News and Events


U.S. Burning Plasma Organization eNews
Feb 29, 2016 (Issue 105)

 

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
Delgado-Aparicio et al.
ITPA Update  
Schedule of Burning Plasma Events  
Contact and Contribution Information

Announcements

USBPO web seminar

We are pleased to announce our second web seminar of 2016:

Date: Wednesday, March 23th, 1pm EST (12 pm CST, 10am PST)

Speaker: Dr. Raffi Nazikian, Princeton Plasma Physics Laboratory

Topic: Progress in understanding of ELM control by resonant magnetic perturbations

Dr. Nazikian has been active in studies of 3-D magnetic perturbations on pedestals and ELMs, on DIII-D and internationally. He is active in the ITPA expert group on Pedestal and ELM physics, and recently co-led the Panel on avoiding deleterious effects of ELMs in the Community Workshop on Transients. There has been great progress recently in understanding the physics of resonant magnetic perturbations and their effects on ELMs. He will give an overview and, as usual, we will have time for questions and community discussion.

We will use Zoom for audio, video and slides (http://zoom.us); connection details have been sent out on February 26th. A reminder will be sent out later in March.

Amanda Hubbard
USBPO Deputy Director

Director’s Corner

C.M. Greenfield

US Fusion Program News

As many of you know, four community-led workshops were organized by the DOE Office of Fusion Energy Sciences (FES) in 2015, on Plasma-Material Interfaces, Transients, Integrated Simulations, and Plasma Science Frontiers (see my column in the March 1, 2015 eNews). The first three of these are now complete and their reports are posted on the DOE website at http://science.energy.gov/fes/ community-resources/workshop-reports/ (the fourth report, on Plasma Science Frontiers, will appear there soon). The leaders of all four workshops also reported on their status and results at the January 13-14 FESAC (Fusion Energy Sciences Advisory Committee) meeting; the slides are available and are linked from the agenda posted at http://science.energy.gov/~/media/fes/fesac/pdf/2016/ 20160113/FESAC_Agenda_January-13-14-2016.pdf (we will post links on the USBPO home page at http://burningplasma.org in the coming days).

I know many of our readers dedicated a great deal of their effort and time to completing these reports, and I want you to know your hard work did not go unrecognized. During the aforementioned meeting, FESAC drafted the following statement that was sent to Cherry Murray, Director of the DOE Office of Science:

“The Fusion Energy Sciences Advisory Committee (FESAC) is pleased with the Fusion EnergySciences (FES, SC-24) initiative in launching four community workshops in 2015: on Integrated Simulation, on Plasma-Material Interactions, on Plasma Transients, and on Plasma Science Frontiers. The selection of these topics is responsive to priorities highlighted by FESAC, particularly in our 2014 Report on Strategic Planning: Priorities Assessment and Budget Scenarios. At this FESAC meeting (13-14 January 2016), we heard from the workshop chairs about the enormous community-wide effort to carry out these workshops, and the high degree of consensus in identifying priority research directions within these topics. We heard from FES that the workshop results are being used to help explain and shape the Fusion Energy Sciences program within the U.S. government. We were pleased to hear the workshop chairs unanimously express their satisfaction with both the communitys support of the workshop goals and with FESs response to the results.“

You may have also heard that FES has now completed their strategic plan, “Fusion Energy Sciences: A Ten-Year Perspective (2015-2025)” (http://science.energy.gov/~/media/fes/pdf/program-documents/ FES_A_Ten-Year_Perspective_2015-2025.pdf). Although the strategic plan was drafted prior to completion of the workshops, it states “the results from these workshops will be incorporated when formulating the details for and executing future FES budgets.”

Accelerating Progress at ITER

As I told you in my December 31 column, the new project schedule for ITER is under review by an external panel, and will hopefully be adopted by the ITER Council later this spring. Meanwhile, progress at the construction site continues as buildings continue to appear. But it isn’t just the site itself. Tokamak components are being produced by the ITER partners. On the ITER site, the Poloidal Field Coils Winding Facility (one of the first buildings to be completed) is being readied to begin operations this summer with the winding of the first “dummy coil".

The interior of the Poloidal Field Coils Winding Facility, including some of the tooling that will be used for on-site production of magnets that will be too large to transport (Photo c ITER Organization).

By the way, ITER has produced a video showing some of the progress on the construction site during 2015. You can find it at https://youtu.be/3dy06XZ353s

Research Highlight

Energetic Particles Topical Group, Leaders: Nikolai Gorelenkov and Eric Bass

Dr. C.S. Collins from University of California at Irvine, CA is an experimental researcher participating in the DIII-D experiments at GA. Her studies focus on energetic beam ion physics and associated Alfvénic instabilities which are believed to be one of the main concerns for future burning plasma experiments such as ITER being build in France. The highlighted work was recently published in the Physics Review Letter journal.

