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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	Greg Wallace & Cornwall Lau
Schedule of Burning Plasma Events
Contact and Contribution Information

 

US Magnetic Fusion Research Strategic Directions Workshop

The second community workshop will be held at the University of Texas in Austin, December 11-15. Working groups have been assembled and holding regular discussions over the past month or more. Please see the following link for more information on the working groups:

https://sites.google.com/site/usmfrstrategicdirections/workshop02_austin/working-groups

By C.M. Greenfield

ITER Project celebrates its first ten years

During the recent ITER Council meeting, the tenth anniversary of the formation of the ITER Or-ganization was celebrated. During the Council meeting, it was also recognized that since the be-ginning of 2016, all 26 major project milestones have been achieved. This is a marked improve-ment from previous years, and gives reason for optimism that the plan now in place, leading to first plasma in 2025, is realistic and achievable.

Another landmark in the life cycle of the ITER project is in the leadership of the Science and Operations Directorate, the group that most of us in the Fusion Science community have the closest ties to. Longtime Director David Campbell is retiring at the end of the year, and his re-placement – a familiar face to many of us in the US and international programs – arrived this month. That would be Tim Luce, formerly of General Atomics and DIII-D. I think I speak for all of us in the US Burning Plasma Organization in wishing David the best in his retirement, and looking forward to continuing to work with Tim.

TPA Coordinating Committee meetings

During the recent ITER Council meeting, the tenth anniversary of the formation of the ITER Or-ganization was celebrated. During the Council meeting, it was also recognized that since the be-ginning of 2016, all 26 major project milestones have been achieved. This is a marked improve-ment from previous years, and gives reason for optimism that the plan now in place, leading to first plasma in 2025, is realistic and achievable.

Earlier this month, I attended the annual ITPA Coordinating Committee meeting at ITER Headquarters. The main purpose of this meeting is to hear reports from each of the ITPA topical groups and discuss ITPA joint experiments. Things were a little bit rushed this year, as the meeting had to be held about a month earlier than usual, leaving very little time between the conclusion of the fall ITPA meetings and these discussions. Nevertheless, there is a rather long list of joint experiments which I hope to be able to share on the USBPO website soon.

The ITPA topical group leaders have three-year terms, and this was the year to select new leaders for most of the groups, the exception being the Diagnostics Topical Group, which Dave Brower (UCLA) took leadership of last year due to his predecessor stepping down. Among the other new leaders and deputy leaders are two other US scientists; Don Spong (ORNL) is the new leader of the Energetic Particles Topical Group, and Max Fenstermacher (LLNL) is the new deputy leader of the Pedestal and Edge Physics Topical Group. The full list of leaders and members for all seven topical groups can be found at https://www.iter.org/org/team/fst/itpa.

Speaking of ITPA topical group membership, Matt Lanctot of DOE is currently in the process of polling the current US members for their interest and ability to continue. This is to identify possible vacancies, and create opportunities for new topical group members in the near future. Anyone interested in increasing their participation in the ITPA topical groups should contact Matt directly.

This meeting also presented another opportunity for me to see the progress on the ITER site; my previous visit was in May, about six months earlier. As has been the case in recent years, progress on the construction site was obvious and significant. One somewhat bittersweet observation is that there seems now to be less to see on subsequent visits, as more and more buildings are closed up (most of them have active construction work going on inside, preventing tourists such as myself from getting a look). If you look back at photos I’ve shared before, it was easy to spot the bioshield that will surround the tokamak. Now the bioshield is nearly complete, but is also mostly surrounded by the walls of the tokamak building.

Since the inception of the USBPO, Nermin Uckan of ORNL has been our Assistant Director for ITER Liaison. We will be saying farewell to her at the end of December as she retires. Nermin’s involvement in burning plasmas goes back much further than the USBPO, as she was involved in ITER from the very beginning of the ITER Conceptual Design (CDA) and Engineering Design Activities (EDA). We wish Nermin the very best in her retirement. I know she’ll be watching us as we move toward the burning plasma that she has spent her career working for.

