Monthly Newsletter of theU.S. Burning Plasma Organization

December 31, 2015 (Issue 103)

Mission StatementAdvance the scientific under-standing of burning plasmasand ensure the greatest ben-efit from a burning plasmaexperiment by coordinatingrelevant U.S. fusion researchwith broad community partic-ipation.

This newsletter providesa monthly update on U.S.Burning Plasma Organiza-tion activities. The USBPOoperates under the auspicesof the U.S. Department ofEnergy, Office of FusionEnergy Sciences (FES).All comments, includingsuggestions for content,may be sent to the Editor.Correspondence may alsobe submitted through theUSBPO Website FeedbackForm.

Become a member of theU.S. Burning Plasma Orga-nization by signing up for atopical group.

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

AnnouncementsDirector’s CornerResearch Highlight

Diagnostics Topical Group

Multi-energy x-ray cameras for magnetically confined fusion plas-mas, L. Delgado-Aparicio et al.

ITPA UpdateSchedule of Burning Plasma EventsImage of the Month

Announcements

USBPO web seminar

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

Date: Thursday, Jan 7th, 2pm EST (1 pm CST, 11:00 PST)

Speaker: Dr. Francesca Poli, Princeton Plasma Physics Laboratory

Topic: Integrated modeling in support of ITER: the path from the commis-sioning phase to demonstration scenarios; issues and progress.

We will use Zoom for audio, video and slides (http://zoom.us/); connec-tion details will be sent in an email reminder in early January.

Please share this announcement with colleagues and students. We hopeyou can participate, and would like to take this opportunity to wish you avery happy holiday season.

Amanda HubbardUSBPO Deputy Director

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Director’s CornerC.M. Greenfield

Holiday wishes

I would like to wish all of our readers a wonderful holiday and a happy and productive 2016.

ITER: Significant progress in 2015

There were a lot of changes at ITER in 2015. As construction progress continued and accelerated, newDirector General Bernard Bigot took charge, who with his team has been working to put the project on arealistic schedule. The ITER Council reviewed this schedule at its November meeting and referred it to anindependent review, due in time for its next meeting in June, 2016. Last year at this time I told you aboutprogress on construction. At that time, the B2 slab supporting the tokamak complex had been completed,and walls starting to rise around the tokamak pit. Since then, the tokamak complex has continued to rise,with the B2 slab long since rendered invisible by walls and additional tokamak support structure. TheTokamak Assembly Hall frame was completed, with sheet metal siding now being applied.

The ITER site in November, 2015. The newly erected Tokamak Assembly Hall is at the left, and thetokamak pit is at the center (Photo c©ITER Organization).

Progress isn’t limited only to development of the site. Recently, the first components of the tokamakarrived in the form of 12 segments of the cryostat, supplied by India. Also, during my recent visit for

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the annual ITPA Coordinating Committee meeting, we were given a site tour including the inside of thePoloidal Field Coil Winding building. Last year, this building was being used to store crates of electricalcomponents, mostly from the US Domestic Agency. But now, the building is being outfitted to begin itsassigned task of winding magnets.

The Poloidal Field Coil Winding Building: No longer just a warehouse!

ITER International School

The 2015 ITER International School was held earlier this month in Hefei, China. Seven post-docs andgraduate students attended via scholarships provided by the USBPO (see photo).

The theme of this year’s school (http://www.iterschool2015.cn/iis/Sitehome.aspx) was “Transportand Pedestal Physics in Tokamaks.” These schools are primarily designed for graduate students, post-docs, and young researchers. The location rotates to different ITER partners, with the topic varying fromyear-to-year, so stay tuned for information on the next school.

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USBPO scholarship winners at the 2015 ITER International School. From left: Tess Bernard (Universityof Texas), Mike Ross (University of Washington), Drew Elliott (West Virginia University), Matt Beidler(University of Wisconsin), Chris Everson (University of Washington), Jonathan Coburn (North CarolinaState), Tim Younkin (University of Tennessee). Photo courtesy of Phil Snyder.

There were also six US-based experts among the lecturers Phil Snyder (General Atomics), Gary Staebler(General Atomics), Rajesh Maingi (PPPL), Raffi Nazikian (PPPL), C.S. Chang (PPPL), and Joshua Burby(NYU).

