1. STATUS OF THE HHFW CURRENT DRIVE EXPERIMENT ON NSTX Phil Ryan, Randy Wilson, David Swain, Bob Pinsker March 3, 2004 run date. This XP is focused on CD operation at k z = 3 m -1, to be compared to previous operation at k z = 7.6 m -1. He, DND plasma, B = 0.45 T, I p = 0.5 MA, n e0 = 1.5 - 2.5x10 19 m -3.

2. Density scan at constant temperature (T e (0) = 2 keV) Temperature scan at constant density (n e (0) = 2e19 m -3 ) CURRAY (Mau) and AORSA (Jaeger) calculations MOTIVATION: Full-wave code and ray tracing calculations both predict better CD efficiency for 3 m -1 Scaling study based on T e, n e profiles from shot 110145 T i /T e = 0.7, D:H::0.96:0.04 Exp points

3. PHYSICS QUESTIONS: Can cold (~ 500 eV) electrons be directly heated to > 1.7 keV at k z = 3 m -1 ? Can T e0 > 1.7 keV be maintained at k z = 3 m -1 ? Is current drive more efficient at k z = 3 m -1 than at k z = 7.6 m -1 ? How does parasitic power absorption (minority H heating, edge ion heating, etc.) change with k z ? Can power deposition profiles be inferred from rf modulation?

4. TECHNICAL/OPERATION QUESTIONS: Can plasma position be controlled at k z = 3 m -1 ? - -Will rf noise pickup in control circuitry limit rf power? - -Will rtEFIT work with high power rf? Can high power operation (> 4 MW) be achieved at k z = 3 m -1 ? - - Will plasma loading be sufficient to avoid antenna voltage limits? If needed, can array phase shift be changed during the pulse? - -Can we pre-heat at 7.6 m -1 and switch to 3 m -1 during the pulse without tripping transmitters?

5. Loading at 3 m -1 was high (11-12  ), as predicted by RANT3D. Power was not voltage limited. Noise in control circuitry was the limiting problem encountered; unable to operate above 2.3 MW. Direct heating of cold electrons was ineffective. - -T e (0) < 650 eV (TS was not working for most of morning). RF pre-heating of electrons was a technical success. - -Were able to find match conditions that permitted switching from -90º to -30º relative phasing during the pulse. - -Power was limited to 2.3 MW due to noise pickup on plasma position control (particularly at -30º). - -T e (0) reached 1.2 keV for -90º. - -T e (0) dropped to 0.65 keV when switched to -30º (need to reach T e (0) ~ 2 keV for effective heating and CD at 3 m -1 ). RF modulation for power deposition studies exacerbated the position control problem because of noise pickup in sensors. OPERATION AT 3 m -1

6. -90º phasing Unmatched Matched -90º-30º Voltage reflection coefficients Shot 111644 maintained  < 0.4 as phase was changed from -90º (-7.6 m -1 ) to -30º (-3 m -1 ) during shot. Cube voltage < 10 kV for 1.8 MW. -30º phasing Unmatched Matched LOADING AND MATCHING

7. LOADING AS A FUNCTION OF PHASE (RANT3D CALCULATIONS) co-CD cntr-CD All 6 voltage reflection coefficients on the untuned side of the match are close in value for ±30º and ±90º, facilitating phase shifting.All 6 voltage reflection coefficients on the untuned side of the match are close in value for ±30º and ±90º, facilitating phase shifting. The high reflection coefficients for cntr-CD indicate lower loading (may limit cntr-CD power).The high reflection coefficients for cntr-CD indicate lower loading (may limit cntr-CD power). Phase shifting during pulse may be more difficult for cntr- CD.Phase shifting during pulse may be more difficult for cntr- CD. Might be desirable to switch from -90º to +30º for cntr-CD operation.Might be desirable to switch from -90º to +30º for cntr-CD operation. Calculated Reflection Coefficients (unmatched)

8. Shot 111644: Phase shift at 0.28 s (7.6 m -1 to 3 m -1 ) -90º -30º 2 MW -90º antenna pressure increases T e0 drops plasma moves outward n e rises -30º X-rays increase

9. Shot 111644: C-III The Edge Rotation Diagnostic shows higher ion temperature for -90º phasing (interpretation complicated by radial movement of plasma) data from T. Biewer RF power T i (poloidal) T i (toroidal) -90º -30º

10. data from T. Biewer Shot 111644 - He-II -90º -30º

11. Soft X-ray signals show sawtooth activity after phase shift. high energy channels low energy channels CENTER CENTER EDGE EDGE

12. LIMITED OPERATION AT 7.6 m -1 Further operation at 3 m -1 was abandoned due to noise problems.Further operation at 3 m -1 was abandoned due to noise problems. Power scan at -7.6 m -1 was started.Power scan at -7.6 m -1 was started. -Reached ~3.6 MW with breakdowns, 3.0 MW without breakdowns. -Plasma density was higher than desired (~2x10 19 as opposed to <1.5x10 19 ); this was related to antenna outgassing. -T e (0) ~ 1.5 keV Did not complete power scan at -7.6 m -1 (co-CD) nor start cntr-CD scan (+7.6 m -1 ).Did not complete power scan at -7.6 m -1 (co-CD) nor start cntr-CD scan (+7.6 m -1 ). V loop similar to comparable LSN shots from 2003.V loop similar to comparable LSN shots from 2003.

13. Operation at 7.6 m -1 : Shot 111654 (3 MW) 3 MW

14. Need better control of plasma position during rfNeed better control of plasma position during rf -Solve noise pickup problem Need more conditioning of the antennasNeed more conditioning of the antennas -Need to run >4 MW reliably. -Need to limit pressure rise with rf power. Need to develop operational strategy to test CD at 3 m -1 with high T e.Need to develop operational strategy to test CD at 3 m -1 with high T e. -Cannot heat electrons directly with k z = 3 m -1. -Can heat electrons with k z = 7.6 m -1. -Can switch from -7.6 to -3 m -1 (+3 m -1 ?) during pulse; preheating electrons with rf is possible. Need to maintain high T e to test CD efficiency at 3 m -1.Need to maintain high T e to test CD efficiency at 3 m -1. NEXT STEPS FOR XP 403