News and Events


U.S. Burning Plasma Organization eNews
Sept 30, 2015 (Issue 100)

 

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

Director’s Corner
C.M. Greenfield
Research Highlight
N.J. Fish
Schedule of Burning Plasma Events  
Photograph of the Month
 
Contact and Contribution Information

Announcements

Remembering Cynthia Phillips

We were extremely saddened this month to learn of the death of Dr. Cynthia Phillips. For those who had not heard the news, Cynthia died on September 1 after a decade long battle with cancer. She was well known to many around the world as a leading expert in RF physics, and a wise voice in the fusion community. A nice description of her career and personal qualities prepared by her colleagues at PPPL can be found here.

We would like to add our acknowledgment and appreciation of the many contributions Cynthia made to the U.S. Burning Plasma Organization. She was very involved in its formation and early leadership. Before, during and after the U.S. Burning Plasma Workshop at ORNL, in Dec. 2005, she argued strongly and persuasively for the need for a topical group on Plasma-Wave Interactions, making the case that this is a distinct community of experts that is not adequately represented in ITPA. It is largely thanks to Cynthia that this topical group exists, and so when the USBPO was launched the following year she was, appropriately, appointed as its first leader. At that time Amanda served as Vice Chair of the Council and Chuck served along with Cynthia on the Research Committee. Many formative decisions were made in that period, and Cynthia shared her wisdom and commitment with the organization. Following the end of her term as topical group leader, she was asked to serve on the USBPO Council, where she again provided much valuable input from 2010-2013. Whether at a meeting, or in a private conversation or email, we always appreciated her advice. We will greatly miss her advice and friendship.

Amanda Hubbard and Chuck Greenfield


Director's Corner

by C.M. Greenfield

US Burning Plasma Organization Council Election

I am happy to announce the results of the recent USBPO Council election, during which Earl Marmar of MIT and David Pace of General Atomics were elected. Earl and David were selected from an excellent slate of candidates that had been put together by our nominating committee (Ted Biewer, Chuck Kessel, Xianzhu Tang, Dan Thomas and Anne White) based on your suggestions. Following the election, and in accordance with the USBPO bylaws, I appointed two additional members to fill out the Council. They are Stan Kaye of Princeton Plasma Physics Laboratory and Susana Reyes of Lawrence Livermore National Laboratory.

I look forward to serving with the new Council, and wish to thank the outgoing members: Jon Menard, Anne White, and Clement Wong. In accordance with the USBPO bylaws, Mark Koepke's term on the Council is being extended for one more year to allow him to complete his term as chair. The 2015-2016 USBPO Council is then as follows (last column is the year their term ends):

Larry Baylor ORNL 2016
David Brower UCLA 2017
Stan Kaye PPPL 2018
Chuck Kessel PPPL Vice-Chair 2016
Mark Koepke West Virginia U Chair 2016
Earl Marmar MIT 2018
David Maurer Auburn 2016
David Pace GA 2018
Juergen Rapp ORNL 2017
Susana Reyes LLNL 2018
Jim Terry MIT 2017
Dan Thomas GA 2016
François Waelbroeck U Texas 2017

Our selection of new topical group leaders and deputy leaders is nearly complete, and will be announced in next month's eNews.

Progress at ITER

Visiting the ITER site several times each year gives me a chance to see occasional snapshots of the facility as it rises from (and below) the ground. During my last couple of visits I watched as the pillars that will support the ITER Assembly Building were erected. Since my last visit in May, the pillars have been completed and, this month, the roof structure, comprised of 730-tons of steel, was raised into place. The process took 14 hours, as 22 hydraulic jacks lifted the roof structure to a height of 50 meters.

The ITER Assembly Building before (left) and after (right) the roof was lifted into place. Photos © ITER Organization.