 

USBPO Leadership

Five of our topical group leaders recently completed their two-year terms. We’re a little late, but we have now completed the selection process for 2017, as follows:

Energetic Particles Topical Group: Nikolai Gorelenkov (PPPL) completed his term, and previous deputy Eric Bass (UCSD) became the new leader. Cami Collins (GA) is the new deputy leader.

Fusion Engineering Science Topical Group: David Rasmussen (ORNL) completed his term, and previous deputy Jean Paul Allain (Illinois) became the new leader. Masa Shimada (INL) is the new deputy leader.

Operations and Control Topical Group: Jim Irby (MIT) completed his term, and previous deputy Eugenio Schuster (Lehigh) became the new leader. The new deputy leader is Dan Boyer (PPPL).

Pedestal and Divertor/SOL Topical Group: John Canik (ORNL) completed his term, and previous deputy Mike Jaworski (PPPL) became the new leader. The new deputy leader is Jerry Hughes (MIT).

Plasma-Wave Interactions Topical Group: Bob Pinsker (GA) completed his term, and previous deputy Greg Wallace (MIT) became the new leader. The new deputy leader is Cornwall Lau (ORNL).

A big thank you to the outgoing and incoming leaders! The 2017-2018 Research Committee now includes:

 

We will select new leaders for the remaining five topical groups – Confinement and Transport, Diagnostics, Integrated Scenarios, MHD and Macroscopic Plasma Physics, and Modeling and Simulation – next summer.

Plasma Wave Interactions Topical Group (Leaders: Greg Wallace & Cornwall Lau)

This month’s research highlight by Dr. Elijah Martin of ORNL describes exciting new measurements of lower hybrid wave electric fields in the Alcator C-Mod tokamak using a passive spectroscopic technique. Dr. Martin presented an invited talk on this subject at the recent APS-DPP 2017 meeting in Milwaukee.

Searching for the physics mechanism behind anomalous loss of lower hybrid current drive in the high density regime

E. H. Martin^1*, C. Lau¹, G. M. Wallace², R. T. Mumgaard², and S. Shiraiwa²

¹Oak Ridge National Laboratory, Oak Ridge, TN 37831

²MIT Plasma Science and Fusion Center, Cambridge, MA 02139

*Email: martineh@ornl.gov

Steady state tokamak operation requires an external means to drive the plasma current using non-inductive methods. It has been well established that electromagnetic waves in the lower hybrid (LH) range of frequencies (1 to 8 GHz) can drive current with high efficiency through Landau damping on the electrons [1]. For limited plasma configurations [2], lower hybrid current drive (LHCD) has no obvious impediments within the density accessibility limit [3]. However, for diverted plasmas LHCD experiences an anomalous drop in efficiency as the density is increased and becomes completely ineffective for line-averaged densities approximately greater than 10²⁰ m^-3 [4]. A thorough theoretical and experimental undertaking to determine the responsible phenomena has been on-going for the last decade. Many mechanisms have been identified as parasitic to LHCD such as low frequency scrape off layer (SOL) density fluctuations [5,6], parametric decay instabilities [7], pondermotive forces [8], and modification of the launched n_|| spectrum [9]. However, the ordering of importance of these phenomena for LHCD operation has not been established. Without a detailed knowledge of the relative significance of each physical mechanism, it has been difficult to proceed forward with an appropriate launcher design and mitigation techniques to address the anomalous drop in LHCD for high density diverted plasmas.

In this research highlight, we present new experimental measurements of the LH wave electric field vector, , in Alcator C-Mod and provide a direct comparison with 3D full wave COMSOL simulations using the cold plasma dielectric tensor and reflectometry measured density profiles. Two key results are reported:

1)  The magnitude of  was found to be in excellent agreement with the simulation results when a global average is taken along the magnetic field.

