1 Status of the 2008 ASC TSG Run plan Presented by D. A. Gates (J. Menard Deputy) At the NSTX Mid-run asessment PPPL April 16, 2008 Supported by Office of Science 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 Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec College W&M 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

2 XP-823 “Robustness of improved error field suppression in long-pulse discharges” – Day 1 Determine optimal n=3 EFC gain relative to I PF5 and/or I P Re-verify existence of n=3 EF in I P =900kA reference discharge  STATUS: re-verified at 700kA with early H-mode.  n=3 EF was less apparent w/o early H-mode Optimize n=3 EFC for two new plasma currents: 700kA and 1.2MA  STATUS: Optimal EFC current at 700kA was similar to level at 900kA Is EFCC proportional to I P ? –Need to optimize at MA to determine proportionality – needs 6-8 shots Test combined n=3 EFC + n=1 RFA suppression for I P =0.7, 0.9, 1.2MA Add n=1 feedback – 2 shots for each I P – use optimal 2007 gain & phase –STATUS: Worked well at 900kA, worked ok at 700kA but plasma still disrupted suggesting higher gain might be beneficial –Need data at MA – need 3-4 shots Day 1 GOAL: Extend optimal EFC to wider range of scenarios and I P STATUS – 1 run day so far for XP-823

3 XP-811 Vertical Stability Physics and Performance Limits in Tokamaks with Highly Elongated Plasmas XP complete in 1/2 run day Measured  z max, the maximum controllable vertical displacement, by turning of the plasma control and then tuning it back after the plasma had drifted vertically Interim report written and distributed to the ITER team which was well received –“Dear David, Many thanks - the report makes very interesting reading and the work behind it is very valuable for us. Best Wishes, David Campbell” Detailed analysis ongoing

4 XP-823 “Robustness of improved error field suppression in long-pulse discharges” - Day 2 Optimize n=1 RFA suppression controller Reproduce kA reference shots which used externally applied n=1 error field to trigger rotation collapse and disruption (3 shots) Scan RWM control proportional gain until feedback system is unstable (4 shots) –Add LPF to control coil currents as necessary to avoid very large SPA currents With gain at highest stable value, increase  LPF from 0 to: –1ms, 3ms, 10ms, 30ms, 100ms (2 shots for each  LPF ) (10 shots) For  LPF where AC RMS control power is reduced by factor 2-4, increase gain again and determine highest stable value (4 shots) Test controller for two new plasma currents: 700kA and 1.2MA (4 shots) STATUS – Day 2 plan has not yet been run – scheduled for April 28 Completing XP-823 may require additional 1.5 days vs. 1 day asked for Day 2

5 XP-826 "X-point limiter plasmas" Investigate plasma configurations where dominant lower X-point is brought very close to, or possibly outside, the outer divertor plate Possible alternative way to reduce divertor heat flux Assess access to H-mode, energy confinement and heat flux on divertor The initial experiment is planned to be run before lithium coating If successful, perform a second round with lithium on the lower divertor Goal: Investigate benefit of this configuration Status: Scheduled for review

6 XP-8** - Impact of 2 LITER system on long- pulse discharges STATUS – XP has not been run – waiting for dual LITER – requests 1.5 days Goal is to determine if usage of 2 LITER system can: –Eliminate He glow, or reduce glow time to  5 mins Will likely be done in boundary physics TSG XPs –Lower the electron density, and achieve density flat-top Likely requires SGI to replace HFS gas –Increase the NBICD fraction of long-pulse discharges Significant shot development will be needed to optimize low n e operation –Obtain sufficient flat-top duration to “measure” NICD profiles w/ V LOOP analysis Methodology –Reduce/eliminate HFS gas by utilizing SGI – 0.5 days Find lower bound of HFS pressure, incrementally add SGI –If/when plasma disrupts in ramp or early flat-top, optimize early shot phase to obtain flat-top sufficient for NBI-CD analysis – 1 days (optimistic!) Vary beam timing and power Vary plasma current ramp-rate and flat-top value Vary early density/SGI fueling rate

7 XP-8** Parametric study of high elongation plasmas Use second LITER and experience gained to optimize wall conditions Use n=1 feedback and n=3 correction to improve performance (higher  ) –Previous attempts limited to  N < 4 Perform current and field scan to optimize non- inductive current fraction Goal: Investigate high elongation low-li scenario first developed in 2007 Status: Waiting for LITER

8 XP status summary