News and Events

U.S. Burning Plasma Organization eNews

May 31, 2018 (Issue 130)

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
C.M. Greenfield
Research Highlight
E.M. Bass1
Schedule of Burning Plasma Events  
Contact and Contribution Information  


ITER internships

An announcement for ITER internship opportunities for undergraduate and graduate students was recently posted. Please see the following link for a description:

The proposed topics can be found here:


Director’s Corner By C.M. Greenfield

DEADLINE EXTENDED: Eleventh Annual APS-DPP Contributed Oral Session on “Research in Support of ITER”

For the tenth time, last year’s APS Division of Plasma Physics annual meeting included a contributed oral session on Research in Support of ITER, which included 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 60th Annual Meeting of the Division of Plasma Physics, which will take place in Portland, Oregon, on November 5-9. Once again, we are looking for 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. We hope to have broad participation once again, so we can highlight the breadth of this work and the institutions performing it, both US and international.

The abstract submission deadlines for this year’s meeting are quite early, so we need to get an early start with this year’s process. If you, or somebody from your institution, are interested in making a presentation in this session, please send a title, brief synopsis (one paragraph is sufficient), and speaker’s contact information as soon as possible (but no later than June 6) to Chuck Greenfield ( The brief synopsis should provide a sufficient description to understand the work and its importance to ITER.

Note that space is limited to 15 talks, so we may not be able to include all talks nominated. We will inform speakers by June 15, so any not selected for the ITER session may indicate a preference for other sessions, or allow the conference program committee to select an appropriate session.

NOTE: I know some of you are waiting to find out about your nominated invited talk, and I understand you may not know about that until mid-June. I don’t know of a good way to handle this, so I will only assure you that if you are offered space in this session I will understand if you decline it because you have an invited talk. But I will need you to tell me that quickly so we can continue to work to fill this session.

A full abstract would still need to be submitted via the conference website no later than 5:00 PM Eastern Daylight Time on June 29. If your talk is accepted for this session, please indicate “Research in Support of ITER” in the placement requests box.

ITER news

I attended the ITER Science and Technology Advisory Committee meeting this month at the ITER site. It had been six months since my last visit, and the construction progress during that time has been phenomenal. The committee was given a tour inside the Cryostat Workshop and the Tokamak Assembly Building (see photos), where we saw not only tooling for assembling the ITER tokamak, but an increasing number of tokamak components. One of my colleagues pointed out that there had been visible progress on some of the structures just during the three days we were there.

Scenes from ITER, May 2018. Clockwise from top left: 750-tonne crane that will lift tokamak components into the bioshield (in the Tokamak Assembly Hall), view from inside the cryostat base, another section of the cryostat, vessel segment assembly tool (in the Tokamak Assembly Hall). In the center is the tokamak complex with the now-completed bioshield in the middle.

Regarding the STAC meeting itself, we considered four charges (paraphrased here):

  1. Assess progress on outstanding issues for ITER’s Disruption Mitigation System (DMS)
  2. Review adjustments being made to ITER’s construction schedule to maintain the objective of first plasma in 2025
  3. Assess the status and plans for heating systems in the early phases of ITER operation
  4. Review progress towards the final design of the In-Vessel Vertical Stability

The US STAC participants were Rob Goldston (PPPL), Earl Marmar (MIT), Juergen Rapp (ORNL), Max Fenstermacher (LLNL), John Mandrekas (DOE), and myself (but as STAC chair I don’t count as part of the US delegation).

I don’t have much to report on charges 2-4 at this time. ITER has a path to stay on schedule for first operation in 2025, and the heating systems that will be available during the first two (non-activated) research campaigns are as previously reported.

Charge 1 represents increasing awareness of the importance of the Disruption Mitigation System (DMS) and the R&D still needed to confidently deploy it on ITER. Shattered Pellet Injection (SPI) has already been identified for the “Day 1” system, but there is still some uncertainty on the geometry (some changes in port allocations are being considered) and its efficacy (currently being tested on DIII-D and JET, and possible tests on KSTAR in the not-too-distant future), especially for mitigating a runaway electron channel that might form during the disruption.

There may still be opportunities to deploy an alternative DMS approach on ITER, but it would need to be brought to maturity before about 2030, in time for the second Pre-fusion-power operating (PFPO-2) period. Of course, if R&D were to be put off until 2029 and it was decided that SPI isn’t good enough, we would have a problem. If we work on this now I am confident we can be ready. But all of the ITER members need to be working (together, hopefully) to develop and qualify alternatives. This requires concerted effort including experiment, theory, and technology R&D. There are ideas already (see for example the 2015 US Transients Workshop Report), and at least one of them is already being tested.


