NSTX EXPERIMENTAL PROPOSAL - OP-XP-825 Title: HHFW Heating/CD phase scans in D L-mode plasmas P. Ryan, J. Hosea, R. Bell, L. Delgado-Aparicio, S. Kubota, B. LeBlanc, F. Levinton, C.K. Phillips, S. Sabbagh, G. Taylor, K. Tritz, J. Wilgen, J.R. Wilson, et al. ET – Wave Physics 1.Objectives of the experiment: Heating in D 2 L mode: Determine if density can be kept low enough to prevent wave propagation near wall Show how efficiency depends on wavelength in deuterium Need to establish behavior in deuterium L mode to optimize current drive for startup and in preparation for H mode studies CD in D 2 L mode: Phase scan for HHFW CD with time-resolved MSE  Use conditions of shots and (at 5.5 kG) if required to show loop voltage change MSE beam blip at end of HHFW pulse and progressively move it forward in time upon succeeding shots to determine the current relaxation time Determine the effect of co-, cntr-CD, and heating on stability of NBI-driven plasmas.

2 Heating and CD in D 2 L mode 2.Theoretical/ empirical justification This XP is a continuation of XPs 712 and 717 which established HHFW heating efficiency and CD properties in helium L mode plasmas Properties in deuterium are to be determined and compared to helium properties and analyzed with advanced RF modeling codes Need to establish behavior in deuterium L mode to optimize current drive for startup and in preparation for H mode studies Need increased power (3-4 MW) to improve the MSE CD measurement.

Edge density appears to affect the heating when it is above the onset density close to the antenna How does efficiency depend on wavelength in deuterium? (XP712 rev) Helium plasma results Can density be held below onset value in deuterium? Helium plasma results

Phase scan needed for deuterium case Phase scan illuminates decrease in heating efficiency at longer wavelength and permits MSE measurements of CD Results in helium suggest movement of onset density to antenna/wall causes losses rather than lack of cancellation of reactive currents Need D 2 scan to provide data set for comparing to helium case

5 co-CD phasingscntr-CD phasings The back lobe at 19 m -1 appears in addition to the front lobe at 13 m -1 when the phase shift is 150º. The asymmetrical response of the plasma yields a directional spectrum for co-CD and a symmetric spectrum for cntr-CD. 30º, 90º, 150º phase shifts give single peak, directional spectra

6 HHFW XP: Heating of L mode deuterium plasma - dependence on edge density and wavenumber 1.Plasma conditions  Deuterium, B T = 5.5 kG, I P = 600 kA, ~ 2x10 19 m -3 for direct comparison with He shot (19 April 2007) 2.RF properties for phase scan  Long pulse ≥ 200 ms, > 3 MW (but stay in L-mode)  Phase scan 180º, -150 º, -90 º, -30 º 3.Diagnostics for phase scan  Thomson scattering for edge density, etc.  90 kV NB pulse at end of RF for MSE  70 kV NB pulse blip during RF for CHERS 4.RF properties for efficiency scan  Repeat conditions for and 90 0 phases but with the RF modulated (10 Hz) to check efficiencies 5.Results  Determine knee in heating efficiency and compare with helium  Adjust conditions to obtain good efficiency at 90 0 for deuterium - density, gap etc

7 Phase scan for HHFW CD with time-resolved MSE 1.Plasma conditions  Continue conditions from heating phase, but may need to reduce density to increase CD efficiency.  This may involve using outer gas feeds so that gas may be turned off before RF comes on (check during XMP26 conditioning day) 2.RF Properties  Same power and pulse length as phase 1. 3.Diagnostics  Start MSE beam at end of HHFW pulse and progressively move it forward in time upon succeeding shots to determine the current relaxation time (3 steps).  Observe effect of HHFW/NBI on plasma stability as a function of phase. 4.Phase scan  Run -90º, +90º (-30º, +30º, if time permits)  If time, phase transition from -90º to -30º(-8 to -3 m -1 ); two beam blips before transition, two after (4 additional shots).

