Plasma Current Start-up Experiments without the Central Solenoid in TST-2 and Future Plans

Y. TakaseGraduate School of Frontier Sciences, University of Tokyo

for TST-2 and TST-2@K Groups

Joint Meeting of the 3rd IAEA Technical Meeting on Spherical Toriand the 11th Internat Workshop on Spherical Torus

St. Petersburg State University, Russia3-6 October 2005

Compact, high plasma with good confinement can be realized in ST

compact burning plasma experiment and fusion reactor

Motivation for CS-less Ip Start-up

Lower aspect ratio and

elimination of central solenoid (CS)

improves economic competitiveness

TST-2 Spherical Tokamak

Design parameters of TST-2:R = 0.38 m / a = 0.25 (A = 1.6)

Bt = 0.3 T (0.3 T achieved)

Ip = 0.2 MA (0.14 MA achieved)

tpulse = 0.05 s (0.3 s achieved)

Main research topics: Plasma start-up optimization RF heating and wave physics MHD instability and reconnection Control of turbulence and transport

CL

1 m

TST-2

R = 0.36 ma = 0.23 mB = 0.4 TI = 0.2 MAtpulse = 0.05 sOH = 0.13 Vs

Achieved (6/01)B = 0.21 TI = 0.11 MAtpulse = 0.10 s

TST-2

Relocation of TST-2(Twice in 2 Years)

U. TokyoHongo~2002

U. TokyoKashiwa2004~

Kyushu U.Fukuoka

2003

TST-2

TST-2 EBW Antenna

Waveguides from8.2GHz klystrons

Typical plasma equilibrium

TST-2 at Kyushu University (2003)

Heating / current drive By ECW and/or EBW

TST-2@K

Plasma Stored Energy Increase (Heating)Observed during RF Injection

15% increase in Wtotal

RF on no RF

Wtotal = Wkin + Wmag(pol)

Wkin

TST-2@K

Plasma Current Formation by ECH

• 1 kA / 1 kW achieved by ECH (2.45 GHz)

　• Higher current for

low gas pressure low collisionality is important

• Requires vertical field with positive curvature trapped particles are important

TST-2

Solenoidless Start-up Experiments

• Forest scenario – “pressure driven current” with mirror Bv

– 4kA maintained for 0.27 s

(with static Bv ~ 2 mT, no induction)

– Te = 160 eV (plasma is collisionless)

0

2

4

6#301567

I p [

kA

]

(a)

0

0.1

0.2

Bt [

T]

@R

0.38

[m]

(b)

RF (~100 kW)

0

0.2

0.4

0.6

0 50 100 150 200 250 300

nel [

1018

m-2

]

@R

0.39

[m]

Time [ms]

(c)

no = ce res.inside vac.ves.

1

10

100

1000

0.6 0.8 1 1.2 1.4 1.6 1.8

#301559-#301570 t=100-300ms

Cou

ntx

E [

keV

/0.0

5keV

]

Energy [keV]

Exp(-E/160eV)

TST-2@K

Reconstructed Equilibrium of the RF Start-up Plasma (I)

8~ ,1~ are paramters Obtained

channels) 80(about tsmeasuremen magnetic toFitted

A - 11

2 4

1

. and parametes free hasfunction Flux

0

2n

00

000

020

0

A

r

r

r

rj

rBff

fr

prj

A

p

pp

p

0.4 0.8

0

-0.4

-0.8

0.4

0.8

R [m]

Z [m]

0

Plasma is limited by the outboard limiter,j is truncated at top and inboard

Features of RF Start-up Plasma Equilibrium

R [m]

R [m]

0

0.7

0 0.7

-80

4

0

j [kA/m2] @ z=0

p [Pa] @ z=0

0

• high p

• large outboard boundary currentOutboard co-PS current is dominant, while inboard counter-PS current is truncted.

• Steep pressure gradient at the outboard boundary

Soft X-ray flux and temperature are roughly consistent with the pressure deduced from equilibrium reconstruction.

