xp817: transient chi – solenoid free plasma startup and coupling to induction office of science r....
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XP817: Transient CHI – Solenoid free Plasma Startup XP817: Transient CHI – Solenoid free Plasma Startup and Coupling to Inductionand Coupling to Induction
Office ofScience
R. Raman, B.A. Nelson, D. Mueller, T.R. Jarboe, M.G. Bell et al.,
University of WashingtonPrinceton Plasma Physics Laboratory
NSTX FY08 Results ReviewAugust 6-7, 2008 (PPPL)
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
JAEAHebrew UIoffe Inst
RRC Kurchatov InstTRINITI
KBSIKAIST
POSTECHASIPP
ENEA, FrascatiCEA, Cadarache
IPP, JülichIPP, Garching
ASCR, Czech RepU Quebec
Supported by
FY08 NSTX Results Review (Solenoid-Free Plasma Startup) August 6, 2008 2
Transient CHI: Axisymmetric reconnection leads to formation of closed flux surfaces
• Demonstration of closed flux current generation– Aided by gas and EC-Pi injection from below divertor plate region
• Demonstration of coupling to induction (2008)– Aided by staged capacitor bank capability
FY08 NSTX Results Review (Solenoid-Free Plasma Startup) August 6, 2008 3
FY08 Result: Proof-of-Principle Demonstration of Coupling a CHI Started Discharge to Induction
8 Total days: 2 days – commissioning & conditioning
2 days – Testing without Cryo pumping capability
4 days – Full capability
March 10: Commissioned new CHI hardware
- Staged capacitor bank operation
- Fast voltage monitoring system
March 11: Conditioned the lower divertor plates
- Operated in stuffed injector mode
- Conducted first D2GDC (in recent history)
March 12: First day of main XP
- Inductive discharge development that had reduced CS pre-charge
- Started CHI discharge with some pre-charge in CS
- Reproduced good Te CHI discharges with zero CS pre-charge
- Saw first evidence for coupling to OH (good Te and ne signals)
FY08 NSTX Results Review (Solenoid-Free Plasma Startup) August 6, 2008
CHI Started Discharges after Inductive Coupling Transition into H-mode and are more reproducible with Li Conditioning
March 31: Inductively coupled discharges reach 180kA and reach Te ~100eV
April 9: Inductively started discharges reach Ip = 600kA and Te = 500eV
- Used position feedback control to increase current
June 2,3: Operated without Cryo Pumping and without Boronization
- Vessel base pressure ~10x higher than usual (4 x 10-7 Torr)
- June 2- Tested CHI discharge formation in He & then switched to D2 plasmas, Ip ~400kA in poor reproducibility discharges
- June 3 - First use of Li evaporation for CHI
- Discharges became reproducible and reached Ip ~600kA
- Tested use of HHFW for heating during the coupling phase to induction
July 8: Used Cryo pumping and 10mg/min Li evaporation
- Central electron temperature reached 1keV
- Ip reached 725kA, discharges transitioned into H-modes
- Discharges with 2min HeGDC + 6min Li were more reproducible than Li-only cases
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FY08 NSTX Results Review (Solenoid-Free Plasma Startup) August 6, 2008 5
March 12: First Evidence of CHI Coupling to Induction
• Final four shots coupled to induction
– Te and ne (from Thomson) showed plasma to be resting on outer vessel during inductive phase
– Later confirmed by EFIT
• On last shot increased vertical field moved plasma further inboard verifying Thomson and EFIT results
FY08 NSTX Results Review (Solenoid-Free Plasma Startup) August 6, 2008 6
March 31: Demonstrated First Good Coupling of CHI Produced Discharge to Induction (in NSTX)
• Started with Final discharge from March 12
– Used 7.5kJ of capacitor bank energy to initiate CHI discharge
– Used pre-programmed PF coil currents to maintain equilibrium
– Discharges >40ms were ramping up in Ip but vertically unstable
FY08 NSTX Results Review (Solenoid-Free Plasma Startup) August 6, 2008 7
CHI started discharge couples to induction and transitions to an H-mode demonstrating compatibility with high-performance plasma operation
Te & Ne from Thomson
Ti from CHERS- Central Te reaches 800eV
- Central Ti > 700eV
Note the broad density
profile during H-mode phase
• Discharge is under full plasma equilibrium position control− Loop voltage is preprogrammed
CHERS: R. Bell
Thomson: B. LeBlanc
FY08 NSTX Results Review (Solenoid-Free Plasma Startup) August 6, 2008
Discharges with Li Conditioning are More Reproducible and reach Higher Currents after Inductive Coupling
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Li makes breakdown more reproducible and the improvements are due to reduced recycling (similar to the effect of Ti-gettering on HIT-II)
FY08 NSTX Results Review (Solenoid-Free Plasma Startup) August 6, 2008 9
Need auxiliary heating or metal divertor plates to compensate for increased radiated power with more capacitors
128400: 5mF (7.6kJ)
128401: 10mF (15.3kJ)
129402: 15mF (22.8kJ)
Plasma Current• Low-z impurity radiation increases
with more capacitors– High Te in spheromaks (500eV)
obtained with metal electrodes– Test with partial metal outer
divertor plates during FY09– Reverse TF polarity to make
outer vessel cathode• Upper divertor radiation also
increases with more capacitors– Need to reduce absorber arcs– Absorber field nulling coils to be
used during FY09• Assess benefits of partial metal
plates + Absorber coils– Discharge clean divertor with
high current DC power supply– Use 350kW ECH during FY11
FY08 NSTX Results Review (Solenoid-Free Plasma Startup) August 6, 2008 10
First Demonstration of Compatibility of CHI with High-Performance Inductive Operation in a Large ST
• Transient CHI is a proven method to generate closed flux (160kA to date)
– Startup & inductive coupling at 100kA demonstrated on NSTX & HIT-II
– CHI initiated and inductively ramped current reached 700kA in H-mode
– Peak Te ~0.9keV obtained in discharges coupled to induction
• Need to reduce Low-Z impurity radiation to increase current
– Electrode conditioning to be improved for FY09
– Reduce absorber arcs using Absorber PF coils
– Use outer metal divertor plates needed for Liquid Li system
• Beyond 2009
– 350kW ECH + higher power HHFW will help considerably
– Results from metal outer plate tests during 2009 will provide additional data on effect of Low-Z impurities
– Higher voltage needed to increase startup current
– Higher TF will increase current multiplication factor
Closed flux startup currents of about 500kA is possible in NSTX through hardware improvements (not a physics limitation)