News and Events


U.S. Burning Plasma Organization eNews
Oct 31, 2015 (Issue 101)

 

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
B.N. Breizman
Schedule of Burning Plasma Events  
Contact and Contribution Information

Announcements

Invitation for collaboration with SPC, at EPFL, Switzerland

On September 22, our Center for Research in Plasma Physics (CRPP) of the Swiss Federal Institute of Technology (EPFL) has been renamed Swiss Plasma Center (SPC) http://spc.epfl.ch/Welcome.

The Swiss Plasma Center will use ad hoc investment funds from the Swiss Confederation and new nation wide synergies in academia and industry to reinforce the impact of Switzerland in fusion research for ITER and DEMO, with further significant upgrades to the TCV tokamak systems, but also to expand research activities in space plasmas and astrophysics, environmental and industrial applications of plasmas.

The doors of the Swiss Plasma Center are wide open for collaborations on all of these areas.

Contact: Prof. Ambrogio Fasoli, SPC Director, ambrogio.fasoli@epfl.ch

Director’s Corner

C.M. Greenfield

USBPO Organization

As you know, the USBPO Research Committee includes the leaders and deputy leaders of our ten topical groups. Each member is appointed for a two-year term, which can be renewed once. Several of our topical group leaders recently completed their terms. We wish to thank David Pace (Energetic Particles), Russ Doerner (Fusion Engineering Science), Egemen Kolemen (Operations and Control), Rajesh Maingi (Pedestal and Divertor/SOL), and David Green (Plasma-Wave Interactions) for their service during the last several years, first as deputies and later as leaders of their respective topical groups. We also thank Peter Stangeby, who after completing his term as vice-chair of the Pedestal and Divertor/SOL Topical Group has chosen not to continue as leader. The new leaders (Nikolai Gorelenkov, David Rasmussen, Jim Irby, and Bob Pinsker) have been promoted from deputy leader to leader of their respective topical groups. I am very happy to be able to welcome our new members: John Canik, Eric Bass, Jean Paul Allain, Eugenio Schuster, Mike Jaworski, and Greg Wallace. It was gratifying to find that all of our first choices agreed to serve.

The 2015-2016 Topical Group leadership is:

 Topical Group  Leader  Deputy Leader
Confinement and Transport Gary Staebler (GA) Saskia Mordijck (William & Mary)
Diagnostics Ted Biewer (ORNL) Brent Stratton (PPPL)
Energetic Particles Nikolai Gorelenkov (PPPL) Eric Bass (UCSD)
Fusion Engineering Science David Rasmussen (ORNL) Jean Paul Allan (Illinois)
Integrated Scenarios Chris Holcomb (LLNL) Francesca Poli (PPPL)
MHD, Macroscopic Plasma Physics Bob Granetz (MIT) Steve Sabbagh (Columbia)
Modeling and Simulation Xianzhu Tang (LANL) Lang Lao (GA)
Operations and Control Jim Irby (MIT) Eugenio Schuster (Lehigh)
Pedestal and Divertor/SOL John Canik (ORNL) Mike Jaworski (PPPL)
Plasma-Wave Interactions Robert Pinsker (GA) Greg Wallace (MIT)

In addition to chairing the Energetic Particles Topical Group, David Pace has also acted as editor of the eNews since late 2012. This can be a challenging task, and he has our gratitude for carrying it out with great skill and diligence. During the last several months we have transitioned, with David’s help, to our new editor, Saskia Mordijck.

Progress at ITER

As promised, I attended the ITER STAC-19 meeting this month, along with Rob Goldston (PPPL), Earl Marmar (MIT), Juergen Rapp (ORNL), Jim Van Dam (DOE), and our counterparts representing each of the other ITER parties. As you can see in the photos, visible progress has been made in construction since my last visit in May, probably the biggest difference I have yet seen from one visit to the next.

(Left) The ITER tokamak pit. Most of the rebar seen in earlier photos is completely covered now. The square crane in the center of the photo is located at what will be the center of the tokamak. (Right) The ITER Assembly Building. Photos by C. Green eld.