8 Previous CD measurements in D2 made at lower density than last year’s MSE measurements in He D 2 CD, April 19, kG He CD, April 19, kG, MSE

Heating and CD in D 2 L mode 3.Experimental run plan -- 1 day of run time  Setup conditions as for XP712 at B = 5.5 kG but with deuterium plasma: LSN, deuterium L-mode, gap ~ cm (same conditions as for shot , -90 degrees) Apply P RF as for ~ 200 ms (at full 0.55 Tesla field) with k || = -8m -1 Apply 90 kV NB pulse at end of RF pulse - use 70 kV beam to measure T i and rotation 3 shots APerform wavenumber scan at ~ 4 cm Scan vs phase is limited by need to complete it in 1/2 day 1.With plasma settings as for shot but with deuterium - Gap at ~ 4 cm: 1 14 m -1 (180 o ) m -1 (-150 o ) 1 -8 m -1 (-90 o ) 1 -3 m -1 (-30 o ) 1 no RF shot (Additional shots may be required to set matching for each k ||. NB should be added 20 ms before end of RF pulse)

10 Heating and CD in D 2 L mode A.Continued Scan with RF pulse modulated to determine tau (10 Hz modulation) 1 14 m -1 (180 o ) m -1 (-150 o ) 1 -8 m -1 (-90 o ) 1 -3 m -1 (-30 º )

11 Heating and CD in D 2 L mode BPhase scan for HHFW CD with time-resolved MSE With NB pulse near end of RF pulse: 1 14 m -1 (180 o ) 1 -8 m -1 (-90 o ) 1 +8 m -1 (+90 o )  Check that voltage is responding to phase. If not change conditions With NB stepped in toward start of RF pulse 2 +8 m -1 (+90 o ) 2 -8 m -1 (-90 o ) 1 no RF shot (Additional shots may be required to set matching for each k ||.)

12 B Continued Put on long NB pulse and see if reaction depends on phase 1 -8 m -1 (-90 o ) 1 +8 m -1 (+90 o ) 1 14 m -1 (180 o ) These shots are intended to see if we can drive current (or even operate) in the presence of high power NBI. May also go into H-mode. May need to go to 70 kV beams. Some of this may be accomplished during the time-resolved MSE measurements. Heating and CD in D 2 L mode

13 Example of Time-Resolved MSE Measurements 1st2nd3rd 90 kV NB I p (0.6 MA) 3+ MW HHFW ms beam blip positioned at the end of the RF pulse Increment beam turn-on time by 100 ms on succeeding shots Establish CD relaxation time and HHFW/NBI stability as a function of phase.

14 Heating and CD in D 2 L mode 4.Required machine, NBI, RF, CHI and diagnostic capabilities Stable or at least reproducible plasma conditions are required for the quantitative comparisons of this XP. Critical diagnostics include: Soft x-ray and Mirnov loops for stability EFIT with high time resolution for Thomson scattering for electrons Edge rotation diagnostic for edge heating NPA for edge and core ion heating Radiated power diagnostic Reflectometry for edge density and PDI Reflectometry for wave measurements for opposite side from antenna Edge probe for PDI Gap RF probes for leakage 3 RF probe(s) for edge RF field CHERS for some shots for T i and velocities MSE for as required for determining effects on current NB pulses needed at 90 kV and 70 kV

15 Heating and CD in D 2 L mode 5.Expected results and planned analysis Expected results: Heating efficiency in deuterium L mode vs wavenumber: 14 m -1, -8 m -1 (co CD), -3 m -1, -13 m -1, etc. – Core heating from EFIT W – Core electron heating from Thomson scattering – Ion heating and core rotation from Chers Edge heating/power loss – Edge ion heating from edge rotation diagnostic – Edge electron heating from Thomson scattering – Rotation effects MSE measurements of current drive –Co vs counter for conditions where loop voltage is reduced for co Loop voltage difference for co/cntr, compare to MSE Plasma profiles, core and edge, for permitting predictions of wave propagation damping and CD characteristics

16 Heating and CD in D 2 L mode Planned analysis: Compare power coupling efficiencies vs wavenumber to those for helium Determine CD profile vs time in RF pulse, CD efficiency and compare with RF code predictions. Determine if stability with NB is dependent on antenna phase Analysis of wave propagation, damping and CD characteristics from onset density into the core of plasma - along field and perpendicular directions of the ray path, and including collisions - for predicting CD and surface losses Benchmarking of RF codes that include surface losses

17 RF Power Flow and Possible Loss Channels Mode conversion at n  ci Ion absorption at n  ci Landau damping on core electrons ANTENNA Evanescent waves (local sheaths, collisional heating) IBW waves, surface waves, PDI Non-absorbed (Far-field sheaths, wall heating) HHFW Power RF Power Shots analyzed (co-CD) (cntr-CD) GLOSI/RANT3D (propagating FW calculation) (co-CD) = 16.2  (cntr-CD) = 8.2  Measurement (co-CD) = 19.3  (cntr-CD) = 7.9  Loading calculations agree with measurements to within 20% for co-CD, 5% for cntr-CD 5-20%? ~ 25% ?? ~35-55% co ~50-70% cntr < 5%