(a)

(b)

(c)

(d)

#302405

(e)

VL01(outboard)

IPF3(kA/turns)

PRF(kW)

Ip(kA)

IPF2-5(KA/turns)

-3

-2

-1

0

1

I PF

3(k

A)

0

2

4

6

8

10

I p(k

A)

-202468

10

VL(V

olt

s)

-2

-1

0

1

I PF

25(k

A)

(f)

-0.2

-0.1

0

0.1

0.2

-0.2

-0.1

0

0.1

0.2

Rp-0.38 Zp

0.137 0.139 0.141 0.143 0.145 0.147

Rp(m

)

Zp(m

)

Time (s)

0

50

100

150

200

Prf(k

W)

Completely CS-less Start-up to Ip = 10 kAAchieved in TST-2

CL

1 m

TST-2

R = 0.36 ma = 0.23 mB = 0.4 TI = 0.2 MAtpulse = 0.05 sOH = 0.13 Vs

Achieved (6/01)B = 0.21 TI = 0.11 MAtpulse = 0.10 s

PF1

PF2

PF4

PF3

PF5

CS

1 turn

6 turns

24 turns

TST-2@K

New Start at the Univ. Tokyo Kashiwa Campus

• Resume operation at Kashiwa

– Solenoidless start-up• Based on results of JT-60U

– Reconnection physics • Reconnection Events• Ion heating

– Turbulence and transport• Develop fluctuation diagnostics

– HHFW heating / current drive• 10-30MHz / 400 kW• k|| control (new antenna)

– Prepare LHCD system• 200MHz / 400kW (from JFT-2M)

TST-2

100kW of RF Power Injected Successfully

Full-wave calculation by TASK/WMHHFW AntennaTST-2

Bt = 0.3 T, f = 21 MHz, n = 10, ne = 2 1019 m-3, Te = 0.3 keV

E

Preparation in Progress for 200 MHz Experiments

E

Bt = 0.3 T, f = 200 MHz, n = 10, ne = 2 1018 m-3, Te = 0.3 keV

Full-wave calculation by TASK/WM

TST-2

Combline antenna

200 MHz transmitters (from JFT-2M)

Reconnection Events

TST-2

li

W(J)

25.0 26.0 27.01.4

radiation

H_alpha

Hard X ray

mag. fluct.

log(b^2)

15.0

40.0

0.0

2.0

0.0

2.0

4.0

-4.0

0.0

-5.0

-1.0

-1.5

1.0

26.025.0

2.2

27.0

Ip

20.0

0.71

0.76

50.0

1.4

2.2

Detailed Time Evolution

q_0

TST-2 t=26.2ms t=26.6ms

0

20

40

60

80

100

35534

Ip[kA]

0

2

4

6

8

Intensty CV [a.u.]

0

150

300

450

600

18 20 22 24 26

T CV [a.u.]

Time[ms]

CV intensity decreases while CIII, OIII intensities increase (loss of electron energy)

CV (core） , andOV, CIII, OIII （ edge）ion temperatures increaseat reconnection events

Reconnection events

Conversion of magnetic energyto ion kinetic energy

Ion Heating Observed at Reconnection Events

TST-2

A New Experiment to Explore Ultra-High Plasma Formation by Plasma Merging

UTST

TST-2 Magnetic Diagnostics

Megawatts of heating power can be obtained by plasma merging / reconnection

Rapid Heating by Plasma Merging / Reconnection

TS-3

Y. Ono, et al.

time [msec]

I tfc=0dW/dt~10[MW]

I tfc=10kA

dW/dt~6[MW]

I tfc=35kAdW/dt~4[MW]

10 20 30

Merging

Single

Merging

Single

Merging

Single0

40

80

120

0

40

80

0

40

80

B +Bt ext

Bp

Iz

B +Bt ext

ST#1 ST#2Bp Bp

IzB +Bt ext High ST

Comparison of thermal energy evolution for merging (solid line) and single (dashed line) formation

FRC

High q ST

Low q ST

Start-up without Center Solenoid Demonstrated

• VTin coil disconnected

• Use VR and VTout only

Discharge duration increases with

improvement of plasma position control

JT-60U

Demonstration of Advanced Tokamak Operation without the Center Solenoid

2002.06.21

Start-up and initial ramp-up

Noninductive ramp-up Transition to self-driven phase

JT-60U

ITB + H-mode (Ip = 0.7MA)p = 3.6, N = 1.6, HH = 1.6, fBS > 90%

Profiles of CS-less Advanced Tokamak with Very High Self-Driven Current Fraction

JT-60U

transport barriers

Backup(I)

0 0.4 0.8

0

-0.4

-0.8

0.4

0.8

R [m]

Z [m]

V.V

1st 2nd 3rd

PF2 Coil

Antennas

n2

n0

00

00

020

- 1 - 11

2 4

1

Arr

rr

j

rBff

fr

prj

pp

The following flux function was tried, but parameters and were not efficient.

External poloidal field

This implies that the present magnetics cannot resolve edge fine structure.

fitting. orseslightly w yields

- 1 of instead - 1 2n

3n AA

Backup (II)

Fitting was poor for inboard Bz

poloidal angle

Flux loop

Pickup coils

Flux function (red) and area of large j (blue).