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Research Highlight

Diagnostics Topical Group, Leaders: Ted Biewer and Brent Stratton

Multi-energy x-ray cameras for magnetically confined fusion plasmas

L. Delgado-Aparicio 1, J. Maddox 1,2, N. Pablant 1, K. Hill 1, K. Tritz 3, D. Stutman 3, M. Bitter 1, J. E. Rice4, A. Hubbard 4, M. Greenwald 4, E. Marmar 4, J. Irby 4, P. Efthimion 1, B. Stratton 1

1 PPPL, Princeton, NJ, 08540, USA2 SULI fellow

3 The Johns Hopkins University, Baltimore, MD, 21218, USA4 MIT - PSFC, Cambridge, MA, 02139, USA

Thanks to important advances in the x-ray detector technology, especially, the manufacturing of two-dimensional hybrid pixel array x-ray detectors of large areas and high count rate capabilities, it is nowpossible to record spatially resolved x-ray photons at multiple energy ranges from highly charged ionsfrom tokamak plasmas [1]-[4]. Multi-energy x-ray imaging of magnetically confined fusion plasmas pro-vides a unique opportunity for measuring, simultaneously, a variety of important plasma properties. Theenergy resolved measurements can be used to produce images of impurity concentrations (nZ & Zeff ) -from the absolute image intensity at different energy bands - and the electron energy distribution function,both thermal (Te) and non-Maxwellian (ne,nM ) from the variation of emissivity with x-ray energy. This novelcapability offers also a unique opportunity to monitor high-Z impurities, calculate impurity transport coeffi-cients and distinguish between contributions from medium-Z (e.g. Ar) to high-Z (e.g. Mo, W) impurities inreactor configurations with metal plasma facing components (PFCs).

Side view

Aperture

+ Be 50 μm foil

2D pixelated

SXR detector

Alcator

C-Mod

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Top

Bottom

x

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Pilatus 100K

detector

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ace

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......

2D radial - poloidal view

d) 1D tangential view

En

erg

y (

19

5 p

ixe

ls)

Space (495 pixels)

E1..................E

13

Figure 1: a) Detector setup with the PILATUS2 detec-tor shown in b). Inset (c) shows a vertical arrangementof energy thresholds which repeats every 13×172µm andis optimum for a 2D radial view. A horizontal arrange-ment of the thresholds useful for a 1D tangential config-uration is shown in d).

A first proof-of-principle diagnostic system was de-ployed for testing at the Alcator C-Mod tokamak atMIT in 2012 with good results [1]. In a much recentinstallation a multi-energy camera was operated in aradial/poloidal configuration (see Fig. 1) and used invarious regimes which include L→H transitions, im-purity injections as well as radio frequency heatingand current drive experiments. At the heart of thenew proposed system is a Pilatus2 [5] x-ray detec-tor depicted in Fig. 1-b) which has been the detectorof choice for various designs of x-ray crystal imag-ing spectrometers. The configuration of pixilated de-tectors used is shown in Fig. 1-c). Since the x-rayemissivity is uniform along the toroidal magnetic field,the pixels in adjacent rows sample nearly the same

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plasma volume. Here, an entire row of pixels would be effectively used for each energy value; it is there-fore possible to obtain coarse spectral resolution by setting the pixels in each column to varying energythresholds, E1, E2, ... E13, etc. (from 4 to 16 keV), where a larger number of pixels can be set to thehigher energy threshold to compensate for the exponential decrease of the photon intensity with energy.The diagnostic envisioned for C-Mod had a spatial and temporal resolution of 1 cm and 5-10 ms, respec-tively. Preselecting a detector response between 6 and 15 keV help eliminating the ‘contamination’ to thecontinuum introduced by the low- and high-energy line-emission from Argon and Molybdenum impurities(see spectra in Fig. 2) and facilitating the electron temperature measurements in Ohmic and ICRH heatedplasmas. The x-ray signals with photon energies below 6 and above 15 keV can be used to calculateimpurity concentrations.

Argon Molybdenum

SX

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ity (

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/cm

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)

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5 10 15 20 25

Photon energy (keV)

“S” curves at 50% cut-off

energies from 4→16 keV

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ard

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Te=2 keV

Te=4 keV

Te=6 keV

5 10 15 20 25

Photon energy (keV)

“S” curves at 50% cut-off

energies from 4→16 keV

with ΔE~ 1 keV

Figure 2: SXR emissivity for Ar and Mo. The 13 de-tector response curves (dotted-lines) ‘bracket’ the con-tinuum eliminating the plasma line-emission.

