News and Events

U.S. Burning Plasma Organization eNews

September 30, 2020 (Issue 147)


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
Announcements for APS-DPP Community Planning Program
Contact and Contribution Information  

Director’s Corner

Chuck Greenfield, US BPO DIrector

Life and fusion research continue…

I write this hoping that all of you are remaining both healthy and productive despite the pandemic. Amidst the “Zoom fatigue” many of us are suffering, work is continuing at a remarkable pace, both on our domestic facilities and on ITER.

ITER from a distance

In a normal year, I would have visited the ITER site once or twice already. This is not a normal year – COVID-19 prevents us from traveling, so I have to watch ITER’s progress remotely. And the progress really is astonishing, not least because it’s continued at a rapid pace in the face of the pandemic. ITER now stands at something over 70% complete for first plasma. This has also forced us to revert to holding ITER meetings remotely… even the ITER Council meeting in June was held that way. Last week I attended an ITER Science and Technology Advisory Committee (STAC) meeting, postponed from May in futile hopes of being able to meet in person. We had attempted a remote meeting once before, in 2018, and it was very difficult. But necessity is the mother of invention, and we managed to have a productive meeting (despite yours truly having to connect and be awake four mornings in a row starting at 3AM).


Assembly of the ITER Tokamak is well under way

Since the cryostat base was lowered into the tokamak pit on May 26, lots more has happened at the ITER site. The next section of the cryostat, the lower cylinder, was lowered into place on August 31. This is the largest component of the tokamak, and had to be inserted with submillimeter tolerances. The next operation will be welding of the lower cylinder to the base; this may already be underway.

A picture containing motorcycle, sitting, mirror, parked

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The lower cylinder being lowered into the ITER tokamak pit. In the photo, the cylinder hangs four meters above the cryostat base as it is carefully positioned to submillimeter accuracy. Photo courtesy of the ITER Organization.

More details about the installation and a video of the procedure are available at https://www.iter.org/newsline/-/3479.

At the same time, major tokamak components, have been arriving on site and are being prepared for installation. These include four (of 18) toroidal field coils, one (of 9) vessel segment, and two poloidal field coils.

There is plenty of other activity going on at the ITER site. Much of the work has now transitioned from building to assembly, with some systems even beginning their commissioning process.

 

A large building

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The first vacuum vessel sector, recently arrived from Korea, lays on its side in the assembly hall. The 440 metric tonne component will be turned upright and attached to one of the giant assembly tools in the background, where a pair of toroidal field coils will be mounted. The full assembly, one vacuum vessel segment and two toroidal field coils, will then be lifted into the tokamak pit as a single unit. Photo courtesy of the ITER Organization.

 

Where I can learn more about ITER?

Most of the information I share here is readily available at the ITER website. In particular, ITER publishes a weekly Newsline (https://www.iter.org/newsline), with articles about construction and assembly, notable burning plasma advances around the world, and occasionally profiles of ITER staff (the latest issue has a profile of Tim Luce, who moved from DIII-D to become the Head of Science and Operation for ITER in 2018). The ITER website (http://www.iter.org) also has a large collection of photos. It’s not quite like being there, but it’s as close as we can get for now.

 

Research in Support of ITER contributed oral session at the Memphis Cyberspace APS-DPP
Conference

As you’ve no doubt already heard, the APS Division of Plasma Physics annual meeting will now be held remotely. We hope you’ll tune in for the 13th annual contributed oral session on
“Research in Support of ITER,” organized by the USBPO:

Larry Baylor (ORNL)

US

Research on Disruption Mitigation Enabled by Shattered Pellet Injection Systems on DIII-D, JET, and KSTAR in Support of ITER

Woong Chae Kim (NFRI)

Korea

Progress of Disruption mitigation with SPI and integration of real-time diagnostics for DECAF in KSTAR

Dmitrii Kiramov (Texas)

US

Pellet sublimation and expansion under runaway electron flux

Yipo Zhang (SWIP)

China

Progress in Disruption Mitigation on the HL-2A tokamak

Charlson Kim (SLS2)

US

NIMROD Shattered Pellet Injection Simulations

Michael Faitsch (MPI)

Germany

Broadening of the power fall-off length in a high density, high confinement H-mode regime in ASDEX Upgrade

Curtis Johnson (Auburn)

