Solenoid-free Plasma Start-up in NSTX using Transient CHI
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Transcript of Solenoid-free Plasma Start-up in NSTX using Transient CHI
Raman, Dec05 1
Solenoid-free Plasma Start-up in NSTX using Transient CHI R. Raman1, T.R. Jarboe1, B.A. Nelson1, M.G. Bell2, D.Mueller2,
R. Maqueda3 , R. Kaita2, B. LeBlanc2, J. Menard2, T. Bigelow4, M. Nagata5, S. Sabbagh6, M.J. Schaffer7, V. Soukhanowskii8, H.R. Wilson2
and the NSTX Research Team
1University of Washington, Seattle, WA, USA2Princeton Plasma Physics Lab., Princeton, NJ,USA
3Nova Photonics, USA4Oak Ridge National Laboratory, Oak Ridge, TN, USA
5University of Hyogo, Japan6Columbia University, New York, NY, USA
7General Atomics, San Diego, CA, USA8Lawrence Livermore National Laboratory, Livermore, CA, USA
NSTX Results ReviewPPPL, Princeton, NJ, 12-13 December, 2005
Work supported by DOE contract numbers DE-FG02-99ER54519 AM08, DE-FG03-96ER54361
Supported byOffice ofScience
College W&MColorado Sch MinesColumbia UComp-XGeneral AtomicsINELJohns Hopkins ULANLLLNLLodestarMITNova PhotonicsNew York UOld Dominion UORNLPPPLPSIPrinceton USNLThink Tank, Inc.UC DavisUC IrvineUCLAUCSDU ColoradoU MarylandU RochesterU WashingtonU Wisconsin
Culham Sci CtrU St. Andrews
York UChubu UFukui U
Hiroshima UHyogo UKyoto U
Kyushu UKyushu Tokai U
NIFSNiigata UU Tokyo
JAERIHebrew UIoffe Inst
RRC Kurchatov InstTRINITI
KBSIKAIST
ENEA, FrascatiCEA, Cadarache
IPP, JülichIPP, Garching
ASCR, Czech RepU Quebec
Raman, Dec05 2
Solenoid-free plasma startup is essential for the
viability of the ST concept
• Elimination of the central solenoid simplifies the engineering design of tokamaks (Re: ARIES AT & RS)
• CHI is capable of both plasma start-up and edge current in a pre-established diverted discharge- Edge current profile for high beta discharges
Raman, Dec05 3
Implementation of Transient CHI
Expect axisymmetric reconnection at the injector to result in formation of closed flux surfaces
Fast camera: R. Maqueda
Raman, Dec05 4
Improved pre-ionization to a level that results in injected gas
amount similar to that used for pre-fill for inductive plasmas
• Novel pre-ionization system– 10x reduced gas injection than in
2004
• Fast Crowbar system• 50mF, 1.5kV capacitor bank
– 15mF used in experimentsEC-Pi glow in gap between divertor plates. No voltage is applied.
Shot 1165651.4 Torr.L gas injection
Shot 1165700.7 Torr.L gas injection
EC-Pi glow along the center stack
Divertorgap
Raman, Dec05 5
Closed flux current
generation by Transient CHI
• Plasma current amplified many times over the injected current.
• Camera images at 12 to 17ms shows clear detachment of plasma from injector region
6 ms 8 ms 10 ms
12 ms 15 ms 17 ms
Hiroshima University (N. Nishino) Camera Images: R. Kaita (PPPL)
Raman, Dec05 6
Movement of discharge towards CS seen in the density profile, consistent with the camera image
>60kA of closed flux current generated using Transient CHI
Unambiguous closed flux current generation is clearly demonstrated by these discharges.
Electron temp. & density profiles during the current persistence phase
Phantom Camera Images: R. Maqueda (Nova Photonics) Thomson scattering: B. LeBlanc (PPPL)
13ms 17ms
13ms 17ms 13ms
17ms
Raman, Dec05 7
Some discharges have current persistence well beyond 20ms
10ms
14ms
16ms
17ms
19ms
20ms
22ms
32ms
35ms
40ms5 to 19ms: Plasma forms and shrinks20 to 35ms: Plasma expands along CS35 to 400ms: Plasma shrinks, becomes faint
Raman, Dec05 8
Fast camera movie of a short duration transient CHI discharge
As time progresses, the CHI produced plasma gradually shrinks in size and forms a ring around the center stack
Raman, Dec05 9
Some discharges persist for t > 200ms
•After plasma shrinks, it continues to persist for nearly 400ms.
•Plasma parameters for this persisting plasma have not yet been measured.
Plasma Current (kA)
Injector Current (kA)
Raman, Dec05 10
Summary
• Generation of a solenoid-free closed flux current discharge by CHI clearly demonstrated in NSTX
• 60kA of closed flux current generated using only 7kJ of capacitor bank energy– Optimization at more energy should easily result in closed flux
currents of >200kA– At this current level, expect HHFW and NBI to couple to CHI
produced discharges for non-inductive current ramp-up
• In some discharges, the current channel shrinks to a small size and persists for more than 200ms
Raman, Dec05 11
Thomson scattering Te & ne profiles show progression towards a
less hollow profile at later times, consistent with CHI startup
• CHI startup initially drives current along the edge
• After reconnection in the injector region, the initially hollow profile should become less hollow with time as current diffuses in
12ms 18ms
13ms15ms
12ms16ms
Thomson scattering: B. LeBlanc (PPPL)
The black traces are at the earlier time, and the red traces are at the later time
Raman, Dec05 12
Preliminary EFIT reconstructions
Shot 118334 at 26ms Shot 118342 at 11ms
For discharge 118334, that has about 15 to 20kA persisting beyond t = 20ms, EFIT indicates the presence of a discharge along the center stack.
EFIT: S. Sabbagh (Columbia U)