Previous attempts to develop this SXR capabilityhave lack temporal-, spatial- or energy-resolution.Single-chord pulse-height-analyzers (PHA, see refs.[6]-[9]) are naturally restricted since they are line inte-grated measurements with limited spatial localization(e.g. one spectrum per instrument and with very poorprofile definition). A better spatial coverage at theexpense of lack of energy resolution can be gainedusing multiple 1D pin-hole x-ray detector arrays fil-tered using individual metallic foils [10]-[19]. This ca-pability have shown remarkable flexibility and couldbe used for fast electron temperature measurements,impurity transport and macroscopic magnetohydro-

dynamic (RWM and NTM) studies. The novel diagnostic system installed in Alcator C-Mod at MIT com-bines the best features from both PHA and multi-foil methods, and represents a very large improvementin throughput and spatial resolution thanks to present state-of-the-art pixelated PILATUS2 detectors witha minimum of 100k pixels.

C−

Mo

d #

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0 10 20 30Channel (Rtg)

t1~0.62 s

H-mode

c)

b)

10-1

101

103

Ave

rag

e c

ou

nts

CORE

CORE

Figure 3: Multi-energy brightness profiles during L-modes and ICRH-heated H-modes.

Details of the line-integrated profiles across C-Modcross section in thirteen different energy ranges forL- and H-modes is shown in Fig. 3. This de-tector has demonstrated an unprecedented flexibil-ity in the configuration of an imaging x-ray detec-tion system having a dynamic range spanning nearly5 orders of magnitude. The strongest signals ob-tained with a detector setup with a 4 keV minimumenergy threshold were of the order of 5 − 6 × 105

counts/sec/pixel, far from the its maximum count-rateof 2 × 106 counts/sec/pixel. The time-history of theinferred core electron temperatures using the multi-energy line-integrated brightness as a proxy of thelocal emissivity is shown in Fig. 4 and is in very goodagreement with the temperatures measured by the electron cyclotron emission (ECE) diagnostic [3, 4].The use of tomographic codes for obtaining the 2D multi-energy SXR emissivities will facilitate the com-putation of Te and n2eZeff profiles from the continuum, as well as obtaining nZ profiles from the signalsdominated by impurity line-emission.

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EC

E-G

PC

ce

ntr

al T

e0 [ke

V]

1.0

3.0

2.0

R=68 cm (core)

R=71 cm

R=74 cm

R=77 cm

SXR <Te0>

R=79 cm

2.0 MW ICRH

Alcator C-Mod # 1140815012

Lin

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ve

rag

ed

<T

e0>

[ke

V]

1.0

3.0

2.0

Time (s)

0.5 1.0 1.5

R=82 cm

Figure 4: ECE and SXR-inferred core electron temper-ature during Ohmic and ICRH-heated plasmas.

Further improvements in 2016 will include the useof new Pilatus3 systems which have maximum pho-ton count rates of 2 × 107 counts/sec/pixel and theuse lower minimum energy thresholds (e.g. 1.6 keV)sampling the line-emission contribution of molybde-num or tungsten. The potential for extracting valuableinformation from this compact x-ray system should befully explored as a possible burning plasma diagnos-tic. Traditional techniques to infer basic plasma quan-tities - based on the slope of the continuum radiation- can still be employed since the tungsten continuumextends from 15 to 55 keV. The use of thicker (1 mm)silicon pixel array detectors will allow also the studyof non-Maxwellian effects by probing higher x-ray energies up to ∼ 30−40 keV. An appropriate alternativefor even higher energies is CdTe, which will allow photon detection up to ∼ 100 keV with nearly 70%efficiency. The latter is of interest of our community especially when radio frequency waves heat plasmasintroducing non-Maxwellian “tails” in the distribution function, which are prone to generate harder x-rays.faster detectors have recently become commercially available and could provide the future frameworkneeded for rapid estimates of impurity accumulation and radiated power for disruption avoidance.

