# Presentation: 106493

## 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
-   Conclusions

- TKMau/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 Profiles**

**T**

**n**

- no/<n>=1.7
- To/<T>=1.5

**-<j********> ****(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

##     75 MHz :  Avoid resonance with D and ; moderate damping on T 

**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

## FWCD Power is Similar for Three Frequency Options

**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

## On-Axis Seed Current Drive with ICRF Fast Waves

-    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

**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

## Off-Axis Seed CD with LH Waves

-    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

## FIRE (AT) is on Development Path to AT Power Plant

- 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