US

Diagnosing metastable populations in fusion edge plasmas using collisional-radiative modeling constrained by experimental observations with extrapolation to ITER parameter space

Nikolai Gorelenkov (PPPL)

US

Microturbulence-mediated route for stronger energetic ion transport and Alfvénic mode intermittency in ITER-like tokamaks

Christian Kiefer (MPI)

Germany

ASDEX Upgrade experiments and validation of theoretical transport models for the prediction of ITER PFPO-1 plasmas

Mireille Schneider (ITER)

France

Simulation of heating and current drive sources for various scenarios of the ITER Research Plan using the IMAS H&CD workflow

Emmi Tholerus (CCFE)

UK

Scenario development of ITER ELMy H-mode hydrogen plasma

Kathreen Thome (GA)

US

Changes in Impurity Transport with Applied Torque in DIII-D ELMy H-mode Plasma

Sun Hee Kim (ITER)

France

Assessment of access to ITER steady-state operation using CORSICA

Zhang Bin (ASIPP)

China

The dominant electron heating with low torque towards ITER baseline on EAST

Andrea Garofalo (GA)

US

High betaP for ITER Q=10 and Q=5 missions

Postponed: 11th ITER International School: The Impact and Consequences of Energetic Particles on Fusion Plasmas

Due to the continuing COVID-19 pandemic, the 11th ITER International School has been postponed again, and now is expected to be held sometime in Spring 2021, still somewhere in the Aix-en-Provence/Marseille area. The subject of the 11th IIS is “The Impact and Consequences of Energetic Particles on Fusion Plasmas.”

As previously announced, we are still planning to send 16 students from the US, supported by USBPO scholarships. In addition, about a half-dozen US researchers are on the agenda as speakers.

The recipients of the 2020 IIS scholarships are:

Gurleen Bal (UCLA)

Genevieve DeGrandchamp (UCI)

Jonah Duran (U Tenn Knoxville)

Kenneth Gage (UCI)

Alvin Garcia (UCI)

Daniel Lin (UCI)

Gabriel Player (UCI)

Quinn Pratt (UCLA)

Aaron Rosenthal (MIT)

Alex Saperstein (Columbia)

Kamil Sklodowski (UCLA)

Elizabeth Tolman (MIT)

Jeff Lestz (Princeton/UC Irvine)

Philip Bonofiglo (PPPL)

Noah Hurst (Wisconsin)

Alex Tinguely (MIT)


More details on this ITER International School are available or forthcoming at https://iis2020.sciencesconf.org/. We are hoping to host the next IIS in the US, but now this will have to be in 2022 at the earliest.

 

Research Highlight

Turbulence and Transport (Leaders: Walter Guttenfelder and Nathan Howard)

Understanding transport and stability mechanisms that enable high bootstrap fraction scenarios in tokamaks is a key goal for achieving steady-state burning plasmas as one potential path to economical fusion energy. In this Research Highlight, Xiang Jian and colleagues at UC-San Diego, General Atomics and ORAU analyze and simulate the mechanisms predicted to control transport in the internal transport barrier (ITB) present in DIII-D high poloidal beta scenarios that lead to relatively large bootstrap fraction.

Role of High-Field-Side MicroTearing Turbulence on DIII-D High Core Plasmas*

X. Jian1, C.Holland1, J.Candy2, S. Ding3 , E. Belli2, V.Chan2, G.M.Staebler2, A.M.Garofalo2, J. Mcclenaghan2 , and P. Snyder2

1 University of California, San Diego

2 General Atomics

3 Oak Ridge Associated Universities

Author e-mail: xijian@ucsd.edu

Developing economically attractive steady-state tokamak reactor scenarios requires simultaneous achievement of high plasma confinement and high bootstrap current fraction, in order to generate the desired amount of fusion power without requiring a significant fraction of that power to “recirculate” into external current drive actuators. Because the bootstrap current fraction (where with and the plasma pressure and poloidal magnetic field), high scenarios have been extensively pursued as a possible steady-state scenario1-3. In these scenarios, high plasma confinement is achieved through the formation of a strong large radius internal transport barrier (ITB). These ITBs are enabled by the use of stabilization, which is an inherent stabilization effect coming from the toroidal geometry of tokamaks. The parameter is proportional to in the limit of infinite aspect ratio shifted-circle geometry, and effectively quantifies the Shafranov shift of a given flux surface. Large values of can sufficiently modify the effective magnetic drift frequency to stabilize both microscopic and macroscopic instabilities. Through this mechanism, potentially attractive operating scenarios with self-sustaining high confinement and self-generated bootstrap current (also driven by density and temperature gradients) can be developed.

