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 kz = 3 m-1, to be compared to previous operation at kz = 7.6 m-1.

• He, DND plasma, B = 0.45 T, Ip = 0.5 MA, ne0 = 1.5 - 2.5x1019 m-3.

1.0x10-1

0.8

0.6

0.4

0.2

0.0

Current driven per power absorbed (A/W)

4.03.53.02.52.01.51.0

Central Temperature Te(0) (keV)

Dotted - CURRAYSolid - AORSA

kz = 7.6 m-1

kz = 3 m-1

0.15

0.10

0.05

0.00

Current driven per power absorbed (A/W)

4.03.53.02.52.01.51.0

Central density ne(0) (x1019

m-3

)

Dotted - CURRAYSolid - AORSA

kz = 3 m-1

kz = 7.6 m-1

Density scan at constant temperature(Te(0) = 2 keV)

Temperature scan at constant density(ne(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 Te, ne profiles from shot 110145Ti/Te = 0.7, D:H::0.96:0.04

Exp points

Exp points

PHYSICS QUESTIONS:

• Can cold (~ 500 eV) electrons be directly heated to > 1.7 keV at kz = 3 m-1?

• Can Te0 > 1.7 keV be maintained at kz = 3 m-1?

• Is current drive more efficient at kz = 3 m-1 than at kz = 7.6 m-1?

• How does parasitic power absorption (minority H heating, edge ion heating, etc.) change with kz?

• Can power deposition profiles be inferred from rf modulation?

TECHNICAL/OPERATION QUESTIONS:

• Can plasma position be controlled at kz = 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 kz = 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?

• 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.- Te(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).- Te(0) reached 1.2 keV for -90º.- Te(0) dropped to 0.65 keV when switched to -30º (need to reach

Te(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

-90º phasing

Unmatched

Matched

-90º -30º

Vo

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• 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 MATCHINGLOADING AND MATCHING

LOADING AS A FUNCTION OF PHASE(RANT3D CALCULATIONS)

co-CDco-CD cntr-CDcntr-CD

• All 6 voltage reflection All 6 voltage reflection coefficients on the untuned coefficients on the untuned side of the match are close side of the match are close in value for ±30º and ±90º, in value for ±30º and ±90º, facilitating phase shifting.facilitating phase shifting.

• The high reflection The high reflection coefficients for cntr-CD coefficients for cntr-CD indicate lower loading (may indicate lower loading (may limit cntr-CD power).limit cntr-CD power).

• Phase shifting during pulse Phase shifting during pulse may be more difficult for cntr-may be more difficult for cntr-CD.CD.

• Might be desirable to switch Might be desirable to switch from -90º to +30º for cntr-CD from -90º to +30º for cntr-CD operation.operation.

Calculated Reflection Coefficients (unmatched)Calculated Reflection Coefficients (unmatched)

Shot 111644: Phase shift at 0.28 s (7.6 mShot 111644: Phase shift at 0.28 s (7.6 m-1-1 to 3 m to 3 m-1-1))

-90º-90º

-30º-30º

2 MW2 MW

-90º-90ºantenna antenna pressure pressure increasesincreases

TTe0e0 drops drops

plasma moves plasma moves outwardoutward nnee rises rises

-30º-30º

X-rays X-rays increaseincrease

Shot 111644: C-III

The Edge Rotation Diagnostic shows higher ion temperature for -90º The Edge Rotation Diagnostic shows higher ion temperature for -90º phasing (interpretation complicated by radial movement of plasma)phasing (interpretation complicated by radial movement of plasma)

data from T. Biewerdata from T. Biewer

RF powerRF power

TTii (poloidal) (poloidal)

TTii (toroidal) (toroidal)

-90º-90º -30º-30º

data from T. Biewerdata from T. Biewer

Shot 111644 - He-II

-90º-90º -30º-30º

Soft X-ray signals Soft X-ray signals show sawtooth show sawtooth activity after phase activity after phase shift.shift.

high energy channelshigh energy channels low energy channelslow energy channels

CE

NT

ER

CE

NT

ER

CE

NT

ER

CE

NT

ER

ED

GE

ED

GE

ED

GE

ED

GE

LIMITED OPERATION AT 7.6 m-1

• Further operation at 3 mFurther operation at 3 m-1-1 was abandoned due to was abandoned due to noise problems. noise problems.

• Power scan at -7.6 mPower scan at -7.6 m-1-1 was started. was started.

- Reached ~3.6 MW with breakdowns, 3.0 MW without Reached ~3.6 MW with breakdowns, 3.0 MW without breakdowns.breakdowns.

- Plasma density was higher than desired (~2x10Plasma density was higher than desired (~2x101919 as as opposed to <1.5x10opposed to <1.5x101919); this was related to antenna ); this was related to antenna outgassing.outgassing.

- TTee(0) ~ 1.5 keV(0) ~ 1.5 keV

• Did not complete power scan at -7.6 mDid not complete power scan at -7.6 m-1-1 (co-CD) nor (co-CD) nor start cntr-CD scan (+7.6 mstart cntr-CD scan (+7.6 m-1-1).).

• VVlooploop similar to comparable LSN shots from 2003. similar to comparable LSN shots from 2003.

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

3 MW3 MW

• Need better control of plasma position during rfNeed better control of plasma position during rf- Solve noise pickup problemSolve noise pickup problem

• Need more conditioning of the antennasNeed more conditioning of the antennas- Need to run >4 MW reliably.Need to run >4 MW reliably.- Need to limit pressure rise with rf power.Need to limit pressure rise with rf power.

• Need to develop operational strategy to test CD at 3 mNeed to develop operational strategy to test CD at 3 m--

11 with high T with high Tee..- Cannot heat electrons directly with kCannot heat electrons directly with kzz = 3 m = 3 m-1-1..- Can heat electrons with kCan heat electrons with kzz = 7.6 m = 7.6 m-1-1..- Can switch from -7.6 to -3 mCan switch from -7.6 to -3 m-1-1 (+3 m (+3 m-1-1?) during pulse; ?) during pulse;

preheating electrons with rf is possible.preheating electrons with rf is possible.

• Need to maintain high TNeed to maintain high Tee to test CD efficiency at 3 m to test CD efficiency at 3 m-1-1..

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