Supported by

1. Supported by Office of Science XP817: Transient CHI – Solenoid free Plasma Startup and Coupling to Induction R. Raman, B.A. Nelson, D. Mueller, T.R. Jarboe, M.G. Bell et al., University of Washington Princeton Plasma Physics Laboratory College W&M Colorado Sch Mines Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Maryland U Rochester U Washington U Wisconsin Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAEA Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec NSTX FY08 Results Review August 6-7, 2008 (PPPL)

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

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)

4. 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

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

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

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

8. Discharges with Li Conditioning are More Reproducible and reach Higher Currents after Inductive Coupling Li makes breakdown more reproducible and the improvements are due to reduced recycling (similar to the effect of Ti-gettering on HIT-II)

9. Need auxiliary heating or metal divertor plates to compensate for increased radiated power with more capacitors • 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 Plasma Current 128400: 5mF (7.6kJ) 128401: 10mF (15.3kJ) 129402: 15mF (22.8kJ)

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)