolai Gorelenkov). This month’s Research Highlight by A. Bortolon concerns experimental observations of changes in the energetic ion distribution and associated Alfvénic instabilities with the application of three-dimensional magnetic perturbations. Controllably adjusting the energetic ion distribution in a burning plasma may provide the means to tailor the current profile or set the fusion gain.

Mitigation of Alfvénic Activity by 3D Magnetic Perturbations on NSTX


A. Bortolon
Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA

It is well known that rapid transport of suprathermal ions induced by Alfvén instabilities may jeopardize the performance of present day magnetic fusion devices or damage vessel hardware. While the large magnetic field and plasma size in ITER may result in low levels of alpha particle transport due to Alfvén eigenmodes, this might not be true for alternative magnetic configurations such as the spherical tokamak, which is inherently characterized by lower magnetic fields. Furthermore, recent studies have emphasized the possible coupling of several modes, resulting in major transport events often referred to as avalanches [1]. Similarly, possible interaction and synergy between different kinds of instabilities acting on different spatial and temporal scales has been reported, as in the case of Toroidal Alfvén Eigenmode (TAE) avalanches triggered by Global Alfvén Eigenmode (GAE) avalanches [2] or the long lived internal kink modes which grow out of events of rapid destabilization of fast-ion driven modes [3].

For these reasons, in a broad fusion perspective, it remains desirable to devise methods to actively suppress fast-ion driven instabilities or mitigate their impact. Research in this area has produced interesting observations in the past, from experiments in conventional tokamak [4], spherical tokamak [5] and stellarator [6] configurations, demonstrating that injection of auxiliary heating waves can strongly affect the dynamic of beam driven Alfvén instabilities.

More recently, evidence emerged from experiments on the NSTX spherical tokamak of mitigation of Alfvén activity in response to externally applied 3D magnetic perturbations (MP). A first series of observations concerned mitigation of Alfvénic bursting-chirping activity on NSTX H-mode plasmas (ELM-free) by use of n = 3 static non-resonant perturbations [7]. The modes, identified as Global Alfvén Eigenmodes (GAE), are a common observation in NSTX neutral beam heated discharges. GAEs occur in the frequency range of 400–700 kHz and propagate in the counter beam direction with relatively high toroidal numbers n = 6–9. The GAE activity consists of persistent bursts at a repetition rate of 4 kHz, with frequency chirps extending as large as 100 kHz (Fig. 1). In response to pulsed external fields the non-linear evolution of the modes is strongly modified; bursting frequency increases while the range of frequency chirp and the mode amplitude are reduced, all by a factor of 2–3.

Figure 1

Figure 1: Rapid decays of neutron production rate in response to MP pulses indicate enhancement of fast-ion transport and losses (a). Spectrograms of signal from Mirnov magnetic probes (b) show broad band MHD activity, consisting of bursting and chirping instabilities (c).

Repeated observations of this effect could be interpreted in terms of a reduction of the drive from resonant fast ions. Since GAEs are driven by velocity space gradients in the fast ion distribution function, this required simulating the dynamical evolution of the fast ion distribution function caused by the magnetic perturbation. This has been achieved by means of full-orbit simulations [8], with perturbation fields numerically determined according to ideal [9] and resistive [10] MHD models. For these cases, the models predict substantial amplification of perturbation fields within the plasma and structures with spatial scales of tens of centimeters, i.e., of the order the beam ion gyro-radius. An important aspect is that fast-ion observables can actually be used to assess the accuracy of the plasma response models. The predicted evolution of neutron production rate was compared with the observed 7% decay, following the application of the MP. The best agreement with the experimental neutron rate is obtained when plasma response from resistive MHD simulations is used. The fast ion distribution function is modified in regions of the velocity space where resonance with the observed modes is expected and with a reduction of the perpendicular gradient that appears consistent with the reduced drive for the bursting modes.

These results emphasize the tailoring of the fast ion distribution as an additional tool to control plasma performance in fusion devices. However, from an operational perspective, achieving this control by means of 3D fields represents a challenging task since perturbing the fast ion distribution, the quantity whose confinement has to be maximized, might engender additional transport and losses that are larger than those associated with the undesirable instabilities. A subtle optimization of the MP spectrum and plasma scenario is required, which has to account for the possible screening and amplifications associated with plasma response.

An alternative approach emerges from second series of observations on NSTX, suggesting that 3D fields can be exploited to enhance the damping rates of Alfvénic instabilities. Pulses of static n = 3 magnetic perturbations were successfully applied to trigger Edge Localized Modes (ELMs) at the desired frequency of 60 Hz, with ELMs consistently triggered 2–3 ms after the rise of the MP coil. A cluster of TAEs with dominant n = 2 (65 KHz) and n = 3 (75 kHz) were observed to be strongly affected by the combined action of MP pulses and ELMs. The TAEs are suppressed after the ELM relaxation. Remarkably, in some cases the TAE amplitude is substantially attenuated before the ELM crash, indicating a direct effect of the MP on the TAE dynamic. In contrast with the previously reported cases, however, here the neutron production rate is only weakly modulated by the MP, suggesting that changes of fast ion drive might play a minor role.