Recent Measurements Reveal Critical Behavior of Fast-Ion Transport Due To Alfvén Eigenmodes

C.S. Collins1, W.W. Heidbrink1, G.J. Kramer2, D.C. Pace3, C.C. Petty3, M.A. Van Zeeland3, R.B. White2 E.V. Belova1, N.N. Gorelenkov1, N.A. Crocker2, E.D. Fredrickson1, K. Tritz3
1 University of California at Irvine, Irvine, CA 92697, USA.
2 Princeton Plasma Physics Laboratory, PO Box 451, Princeton, NJ 08543-0451, USA.
3 General Atomics, PO Box 85608, San Diego, CA 92186-5608, USA.

Recent measurements in the DIII-D tokamak show that many overlapping, small-amplitude Alfv ´en eigenmodes (AEs) cause fast-ion transport to become “stiff” above a critical threshold gradient [1]. Three key features of critical gradient behavior have been observed; 1) a sudden increase in incremental transport occurs above the AE linear stability threshold, 2) fast-ion losses become intermittent above threshold, and 3) stiff transport causes the fast-ion density profiles to become fixed despite increased source. These measurements are helping to develop and validate numerical models that aim to predict alpha profiles, beam ion profiles, and losses to aid in the design of optimized scenarios for future burning plasma devices.

In fusion plasmas, large gradients in either the fastion velocity space or pressure profiles can provide free energy to excite AEs through wave-particle interactions. The AEs cause fast ions to move away from the core of the plasma, which can affect the current profile, lead to reduced fusion performance, and cause losses that could damage reactor walls. Understanding, predicting, and controlling these losses is essential: AEs are expected to be present in ITER, which must achieve less than 5% loss of fusion alpha particles to reach performance goals.

fig1.jpg

Figure 1: (a) As AE activity increases with beam power, fast-ion transport inferred from the (b) NPA and (c) neutron emission suddenly increases are used to measure the time evolution of the above a phase-space dependent threshold.

Since AEs can perturb only a portion of phase space and leave other parts unaffected, the measured threshold for appreciable transport is found to vary between fast-ion diagnostics that are sensitive to different regions in fast-ion phase space (Fig. 1). In the experiment, the AE activity varies with total neutral beam injected power during the current ramp of a low-confinement (L-mode) plasma, while the fast-ion pressure profile is modulated using an off-axis neutral beam. A variety of diagnostics are used to measure the time evolution of the modulated fast-ion population, which depends on the source (the modulated beam), the sink (fast-ion thermalization), and transport (due to resonant wave-particle interactions with AEs) [2]. In Fig. 1, the inferred transport threshold is found to be lower for diagnostics with broad sensitivity in phase space (such as the neutrons in Fig. 1c) than for diagnostics with narrow sensitivity (such as the neutral particle analyzer (NPA) in Fig. 1b). The threshold changes when different beams are used to drive AEs in different regions of phase space. Comparison with theoretical analysis using the NOVA and ORBIT codes shows that the threshold corresponds to when particle orbits become stochastic due to wave- particle resonances with AEs in the region of phase space measured by the diagnostic.

fig2.jpg

Figure 2: Intermittent fast ion losses appear as a tail in the event distribution function of the raw FILD signal divided by 0.1 ms running average.

As beam power increases, the fast-ion loss detector (FILD) records larger, more frequent transient bursts, appearing as a growing tail on the probability distribution function of the intermittency (Fig. 2). Intermittency is strongest in the presence of multiple, nearly constant frequency Toroidal Alfv ´en Eigenmodes (TAEs) and frequency sweeping Reverse Shear Alfv ´en Eigenmodes (RSAEs). However, intermittency is largely reduced by applying ECH near qmin to create a TAE dominant spectrum. In theory, if many overlapping modes are present, particle diffusion can occur over a larger portion of phase space, leading to an avalanche of global redistribution and losses [3]. Current critical gradient models do not account for intermittent transport, and further analysis to assess the significance of intermittency is underway.

fig3.jpg

Figure 3. Stiff transport causes FIDA density pro les to be unchanged despite increased source (beam power).

In the end, critical gradient behavior causes the equilibrium fast-ion density profiles to become “clamped” with peak density that no longer increases despite increased beam power, as shown by fast-ion deuterium alpha (FIDA) measurements in Fig 3. In the strongly driven cases, the magnitude of the measured neutron rate is 50% of the expected classical neutron rate calculated by TRANSP. Similar profile resiliency has also been observed in [4] where fast-ion profiles were insensitive to beam profile scans.

