Raman, APS05 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

47th Meeting of the American Physical Society, DPPDenver, Colorado, 24 – 28 October, 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, APS05 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, APS05 3

Implementation of Transient CHI

Expect axisymmetric reconnection at the injector to result in formation of closed flux surfaces

Fast camera: R. Maqueda

Raman, APS05 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, APS05 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, APS05 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, APS05 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, APS05 8

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, APS05 9

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, APS05 10

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, APS05 11

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, APS05 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)