By

Y. S. ParkIn collaboration with

Y. S. Hwang

Presented at IAEA Technical Meeting on Control,DAQ and Remote Participation for Fusion ResearchInuyama, Japan, June 4th~8th 2007

Simulation of ECCD Optimization for Neoclassical Tearing Mode Control in KSTAR

Department of Nuclear Engineering, Seoul National University, Seoul, Korea

Motivation

● Control of NTMs is a key issue for achieving initially proposed high performance,

steady state operation of KSTAR

● 170GHz, max. 5MW ECCD system will be implemented to suppress NTMs in KSTAR

● ECCD system will be installed in an equatorial port of KSTAR but the specific location

of launcher(s) inside the port is not determined yet

● ECCD ray tracing analysis must be carried out to optimize ECCD launch location and

to derive current deposition parameters on NTM relevant radii

● As an alternative method of current drive, 110GHz ECCD is being considered in KSTAR

and the performance of 110GHz ECCD must be evaluated

Research Objective - Suppression of NTM by ECCD in KSTAR

● Neoclassical tearing modes sustained by helically perturbed local bootstrap current

– O-point of ‘seed’ island flattens the radial pressureprofileNegatively perturbed B.S. current is generatedPerturbed B.S. current enhances perturbed helical B-field(only in positive magnetic shear)Mode is destabilized and magnetic island grows(NTM severely degrades plasma beta)

pB

jp

21

bs ∇≈ δεδ

/

- Suppression of q=3/2 NTM by using 170GHz ECCD in KSTAR

O

X

j-profile due to perturbed b.s. current

Compensate theperturbed bootstrapcurrent by localized current drive from ECCD

Flattened p-profilein island O-point

RealReal--time MSEtime MSE--EFITEFIT(q-profile reconstruction)

ECE Algorithm ECE Algorithm [1]

Diagnostics (MSE, ECE, Mirnov, …)

ECE

ECCD launch angle, power, phase modulation

Plasma radial position movement, magnetic perturbation (n=2)*

q=3/2, 2/1 location

Island location

Mirnov

IVCCIVCC

Island width, phase

Island phase

NTM ControllerNTM Controller(in the PCS)

TORAYTORAY

Island width (w)

ECCD deposition location, driven current, profile

w > wc w < wc

Steering Mirror(2.8m, -0.3m)

ECCDECCD(170GHz, max. 5MW)

ECE

Conceptual Design of KSTAR NTM Control System

3/2 NTM

2/1 NTM

2

2

ECHf: 170.000 GHz

1.5

2.0

2.0

2.5

2.5

3.0

3.0

4.0

4.0

4.0

5.0

5.0

5.0

6.0

6.0 6.0

7.0

7.0

2

2

ECHf: 170.000 GHz

1.5

2.0

2.0

2.5

2.5

3.0

3.0

4.0

4.0

4.0

5.0

5.0

5.0

6.0

6.0 6.0

7.0

7.0

* Using magnetic perturbation to NTM suppression in not yet verified in KSTAR

[1] : Y.S. Park and A.S. Welander, PPCF, vol.48, 2006

KSTAR Double Null Reference Equilibrium for TORAY Analysis

Plasma Parameter

KSTAR ReferenceDN Equilibrium

Reference EFIT

EQDISK File -- g010004.01020

q95 -- 3.9

BT 3.5T 3.5T

IP 2.0MA 2.0MA

R0 1.8m 1.79m

a 0.5m 0.501m

2.0 2.01

0.8 0.80

βN 3.5 3.53

βp -- 1.91

li(1) -- 1.01

li(3) 0.8 ~0.8*

*EFIT calculates only li(1) ; li(3)~0.8 li(1) ; (--) information not available

xκ

xδ

KSTAR 10004.1020 jphi [MA/m2]

Input Electron Kinetic Profiles for TORAY Analysis

ne Te

● Kinetic profiles obtained from predictive modeling of KSTAR integrated scenario [2]– Density profile is taken from ASDEX-U H-mode discharge (multiplied by constant factor)– Temp. profile is calculated by ASTRA code – Weak ITB formed RS plasma under 2MA, 3.5T condition with βN=3.37– 16.2MW NBI, 6MW ICRH and 5MW LHCD are applied for heating & CD