In principle, the TAE damping rates (for instance those associated with Landau damping on electrons or ions) could increase as a result of modification of the background thermal profiles. However, measurements of electron temperature profiles show significant changes only after ELM crash. At the same time, 3D magnetic perturbations break the axisymmetry of the system and introduce new toroidal couplings, which can strongly affect the stability of Alfvén eigenmodes, as has been established in stellarator research [11]. A key aspect is that while in axisymmetric configurations eigenmodes are toroidally decoupled and a single toroidal number n is sufficient to define each eigenmode, in non-axisymmetric geometries each eigenmode is associated with a family of toroidal components, with toroidal numbers spaced by an integer times the MP field period, nMP. The first consequence is that 3D MP can potentially alter the ensemble of strongly damped solutions, referred to as Alfvén continuum [11]. Figure 2(a) represents the structure of the n = 2 Alfvén continuum, computed for the experimental case, assuming axisymmetric equilibrium, i.e., without MP. Large frequency gaps correspond to locations where Alfvén modes could grow avoiding interaction with continuum modes and the resulting damping. The observed n = 2 TAE at 65 kHz lies within the lower gap, the TAE gap, which extend out to the plasma edge. The computation performed on a 3D perturbed equilibrium (with MP) finds a strong toroidal coupling close to the plasma boundary [Figure 2(b)], where a new class of continuum modes combining strong toroidal n = 2 and n = 5 components effectively reduces the frequency extent of the lower gap and closes the upper gap. The observed TAE is expected to couple with this continuum and experience an additional continuum damping. Analysis is still in progress and a complete comparison with the experiment, which requires rotation effects to be taken into account, has not been accomplished yet. These results indicate, however, that small, appropriately designed, 3D perturbations could be also exploited to effectively damp Alfvénic instabilities.

Figure 2

Figure 2: Structure of n = 2 Alfvén continuum modes computed for an axisymmetric magnetic configuration (a), and in presence of external magnetic perturbations (b). The toroidal coupling induced by the 3D fields reduces the frequency gaps where weakly damped Alfvén eigenmodes can grow. The dotted line indicates the frequency of an n = 2 TAE, attenuated in presence of MP.

In a future perspective this represents an interesting option. Magnetic perturbation coils are becoming a standard tool in support of tokamak plasma operation, in particular for what concerns the pedestal stability, and are likely to be an integral element of fusion devices including ITER.

References

[1] M. Podesta, et al., Nucl. Fusion 51, 063035 (2011)

[2] E.D. Fredrickson, et al., Nucl. Fusion 52, 043001 (2012)

[3] M. Gryaznevich, et al., Nucl. Fusion 48, 084003 (2008)

[4] M.A. Van Zeeland, et al., Nucl. Fusion 49, 065003 (2009)

[5] W.W. Heidbrink, et al., Plasma Phys. Control. Fusion 48, 1347 (2006)

[6] K. Nagaoka, et al., Nucl. Fusion 53, 072004 (2013)

[7] A. Bortolon, et al., Phys. Rev. Lett. 110, 265008 (2013)

[8] G.J. Kramer, et al., Plasma Phys. Control. Fusion 55, 025013 (2013)

[9] J.–K. Park, A.H. Boozer, and A.H. Glasser, Phys. Plasmas 14, 052110 (2007)

[10] N. Ferraro, et al., Nucl. Fusion 53, 073042 (2013)

[11] D.A. Spong, R. Sanchez, and A. Weller, Phys. Plasmas 10, 3217 (2003)

back to top


ITPA Update

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

Diagnostics Topical Group
  26th Meeting, Pohang Univ. of Sci. and Tech., Republic of Korea, May 19–22, 2014
 
Energetic Particles Topical Group
  12th Meeting, Madrid, Spain, March 31–April 3, 2014
  A summary written by D. Pace with contributions from P. Bonoli, D. Brower, B. Harvey, and D. Spong is available on the BPO Forum (EP).
 
Integrated Operation Scenarios Topical Group
  12th Meeting, Massachusetts Institute of Technology, Cambridge, MA, United States, March 31–April 3, 2014
  A summary written by S. Gerhardt with help from T. Luce, C. Kessel, and C. Holcomb is available on the BPO Forum (IS).
 
