Supported byOffice ofScience
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
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
CHI during ohmic discharges in spherical tori
D. Mueller, M.G. Bell, Princeton Univ.W.T. Hamp, A.J. Redd, B.A. Nelson,
T.R. Jarboe, R. Raman, Univ. of Wash.
S.A. Sabbagh, Columbia Univ. 47th APS – DPP Meeting
Oct 24-28, 2005Denver, Co.
Mueller, D. APS’05 2
Coaxial helicity injection (CHI)
• Used to provide solenoid-free plasma startup– transient CHI (Raman et al.)
• Steady-state CHI– Relaxation current drive
• Edge current drive– Control edge SOL flows– Improve stability limits– Induce edge rotation– Provide means to study current penetration mechanisms
• Persistent current• Well-characterized plasma
Mueller, D. APS’05 3
Experimental setup
Direction of toroidal and poloidal fields and the applied electric field are chosen so that
1) ExB direction is into the vessel
2) Current following the field lines connecting the the electrodes will have Ip in the desired directionVinj
Mueller, D. APS’05 4
Target shapes
• SN plasma shape• ExB is up• Strike points bridge
insulator • Different insulator
configurations
• Vinj
– HIT-II IGBT supplies
– NSTX Capacitor plus crowbar circuit
HIT-II NSTX
Mueller, D. APS’05 5
HIT-II results indicate persistent Ip after CHI
• Successful in demonstrating persistent plasma current– When inj > tok , where inj = Iinj / inj , tok = Ip/ tok
tok
inj
Ip(kA)
Vinj(kV)
Iinj(kA)
0
0.8
0
2
1
2
0
4
80
120
inj > tokinj < tok
TIME(ms)14 16 18 16 1814
0
0.8
0
2
1
2
0
4
80
120
Mueller, D. APS’05 6
HIT-II results indicate broader current profileafter CHI
• EFIT analysis indicates that li is lower after Iinj = 0• li is leading term in current distribution and indicates a
broader current profile
Mueller, D. APS’05 7
NSTX progress towards edge current drive
• Modifying shape avoids arcs and increases toroidal current
Mueller, D. APS’05 8
Early NSTX experiments clarify path forward
• inj > tok, feedback on Ip lowers Vloop (and Ip)
- persistent Ip not readily discernable
• n=1 tearing mode starts before CHI is applied
Mueller, D. APS’05 9
Identified needed improvements in the approach used on NSTX
• Need to apply constant Vloop, using feedback on Ip
– confuses determination of CHI driven current
• Faster turn-off of Iinj would be helpful
• Need to avoid tearing mode in target plasma– observation of coherent n=1 activity
• Dynamo probe tip on fast reciprocating probe will measure
ne,Te, s at 2 poloidal and radial positions
B, Br, Bat one location
- This can provide crucial information regarding models of the CHI mechanism by directly measuring the candidate fluctuations
~ ~ ~~ ~ ~
Top Related