ST research plans at the University of Tokyo

Plasma Current Start-up Experiments without the
Central Solenoid in TST-2 and Future Plans
Y. Takase
Graduate 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 Tori
and the 11th Internat Workshop on Spherical Torus
St. Petersburg State University, Russia
3-6 October 2005
Motivation for CS-less Ip Start-up
Compact, high b plasma with good confinement can be realized in ST
 compact burning plasma experiment and fusion reactor
Lower aspect ratio and
elimination of central solenoid (CS)
improves economic competitiveness
TST-2 Spherical Tokamak
TST-2
C
L
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)
TST-2
R = 0.36
a = 0.23
B = 0.4 T
I = 0.2 M
tpulse = 0.0
OH = 0.1
Main research topics:
 Plasma start-up optimization
 RF heating and wave physics
 MHD instability and reconnection
 Control of turbulence and transport
1m
Achieved
B = 0.21
I = 0.11 M
tpulse = 0.1
Relocation of TST-2
(Twice in 2 Years)
TST-2
Kyushu U.
Fukuoka
2003
U. Tokyo
Hongo
~2002
U. Tokyo
Kashiwa
2004~
TST-2 at Kyushu University (2003)
TST-2@K
Heating / current drive
By ECW and/or EBW
TST-2
Waveguides from
8.2GHz klystrons
EBW Antenna
Typical plasma equilibrium
Plasma Stored Energy Increase (Heating)
Observed during RF Injection
TST-2@K
RF on
no RF
Wkin
15% increase in Wtotal
Wtotal = Wkin + Wmag(pol)
Plasma Current Formation by ECH
TST-2
•
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
Solenoidless Start-up Experiments
TST-2@K
• Forest scenario
no w = wce res.
inside vac.ves.
– “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)
6
#301567
4
p
I [kA]
#301559-#301570 t=100-300ms
(a)
2
B [T] @R0.38[m]
100
0
0.2
(b)
RF (~100 k W)
0.1
t
Exp(-E/160eV)
1
0.6
0
0.6
@R0.39[m]
(c)
10
nel [1018m-2]
CountxE [keV/0.05keV]
1000
0.4
0.2
0
0.8
1
1.2
1.4
Energy [keV]
1.6
1.8
0
50
100
150
Time [ms]
200
250
300
Reconstructed Equilibrium
of the RF Start-up Plasma (I)
0.8
Plasma is limited by the outboard limiter,
j is truncated at top and inboard
Flux functionhas free parametesb p 0 and A.
j  r
p 1 0
f