In summary, due to its intrinsic energy-resolution, the multi-energy SXR technique can be used to pro-vide simultaneous measurements of Te, nZ , Zeff and ne,nM in high-temperature plasmas; intense line-emission from high-Z impurities from metal PFCs can be ‘filtered’-out from the continuum using appropri-ate energy thresholds. This technique should be explored also as a burning plasma diagnostic in-view ofits simplicity and robustness.

References[1] N. Pablant, et al., Rev. Scientific Instrum., 83, 10E526, (2012).

[2] L. Delgado-Aparicio, et al., PPPL-report, 4977, (2014).

[3] J. Maddox, et al., proc. of the 57th APS-DPP, November, Savannah, GA, (2015).

[4] J. Maddox, et al., to be submitted to Nucl. Fusion, (2016).

[5] See https://www.dectris.com

[6] E. H. Silver, et al., Rev. Sci. Instrum., 53, 1198, (1982).

[7] K. W. Hill, et al., Rev. Sci. Instrum., 56, 840, (1985).

[8] K. W. Hill, et al., Nucl. Fusion, 26, 1131, (1986).

[9] J. E. Rice, et al., Phys. Rev. A, 25, 1645, (1982).

[10] J. Kiraly, et al., Rev. Sci. Instrum., 56, 827, (1985).

[11] L. Delgado-Aparicio, et al., Plasma Phys. Control. Fusion, 49, 1245, (2007).

[12] L. Delgado-Aparicio, et al., Journal of Applied Physics, 102, 073304, (2007).

[13] L. Delgado-Aparicio, et al., Rev. Sci. Instrum., 81, 10E303, (2010).

[14] K. Tritz, et al., Rev. Sci. Instrum., 83, 10E109, (2012).

[15] D. J. Clayton, et al, Plasma Phys. Control. Fusion, 55, 095015, (2013).

[16] L. Delgado-Aparicio, et al., Nucl. Fusion, 49, 085028, (2009).

[17] D. J. Clayton, et al., Plasma Phys. Control. Fusion, 54, 105022, (2012).

[18] L. Delgado-Aparicio, et al., Nucl. Fusion, 51, 083047, (2011).

[19] L. Delgado-Aparicio, et al., Plasma Phys. Control. Fusion, 53, 035005, (2011).

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

Energetic Particles Topical Group

This meeting was held in Vienna September 7-9, 2015 immediately following the IAEA technical commit-tee meeting on alphas particles in fusion research. The meeting was opened by Dr. Simon Pinches whoreviewed recent developments at ITER and R&D modeling needs relevant to the energetic particle com-munity. One particular problem he mentioned was the flexibility in the toroidal mode spectrum and rotationof the field by ELM/RWM coils is in need to reduce the potential heat fluxed to the level of < 10MW/m2.Another specific need he described for energetic particle physics community is the transport due to theAlfvenic modes and the need to control it. The joint EP experiments and code benchmarking activitieswere discussed as well which include linear AE instability analysis for the ITER 15 MA beseline and halffield/half current cases, nonlinear evolution studies, impact of both ECH and ICH on the stability of AEs.Important for future ITER operations were the discussions of the ICE (Ion Cyclotron Emission) physics tobe used as a diagnostic tool for the burning plasmas. The location and the dates for the next ITPA-EPmeeting were given as the spring of 2016 in the ITER site in Cadarach.