Research Highlight

Energetic Particles (Leaders: Eric Bass & Cami Collins)

An outstanding problem in energetic particle physics is to be able to efficiently calculate Alfvén eigenmode induced transport and the resulting fast ion profile in order to help design optimal scenarios for fusion devices such as ITER. In this month’s research highlight, Dr. Eric Bass of General Atomics describes recent progress using a critical gradient model that makes it possible to simulate both alpha particle and beam ion confinement relatively quickly. This work will be the subject of an invited talk at the upcoming IAEA Fusion Energy Conference.

Recent developments in 1D critical gradient models of energetic particle transport

E.M. Bass1, R.E. Waltz2, and H. Sheng3

1University of California San Diego, San Diego, CA, USA

2General Atomics, San Diego, CA, USA

3School of Physics, Peking University, Beijing, China

Author e-mail:

Efficient heating of a fusion plasma by energetic particles (EPs), whether fusion-born alpha particles or neutral beam ions, requires these fast ions to remain confined long enough to impart their energy to the electron population by collisions. The collisional slowing-down time of the energetic particles is short compared to their corresponding classical transport time scales, but Alfvénic instabilities called Alfvén eigenmodes (AEs) can be kinetically destabilized by the EPs and cause rapid radial transport that jeopardizes heating and, at the scale of ITER, risks damage to plasma-facing components. Large EP orbits, non-Maxwellian EP distributions, and sparse AE spectra – leading to sometimes highly intermittent transport dynamics with order zero nonlinearities – all make calculating EP transport in realistic scenarios extremely difficult. Nevertheless, a greatly simplifying assumption of local stiff transport triggered at a critical gradient in the EP radial pressure profile enables reasonable estimates of the steady-state EP profiles and AE-induced transport coefficients.

The stiff transport, critical gradient paradigm has proved remarkably valid in experiments1,2 and has been verified in nonlinear gyrokinetic simulations with fixed equilibrium driving gradients3,4. A 1D radial EP transport reduced model based on this critical gradient assumption5 has been validated against experiment6 and recently been extended to include the suppressing effect of rotational shear4. This 1D transport model includes EP transport by background transport (generally low but non-negligible), EP sources from fusion and/or heating beams, an effective sink representing collisional slowing down to thermal plasma levels, and a rapidly rising diffusion coefficient above the AE critical gradient. Incorporation of further simplifying assumptions about the role of kinetic drive from thermal species has enabled an inexpensive and flexible implementation7 of the model based on the gyro-Landau fluid transport model TGLF8. The model now incorporates self-consistent simultaneous drive of multiple EP species to make estimates of transport in beam-heated ITER scenarios.

Nonlinear verification of the stiff transport critical gradient consists of running a sequence of local nonlinear GYRO simulations at varying EP drive levels by increasing the EP density while Text Box:  
Figure 1: Normalized growth rates at the local critical gradients found by nonlinear runaway at several radii of DIII-D discharge 146102 and values of the E×B shearing rate γ_E. The two sides of the linear critical gradient condition are the two axes. The fitting parameter a=0.15.
keeping the local gradient length fixed. Below the critical gradient, interaction with microturbulence-driven zonal flows saturates AEs at a low level of EP transport comparable to that driven by microturbulence (so-called “soft” AE transport)3. Above the critical gradient, nonlinear transport runs away without bound. In GYRO, the order zero equilibrium driving gradients are fixed, and runaway signifies equilibrium profile flattening is the required saturation mechanism. The crucial simplification going into the present critical gradient models is that the nonlinear critical gradient is well approximated by the linear condition  Here, is the AE growth rate with EP and thermal kinetic drives included, is the local microturbulent growth rate at the same low toroidal n, is the E´B shearing rate,  is the magnetic shear, and a is a fitting parameter4.

Text Box:  
Figure 2: Parametric scaling of the critical EP pressure. Note the dependence on (ks ̂/q)^2.
In Fig. 1, the two sides of the linear critical gradient condition equation are plotted for the EP drive where runaway first occurs – the critical gradient – at a variety of radii in beam-heated DIII-D discharge 146102. The E´B shearing rate is also artificially varied. The linear condition is found to agree within one estimated error bar for most cases tested. Whereas each point in Fig. 1 represents hundreds of thousands of CPU hours, the linear condition can be mapped out well with a few hundred CPU hours. A similar linear condition that completely neglects thermal drive, , works approximately as well. Here  is the AE linear growth rate with the kinetic drive from thermal species artificially removed from the gyrokinetic equations.  The linear condition including thermal-species effects on both sides reflects the cross-scale interplay between microturbulence, zonal flows, and AEs. Apparently though, the nonlinear suppression of AEs by microturbulence-driven zonal flows is cancelled (within error) by the upward shift of the AE growth rate due to thermal-species kinetic drive.

