Mid-Run Assessment - ISD S. Kaye, D. Gates 10 May 2006

ISD Priorities: Co-Injection Menard: Long pulse development at low density using EF correction coil Maingi: Extension of enhanced H-mode through current profile and shape control Gates: Long pulse double null development with rtEFIT Kaye: Dependence of ELM severity and confinement on boundary shape Kessel: Systematic Variation of the Front-End of Long Pulse Discharges Kessel: Non-Solenoidal Ip Rampup Soukhanovskii : Divertor detachment in highly shaped long pulse LSN plasmas Soukhanovskii : Gas fueling efficiency and H-mode access with various gas jet injectors Leuer: NSTX MIMO control collaboration Total:14611 Requested ContingencyPriorityAssignedNeeded

Progress on XP603 (2 x 0.5 run days) - Gates Attempted to achieve early H-mode by: –Divert earlier - failed PF1A problem –Larger I p flat-spot, les dI p /dt - failed –Adjust early gas - failed –Requires higher  early with PF3U/L (a few more shots) Raised elongation to  = 2.45 (maintained ) –Led to record 1MA pulse length (at the time) After remaining adjustments made push wall conditions to improve confinement –He discharges, Li, B, - no bakeout Need field and current scan broaden operating space (see Fig.) Plot showing improvement in pulse averaged  and pulse length with shaping over narrow range (for 2006)

XP526:  Scans – Effect on Confinement & ELMs (Kaye) Initial attempt (1 day) unsuccessful –Facility, plasma issues Spent several hours on 5/2 to develop target –Successful Will attempt low-  - scan first, then high-   -scan, then mid-   - scan Shot

XP602 run plan status (Menard) Day 1 – 30 shots  need to finish phase scan Re-obtain long-pulse discharge at 4-4.5kG and IP = 0.8MA  done –Implemented rt-EFIT control of LSN long-pulse shots – took ½ day Scan ramp-up density to determine MHD locking threshold  started Scan EFC amp & phase during locking  scanned amp, not phase Day 2 – 30 shots  only have 2 shots at lower ne If EFC enables lower n e operation, reduce n e again (12 shots) –From May 5 data, lower n e delayed early H-mode, shot dev. required Increase IP to 0.9, 1.0, 1.2MA (18 shots) –Developed a 700kA target via XP614 – obtained info about optimal P NBI Day 3 (1/2 day) – 15 shots  Unlikely to get here this year Obtain density flat-top in longest-pulse obtained with EFC at 0.8MA Scan Li deposition to achieve desired pumping for n e control (10 shots) Increase fueling for constant line-average density = 3e19 m -3 (5 shots)

XP602: Long-pulse development at reduced n e using EFC - Developed shot with 30% lower density early - q-min higher initially even w/ lower heating - EFC used during early phase of shot

XP602: Long-pulse development at reduced n e using EFC - Applying early EFC can increase early plasma rotation - Other shots (120336) show smaller increase Predictive OHxTF EFC on by t=150msEFC off

Run plan wish-list Start and finish EFC phase scan –8 shots lower ne  multiple He-cond shots needed? –H-mode threshold strongly affected at lowest ne values –8-15 shots Increase IP to 1, 1.2MA –Tested at 700 and 800kA so far –5-10 shots

XP627 Non-Solenoidal Ip Rampup (Kessel) Part A: HHFW (1/2 day) –Use k|| = 14 m-1 heating, run at Ip = 250 kA, utilize trip avoidance (power reduction before voltage reaches trip limit) –Use k|| = 10 m-1 heating, co-CD, and cntr-CD, run Ip = 250 kA –Using best phasing result attempt OH clamp –For additional run time attempt lower Ip values (200, 150 kA) for both 14 and 10 m-1 Part B: NBI (1/2 day) –At Ip = 600 kA, inject 70 keV, inject 70 keV, and inject 70 keV –Repeat at Ip = 500 kA –Repeat at Ip = 400 kA –Repeat at Ip = 300 kA –For additional run time try source 70 keV, and sources A and higher energy Examine the replacement of inductive current by non-inductive current in the form of CD and bootstrap current from HHFW and NBI, to determine the efficiency of these sources to rampup the plasma current