In order to fully develop these scenarios and confidently extend them to future reactor parameters, it is essential to have a comprehensive understanding of the underlying transport physics, particularly of the crucial ITB region which is essential for achieving the needed pressure and confinement levels. Recent work has shown that in the ITB region of DIII-D high discharges, the stabilization process suppresses conventional ballooning drift-wave turbulence. Transport modeling of these discharges indicates that the ion thermal transport is neoclassical across almost the entire plasma volume, while the electron transport remains anomalous4,5, and not well-described by the TGLF quasilinear transport model6. Motivated by this result, extensive linear and nonlinear gyrokinetic simulations of the ITB region in a typical high discharge were performed. These simulations have revealed that a novel slab-like microtearing mode (MTM) localized to the high-field side of the plasma controls the electron thermal transport in the ITB region.

To investigate the local gyrokinetic stability of the ITB region, we employ the CGYRO code7 and run it with a very high numerical resolution. By a systematic scaling of in the electrostatic limit, it is shown that all drift waves, from long-wavelength trapped electron modes (TEMs) to short-wavelength electron temperature gradient (ETG) modes ( ranges from 0.1 to 50) are fully stabilized at ~70% of the experimental value (Fig. 1(a)). In these plasmas, the ion temperature gradient (ITG) mode is stable in the ITB region even when a = 0. More realistic electromagnetic calculations which include both perpendicular and parallel magnetic field fluctuations show that the kinetic ballooning mode (KBM), instead of the TEM, is in fact the dominant instability in the low-k region. Similar to the electrostatic case, the KBM can be fully suppressed by stabilization. We note that the analysis presented here is a local gyrokinetic one, and nonlocal effects which might destabilize a more ‘global’ KBM are not included. While all modes remain stable at the experimental value of in the electrostatic case, in the electromagnetic case a new mode in the low-k region is destabilized, as shown in Fig. 1(b). In order to clearly see how the dominant mode evolves with an increase of the frequency and growth rate for = 0.2 as a function of are shown in Fig. 1(c) and (d). The = 0.2 KBM is fully suppressed by ~50% of the experimental value, leaving a stable gap at larger values. However, above 75% of the experimental value, a new mode with phase velocity in the electron diamagnetic direction is destabilized by further increases in (Fig. 1d), which has been identified as microtearing mode based on its mode parity, parametric dependencies, and transport characteristics (both linear and nonlinear)8. Beyond these linear characteristics, nonlinear gyrokinetic simulations predict that this MTM branch can drive electron energy fluxes consistent with the experimental levels but drives no ion thermal transport. When combined with the complete stabilization of all other turbulent modes, these findings demonstrate that the MTM instability uniquely regulates the electron energy flow through the ITB region of these scenarios and helps prevent the plasma pressure from growing to the global MHD limit.

A novel aspect of this new MTM branch is the intimate connection between its destabilization by large and its slab-like mode-structure and localization to the high-field-side of the plasma. Visualizations of the electrostatic and magnetic potential components of the linear eigenmode in the (R,Z) plane are shown in Fig. 2a and 2b. Both fluctuation fields’ amplitudes peak at the inboard midplane, and exhibit radial structures tightly localized around individual rational surfaces. These properties persist in the nonlinear simulation. Snapshots of turbulent fluctuations from a nonlinear simulation are shown in Fig. 2c and 2d. As can be seen, the eddies in both and are always radially narrow and poloidally extended. This structure is particularly different from either the streamer-like linear eigenmodes of typical ballooning instabilities or the much more isotropic eddies typically observed in nonlinear simulations of those instabilities, e.g. in simulations of ITG turbulence. The narrow radial extent of these MTM fluctuations likely makes them more resistant to the flow shearing that can suppress ballooning-type modes through radial decorrelation of the fluctuations. In fact, no impact on the predicted transport levels is found by including equilibrium ExB shear in the simulations, despite the fact that the shearing rate is approximately four times larger than the maximum MTM linear growth rate.

