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Status of Advanced Tokamak Modes for FIRE

Status of Advanced Tokamak Modes for FIRE. C. Kessel, PPPL NSO/PAC Meeting, MIT, January 17-18, 2001. Advanced Tokamak Modes for FIRE. AT modes could be divided into 4 major areas: Transient (significant inductive component) Quasi-stationary (small if any inductive component)

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Status of Advanced Tokamak Modes for FIRE

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  1. Status of Advanced Tokamak Modes for FIRE C. Kessel, PPPL NSO/PAC Meeting, MIT, January 17-18, 2001

  2. Advanced Tokamak Modes for FIRE • AT modes could be divided into 4 major areas: • Transient (significant inductive component) • Quasi-stationary (small if any inductive component) • Without external kink stabilization • With external kink stabilization

  3. Advanced Tokamak Modes in FIRE • Transient AT modes • Current is all or mostly inductive, but could have insufficient non-inductive current component to fix q-profile • Value of q(min) and r/a(qmin) will be changing • These modes can only be maintained at desired parameters for approximately a few seconds • Even FIRE’s shortest flattop (20 s) will allow these modes to evolve significantly

  4. Advanced Tokamak Modes in FIRE • Quasi-stationary AT modes • The safety factor profile is held by non-inductive current sources • Values of q(min) and r/a(qmin) don’t change much during the flattop • Over the longest pulse lengths (about 45 seconds) only small variations in q profile occur

  5. TSC Simulation of FIRE Burning AT Discharge

  6. TSC Simulation of FIRE Burning AT Discharge

  7. Advanced Tokamak Modes in FIRE • With no stabilization of the external kink mode • To maximize b, q(min) is roughly limited to 1.2<q(min)<1.5 and 2.1<q(min)<2.3 • Location of r/a(qmin) determines Ip achievable • Lower aspect ratios give slightly higher bN values (over range of A = 3.0-4.5) • There is a pressure profile dependence to obtain the highest bN • Take lesser of 4*li or 1.15*bN(no wall) (typical of DIII-D experimental observations)

  8. Reconstruction from TRANSP DIII-D AT Mode #98549 (t=1.3 s) Ip=1.2 MA, Bt=1.7 T, R=1.6 m, a=0.6 m, k=1.93, d=0.65, q(0)=1.9, q(min)=1.63,q*=3.75, li(1)=0.94, li(3)=0.71, bN=3.25, b=3.8%, bN(no wall)=2.75, 4*li=3.76, 1.15*bN=3.16, fbs=0.42, stable with wall at 1.5

  9. Advanced Tokamak Modes in FIRE • With stabilization of the external kink mode • Only stabilization of n=1 mode, so n=2 determines beta-limit, bN will rise (typical of an n=1 feedback system) • Stabilization of n=1-3 or so, typical of ARIES-RS and ARIES-AT equilibria, leading to the highest possible bN and fbs values

  10. n(0)/<n>=1.5; * balloon limited; n=1,2,3 checked for n=1 stabilized FIRE AT Modes; Bt=8.5 T, A=3.8, k=1.9, d=0.65

  11. FIRE AT Mode r/a(qmin)=0.8, qmin=2.19, Ip=5.4 MA, bN=2.54, I(LH)=2.2 MA, fbs=0.58

  12. FIRE AT Mode r/a(qmin)=0.65, qmin=2.12, Ip=4.54 MA bN=2.8, I(LH)=1.7 MA, fbs=0.58 more broad pressure

  13. FIRE AT Mode r/a(qmin)=0.65, qmin=2.10, Ip=4.5 MA, bN=2.85, I(LH)=1.75 MA, fbs=0.59 more peaked pressure

  14. n(0)/<n>=1.5; * balloon limited; n=1,2,3 checked for n=1 stabilized FIRE AT Modes; Bt=8.5 T, A=3.8, k=1.9, d=0.65

  15. Advanced Tokamak Modes in FIRE • Issues for AT modes in burning plasmas • Ip must be high enough to avoid excessive ripple losses and AE losses • Want maximum Ip to provide longest confinement time • Want to avoid (3,2) and (2,1) NTM’s (making qmin>2 more desirable than qmin<2) • Want to operate at low temperature to weaken AE’s, but need high temperature for CD • Current profile shapes limited by CD sources • Want to provide Q=5, so relying on alpha heating and bootstrap current

  16. Conclusions • For no external kink stabilization, qmin>2 appears to be most viable for minimizing CD power and avoiding NTMs, however, need higher bN and fbs • Approximately 2 MA of LHCD would be necessary which is about 30 MW (pending CD calculations) • Stabilization of the n=1 kink would yield attractive configurations (n=1 feedback) for qmin>2, and allow greater flexibility in choosing qmin • TSC simulations indicate we can create quasi-stationary plasmas for flattop burn

  17. Future Work • Continue ideal MHD search for AT modes • Pressure profile variations • Finite edge densities, and H-mode edge conditions • n=1 stabilized b-limits vs. qmin • Include LH profile from CD calculations • Examine DIII-D AT modes for FIRE • Observed edge and core conditions • Are ITBs present • Comparison of theory and observed b-limits • RWM feedback

  18. Future Work • CD analysis • LH calculations to optimize frequency and n|| for penetration and efficiency • Feasibiliy of making ICRF ion heating system tunable and with phasable antenna for FWCD • Is another CD source necessary to drive current in the range 0.2 < r/a < 0.6; ECCD, HHFW • Continue TSC calculations with identified stable target equilibria • How to form quasi-stationary plasmas in the shortest time • Do coupled TSC/LSC simulations

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