Summary of XP627 Part A: HHFW Part A of this XP were run for 1/2 day to examine the effectiveness of HHFW to replace inductive current and provide non-solenoidal plasma current rampup. The experiments used low plasma currents kA, isoflux/rtEFIT control of the outer gap for antenna coupling, HHFW powers ranging from MW, and HHFW heating phasing at 14 m -1. Initially there were difficulties getting the plasma control system to function at low Ip, but these were corrected, and reliable discharges were produced, but resulted in the loss of 1/4 day. The HHFW system was choppy at first due to gap control oscillations and non-optimal matching, however, this improved significantly as the matching was tuned. The plasma did enter H-mode in several discharges, however, it did not stay in H- mode, which appears to be correlated to the HHFW power dropping out. The HHFW power required to enter the H-mode is lower than previously observed at these Ip values by about times, and more work is required to understand the HHFW power and H-mode sustainment.

More Run Time for XP627 Part A: HHFW Lost 1/4 day did not allow the time necessary to get good matching with the antenna, this must be improved to provide longer steady HHFW power input Expand power scan and power trajectory (step up in power) of HHFW to identify reliable entry into H-mode and sustainment of H-mode, including gap adjustments after plasma is in H-mode Extend pulse lengths (to 700 ms) to get HHFW conditioning over long periods (HHFW on at 100 ms and off at 650 ms) Keep plasma current LOW to (250 kA) to make HHFW heating effects strong, unless control issues force Ip to higher values Try intermediate phasing at = 10 m -1 to see CD and heating effects Have good starting discharge for this work, , with reasonable HHFW antenna matching

Summary of XP627 Part B: NBI Part B of this XP was run for ½ day, examining NBI into low Ip plasmas to establish database for non-solenoidal plasma current rampup. The plasma stored energies under a single NB source reached 120 kJ at 600 kA, kJ at 500 kA, and 60 kJ at 400 kA. With 2 NB sources the plasma stored energy reaches 120 kJ at 600 kA, 120 kJ at 500 kA, and kJ at 400 kA. With 3 NB sources at 500 kA, the stored energy was 120 kJ, indicating that source C is not well confined at these low Ip values. The li values were at 600 kA, at 500 kA, and 0.85 at 400 kA. The lowest surface voltage was 0.1 V, although more typically across these discharges about 0.2 V. The density regularly exceeded the Greenwald density by about 50% due to the low plasma currents and strong NB fueling. Analysis of the NB characteristics with TRANSP will help to understand the trade-offs of NB confinement vs Ip, bootstrap and NBCD, and single and double source effects. The diminishing returns of NBI for non-solenoidal current rampup are becoming evident at 400 kA, although the easy transitions to H-mode are encouraging.

More Run Time for XP627 Part B: NBI Add source 70 keV to the 2 NB source cases at all currents Examine Ip = 300 kA to find the “cliff” for NB confinement, where it is no longer effective. So far the trend is smooth. Begin NB injection into plasmas at low Ip with HHFW heating (Ip = kA) to examine the parasitic absorption effects when Ip is low and the NB is poorly confined. This serves as the transition from the HHFW-only rampup phase to the HHFW+NBI phase

Counter-Injection Campaign Priorities Kaye:Overview and issues, Thermal confinement trends Akers:Ideas from across the ocean0 Bush:H-mode power threshold Menard: J-profile modifications during ctr with early H-mode startup2 112 Lee: Assessment of the magnitude and direction of ELMs with FIRETIP1 Darrow:Ctr-inj beam blips0.5 1 West: Search for the QH-mode with ctr-inj and low target density1 111 Bernabei:HHFW operation with reversed fields2 1 2 SoukhanovskiiEdge and boundary characterization in reversed Bt Bp plasmas0.5 2 Stutman:Development of ctr-inj L-modes1 2 1 Petty: Displacement of neutral beam ions by MHD instabilities Requested ContingencyPriorityAssignedNeeded