MHD, Disruptions, and Control Topical Group

The 26th Meeting of the ITPA Topical Group on MHD, Disruptions and Control was held October 19-22 in Naples, Italy. The agenda included sessions on ITER high priority needs (with a talk given byYuri Gribov), contributed talks on a wide range of topics including experimental results on disruptionmitigation (massive gas injection (MGI), shattered pellet injection (SPI), comparison of injection in normalplasma vs. ones with locked modes present), runaway electrons, MHD mode/error field control with sparecoil configurations, and disruption simulations with non-linear MHD codes. Aspects of disruptions (theirprediction, avoidance, and mitigation) remain among the most important and urgent unresolved issuesfor ITER, with special attention on the practical aspects of mitigation, as the final design review for thissystem on ITER will occur in 2017. Reports updating the status of MGI and SPI were given under jointexperiment MDC-1 and radiation asymmetry during MGI in a summary of working group WG-08. A topicalpresentation on the comparison of MGI effectiveness in normal plasmas vs. plasmas with locked modes(by R. Granetz) made a favorable conclusion that based on global mitigation parameters and measuredtoroidal peaking of radiated power in C-Mod that MGI performance did not degrade in plasmas with lockedmodes. The ITER requested assessment of the levels of large scale plasma disturbances tolerated beforeplasma disruptions occur were assessed in NSTX plasmas disrupted by global mode destabilization andreported under joint experiment MDC-21 (S.A. Sabbagh). The magnitude of toroidal mode number n = 1magnetic field perturbation,δB/B0, reached prior to disruption was shown to increase strongly with plasmacurrent. A further striking conclusion was that when expressed as scalings depending on combinationsof Ip, li, a, and q95 as used for more localized modes (i.e. tearing modes), the maximum δB/B0 of globalmodes scaled with similar dependences to locked tearing modes with respect to these parameters. Also,in contrast, the maximum δB/B0 did not depend on parameters normally associated with the marginalstability point of the global modes (e.g. li, or pressure peaking). Joint experiment MDC-22 (G. Pautasso)on disruption prediction reported results of work on an extended disruption database in C-Mod includingdata at more time points as would be needed for work on disruption warning evaluation, a study of lockingand disruptivity of initially rotating 2/1 tearing modes, and initial results from a new Disruption EventCharacterization And Forecasting code (DECAF) utilizing NSTX data.

Schedule of Burning Plasma EventsUSBPO Public Calendar: View Online or Subscribe

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

2016 — 10th Anniversary of USBPO Formation —

January 13-14, FESAC Meeting (in the Washington DC area), USA

January 25-28, 22nd ITPA DivSol, ENEA Research Center, Frascati, Italy

March 16-18, ITPA T&C, Institute for Plasma Research, Gandhinagar, India

March 16-18, ITPA PEP, Institute for Plasma Research, Gandhinagar, India

May 30 - June 3, PSI Conference, Rome, Italy

June 19-23, International Conference on Plasma Sciences, ICOPS, Banff, Alberta, Canada

June 27- July 1, 18th International Conference on Plasma Physics (ICPP2018), Kaohsiung, Taiwan

July 4-8, European Physical Society Conference on Plasma Physics (EPS), Leuven, Belgium

October 13-15, ITER STAC Meeting, Kizu, Japan

October 17-22, 26th IAEA Fusion Energy Conference, Kyoto, Japan

October 24-26, ITPA T&C, JAEA, Naka, Japan

October 31 - November 4, 58th APS Division of Plasma Physics, San Jose, California, United States

2019 — JET DT-campaign — JT60-SA First Plasma —

Image of the Month

A fusion reactor is designed to maintain the necessarily high plasma temperatures through the confine-ment of fusion-produced ions. Ongoing research aims to develop a predictive understanding of the waysin which these energetic ions both drive coherent waves and, through further interaction with those samewaves, experience transport through velocity and real space. The graphic demonstrates energetic iontransport in the DIII-D tokamak (the center post diameter is 2 m). A single, trapped, energetic ion orbitresulting from neutral beam injection is shown as the black trace. The red and blue contours representa synthetic image of a plasma wave (e.g., the normalized density or temperature perturbation causedby an Alfven eigenmode) that perturbs the ion orbit and causes it to impact the outer wall on the right.The ending location of the orbit corresponds to the location of the energetic ion loss detector diagnosticsystem. Various resonant interactions between energetic ions and coherent waves result in fluctuationsof the measured lost ion flux that occur at the frequencies of the waves. Measurements of the energeticion transport and the waves are compared with results from simulation codes that are rapidly evolving todevelop increasingly realistic descriptions of the physics, including non-linear effects and impacts on thebackground plasma. This work was done at the DIII-D National Fusion Facility, a DOE Office of ScienceUser Facility.

Additional InformationWave-particle Resonances: D.C. Pace, W.W. Heidbrink, and M.A. Van Zeeland, Physics Today 68, 34 (2015)Review of Alfven Eigenmodes: W.W. Heidbrink, Phys. Plasmas 15, 055501 (2008)Energetic Ion Loss Detector System: X. Chen, et al., Rev. Sci. Instrum. 83, 10D707 (2012)Simulation of Experiments: Y. Todo, et al., Nucl. Fusion54, 104012 (2014)

Graphic by M.A. Van Zeeland and D.C. Pace (DIII-D vessel photo courtesy Steve Allen)