While the isotropic, fusion produced alpha particle distribution function in a thermonuclear plasma such as ITER cannot be produced in present day devices where neutral beams drive anisotropic fast ions, these results can be used to quantitatively validate AE critical gradient “stiff” transport models, giving greater confidence when applying the numerical tools to ITER. Reduced models can make computation efficient USBPO Newsletter, February 29, 2016, Issue 105, BurningPlasma.org Page 5 of 8 by avoiding detailed nonlinear calculations of wave-particle resonances and saturated mode amplitudes. In recent work, the relaxed fast-ion pressure profile is calculated by assuming that AE induced fast-ion transport is stiff above either the AE linear stability threshold [5] or a microturbulent threshold [6]. The experimental results in Fig 1. show that incremental transport occurs at a stochastic threshold above the AE linear stability threshold, suggesting that the use of a linear stability threshold could yield unrealistically pessimistic predictions. Future validation work will involve detailed comparisons of the phase-space sensitive measurements to models that evolve the fast ion distribution function with velocity-space dependent transport.

The results of this work are being applied to guide the development of the Advanced Tokamak scenario to high N in DIII-D through the use of tools such as upgraded off-axis neutral beam current drive and electron cyclotron heating to develop profiles and parameters that are more robust to fast ion redistribution.

This work was supported by the US Department of Energy under SC-G9034021, DE-AC02-09CH114662, and DE-FC02-04ER546983.

References

[1] C.S. Collins, et al, Phys. Rev. Lett. 116, (2016) accepted
[2] W.W.Heidbrink, et al, Nucl. Fusion 56 (2016) submitted
[3] H. L. Berk, et al, Nucl. Fusion 35, 1661 (1995)
[4] Heidbrink et al, Nucl. Fusion 53, (2013)
[5] K. Ghantous, et al, Phys. Plasmas 19, 092511 (2012)
[6] R.E. Waltz , et al, Nucl. Fusion 55, 123012 (2015)

ITPA Update

More information concerning the ITPA may be found at the Official ITPA Website.

Transport and Con nement Topical Group

The Transport and Confinement ITPA took place in Garching after the H-mode workshop on October 22nd and 23rd 2015. On the first day of this short meeting, an update was given on the status of Lmode edge heat short fall problem with the different gyro-kinetic codes and upgrades to saturation rules in quasi-linear codes to better match non-linear multi-scale simulations. The second day, the focus was on momentum transport, intrinsic torque and the construction of a multi-device experimental database to provide data to test and validate theoretical models of momentum transport. Aside from these two main topics, new results with respect to core transport on stiffness, e.m. stabilization and ETG scale turbulence were presented. There was also a short session on particle transport at the end of the meeting and a presentation on WEST. The 16th transport and confinement ITPA meeting will take place in Ahmedabad, India on 16-18 March 2016. The session will cover an update on a new ITER confinement database, low Z impurity transport, I-mode, L-H transition,  scaling of intrinsic torque, updates to quasi-linear models, 3D effects on transport and a session to prepare for the fall meeting.

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Schedule of Burning Plasma Events

USBPO Public Calendar: View Online or Subscribe

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

2016         — 10th Anniversary of USBPO Formation —

March 16-18ITPA T&C, Institute for Plasma ResearchGandhinagar, India
March 16-18ITPA PEP, Institute for Plasma ResearchGandhinagar, India
March 29 - April 1US Transport Task Force Workshop, Denver, Colorado, USA
April 26-2916th IOS ITPA meetingGarching, Germany
May 30-June 3PSI ConferenceRome, Italy
June 19-23International Conference on Plasma Sciences, ICOPSBanff, Alberta, Canada
June 21-2430th Diagnostics ITPA meetingNovsibirsk, Russia
June 27-3016th EP ITPA meetingSt. Paul-lez-Durance, France
June 27-July 118th International Conference on Plasma Physics (ICPP2018)Kaohsiung, Taiwan
July 4-8European Physical Society Conference on Plasma Physics (EPS)Leuven, Belgium
September 4-8Joint EU-US Transport Task Force MeetingLeysin, Switzerland
October 13-15ITER STAC MeetingKizu, Japan
October 17-2226th IAEA Fusion Energy ConferenceKyoto, Japan
October 24-2617th T&C ITPA meeting JAEANaka, Japan
October 24-2717th T&C IOS meeting JAEANaka, Japan
October 31-November 458th APS Division of Plasma PhysicsSan Jose, California, USA

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

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