Preparations are currently underway for the nineteenth meeting of the ITER Science and Technology Advisory Committee (STAC-19). Once again, the US participants will be Rob Goldston (PPPL), Earl Marmar (MIT), Juergen Rapp (ORNL), Jim Van Dam (DOE) and myself. We will consider the following 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)

STAC-19 will produce a report that will provide input to the ITER Council at its November meeting. Similarly, the Management Advisory Committee (MAC) will meet in a few weeks 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 year's agenda is as follows:

Speaker Institution Title
Joseph Snipes ITER ITER Plasma Control System Development
Eugenio Schuster Lehigh University Nonlinear Control and Online Optimization of the Burn Condition in ITER
Menno Lauret Lehigh University Sawtooth period control by power modulation
Antonius J. Donne EUROfusion Risk mitigation for ITER by a prolonged and joint international operation of JET
R.A. Moyer UC San Diego Testing RMP ELM suppression models in low torque ITER Baseline Scenario
Guosheng Xu Chinese Academy of Sciences Advances in ELM control towards long-pulse H-mode plasmas on EAST
S. Brezinsek FZJ ELM-induced W sputtering sources in JET
Larry Baylor ORNL Application of Pellet Injection to Mitigate Transient Events in ITER
R. Granetz MIT Disruption Mitigation of Plasmas with Locked Modes
R.J. La Haye General Atomics Effect of thick blanket modules on neoclassical tearing mode locking in ITER
Mike Dunne IPP-Garching Predictive modelling of the impact of a radiative divertor on pedestal confinement on ASDEX Upgrade
B.A. Grierson PPPL Time Dependent Predictive Modeling of DIII-D ITER Baseline Scenario using Predictive TRANSP
Junya Shiraishi Japan Atomic Energy Agency Status of the ITER plasma modeling activities in JAEA
G.M. Staebler General Atomics The Impact of Zonal Flows on the Performance Predictions for ITER
E.J. Doyle UCLA Progress in the Design and Development of the ITER Low-Field Side Reflectometer (LFSR) System

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 Community Workshops. Please refer to the conference agenda for more information.

ITER International School

This year's ITER International School will be held on December 14-18, at the University of Science and Technology in Hefei, China. The topic will be Transport and Pedestal Physics in Tokamaks. More information can be found here.

We are once again planning to organize a scholarship program for several postdocs and graduate students. We will announce this soon.



Research Highlight

Integrated Scenarios Topical Group, Leaders: D. Green and R. Pinsker

This month's Research Highlight summarizes recent theoretical work by Nathaniel Fisch on possible applications of the Lower-Hybrid wave to enable the channeling of power from fusion born alphas to the fuel ions via wave-particle interactions (Alpha Channeling). Such channeling may lead to the desirable property of higher ion temperatures (relative to electron temperatures) in Tokamak plasmas.

The Alpha Channeling Effect

N.J. Fisch 1
1Princeton Plasma Physics Laboratory, Princeton, New Jersey USA

Alpha particles born through fusion reactions in a tokamak reactor slow down mainly through collisions with electrons. By collisions also mainly with the electrons, the fuel ions then reach thermonuclear temperatures, sustaining the fusion reaction. But, with power flow in this direction, the electrons would then necessarily be hotter than the fuel ions. It would, however, be highly desirable in a self-sustained tokamak fusion reactor that ions be hotter than electrons. After all, without contributing to fusion reactions, the electrons take up valuable pressure that could otherwise be reserved for ions. With ions hotter than electrons, the fusion reactivity is higher at constant confined pressure. Also, the electron heat losses, such as through radiation or transport, are difficult to control, and the lost energy will not then be captured by the fuel ions. Thus, it would be highly useful if the fuel ions might directly capture the alpha particle energy, rather than relying on the electrons as an intermediary.

Power flow in fusion reactors. The normal power flow follows the green arrows, as α particles predominantly slow down on electrons. The electrons then heat the fuel ions on a collisional time scale. Under α channeling, this flow is disrupted. The red arrows indicate the flow of power when waves channel power from α particles to energetic fuel ions on a collisionless time scale. On a collisional time scale, the energetic fuel ions then equilibrate with the bulk fuel ions, which then heat the electrons.

Fortunately, although the α particles predominantly lose their energy to electrons, that process could in a tokamak reactor take up to hundreds of milliseconds. That leaves time for waves to extract energy from the α particles on a collisionless timescale []. Thus, this energy might instead be channeled into useful energy, catalyzed by injected waves, so as to heat fuel ions or to drive current. The way that channeling might happen is depicted schematically in Fig. *. If this can be done quickly then a further advantage is that the α particle energy would also not be available to destabilize toroidal Alfven modes and other waves, in a way deleterious to energy confinement.