The STAC considered the following three charges (condensed version):

  1. Assess the technical aspects of the Updated Long-Term Schedule
  2. Assess progress on the resolution of neutronics issues, including cost and schedule impact
  3. Assess progress in several aspects of the in-vessel coils (for vertical stabilization and ELM control)

We were encouraged by progress in all three areas, and I expect more information about each of these to be available in coming months. I will comment that the physics community can expect an action item in connection with charge 3. There remains an open issue with regard to heat flux asymmetries due to the 3-D field structure used to control ELMs, and specifically whether these may lead to sufficient localized heat fluxes to require mitigation. The present mitigation strategy utilizes a 5 Hz rotation of the magnetic perturbation to toroidally spread the heat flux. There are still questions about whether this is needed, or if slower rotation or even replacing the rotation with an oscillation can provide sufficient mitigation. The ITER Organization will be requesting both experimental and theoretical work to reduce the uncertainties in this area. From the engineering side, the rotation is a challenge, but it now appears this may be manageable. STAC-19 has produced a report that will provide input to the ITER Council at its November meeting. Similarly, the Management Advisory Committee (MAC) met recently to develop its own report.

APS-DPP Activities

The eighth annual Research in Support of ITER contributed oral session will be held on Thursday morning, November 19, during the upcoming annual meeting of the APS Division of Plasma Physics. This years’ agenda is as follows:

SpeakerInstitutionTitle
Joseph SnipesITERITER Plasma Control System Development
Eugenio SchusterLehigh UniversityNonlinear Control and Online Optimization of the Burn Condition in ITER
Menno LauretLehigh UniversitySawtooth period control by power modulation
Antonius J. DonneEUROfusionRisk mitigation for ITER by a prolonged and joint international operation of JET
R.A. MoyerUC San DiegoTesting RMP ELM suppression models in low torque ITER Baseline Scenario
Guosheng XuChinese Academy of SciencesAdvances in ELM control towards long-pulse H-mode plasmas on EAST
S. BrezinsekFZJLM-induced W sputtering sources in JET
Larry BaylorORNLApplication of Pellet Injection to Mitigate Transient Events in ITER]
R. GranetzMITDisruption Mitigation of Plasmas with Locked Modes
R.J. La HayeGeneral Atomics]Effect of thick blanket modules on neoclassical tearing mode locking in ITER
Mike DunneIPP-GarchingPredictive modelling of the impact of a radiative divertor on pedestal confinement on ASDEX Upgrade
B.A. GriersonPPPLTime Dependent Predictive Modeling of DIII-D ITER Baseline Scenario using Predictive TRANSP
Junya ShiraishiJapan Atomic Energy AgencyStatus of the ITER plasma modeling activities in JAEA
G.M. StaeblerGeneral AtomicsThe Impact of Zonal Flows on the Performance Predictions for ITER
E.J. DoyleUCLAProgress in the Design and Development of the ITER

We look forward to another in a series of well-attended sessions highlighting compelling results that support ITER reaching its technical goals. The USBPO will not be hosting a town meeting at this year’s conference. However, the Thursday evening slot we would normally fill will instead be devoted to reports on the recent FES Workshops. Please refer to the conference agenda for more information.

ITER International School

The scholarship deadline is rapidly approaching. Please read on . . .

The 8th ITER International School will be held at the University of Science and Technology of China, in Hefei, China, December 14-18 2015. The theme of this years school will be “Transport and Pedestal Physics in Tokamaks”. These Schools are primarily designed for graduate students, post-docs, and young researchers. If you are interested in attending, please go to the School’s website and register. The registration deadline is November 15, but you should keep in mind that you’ll need some extra lead time to apply for a visa.

The US Burning Plasma Organization is once again making available several scholarships for US participants to this year’s ITER International School. The scholarships will cover your round-trip airfare and the registration fee; the hosts are providing meals and housing at no cost to the participants. Participants’ USBPO Newsletter, October 31, 2015, Issue 101, BurningPlasma.org Page 4 of 10 home institutions are encouraged to supplement the scholarships to cover other travel-related expenses.

Please note that these scholarships are limited to graduate students and post-docs who are US citizens. Others, of course, are welcome to attend the school, but will have to find other support. I apologize for any inconvenience this late information may cause.

Please send applications to Dr. Xianzhu Tang (xtang@lanl.gov), chair of the selection committee. In each application, please include (1) a vita, (2) a list of publications, (3) a statement about the reasons why your participation at this School would be beneficial, and (4) a letter of reference from a senior scientist who is knowledgeable about you. Due to the need to get a quick start on visa applications (we will provide assistance with this for the scholarship winners) we ask that your applications be received no later than Monday, November 2.

The USBPO scholarships to the IIS have been very popular in previous years, and we have not been able to support all worthy candidates. I would hope that some of the applicants’ home institutions might be able to provide assistance for additional participants to attend what promises to be a very valuable educational experience.