f
2
 r 4

0 f  2rB



r 
r
2
 j0  b p 0  1  b p 0  0  1 - A n
r0
r

Fittedto magneticmeasurements (about 80 channels)
Obtainedparamtersare b p 0 ~ 1, A ~ 8
0.4
Z [m]
0
-0.4
-0.8
0
0.4
R [m]
0.8
Features of RF Start-up Plasma Equilibrium
j [kA/m2] @ z=0
0
• high bp
• large outboard boundary current
Outboard co-PS current is dominant,
while inboard counter-PS current is
truncted.
• Steep pressure gradient at the
outboard boundary
-80
0
R [m]
0.7
p [Pa] @ z=0
4
Soft X-ray flux and temperature are
roughly consistent with the pressure
deduced from equilibrium reconstruction.
0
0
R [m]
0.7
Completely CS-less Start-up to Ip = 10 kA
Achieved in TST-2
TST-2@K
#302405
1
1m
(kA)
Achieved (6/01)
B = 0.21 T
I = 0.11 MA
tpulse = 0.10 s
I PF3(kA/turns)
0
I
PF3
(b)
-1
-2
V (Volts)
L
-3
10
8
6
4
2
0
-2
10
8
(c)
V L01 (outboard)
I p (kA)
(d)
6
p
24 turns
R =PF5
0.361 m
turn
a = 0.23 m
B = 0.4 T
I = 0.2 MA
tpulse = 0.05 s
OH = 0.13 Vs
CS
-1
-2
1
I (kA)
PF4
TST-2
PF3
I PF2-5(KA/turns)
(a)
0
4
2
0
200
150
P RF (kW)
(e)
100
50
0
0.2
0.2
0
Zp
Rp-0.38
0.1
0
(f)
-0.1
-0.1
-0.2
0.137
0.1
0.139
0.141
0.143
Time (s)
0.145
-0.2
0.147
Z p(m)
6 turns
P (kW)
rf
PF2
I PF25(kA)
PF1
R p(m)
C
L
New Start at the Univ. Tokyo Kashiwa Campus
TST-2
• 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)
100kW of RF Power Injected Successfully
TST-2
HHFW Antenna
Full-wave calculation by TASK/WM
Eq
Bt = 0.3 T, f = 21 MHz, n = 10,
ne = 2  1019 m-3, Te = 0.3 keV
Preparation in Progress for 200 MHz Experiments
TST-2
200 MHz transmitters (from JFT-2M)
Full-wave calculation by TASK/WM
Eq
Combline antenna
Bt = 0.3 T, f = 200 MHz, n = 10,
ne = 2  1018 m-3, Te = 0.3 keV
Reconnection Events
TST-2
Detailed Time Evolution
t=26.6ms
t=26.2ms
Ip
TST-2
40.0
15.0
25.0
26.0
27.0
radiation
2.0
0.0
2.2
H_alpha
2.0
q_0
0.0
2.2
Hard X ray
4.0
1.4
1.4
0.0
25.0
26.0
li
-4.0
mag. fluct.
0.76
1.0
0.71
-1.5
W(J)
log(b^2)
50.0
-1.0
-5.0
20.0
27.0
Ion Heating Observed at Reconnection Events
TST-2
Conversion of magnetic energy
to ion kinetic energy
100
35534
Ip[kA]
80
60
40
Reconnection events
T CV [a.u.]
Intensty CV [a.u.]
20
CV intensity decreases
while CIII, OIII intensities
increase (loss of electron
energy)
0
8
6
4
2
6000
450
300
150
0
18
20
22
Time[ms]
24
26
CV (core）, and
OV, CIII, OIII （edge）
ion temperatures increase
at reconnection events
A New Experiment to Explore Ultra-High b
Plasma Formation by Plasma Merging
UTST
TST-2 Magnetic Diagnostics
Rapid Heating by Plasma Merging /
Reconnection
TS-3
120
Merging
Megawatts of heating
power can be obtained
by plasma merging /
reconnection
I tfc =0
dW/dt
~10[MW]
80
Y. Ono, et al.
40
Single
0
FRC
I tfc =10kA
80
ST#1
Bp
ST#2
Bp
Bp
Merging
dW/dt
~6[MW]
40
Single
zI
B t +B ext
B t+B ext
Bt+Bext
Iz
Low q ST
0
High b ST
dW/dt
~4[MW]
80
Comparison of thermal energy
evolution for merging (solid line)
and single (dashed line) formation
40
I tfc =35kA
Merging
Single
0
10
20
30
time [msec]
High q ST
Start-up without Center Solenoid Demonstrated
JT-60U
• VTin coil disconnected
• Use VR and VTout only
Discharge duration increases with
improvement of plasma position control
Demonstration of Advanced Tokamak Operation
without the Center Solenoid
JT-60U
Start-up and
initial ramp-up
Noninductive
ramp-up
Transition to self-driven phase
2002.06.21
Profiles of CS-less Advanced Tokamak with
Very High Self-Driven Current Fraction
JT-60U
ITB + H-mode (Ip = 0.7MA)
bp = 3.6, bN = 1.6, HH = 1.6, fBS > 90%
transport
barriers
Backup(I)
0.8
PF2 Coil
0.4
The following flux function was tried, but
parameters  and  were not efficient.
1st 2nd 3rd
j  r
Z [m]
p 1 0
f

f
2
 r 4

0f  2rB

0
Antennas
-0.4 V.V
3
2
yields slightly worse fitting.
0.4
0.8
R [m]
External poloidal field


This implies that the present magnetics
cannot resolve edge fine structure.
1 - A n insteadof 1 - A n
-0.8 0


r 
r
2

 j 0  b p 0  1  b p 0  0  1 - A n 1 - n
r0
r 

Backup (II)
Pickup coils
Flux loop
poloidal angle
Fitting was poor for
inboard Bz
Flux function (red) and
area of large j (blue).

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