The interaction between waves and α particles is expected to be stochastic; in other words, the α particles randomly gain or lose energy in interacting with the wave, resulting in diffusion in energy. It is also possible that the random gain or loss of energy is accompanied by a change in position related to the energy change, resulting in diffusion in energy in a way that is strictly coupled to diffusion in space. If these diffusion paths in energy-position space point from high energy in the center of the tokamak to low energy on the periphery, then α particles will be cooled while forced to the periphery. The energy from the α particles is absorbed by the wave. The amplified wave can then heat ions or drive current. This process or paradigm for extracting α particle energy collisionlessly has been called Òα channelingÓ. While the effect is speculative, the upside potential for economical fusion is immense [].

Since α-particles are born at 3.5 MeV, with spatial localization at the center of the tokamak, there is the opportunity for such an inverted energy distribution. However, for energy extraction by an electrostatic wave, the diffusion in energy must be coupled to diffusion in space, since the projection of an isotropic velocity distribution along any one velocity direction is not inverted. However, there are few high energy α particles at the periphery, so diffusion paths in energy-position space can readily produce the inversion.

There were a number of interesting experiments performed on TFTR in the 1990's that showed that mode-converted ion Bernstein waves could produce diffusion paths in energy-position space. However, in those experiments, since there were few fusion-produced α particles, the wave parameters were chosen so that the diffusion paths connected cold in the center with hot on the periphery, diffusing 80 keV beams of deuterium ions so that they could be detected at 2.2 MeV at the periphery [,]. This was of course not the cooling effect desired, but it did show that in principle the diffusion paths could operate as expected. There is reason to expect that this effect could be extrapolated to reactors using a combination of waves [,].

Orbit of an α-particle in a uniform z-directed (into the paper) magnetic field. An electrostatic wave, traveling with phase velocity ω/ky in the y-direction gives an impulse at the resonance point ω = ky vy. If the particle gains energy, it moves to the red orbit; if it loses energy, it moves to the green orbit.

To see that diffusion in energy can be strictly correlated to diffusion in space, consider the α-particle orbits in Fig. *. For simplicity, we consider cylindrical geometry. Here an electrostatic wave, with phase velocity in the y-direction diffuses α-particles such that if the particle gains energy it moves up (larger x), and if it loses energy, it moves down. The interaction can be repeated, with the guiding center moving up with increasing energy and down with decreasing energy of the α-particle. By associating the up direction with the tokamak center, and down with the periphery, this accomplishes the basic idea of the α-channeling effect.

What are some current trends in α-channeling research? One is to recognize that the paradigm also operates more generally in other configurations of magnetically confined plasma. In different machines, different waves would be appropriate. Alpha channeling can be practiced in particular in mirror machines, where the concept of plasma periphery now includes the loss cone in velocity space []. In supersonically rotating plasma, there is additional axial confinement due to the rotation, and there is also the opportunity to store energy in the plasma potential. A generalization of the channeling effect, in which some of the particle energy ends up in electric potential energy, can be useful in such centrifugal confinement devices for fusion []. In fact, waves with low frequency, which includes a fixed azimuthal perturbation (zero frequency), can be used instead to support the radial potential []. This (generalized) channeling effect might then be used to replace the electrodes that produce the radial potential, which would be advantageous technologically in rotating plasma devices such as plasma centrifuges []. A second trend is to identify how α channeling works together with other tokamak procedures. For example, oscillating the current drive on a slow time scale in a tokamak, but fast compared to the L/R timescale, while varying other parameters, produces extraordinary current drive efficiencies. It turns out that this prescription for optimizing the current drive efficiency works synergistically with the α channeling effect []. Here, the α channeling is employed to produce a hot ion mode in the low density phase of the oscillating resistivity. A second example of this trend is the extent to which the same wave used to extract α particle energy can also be used for current drive. It turns out that there is a strong constraint relating current drive by lower hybrid waves and α channeling by lower hybrid waves []. It is possible to accomplish both with the same wave, most readily through inside launch of the lower hybrid wave.

Acknowledgments:

This work was supported by the U.S. DOE under Contract No. DE-AC02-09CH11466.