MHD, Disruptions, and Control Topical Group
  23rd Meeting, Toki, Japan, March 10–14, 2014
 
Pedestal and Edge Physics Topical Group
  26th Meeting, IPP, Prague, Czech Republic, April 15–17, 2014
  An excerpt from the Executive Summary of this meeting, as prepared by H. Urano, R. Maingi, and G. Huysmans, appears below. The full summary was emailed to members of the USBPO Pedestal and Divertor/SOL Topical Group.
  The 26th meeting of the Pedestal and Edge Physics topical group was held at Institute of Plasma Physics, Prague, Czech Republic. The scientific program of the meeting covered many key issues for ITER including:
  1) Core performance in ELM suppressed/mitigated regimes (IO session request)
2) ELM control using RMP and pellet pacemaking 3) Pedestal structure and P/B stability
4) Small ELMs and impurity seeding
5) Pedestal physics, including lithium effects
6) Summaries from outstanding PEP joint experiments including IAEA papers
  On RMP control, KSTAR reported ELM mitigation/suppression by n = 1,2 fields. ELM suppression appears by a delayed and secondary effect. A certain transition under static RMP fields is activated and confinement enhancement accompanied is observed as a new H-mode state. In DIII-D ITER similar shape and low collisionality (νe*) plasmas with RMP fields, the pedestal pressure scales linearly with the pedestal density over a wide range. In JET, the application of n = 1 fields deteriorates the pedestal energy by 20%, but this is due to the particle confinement degradation. There is nearly no difference or a small improvement in the thermal confinement with n = 1 fields. MAST succeeded in avoiding the particle confinement degradation accompanied by RMP fields with optimizing the gas fuelling rate. As a result, the pedestal pressure becomes nearly the same before and after the application of RMP fields whereas ELMs are mitigated. The quantitative condition necessary to achieve ELM mitigation or suppression with RMP fields was requested to determine by IO as the first priority on the RMP research.
 
Transport and Confinement Topical Group
  12th Meeting, Massachusetts Institute of Technology, Cambridge, MA, United States, April 9–11, 2014

back to top


Schedule of Burning Plasma Events

2014
NSTX-U First Plasma —
 
 
July 2, BPO Web Seminar (13:00 EDT)
Fusion Nuclear Science Facility, What is it and What are the Plasma Requirements?
C. Kessel, Princeton Plasma Physics Laboratory
 
August 25–29, 7th ITER International School, Aix-en-Provence, France
 
September 8–11, 19th Joint EU-US Transport Task Force Meeting (TTF), Culham, United Kingdom
 
October 13–18, 25th IAEA Fusion Energy Conference (FEC 2014), St. Petersburg, Russia
 
October 27–31, 56th APS Division of Plasma Physics Conference, New Orleans, LA
 
2015
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.
 
2016
— 10th Anniversary of USBPO Formation —
 
2017
JET DT-campaign —
 
2019
JT60-SA First Plasma —

back to top


Image of the Month

Image of the Month

40 Years of HTPD

The 20th High-Temperature Plasma Diagnostics Conference (HTPD) was held during June 1–5, 2014 in Atlanta, Georgia and featured the largest international attendance in its 40-year history. The 335 participants (139 international), along with organizers from Oak Ridge National Laboratory, are shown in the bottom portion of this month’s Image. Students made up a sizable group totaling 95 attendees with the majority of them, 53, studying internationally. The program included 308 contributions from which 27 were presented as Invited Talks with the rest appearing during poster sessions such as the one shown in the upper-right. One of the magnetic confinement fusion invited talks was given by R. Mumgaard† concerning the reactor relevant motional Stark effect (MSE) system on Alcator C-Mod. A diagnostic challenge highlighted in this talk is compensation of polarized background light. The polarized light is identified to arise from reflections off the ICRF antennas that serve as the MSE “view dump” in the compact tokamak. Measurements of these polarized light contributions are shown in the middle-left panel. A multi-spectral MSE approach where the polarization is simultaneously measured in 4 wavelength regions along the same sightline is successfully used to wavelength-interpolate the background polarization and overcome this difficulty. In addition to hosting the largest meeting of high-temperature plasma diagnosticians, the city of Atlanta, Georgia is also home to one of the largest aquariums in the world, Georgia Aquarium. A whale shark is seen swimming past visitors to the aquarium’s Ocean Voyager exhibit in the middle-right panel. The next HTPD will be held in 2016.

Contributed by T.M. Biewer, Oak Ridge National Laboratory, and R.T. Mumgaard, Massachusetts Institute of Technology.

R.T. Mumgaard, S.D. Scott, and R.S. Granetz, “Toward Reactor Relevant MSE: In-situ Calibration and Polarized Background Subtraction on Alcator C-Mod,” Invited Talk, 20th High-Temperature Plasma Diagnostics Conference, Atlanta, GA, June 1–5, 2014

† Presently a graduate student in Nuclear Science and Engineering at the Massachusetts Institute of Technology studying current profile effects during lower-hybrid current drive on the Alcator C-Mod tokamak.


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)

back to top

Privacy Policy
Who's in the USBPO News and Events References and Links Media Forums Contact Us