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

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

• ConclusionsTKMau/02

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 (fBS) 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

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, Ip ~ 13 MA, Bo ~ 6 T, Pnet = 1000 MW.

Full N (%) <Te>(keV) Ibs/Ip PIC(MW) PLH(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

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, Bo = 6.75 T, Ip = 4.50 MA, Teo = 13.9 keV, neo = 5.10x1014 cm-3, Zeff = 1.38, = 5.62%, N = 4.38 (with wall stabilization of kink) IBS/Ip = 0.926, Iseed = 0.354 MA

n, T

Pro

file

s

T

nno/<n>=1.7To/<T>=1.5

-<j

> (A

/cm

2 )

EQ

SD

BS

DiaSD

• 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

T

Be D

2T

2Be

2D,3T

4T,3Be 3D4Be

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

FWCD Power is Similar for Three Frequency Options

f (MHz) N|| Pe/P PD/P PT/P PHe/P PCD(MW) fspa

28 2.5 0.99 0 0.01 0 3.7 0.29 28 3.4 0.99 0 0.01 0 3.6 0.39

75 2.5 0.79 0 0.21 0 4.1 0.67 75 3.4 0.91 0 0.09 0 3.8 0.81

120 2.5 0.65 0.10 0.21 0.04 4.6 0.97 120 3.4 0.83 0.02 0.13 0.01 4.3 0.99

• Ion species mix : fD = fT = 0.394, fHe = 0.208, fBe = 0.004• damping is not calculated in 120 MHz case. Would increase PCD

somewhat if included.• 15 rays are used along 1.0 m antenna poloidal length with P ~ cos2koy.• fspa is initial single pass absorption fraction for central ray.

TKMau/07

• CURRAY ray tracing code is used.

• Power is launched from 10o 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: PCD = 3.8 MW @ I/P = 0.028 A/W, Iseed = 0.11 MA single-pass absorption = 0.81, 9% of power to T at 2fcT.

Driven j

Seed j

On-Axis Seed Current Drive with ICRF Fast Waves

TKMau/08

LH Launching Parameters for Off-Axis CD

• Required penetration to = 0.67, where R=2.43 m on OB midplane, B = 5.61 T, ne = 3.7x1014 cm-3, and Te = 9.8 keV.

• To avoid parametric process, f > 2 fLH (0.67) = 2.65 GHz.• To avoid damping, f > 1.86 fpe(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

• Requires 4 waveguide modules, launching different N|| and located at 30o below OB midplane.

• Wave parameters: f = 4 GHz, N|| = 1.8 - 2.5.

• PCD = 3.5 MW @ I/P = 0.071 A/W. Iseed = 0.25 MA Efficiency is sensitive to local Te and ne. High efficiency here is due to high Te and low ne 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/104

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

0.001

0.01

0.1

1

10

1 10 100

DIII-D (no preheat)DIII-D (ECH preheat)DIII-D (NB preheat)OthersBest LHCD DataPower PlantsFIRE(AT)

ST AT

RS

FSSS

FIRE(AT)

JET (LH+FW)

JT-60 (LH)

DIII-D

TFTRTore-Supra

DIII-D

DIII-D

Peak Electron Temperature, Te0

(keV)

B = <ne> IpRo / PCD

CD = (1-fBS) 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

Conclusions and Discussions

• RFCD power was assessed for optimized FIRE DT-burning AT mode. PCD ~ 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