References

[1] N. J. Fisch and J. M. Rax, Phys. Rev. Lett. 69, 612 (1992).
[2] N. J. Fisch and M. C. Herrmann, Utility of Extracting Power from Alpha Particles by Waves, Nucl. Fusion 34, 1541 (1994).
[3] N. J. Fisch and M. C. Herrmann, A Tutorial on Alpha Channeling, Plasma Physics and Controlled Fusion 41, A221 (1999).
[4] N. J. Fisch, Physics of alpha channelling and related TFTR experiments, Nuclear Fusion 40, 1095 (2000).
[5] N. J. Fisch and M. C. Herrmann, Alpha Channeling with Two Waves, Nuclear Fusion 35, 1753 (1995).
[6] M. C. Herrmann and N. J. Fisch, Cooling energetic alpha particles in a Tokamak with waves, Phys. Rev. Lett. 79, 1495 (1997).
[7] N. J. Fisch, Alpha Channeling in Rotating Plasmas, Phys. Rev. Lett. 97, 225001 (2006).
[8] A. J. Fetterman and N. J. Fisch, Alpha Channeling in Rotating Plasmas, Phys. Rev. Lett. 205003, 612 (2008).
[9] A. J. Fetterman and N. J. Fisch, Alpha channeling in rotating plasma with stationary waves, Phys. Plasma 17, 042112 (2010).
[10] A. J. Fetterman and N. J. Fisch, Wave-particle interactions in rotating mirrors, Phys. Plasma 18, 055704 (2011).
[11] N. J. Fisch, Transformer Recharging with Alpha Channeling in Tokamaks, J. Plasma Phys. 76, 627 (2010).
[12] I. E Ochs, N. Bertelli and N. J. Fisch, Coupling of alpha channeling to parallel wavenumber upshift in lower hybrid current drive, Phys. Plasma 22, 082119 (2015).

Schedule of Burning Plasma Events

USBPO Public Calendar: View Online or Subscribe

2015  - NSTX-U First Plasma - August 10 - W7-X First Plasma -
September 30 - October 2, IAEA TCM on Innovative Divertors, Vienna, Austria
October 11 - 16, 17th International Conference on Fusion Reactor Materials, Aachen, Germany
October 12-15, 15th ITPA : Integrated Operation Scenarios group meeting, Hefei, China
October 19 - 21, H-mode workshop, Garching, Germany
October 22 - 23, ITPA: Transport & Confinement Topical Group Meeting, Garching, Germany
October 22 - 23, ITPA: 28th Meeting of the Pedestal and Edge Physics Topical Group, Garching, Germany
November 3 - 6, 18th International Spherical Torus Workshop (ISTW-2015), Princeton, NJ, United States
November 3 - 6, 25th International TOKI Conference, Gifu, Japan
November 16 - 20, 57th APS Division of Plasma Physics Meeting, Savannah, GA, United States
November 22 - 24, 20th MHD Stability Control Workshop, Princeton, NJ, United States
December 16-17, Fusion Power Associates 26th Annual Meeting and Symposium: Strategies to Fusion Power, Washington, DC, United States
2016  - 10th Anniversary of USBPO Formation -
2017  - JET DT-campaign -
2019  - JT60-SA First Plasma -

Image of the Month

C-Mod (Greg Wallace and Bob Mumgaard): Lower hybrid current drive (LHCD) in Alcator C- Mod. The color along the ray trajectories (red to blue) indicates the power remaining in each of the four rays as they propagate around the tokamak starting at the LH antenna (in the back of the tokamak just right of the central column), as calculated by GENRAY [A. P. Smirnov and R.W. Harvey, Bull. Amer. Phys. Soc., 40:1837, 1995.]. The four rays experience different upshifts in kk, and thus damping, as a result of the poloidal launch angle. The green shading represents a “virtual diagnostic camera” view of the LH driven current as calculated by CQL3D [R. W. Harvey and M. McCoy, “The CQL3D Fokker-Planck Code.” Proc. IAEA Tech. Comm. Meeting on Simulation and Modeling of Thermonuclear Plasmas, pages 489526, 1992.].

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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: Saskia Mordijck (mordijck@fusion.gat.com)

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