Research Highlight

Modeling and Simulation Topical Group, Leaders: Xianzhu Tang and Lang Lao

A major disruption posts a significant operational risk for ITER. It exacerbates the already challenging plasmamaterials interaction problem in plasma-facing components (PFC). The primary culprit is the disruption-induced runaway electrons, which if not adequately mitigated, can locally melt and even burn through the thin first layer of the actively cooled PFCs. Much progress has been made recently in laying down the fundamental theory and developing the predictive modeling tool to understand the generation and saturation mechanisms of runaway electrons in tokamak geometry.


Recent Developments in Runaway Electron Theory

B.N. Breizman Institute for Fusion Studies, The University of Texas, Austin, Texas 78712, USA

The importance of runaway electron production in plasma was recognized in a seminal work by Dreicer [1], followed by enlightening subsequent studies by Gurevich [2]. The initial nonrelativistic results [1,2] have been generalized to the relativistic case by Connor and Hastie [3]. Their work, as well as [1] and [2], employs a small-angle scattering approximation for Coulomb collisions. The missing large-angle (knock-on) collisions are known to be weak compared to the small-angle collisions, but they can cause an avalanche-type growth of the runaway population, as pointed out in Ref. [4] and substantiated in Refs. [5,6].

In magnetically confined plasmas, acceleration of the runaway electrons can be limited by synchrotron losses that accompany pitch-angle scattering. The significance of this mechanism was first shown in Ref. [7] and then emphasized in Refs. [8,9].

Figure 2

Figure 1: Dependence of the avalanche growth rate on the normalized inductive electric eld. The gure shows the growth rate predicted in Ref. [10] (solid curve) in comparison with Ref. [6] (dashed curve) and the growth rate inferred from the dynamical model of Ref. [7] (dotted curve).

Runaway electrons have attracted increased attention in recent years as a potential risk factor for ITER where they can develop easily during plasma disruptions. Of particular interest is the near-threshold regime of runaway production. It is important to have an accurate theory for the nearthreshold regime, because it represents long-term behavior of the runaways and is critical for the runaway mitigation process. Even a very strong initial inductive electric field is reasonably expected to drop down to the threshold-level values with the growth of the runaway population. The key questions in that regard are: what is the threshold electric field and what is the growth rate of the avalanche when the electric field exceeds the threshold?

These questions have recently been addressed in Ref. [10] via rigorous kinetic description of relativistic runaway electrons in the near critical electric field in USBPO Newsletter, October 31, 2015, Issue 101, BurningPlasma.org Page 6 of 10 tokamaks. The theory developed in Ref. [10] demonstrates that the electric field for runaway avalanche onset is higher and the avalanche growth rate is lower than previous predictions. This theory also predicts peaking of the runaway distribution function at the phase-space attractor and the existence of two different threshold fields that produce a hysteresis in the runaway evolution. These findings open a possibility for improved interpretation of the corresponding experiments, including interpretation of the x-ray and synchrotron emission measurements. The existence of threshold electric fields for sustainment and growth of the runaway population explains the linear decay of the toroidal current in the runaway mitigation experiments where the avalanche-produced runaway current has to be in a self-sustained regime of marginal criticality [11].

Another recent development in runaway theory concerns microinstabilities that are potentially able to enhance scattering of the runaways and thereby facilitate the mitigation process. In the early tokamaks, such as TM-3, T-6, TFR and others, the fan instability [12, 13] was observed frequently in the presence of runaway electrons. Parail and Pogutse [14, 15] have attributed this phenomenon to excitation of magnetized electron plasma waves. Their local linear and quasilinear analysis has been instrumental in understanding the origin of enhanced scattering. Yet, the local theory is insufficient for runaway stability analysis. The point is that it does not cover the effect of plasma non-uniformity on the excited waves and the system size constraints on the wave growth. Also, the analysis of magnetized plasma waves needs to be extended to other potentially unstable modes. References [16-18] reflect the efforts motivated by these unsettled issues. In particular, they emphasize the role of whistler waves and suggest an estimate for their convective damping, in addition to collisional dissipation. However, the expression for the instability threshold obtained in [16-18] is problematic for two reasons. First, the collisional damping rate for whistlers is overestimated. Second, the explanation of convective damping misses the possibility of wave ducting due to internal reflection that enables amplification of the wave over multiple radial passes.