[2] : Y.S. Na et al, EPS Conf. on Plasma Phys., ECA vol.30I, P-2.177, 2006

Definitions of ECCD Launch Angles

steering mirror

Rin

Rmag

β

170GHz2nd harmonic

Allowable rangeof steering mirrorvertical location

α

TB

PI

+ direction in TORAY

Rout

● Two ECCD launch angles in TORAY analysis– Poloidal launch angle, α – Toroidal launch angle, β

z=+30cm

z=-30cm

Optimization of ECCD Launch Location for NTM Suppression

IEC(kA)

IEC/δ2EC (kA/rho2)

δEC (rho)

Maximum figure of meritfor both NTM surfaces

Among the seven vertical launch locations, ECCD launch from the lowest allowable location, z=-30cm, shows maximum profile figure of merit for both q=3/2 and 2/1 surfaces

● As an criterion for the optimization, a figure of merit of driven current profile is defined as 2EC ECI /δ

ECCD launch from z=-30cm shows the mosthighly localized driven current profile for both NTM surfaces

q=3/2(rho=0.546)

q=2/1(rho=0.709)

Optimal Profiles Obtained for Different Launch Locations

Optimal ECCD Depositions on 3/2 & 2/1 NTM Surfaces

● Optimal ECCD deposition parameters for 3/2 & 2/1 NTM surfaces(170GHz, 5MW, X2 ECCD)

- ECCD ray trajectories from TORAY-GA

q=2/1q=3/2

Deposition Parameters on q=3/2 and 2/1

Rmirror (m) 2.785

Zmirror (m) -0.30

Polar angle, α 59.37o 56.0o

Azimuth. angle, β 162.40o 155.81o

rho 0.5461 0.7098

Peak jEC (kA/m2) 412.15 405.05

IEC (kA) 34.51 45.08

δEC (rho) 0.0505 0.0568

δEC (cm) * 2.1 2.3

IEC/ δ2

EC (kA/rho2) 13.54E3 13.97E3

* Radial widths in cm unit are calculated in the outboard midplane

Current Drive Simulation by Using 110GHz ECCD

* Value in brackets are from 170GHz ECCD

- Optimal driven current profiles for 3/2 and 2/1 NTM surfaces using 110GHz and 170GHz ECCDunder the same launch location zmirror=-30cm

● Under the same launch conditions, 110GHz ECCD shows higher driven current than 170GHz ECCD but the profile figure of merit, , is not much improved due to broader profile2EC ECI /δ

Deposition Parameters on q=3/2 and 2/1

Rmirror (m) 2.785

Zmirror (m) -0.30

Polar angle, α 88.94o 95.45o

Azimuth. angle, β 167.19o 169.50o

rho 0.5461 0.7095

Peak jEC (kA/m2)941.88

(412.15)*599.25

(405.05)*

IEC (kA)138.12

(34.51)*106.84

(45.08)*

δEC (rho) 0.0906 0.0926

δEC (cm)* 3.7 (2.1)* 3.8 (2.3)*

IEC/ δ2

EC (kA/rho2)16.80E3

(13.54E3)*12.45E3

(13.97E3)*

Contours of Current Deposition Parameters (170GHz, 5MW ECCD)● Profile width(rho) and peak rho

q=3/2

q=2/1

0.055

0.05

0.06

0.07

0.09

0.1

0.08

0.5

0.6

0.65

0.75q=3/2

q=2/10.5

0.6

0.65

0.75

● Driven current(kA) and peak rho ● Figure of merit(kA/rho2) and peak rho

30

40

50 55

20

10qq=3/2=3/2

qq=2/1=2/1

Green circle ( ) represents optimal launch angles for q=3/2 and 2/1 depositions

0.50.5

0.60.6

0.650.65

0.750.75

Summary

A ray tracing analysis using TORAY-GA is performed to simulate ECCD on NTM surfacesin KSTAR reference double-null equilibrium plasmaFrom optimization simulation, it is confirmed that ECCD launch from z=-30cm will give the most highly localized current profile which may lead to the highest efficiency in NTM suppression For 110GHz ECCD, driven current is larger but a profile figure of merit is not much improvedbecause of the broad profile width The low current drive efficiency of 170GHz ECCD may be caused by strong electron trappingin outboard regionDetailed stability analysis of NTMs in KSTAR plasmas will be followed by using optimizedcurrent deposition parameters