2)  The direction of  was found to have a substantial poloidal component and is in strong disagreement with the radially predicted simulation results.

Result (2) is of particular importance because LHCD can be severely affected by a modification to the direction of . It is expected that diffraction by SOL density fluctuations is the responsible mechanism [10].

Polarized passive optical emission spectroscopy is implemented to determine . This technique entails measuring two orthogonally polarized  spectral line profiles. The polarized spectra are referred to as  and  components and are polarized approximately perpendicular and parallel to the equilibrium magnetic field, respectively. The spectra are simultaneously fit to the Schrodinger equation containing both magnetic and time periodic electric field operators [11]. The three components of  are the only fit variables, all other important parameters such as the magnetic field vector, neutral temperature, and SOL density are known. The diagnostic was designed to allow for 27 magnetic field aligned measurement locations in front of the LH launcher. The collection volume associated with the optical emission is cylindrical with a diameter and length of approximately 40 mm, the length is constrained by the SOL D neutral density and is calculated using KN1D.

The experimental results were directly compared to 3D full wave COMSOL simulations via a synthetic diagnostic. The COMSOL model used the cold plasma dielectric tensor in toroidal axisymmetry with a superposition of multiple mode numbers to reproduce the 3D LH electric field structure. The simulated magnitude of  is very sensitive to the density profile, requiring the use of local reflectometry measurements for each condition investigated. However, it should be noted that the direction of  is quite insensitive to the density profile, only varying by a few degrees. Figure 1 presents a 3D simulation of the  magnitude for a LH net power of 330 kW and a line averaged density of 1.3 x 10²⁰ m^-3. A composite image of the LH launcher showing the 27 measurement locations as red circles is superimposed. The four resonance cones associated with the four rows of the LH launcher are clearly visible.

Figure 1. 3D full wave COMSOL simulation of  for C-Mod discharge 1160818010 at t=0.95 sec. The net LH power was 330 kW and the line averaged density was 1.3 x 10²⁰ m^-3. A composite image of the LH launcher showing the 27 measurement locations as red circles is superimposed. The locations highlighted in white are associated with the presented data.

Comparing the experimental and simulation results, good agreement was found with regard to the magnitude of  when a spatial average was taken along the magnetic field. Figure 2a presents the magnitude of  averaged over the white highlighted horizontal locations of Fig. 1. The cold-plasma theoretical P^1/2 trend was observed and is presented as the solid black line. These results suggest that all power is accounted for in the -n_|| portion of the spectrum and absorption near the LH launcher in the SOL does not seem to be occurring. The LH wave having –n_|| is responsible for LHCD.

Figure 2. (left) Spatially averaged magnitude as a function of net LH power. The data was averaged over the white highlighted row of Fig. 1. The experimental data is proportional to the square root of the lower hybrid power as dictated by the theory (black curve). (right) Direction of averaged over net LH power as a function of vertical location in the highlighted column of Fig. 1. Locations 1C and 6C refer to bottom and top of the LH launcher, respectively. The poloidal and radial directions correspond to 0 and 90 degrees, respectively.

Experimentally, it was determined that  contained a significant poloidal component having a magnitude on the order or greater than that of the radial component. Additionally, the poloidal component was found to increase towards the midplane. Figure 2b presents the direction of  averaged over 200 to 400 kW of net LH power for the white highlighted vertical locations of Fig. 1. This finding is in direct disagreement with the nearly radial direction predicted by the simulations. A sensitivity study of  on the density profile was conducted to determine a potential cause for the discrepancy. Little to no impact on the direction of  was observed while a large change in the magnitude occurred. It is expected that low frequency SOL density fluctuations are the responsible mechanism for the poloidal alteration in  direction [3] and will be the focus of future work.

In conclusion, experimental measurements of the  vector in the high density regime are presented. The results indicate that the expected power is accounted for in the –n_|| portion of the spectrum and that the direction of  is significantly altered poloidally.