The characteristic wavelengths of the runaway-driven modes are typically smaller than the plasma radius, which suggests the use of the Wentzel-Kramers-Brillouin (WKB) approximation rather than a full wave description of the waves of interest. This approach has been implemented in a ray-tracing code COIN (convective instability) that is designed to examine kinetic instabilities of a runaway beam in a tokamak for any given equilibrium configuration of the plasma and any distribution function of the runaway electrons [19]. The code incorporates refined expressions for the drive and damping and it covers convective aspects of the instability as well as the effect of linear mode coupling in non-uniform plasmas. Based on the experimentally measured parameters of the runaway electron beam in DIIID, the COIN code predicts robust stability of such a beam with respect to high-frequency kinetically driven modes. Preliminary calculations for ITER indicate that the minimal temperature for the whistler instability onset is 22 eV in the case of a perfectly reflective plasma boundary. The calculations were done for a flat temperature profile, runaway current of 12 MA (1MA=m2), electron density of 1:3  1020m􀀀3 and average runaway energy of 15MeV. The COIN code can serve as a convenient computational module for stability assessment of the runaway population.

References

[1] H. Dreicer, Phys. Rev. 115, 238 (1959); 117, 329 (1960).

[2] A. V. Gurevich, J. Exp. Theor. Phys. 39, 1296 (1960).

[3] J.W. Connor and R. J. Hastie, Nucl. Fusion 15, 415 (1975).

[4] Yu. A. Sokolov, JETP Lett. 29, 218 (1979).

[5] R. Jayakumar, H. H. Fleischmann, and S. Zweben, Phys. Lett. A 172, 447 (1993).

[6] M. N. Rosenbluth and S. V. Putvinski, Nucl. Fusion 37, 1355 (1997).

[7] J. R. Martin-Solis, J. D. Alvarez, R. S´anchez, and B. Esposito, Phys. Plasmas 5, 2370 (1998).

[8] F. Andersson, P. Helander, and L-G. Eriksson, Phys. Plasmas 8, 5221 (2001).

[9] A. Stahl, E. Hirvijoki, J. Decker, O. Embreus, and T. F¨ulop, Phys. Rev. Lett. 114, 115002 (2015).

[10] P. Aleynikov and B. N. Breizman , Phys. Rev. Lett. 114, 155001 (2015).

[11] B. N. Breizman, Nucl. Fusion 54, 072002 (2014).

[12] V.V. Alikaev, K.A. Razumova and Yu A. Sokolov, Sov. J. Plasma Phys. 1, 303 (1975).

[13] V.S. Vlasenkov, V.S. Leonov, V.G. Merezhkin and V.S. Mukhovatov, Nucl. Fusion 13, 509 (1973).

[14] V.V. Parail and O.P. Pogutse, Nucl. Fusion 18, 303 (1978).

[15] V.V. Parail and O.P. Pogutse, in Runaway electrons in a tokamak Reviews of Plasma Physics vol. 11, ed M.A. Leontovich (New York: Consultans Bureau) 1986.

[16] T. F¨ulop, G. Pokol, P. Helander and M. Lisak, Phys. Plasmas 13, 062506 (2006).

[17] G. Pokol, T. F¨ulop and M. Lisak, Plasma Phys. Control. Fusion 50, 045003 (2008).

[18] T. F¨ulop, H. Smith. and G. Pokol, Phys. Plasmas 16, 022502 (2009).

[19] P. Aleynikov and B. N. Breizman, Nucl. Fusion 55, 043014 (2015).

This work was supported by ITER under Contract No. ITER-CT-12-4300000273, and by the U.S. Department of Energy Contract No. DEFG02-04ER54742. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.

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Schedule of Burning Plasma Events

USBPO Public Calendar: View Online or Subscribe

2015         NSTX-U First Plasma — August 10 W7-X First Plasma —

Nov 3-618th International Spherical Torus Workshop (ISTW-2015)Princeton, NJ, USA
Nov 3-625th International TOKI ConferenceGifu, Japan
Nov 16-2057th APS Division of Plasma Physics MeetingSavannah, GA, USA
Nov 22-2420th MHD Stability Control WorkshopPrinceton, NJ, USA
Dec 16-17Fusion Power Associates 26th Annual Meeting and Symposium: Strategies to Fusion PowerWashington, DC, USA

2016         — 10th Anniversary of USBPO Formation —

Jan 25-28,22nd ITPA DivSol, ENEA Research CenterFrascati, Italy
May 30-June 3PSI ConferenceRome, Italy

2019          JET DT-campaign — JT60-SA First Plasma —

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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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