1. Current Drive for FIRE AT-Mode T.K. Mau University of California, San Diego Workshop on Physics Issues for FIRE May 1-3, 2000 Princeton Plasma Physics Laboratory TKMau/01

2. OUTLINE Status of CD / rotation drive scenarios for ARIES-AT RFCD for FIRE DT-Burning AT mode: - On-axis drive with ICRF - Off-axis drive with LHW Issues: - CD for non-burning AT modes - Current profile control and analytic tools - Database Conclusions TKMau/02

3. CD / Rotation Drive Scenarios for ARIES-AT ARIES-AT is a 1-GWe fusion power plant design based on a high elongation (  = 2.2), high bootstrap fraction (f BS  ) RS plasma with wall stabilization (  N ~6.0). CD and rotation drive both involve external power, and are considered together. Two scenarios are being considered: Base Case: (1) ICRF/FW for on-axis CD; ECCD an alternative (2) LHW for off-axis CD (3) some form of RF power for rotation drive Back-up Case:(1) ICRF/FW for axis CD; ECCD an alternative (2) low-energy NBI for off-axis CD (3) same beam for rotation drive TKMau/03

4. RFCD Power Requirements are Modest for ARIES-AT Power requirements were calculated for on-axis CD with ICRF/FW and off-axis CD with LHW, for three ARIES-AT design points. R = 5.2 m, A = 4,  = 2.2,  = 0.8, I p ~ 13 MA, B o ~ 6 T, P net = 1000 MW. Full  N  (%) (keV) I bs /I p P IC (MW) P LH (MW) 5.6 8.4 15.8 0.925 3.0 21.7 6.0 9.2 15.9 0.943 3.9 21.2 6.8 10.6 17.8 0.915 4.2 65.1 The  N = 6.0 case has been picked as the reference equilibrium, based on CD power consideration. On-axis seed current is small, requiring only ~4 MW of ICRF power. ECCD may be an attractive alternative. TKMau/04

5. CD Power can be Very Low for FIRE Burning AT Mode Based on a FIRE DT-burning AT mode equilibrium (from Kessel): R = 2 m, a = 0.52 m, B o = 6.75 T, I p = 4.50 MA, T eo = 13.9 keV, n eo = 5.10x10 14 cm -3, Z eff = 1.38,  = 5.62%,  N = 4.38 (with wall stabilization of kink) I BS /I p = 0.926, I seed = 0.354 MA   n, T Profiles T n n o / =1.7 T o / =1.5 - (A/cm 2 ) EQ SD BS Dia SD Using ICRF to drive on-axis seed (0.1 MA), and LHW to drive off-axis seed (0.25 MA), total CD power can be as low as 7.3 MW !!  Normalized efficiency  CD = 0.29. TKMau/05

6. T Be D 2T 2Be 2D,3T 4T,3Be 3D 4Be 75 MHz axis R+a 5T 112-126 MHz R-a 28 MHz Frequency Options for Fast Wave On-Axis Current Drive 75 MHz : Avoid resonance with D and  ; moderate damping on T 28 MHz : Avoid ion resonance altogether; large antenna size 112-126 MHz : Significant ion absorption; requires strong single-pass electron absorption. TKMau/06

7. FWCD Power is Similar for Three Frequency Options f (MHz) N || P e /PP D /PP T /PP He /PP CD (MW) f spa 28 2.5 0.9900.010 3.7 0.29 28 3.4 0.9900.010 3.6 0.39 75 2.5 0.79 00.210 4.1 0.67 75 3.4 0.9100.090 3.8 0.81 120 2.5 0.650.100.210.04 4.6 0.97 120 3.4 0.830.020.130.01 4.3 0.99 Ion species mix : f D = f T = 0.394, f He = 0.208, f Be = 0.004  damping is not calculated in 120 MHz case. Would increase P CD somewhat if included. 15 rays are used along 1.0 m antenna poloidal length with P ~ cos 2 k o y. f spa is initial single pass absorption fraction for central ray. TKMau/07

8. CURRAY ray tracing code is used. Power is launched from 10 o above OB midplane with N || spectrum for strong single-pass absorption and best current profile alignment. Wave parameters : f = 75 MHz, N || = -3.4. Results: P CD = 3.8 MW @ I/P = 0.028 A/W, I seed = 0.11 MA single-pass absorption = 0.81, 9% of power to T at 2f cT. Driven j Seed j On-Axis Seed Current Drive with ICRF Fast Waves TKMau/08

9. LH Launching Parameters for Off-Axis CD Required penetration to  = 0.67, where R=2.43 m on OB midplane, B = 5.61 T, n e = 3.7x10 14 cm -3, and T e = 9.8 keV. To avoid parametric process, f > 2 f LH (0.67) = 2.65 GHz. To avoid  damping, f > 1.86 f pe (0.67)N ||,min ~ 9 GHz Since  damping will be weak for  > 0.67, we can set f = 4.0 GHz. From linear picture, accessible only to  =0.72; Found some rays that reflect off the edge can penetrate slightly further. N || vs  Accessible TKMau/09

10. Requires 4 waveguide modules, launching different N || and located at 30 o below OB midplane. Wave parameters: f = 4 GHz, N || = 1.8 - 2.5. P CD = 3.5 MW @ I/P = 0.071 A/W. I seed = 0.25 MA Efficiency is sensitive to local T e and n e. High efficiency here is due to high T e and low n e near edge. 1% of power to energetic  ’s. [  ’s treated as thermal @ ~800 keV ] N || = 2.2 Driven j Seed j Off-Axis Seed CD with LH Waves TKMau/10 4

11. CD and Profile Control Issues for FIRE AT Modes CD power requirements for non-burning AT modes and for transients to DT-burning AT modes with lower bootstrap fraction need to be investigated. Realistic edge n,T profiles are required to truly assess LH off-axis CD power. Quasilinear LHCD analysis may be needed. Current profile control while accessing flattop AT modes is critical, and modeling in conjunction with transport codes will be required. Ref. D. Moreau, et al, Nucl. Fusion 39 (99) 685. An analytical tool for self-consistent analysis of CD and equilibrium/ stability will be useful. For LH off-axis CD, interaction with energetic alphas should be studied in more detail. TKMau/11

12.  B = I p R o / P CD  CD = (1-f BS )  B AT: advanced tokamak RS: reverse shear FS: first stability ST: spherical torus SS: second stability FIRE (AT) is on Development Path to AT Power Plant from Current Drive / Bootstrap Current Perspective RS formation with off-axis LHCD on JT-60U and Tore Supra FWCD data TKMau/12

13. Conclusions and Discussions RFCD power was assessed for optimized FIRE DT-burning AT mode. P CD ~ 8 MW. ICRF on-axis CD and LH off-axis CD are adequate for the seed current profiles. CD assessments should be carried out for non-burning AT modes and for access to flattop AT modes. Current profile control during transients for AT flattop is critical and should be investigated and modeled. Should expand experimental data base on RS formation with LH off-axis CD, and possibly with ICRF on-axis CD. - DIII-D : off-axis ECCD - C-Mod: off-axis LHCD TKMau/13