1. 1 R Raman, B.A. Nelson, D. Mueller 1, T.R. Jarboe, M.G. Bell 1, J. Menard 1, R. Maqueda 2 et al. University of Washington, Seattle 1 Princeton Plasma Physics Laboratory 2 Nova Photonics Transient CHI Startup XP606 Summary NSTX Results Review PPPL, Princeton, NJ, 26-28 July 2006 Supported by Office of Science 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 JAERI Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep

2. 2 Implementation of CHI in NSTX

3. 3 Hardware improvements since 2005 Branch 5 plenum volume increased from 0.9cc to 1.2cc -Previously operated most discharges at highest regulator pressure MOV ratings increased to support operation up to 1.75kV -New capacitor snubber installed -Noise spikes during voltage application generally do not exceed 1.8kA Response time of capacitor bank current monitor improved

4. 4 Parameters partially explored this year Varied capacitor bank size -20, 25, 35, 45mF Varied injector flux and toroidal field -PF1B from 4400 to 6000A -TF from 0.3T to 0.55T Operated most resent discharges at ~1.75kV -1.6 to 1.85kV - ~250V increase from 2005 Generated up to 160kA of closed flux current -Several discharges contained 150kA -60kA produced in 2005

5. 5 Dramatic improvement in closed flux current generation from 2005 120874: 2006 results 118326: 2005 results LRDFIT (J. Menard) Inj. current

6. 6 Movie of a high current discharge Fast Camera: R. Maqueda & L. Roquemore

7. 7 Compared to 2005 results, equilibrium reconstructions are much more robust during the current decay phase after injector current is zero Plasma and Injector current EFIT (S. Sabbagh)

8. 8 Electron temperature magnitude and time- evolution for Ip ~ 70kA discharges, as in 2005 120814: Black: 8ms, Red: 12ms 120842: Black: 8ms, Red: 10ms Thomson (B. LeBlanc) Profile becomes less hollow with time Plasma and Injector current

9. 9 Effect of increased edge neutral pressure on current persistence is similar to that seen on HIT-II 119166: Beams conditioning, NBI valve open 119167: NBI valve closed 119168: NBI valve open, No NB conditioning Plasma currentVessel neutral pressure

10. 10 On HIT-II increased electron density lowers Ip Discharges repeated without between shot wall conditioning. Two plasma Injector sources for shots 25731 to 25742. One source for remaining shots.

11. 11 MOV’s clamp the injector voltage at about 1.75kV The capacitor bank is discharged into an open load with the snubber disconnected. The MOV’s significantly conduct starting at 1.7kV. Capacitor Bank Charge Voltage:121699: 1.5kV, 121703:1.7kV, 121704:1.8kV, 121705:1.85kV, 121706: 1.9kV, 121709: 2.0kV

12. 12 Record startup current produced in NSTX 160 kA produced using transient CHI –Verifies high current feasibility of CHI startup High current discharges not yet optimized –Extension to about 300kA should be possible with present system at 2kV Hardware improvements needed –Higher voltage MOVs to allow 2kV operation –Higher power DC charging power supply –200kW ECH to heat the CHI plasma