Text Box:  
Figure 3: Transported profiles in ITER predicted in the 1D critical gradient model using TGLFEP critical gradient pre-dictions. Blue curves are classical profiles, green curves are transported profiles with alpha particles and NBI ions consid-ered separately, and red curves show self-consistent transport with simultaneous NBI and alpha particle drive.
The critical gradient linear condition without thermal-species effects leads to some simple parametric scalings of the critical gradient7. In particular, the critical gradient is expected to be approximately proportional to . Higher equilibrium current is thus generally stabilizing, as is higher ellipticity. In reverse-shear discharges, the  surface is particularly dangerous because the critical gradient drops to near zero. The TGLFEP code, a parallel wrapper for TGLF, demonstrates this scaling over several decades in Fig. 2, from Ref. 7.

Neglecting thermal-species drive from the linear critical gradient condition also enables the generalization of the condition to multiple driving EP species with the formula . Here  is the EP pressure for species  and  is the local EP species critical gradient for the same species in the absence of any other driving EP species. The simple sum relationship means the simultaneous drive of AEs by multiple species can be accounted for by calculating the critical gradient for each species independently. Figure 3 shows the estimated effect the heating beam has on alpha-particle confinement in ITER. In Fig. 3, the independent NBI ion and alpha particle critical gradients have been calculated using the TGLFEP code for the ITER base case considered first in Ref. 5.


This material is based upon work supported by U.S. Department of Energy under Grants DE-FG02-95ER54309 (theory), DE-FC02-08ER54977 (SciDAC-GSEP project), and DE-SC0018108 (SciDAC-ISEP project). Disclaimer: "This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof."


1W. W. Heidbrink, M. A. Van Zeeland, M. E. Austin, E. M. Bass, K. Ghantous, N. N. Gorelenkov, B. A. Grierson, D. A. Spong, and B. J. Tobias, Nucl. Fusion 53, 093006 (2013).

2C. S. Collins, W. W. Heidbrink, M. E. Austin, G. J. Kramer, D. C. Pace, C. C. Petty, L. Stagner, M. A. Van Zeeland, R. B. White, and Y. B. Zhu, and DIII-D Team, Phys. Rev. Lett. 116, 095001 (2015).

3E. M. Bass and R. E. Waltz, Phys. Plasmas 17, 112319 (2010).

4E.M. Bass and R.E. Waltz, Phys. Plasmas 24, 122302 (2017)

5R. E. Waltz and E. M. Bass, Nucl. Fusion 54, 104006 (2014).

6R. E. Waltz, E. M. Bass, W. W. Heidbrink, and M. A. Van Zeeland, Nucl. Fusion 55, 123012 (2015).

7He Sheng, R. E. Waltz, and G. M. Staebler, Phys. Plasmas 24, 072305 (2017).

8G. M. Staebler, J. E. Kinsey, and R. E. Waltz, Phys. Plasmas 12, 102508 (2005).

Calendar of Burning Plasma Events


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.

August 27-31

Theory of Fusion Plasmas , Joint Varenna-Lausanne International Workshop

Varenna, Italy

Sept 3-5

ITPA Energetic Particles Topical Group meeting

Lisbon, Portugal

Sept 11-14

EU Transport Task Force (EU-TTF) meeting

Seville, Spain

Sept 17-20

ITPA Transport & Confinement Topical Group meeting

ITER HQ, Franc

October 1-3

ITPA MHD Disruptions & Control Topical Group meeting

Napoli, Italy

October 22-27

IAEA Fusion Energy Conference

Gandhinagar, Gujarat, India

October 29-31

ITPA Integrated Operation Scenarios Topical Group meeting

ITER HQ, France

October 29-31

ITPA Pedestal & Edge Physics Topical Group meeting

ITER HQ, France

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 12-14

21st MHD Stability Control Workshop


November 12-18

2nd Asia-Pacific Conference on Plasma Physics

Kanazawa, Japan

December 4-5

Fusion Power Associates 39th Annual Meeting & Symposium, Fusion Energy: Strategies & Expectations through the 2020s

Washington, DC

December 4-6

ITPA Coordinating Committee & CTP ExComm

ITER HQ, France


JET DT-campaign (

October 21-25

61st Annual Meeting of the APS Division of Plasma Physics

Fort Lauderdale, Florida, USA


JT60-SA First Plasma (

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.

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Editor: Walter Guttenfelder (


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