Acknowledgements

The authors would like to thank the Alcator C-Mod team for their hospitality and efforts.  This work was funded by the DOE OFES (DE-AC05-00OR22725​ and DE-FC02-99ER54512).

References

[1] P. T. Bonoli, Trans. Plasma Sci. 12, 95 (1984).

[2] M. Porkolab et al, Phys. Rev. Lett. 53, 450 (1984)

[3] V. E. Golant, Sov. Phys. Tech. Phys. 16, 1980 (1972).

[4] G. M. Wallace et al, Phys. Plasmas 17, 082508 (2010).

[5] R. L. Watterson et al, Phys. Fluids 28, 2622 (1985)

[6] P. T. Bonoli and E. Ott, Phys. Fluids 25, 359 (1982).

[7] M. Porkolab, Phys. Fluids 17, 1432 (1974).

[8] V. Petrzilka et al, Nucl. Fusion 31, 1758 (1991).

[9] R. Cesario et al, Plasma Phys. Control. Fusion 53, 085011 (2011).

[10] M. Madi et al, Plasma Phys. Control. Fusion 57, 125001 (2015).

[11] E. H. Martin et al, Plasma Phys. Control. Fusion 57, 065011 (2015).

 

December 5-8	Joint 26th Int. Toki Conference & 11th Asia Plasma & Fusion Association Conference	Toki, Japan
December 6-7	Fusion Power Associates Annual Meeting	Washington, DC, USA
December 11-15	U.S. Magnetic Fusion Research Strategic Directions Community Workshop	Austin, Texas, USA

2018                                               

January 30-February 2	ITPA Scrape-off Layer & Divertor Topical Group meeting	Chengdu, China
March 5-9	ITPA MHD, Disruptions & Control Topical Group meeting	Naka, Japan
April 4-6	ITPA Pedestal & Edge Physics Topical Group meeting	Stockholm, Sweden
April 9-11	ITPA Transport & Confinement Topical Group meeting	Daejeon, South Korea
April 16-19	High Temperature Plasma Diagnostics (HTPD) conference	San Diego, CA
April 23-25	Sherwood Theory Conference	Auburn, AL
April 23-26	ITPA Diagnostics Topical Group meeting	San Diego, CA
April 23-26	ITPA Integrated Operating Scenarios Topical Group meeting	Daejeon, South Korea
May 8-11	US Transport Task Force (US-TTF) meeting	San Diego, CA
May 23-25	ITPA Energetic Particles Topical Group meeting	ITER HQ, France
June 17-22	International Conference on Plasma Surface Interactions (PSI)	Princeton, NJ
June 24-28	2018 IEEE International Conference on Plasma Science (ICOPS)	Denver, CO
July 2-6	EPS Conference on Plasma Physics	Prague, Czech Rep.
Sept 11-14	EU Transport Task Force (EU-TTF) meeting	Seville, Spain
October 22-27	IAEA Fusion Energy Conference	Gandhinagar, Gujarat, India
November 5-9	60th Annual Meeting of the APS Division of Plasma Physics	Portland, OR
November 11-15	ANS 23rd Topical Meeting on the Technology of Fusion Energy (TOFE)	Orlando, FL
November 12-18	2nd Asia-Pacific Conference on Plasma Physics	Kanazawa, Japan
December 4-6	ITPA Coordinating Committee & CTP ExComm	ITER HQ, France

2018                                               

June 24-28	2018 IEEE International Conference on Plasma Science (ICOPS)	Denver, Colorado, USA
October 22-27	IAEA Fusion Energy Conference	Gandhinagar, Gujarat, India
November 5-9	60th Annual Meeting of the APS Division of Plasma Physics	Portland, Oregon, USA

2019

JET DT-campaign and JT60-SA First Plasma
October 21-25	61st Annual Meeting of the APS Division of Plasma Physics	Fort Lauderdale, Florida, USA

 

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: Walter Guttenfelder (wgutten@pppl.gov)

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