Figure 1. The (where is the linear growth rate) of the electrostatic instabilities (a) and of the electromagnetic run (b) for different scaling factors of experimental (legend is ). The frequency (c) and growth rate (d) of dominant electromagnetic instability of
= 0.2 versus . 8

 

Figure 2. Linear eigenfunction structure of (a) and (b) of the MTM mode. Nonlinear fluctuation contour plot of the MTM are shown in (c) and (d) with only finite-ky components included.

In conclusion, a detailed transport analysis has convincingly identified a novel high-field-side MTM as the unique cause for the thermal transport in the ITB region of the high scenario with the conventional micro-instabilities candidates, like ITG, TEM, ETG, and local KBM fully suppressed by the strong stabilization. More broadly, this finding generalizes the conclusions of other recent transport studies9, which identify MTMs as a “mode of last resort” in controlling the structure of transport barriers from edge to core, and therefore, to the whole plasma, when conventional instabilities are suppressed by mechanisms such as stabilization or shear. For more details, please see Ref 8.

Acknowledgments: This work was supported by the U.S. Department of Energy under awards DE-SC0018287, DE-SC0017992, DE-FG02-95ER54309, DE-SC0017992 and DE-FC02-04ER54698. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under Contract No. DEAC02-05CH11231

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.

 

References:

1 Gormezano, C. et al. Steady state operation [Progress in the ITER Physics Basis (PIPB)]. 47, S285-S336 (2007).

2 Garofalo, A. M. et al. Compatibility of internal transport barrier with steady-state operation in the high bootstrap fraction regime on DIII-D. 55, 123025 (2015).

3 Fujita, T. et al. Quasisteady high-confinement reversed shear plasma with large bootstrap current fraction under full noninductive current drive condition in JT-60U. 87, 085001 (2001).

4 Ding, S. et al. Confinement improvement in the high poloidal beta regime on DIII-D and application to steady-state H-mode on EAST. 24, 056114 (2017).

5 McClenaghan, J. et al. Transport modeling of the DIII-D high scenario and extrapolations to ITER steady-state operation. 57, 116019 (2017).

6 Staebler, G., Kinsey, J. & Waltz, R. J. P. o. P. A theory-based transport model with comprehensive physics. 14, 055909 (2007).

7 Candy, J., Belli, E. A. & Bravenec, R. J. J. o. C. P. A high-accuracy Eulerian gyrokinetic solver for collisional plasmas. 324, 73-93 (2016).

8 Jian, X. et al. Role of Microtearing Turbulence in DIII-D High Bootstrap Current Fraction Plasmas. 123, 225002 (2019).

9 Kotschenreuther, M. et al. Gyrokinetic analysis and simulation of pedestals to identify the culprits for energy losses using ‘fingerprints’. 59, 096001 (2019).

* This work was supported by the US DoE under Grants DE-FG02-99ER54531 and DE-FC02-04ER54698.

 

Calendar of Burning Plasma Events

Many upcoming meetings are being impacted by the COVID-19 situation. We suggest that you not rely too heavily on the schedule below - it is best to check with the meeting organizers before making any plans.

2020

JET DT-campaign (https://www.burningplasma.org/resources/ref/Web_Seminars/Litaudon-JET-%202019-05-02-vf.pdf)

JT-60SA First Plasma (http://www.jt60sa.org/)

Oct 12-16, 2020

Theory of Fusion Plasmas Joint Varenna-
Lausanne International Workshop

Varenna or Lausanne

 

Oct 12-15, 2020

38th ITPA Diagnostics Topical Group Meeting

Remote only

 

Oct 12-22, 2020

29th Scrape-Off Layer & Divertor ITPA Topical Group Meeting

Remote only

 

Nov 9-13, 2020

62nd Annual Meeting of the APS Division of Plasma Physics

Remote only

 

Nov 15-19, 2020

Technology of Fusion Energy (TOFE) 2020

Chicago, IL

 

Nov 16-20, 2020

ITER International School

Marseille, France

 

Dec 6-10, 2020

47th International Conference on Plasma
Science (ICOPS)

Singapore Virtual

 

Dec 13-17, 2020

High Temperature Plasma Diagnostics
Conference

Santa Fe, NM Virtual

 

Dec 16-17, 2020

Fusion Power Associates 41st Annual Meeting and Symposium

Washington, D.C. Virtual

 

 

2021

Jan 24-29, 2021

International Conference on Plasma Surface Interactions

Jeju, South Korea

May 10-15, 2021

28th IAEA Fusion Energy Conference (FEC2020)

Nice, France

 

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