Off-axis Current Drive and Current Profile Control in JT-60U

Off-axis Current Drive andCurrent Profile Control in JT-60U

T. Suzuki, S. Ide, T. Fujita, T. Oikawa, M. Ishikawa,G. Matsunaga, M. Takechi, M. Seki, O. Naito, K. Hamamatsu,M. Sueoka, H. Hosoyama, M. Nakazato, and the JT-60 Team

Japan Atomic Energy Agency

21th IAEA Fusion Energy Conference(19 Oct. 2006, Chengdu) EX/6-4 (17+3min.)

This work was partially supported by Grand-in-Aid for Young Scientists (B) No. 18760650 and Grand-in-Aid for Scientific Research No. 18560798 and 16082209 from MEXT.

JT-60U

Introduction

Optimization or control of q/j profile is crucial. For higher confinement and stability such as

in ITER SS & hybrid scenarios In a self-organized plasma, real-time feedback

control is essential. Minimum but efficient control is preferable.

Minimum q (qmin) is one of the key parameters for stability at high and resulting confinement. Raising qmin can avoid low m/n MHD, such as

NTM and sawtooth. For the qmin control, off-axis current drive is

required. LHCD & NBCD

JT-60U

Contents

Current drivers and MSE diagnostic for current profile measurement

Real-time control of qmin using off-axis LHCD in high plasmas

Measurement of beam driven current profile by off-axis NBCD

Summary

JT-60U

Off-axis NBCD 2MW/2MW for co/ctr Investigated here

Off-axis Current Drivers and high resolution MSE diagnostic in JT-60U

LHCD (2GHz, <1.5MW for co) Continuous control of power and N//

possible at every 10ms Used as current driver for real-time

control of qmin

q(r) measurement using 30ch MSE dR~0.06-0.1m (a~1m) at every 10ms for real-time calc.

JT-60U

Real-time control of qmin using off-axis LHCD in high plasmas

JT-60U

In 2006, qmin is controlled in real-time using LHCD in high plasmas

In 2004, q profile control at low demonstrated Real-time evaluation of q(r) using MSE Real-time control of CD location through N//

In 2006, qmin control at high for better core performance

Control of key parameter at high : qmin

Real-time control of LH power: PLH ILH

N// is fixed to keep CD location at higher Te region for better CD efficiency.

LH power control: dPLH/dt=-(qmin - qmin,ref) : positive constant LH power increases when qmin < qmin,ref.

JT-60U

Real-time qmin control demonstrated atN=1.3-1.6, fBS=0.46, fCD=0.87

High-p ELMy H-mode Ip=0.8MA, Bt=2.5T, q95=5.8,

ne=1.8x1019m-3, p=1.2-1.5.

qmin followed the given reference qmin,ref. =2MW/s

Without control, qmin goes down to 1.3.

1.31.7

interlocksby arcing

N//=1.7

qmin raisedqmin=1.7

0

1

2

3

4

0 0.2 0.4 0.6

e46965

q(t=7.00s)q(t=8.00s)q(t=13.00s)q(t=14.80s)

ρ

JT-60U

0

0.2

0.4

0.6

0.8

0 0.2 0.4 0.6 0.8 1ρ

=7.0t s

=13.5t s

Complex behavior in current profile evolution during qmin control in high

LHCD spatially localized at ρ=0.3-0.5 decrease j by reduction of jOH inside

ρ=0.3 Complex interaction between j, p, and

Te(or NC) at high during qmin control

q(r) change through qmin control

Te increases

jOHNC and jBS increase

qmin decreases

Control system increases PLH

contour plotj increase

jLH

jBS+jOH

qmin control

0

4

8

0 0.2 0.4 0.6 0.8 1ρ

=12.0t s

=13.0t s

JT-60U

m/n=2/1 NTM in high-p mode plasma atN~1.7, p=1.5

Ip=0.8MA, Bt=2.4T, q95=5.4

22% decrease in Wdia

qmin rises above 2

overshoot of control

during qmin control to 1.7

m/n=2/1 NTM disappears Wdia recovers

Central ne, Te, Ti increase.

No change in peripheral

MHD stabilization and confinement recovery by qmin control in high

m/n=2/1 NTM

confinementrecovery

JT-60U

Measurement ofbeam driven current profile

by off-axis NBCD

JT-60U

Off-axis NBCD investigation for real-time current profile control

Off-axis NBCD has been known to drive current, raise central q and decrease Vloop in JT-60U. working as one of standard off-axis

current drivers in JT-60U But, off-axis NBCD “profile” has not

been fully recognized, yet. difficult to measure, veiled by large

Ohmic current. Important to know its character in order

to use for optimization and real-time control of j(r).NBCD profile measurement exploiting progress in diagnostics (high resolution

MSE, neutron emission profile) flexible NBI system (perp. NB w/o

NBCD) improvement in analysis technique

typical configuration for off-axis NBCD

JT-60U

Spatially localized off-axis NBCD profile is measured using MSE diagnostic.

Ip=1.2MA, Bt=3.8T, q95=5.4, fixed ne=3.3x1019m-3, ELMy H-mode, No MHD except ELMs

Temporal evolution of increment of current I from reference current profile, measured by MSE spatially localized NBCD at ρ=0.65-0.8

Off-axis beam driven current profile jBDdS agrees with increase in neutron emission Sn(r) representing beam population profile.

th-th neutron < 10%, bulk density constant

tangential minor radius ρmin of diag. sight line

0

0.5

1

1.5

0 0.2 0.4 0.6 0.8 1ρ

before NBCD=8.9t s

during NBCD=12.5t s

46214e

current increase

0.9

1

1.1

1.2

0 0.2 0.4 0.6 0.8 1ρmin

=13.0t s( )during NBCD

0 0.2 0.4 0.6 0.8

e46214

ρ1

measurementusing MSE

15

10

5

0

(reference)

JT-60U

0 0.2 0.4 0.6 0.8

e46214

ρ1

15

10

5

0

measurement

0 0.2 0.4 0.6 0.8

e45466measurement

1ρ

15

10

5

0

Measured IBD agrees with calc., but CD location in calc. shifts inward than meas.

Ip=0.8MAIp=1.2MA Measured off-axis NBCD is spatially localized both at Ip=0.8&1.2MA.

consistent with neutron emission profile

Peak CD location in calc. shifts inward than exp. by dρ~0.2 in Ip=0.8&1.2MA. But, total NBCD current

in exp. agrees with calc. in Ip=0.8&1.2MA.

Difference between CD locations in exp. and calc. further study required

12732kA

103kA

10641kA

90kA

0.9

1

1.1

1.2

0 0.2 0.4 0.6 0.8 1ρmin

=13.0t s( )during NBCD

0.9

1

1.1

1.2

0 0.2 0.4 0.6 0.8 1ρmin

=11.0t s( )during NBCD

calculationcalculation

JT-60U

Summary

Real-time control of qmin was demonstrated in high plasma having N=1.3-1.6, fBS=0.46, fCD=0.87. qmin was evaluated by MSE, and current profile was modified by off-

axis LHCD at ρ=0.3-0.5. qmin followed the given reference rising in time. Complex interaction between j, p and Te was observed.

NTM (m/n=2/1) was stabilized through qmin increase above 2 during qmin control, and confinement was recovered. Development of current profile control system is important for higher

confinement and stability in advanced scenarios in ITER. Spatially localized off-axis NBCD is possible.

Measured CD location agrees with neutron emission profile. Measured total driven current agrees with the ACCOME calc. CD location in the ACCOME code shifts inward than measurement by

dρ~0.2. Some mechanism is required for the explanation. further study