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Initial Exploration of HHFW Current Drive on NSTX

Initial Exploration of HHFW Current Drive on NSTX. J. Hosea, M. Bell, S. Bernabei, S. Kaye, B. LeBlanc, J. Menard, M. Ono C.K. Phillips, A. Rosenberg, J.R. Wilson Princeton Plasma Physics Laboratory M. Carter, P. Ryan, D. Swain Oak Ridge National Laboratory R. Pinsker

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Initial Exploration of HHFW Current Drive on NSTX

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  1. Initial Exploration of HHFW Current Drive on NSTX J. Hosea, M. Bell, S. Bernabei, S. Kaye, B. LeBlanc, J. Menard, M. Ono C.K. Phillips, A. Rosenberg, J.R. Wilson Princeton Plasma Physics Laboratory M. Carter, P. Ryan, D. Swain Oak Ridge National Laboratory R. Pinsker General Atomic P. Bonoli Massachusetts Institute of Technology T.K. Mau University of California at San Diego NSTX Team APS DPP Meeting 11-15 November 2002 Orlando, Florida

  2. Goal: Develop HHFW to support non-inductive operation of the ST concept Outline: • HHFW antenna arrangement • Phase feedback control configuration for selecting antenna spectra • Selected case for evaluating co/counter current drive effects • -/+ 90° phasing for kf = 7.6 m-1 • Closely match plasma parameters [Te(r), ne(r)] • Measure change in loop voltage • Modeling of current drive effects • Conclusions and future directions

  3. HHFW 12-strap antenna array on NSTX NSTX antennas installed in the vacuum vessel B • Antenna takes up almost 90° toroidally • Provides high power capability with good spectral selectivity

  4. Phase Feedback Control Configuration RF Power Sources P5 P6 P1 P2 P3 P4 Decoupler Elements D6 p Cube Voltages V1 V2 V3 V4 V5 V6 D1 D2 D3 D4 D5 p p p p p 5 Port Cubes 1 2 3 4 5 6 7 8 10 11 9 12 I1 I7 DfV21 Antennas • Digital based phase feedback control is used to set the phase between the voltages • of antenna elements 1 through 6 • Decouplers compensate for large mutual coupling between elements and facilitate • phase control

  5. Spectra Launched for Co and Counter Current Drive with kf = 7.6 m-1 GLOSI/RANT3D calculations of power spectra Co Df = - 90∞ Counter Df = + 90∞ Spectral Power (au) Dipole ooppoo kf (m-1) • Largepitch angle of the magnetic field results in asymmetric spectra • Loading is larger for co-CD and heating efficiency is larger for counter-CD • To compare VLoop between co and counter cases we use different RF powers to • produce very similar electron parameters

  6. Electron Parameters Made Similar for Co and Counter CD By adjusting PRF and Gas Feed IP = 500 kA, BT = 4.5 kG, D2 107899: Co-CD PHHFW = 2.1MW ( solid lines) 108907: Counter-CD PHHFW = 1.2MW ( dotted lines) Te0 (keV) time (s) neL (cm-2)

  7. Co Counter Tene Te (keV) ne (1019 m-3) Radius (m) Radius (m) Electron Temperature and Density Profiles are Very Similar for Co and Counter Cases

  8. A Significant Difference in Loop Voltage is Observed Between Co and Counter Current Drive Counter-CD DV ≈ .23V Loop Voltage (V) Co-CD RF on time (sec) • Less loop voltage is required to maintain IP constant when driving HHFW • current in the co direction • Internal inductance is similar for the two cases and DV is not caused by dli/dt

  9. ICD from Circuit Analysis is Bracketed by Current Drive Modeling Predictions Circuit analysis (0D): IP = (V- 0.5*IP*dLi/dt)/RP + IBS + ICD (Assumes steady state, RP and IBS (pressure profiles) independent of array phasing, ICD µ PRF/ne) • ICO ≈ 110 kA (0.053 A/W) Codes - Calculated electron power absorption profiles are coupled to Ehst-Karney adjoint solution for current drive efficiency to obtain current density profiles • TORIC: Full wave ICRF field solver [(k^ri)2 << 1, Bq = 0 for electric field polarization] • ICO ≈ 96 kA (0.046 A/W) • CURRAY: Ray tracing code (damping is linear on Maxwellian species, all orders in k^ri, k^ determined locally) • ICO ≈ 162 kA (0.077 A/W) See posters - P.M. Ryan et al., GP1.121; T.K. Mau et al., GP1.124; and C.K. Phillips et al., GP1.123 - Tuesdayafternoon

  10. DIII-D (With NBI) C. Petty et al., Plasma Physics and Controlled Fusion 43 (2001) 1747 HHFW Current Drive on NSTX is Consistent with DIII-D Results (HHFW only) • Current drive figure of merit, gfw, falls in range of DIII-D data at lower Te(0) • Dimensionless CD efficiency, zfw = gfw *3.27/Te(0) (keV), is comparable to that for DIII-D at • lower temperatures • RF power losses are important in reducing the HHFW current - - trapped electrons are • predicted to reduce gfw significantly for NSTX

  11. TORIC Code Predicts a Large Reduction in Current Drive Due to Trapped Electrons Calculated Driven Current Density Profiles JRF (A/m2/Winc) • The “no trapping” profile is indicative of the power deposition profile

  12. Summary and Future Directions • Digital phase feedback control has been used successfully to compare co and counter current drive with HHFW on NSTX • A significant reduction in VLOOP is observed for co-CD relative to counter-CD for comparable discharge parameters • Heating effects on VLOOP are mitigated by closely matching Te(r) and ne(r) • Ohmic Poynting flux reduction of ~ 30% is observed (DVLOOP ~ 0.23V) • Modeling gives values of dimensionless current drive efficiency comparable with high harmonic DIII-D results • Future directions for extending the study of HHFW CD on NSTX include: • Increasing HHFW CD by pushing RF power toward 6 MW and increasing Te • Bringing the MSE system on-line to afford direct measurement of the HHFW CD effects

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