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R 0 = 0.38 m a = 0.25 m A = R 0 /a = 1.5 B t = 0.3 T I p = 0.1 MA . Overview of TST-2 E xperiment. Y . Takase for the TST-2 Group The University of Tokyo, Kashiwa 277-8561 Japan. R 0. a. The Second A3 Foresight Workshop on Spherical Torus Room 105, Liu-Qing Building

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overview of tst 2 e xperiment

R0 = 0.38 m

a = 0.25 m

A = R0/a = 1.5

Bt= 0.3 T

Ip = 0.1 MA

Overview of TST-2 Experiment

Y. Takase for the TST-2 Group

The University of Tokyo, Kashiwa 277-8561 Japan

R0

a

The Second A3 Foresight Workshop on Spherical Torus

Room 105, Liu-Qing Building

Tsinghua University, Beijing, China

6-8 January 2014

motivation and goal of research
Motivation and Goal of Research
  • Economically competitive tokamak reactor may be realized at low aspect ratio (A = R0/a) by eliminating the central solenoid (CS)

CS

no CS

higher Bt

lower A  higher bt

S. Nishio, et al., in Proc. 20th IAEA Fusion Energy Conf., FT/P7-35 (Vilamoura , 2004).

slide3

Noninductive

ramp-up(LH)

Transition to

self-driven phase

Start-up and initial ramp-up

2002.06.21

  • Formation of Advanced Tokamak Plasma without CS was Achieved on JT-60U
  • Is plasma current (Ip) ramp-up by LHW possible in ST?

Demonstrate on TST-2

advanced tokamak

S. Shiraiwa, et al., Phys. Rev. Lett. 92 (2004) 035001.

slide4

Three Antennas used on TST-2

Grill Antenna

ComblineAntenna

ECC Antenna

traveling wave

traveling wave

traveling

wave

  • excites traveling FW
  • Ip driven by SW (LHW)
  • requires mode conversion
  • from FW to SW
  • excites traveling SW
  • excites traveling SW
  • sharper k spectrum
  • & higher directivity
n dependence of i p and hx spectrum grill antenna
n|| Dependence of Ip and HX Spectrum(Grill Antenna)

[kA]

  • Highest plasma current was obtained for

1.5 < n|| < 4.5

  • Count rate of high energy photons was lower when

n|| > 7.5

n||

T. Wakatsuki

calculated electric field e z
Calculated Electric Field (Ez)

Ez (Without Plasma)

T. Inada

r amp up to 12 ka by lhw ecc antenna
Ramp-up to 12 kA by LHW(ECC Antenna)

Bt

Bv

Ip

limiter

nel

FWD

REF

trans

LCFS

ECH

#2 #4#6#9

AXUV

Ha

TST-2 Shot 98362

T. Shinya

scaling of i p with b v and b t
Scaling of Ip with Bv and Bt

co-drive

counter-drive

  • Ip increases with Bv .
  • Upper bound of Ipincreases with Bt.

T. Shinya

slide9

Scaling of Ip with PRF and ne

1 A/W

  • Higher Ipis obtained with ECCA for the same PRF .
  • Higher neis obtained with ECCA.

T. Shinya

comparison of the current d rive f igure of merit
Comparison of the Current Drive Figure of Merit

ηCDvs IP

ηCD [1016 A/m2/W ]

: plasma current

: average electron density

: major radius

: RF power

IP [kA]

  • Higher hCD is obtained with ECCA (mainly because of higher ne).
  • An order of magnitude improvement in hCD may be possible by suppression of edge wave power loss and fast electron loss
  •  operation at higher Bt, ne, Ip , PRF, Te should help.

T. Wakatsuki

hard x ray spectra for co ctr current drive directions combline antenna
Hard X-ray Spectra for Co/Ctr Current Drive Directions(Combline Antenna)

HX view

ctr

Ip

co

wave

HX view

antenna

  • Photon flux is an order of magnitude higher in the co direction.
  • Photon temperature is higher in the co direction (60 keV vs. 40 keV).
  • Consistent with acceleration of electrons by a uni-directional RF wave.

T. Wakatsuki

slide12

Hard X-ray Spectra for Co/Ctr Current Drive Directions(ECC Antenna)

[kA]

Ctr

[1/m^3]

Co

17

2

[ms]

1.5

Ch1

1.0

0.5

0

Ch2

[a.u.]

[j/m^2]

[ms]

■:Ch1,Co

▲:Ch2,Ctr

…SBD PP

__ SBD Be

SBD Be&SBD P.P

Similar co and counter “temperatures”,

but co flux is larger than counter flux.

Analysis section

[ms]

K. Imamura

[keV]

E

slide13

Radial Profile of the Floating Potential

(Combline Antenna)

・Floating potential (where Iprobe = 0) is sensitive to the presence of high energy electrons.

Limiter

3

LCFS

antenna

wave

1

6

7

5

R=125 mm

probe

R= 585 mm

R=700 mm

9 mm

5.6 mm

5.7 mm

・Vf has a large gradient near the limiter radius.

H. Kakuda

ion temperature toroidal flow and poloi dal flow grill antenna i p 6ka
Ion Temperature, Toroidal Flow and Poloidal Flow(Grill Antenna, Ip ~ 6kA)

Right sightline

Left sightline

Ip

Bt

Upper sightline

Lower sightline

S. Tsuda

slide15

One-Fluid Equilibrium (EFIT)

Reconstructed equilibrium

Ip = 11 kA

bp = 0.9

current density profile peaked on the outboard side

Visible light image

A. Ejiri

slide16

Two-Fluid Equilibrium (Initial Result)

TST-2 Shot 75467

  • Plasma pressure max ~40 Pa (?)
  • Peaked toroidal current distribution (?)
  • What is plasma sound speed?
  • Large Er shear  ion orbit compression
  • Electron: largely satisfies pe = -JB
  • Ion (outboard): roughly equal pi, centrifugal, and electrostatic forces balanced by-JB

M. Peng & A. Ishida

floating potential measurement at 200 mhz es probe with embedded high impedance resistor
Floating Potential Measurement at 200 MHz :ES Probe with Embedded High Impedance Resistor

2

5

Chip resistor 100 kΩ

3

4

Absolute Value of Impedance

[Ω]

105

Black solid line :

Electrostatic Probe with

a 100 kΩ Chip Resistor

104

2

Green solid line :

Ordinary Langmuir Probe

5

Electrode 1, 2, 3 ・・・ With 100 kΩ

Electrode 4    ・・・ Magnetic Probe

Electrode 5 ・・・ Ordinary Langmuir Probe

3

4

103

Red broken line : Sheath impedance

H. Kakuda

0.1

[MHz]

1

10

100

1000

phase difference and wavenumber measurement
Phase Difference and Wavenumber Measurement

Electrode Separation

14.2mm

2

3

H. Kakuda

frequency spectra measured by rf magnetic probes combline antenna
Frequency Spectra Measured by RF Magnetic Probes(Combline Antenna)

pump

toroidal

poloidal

lower

sideband

  • Combline antenna excites the FW, but LHW generated by PDI?
    • Pump wave (f = 200 MHz ± 1 kHz) has FW polarization (|Bt| > |Bp|).
    • PDI sidebands have SW (LHW) polarization (|Bt| < |Bp|).
  • Pump wave weakens when sidebands intensify.

upper

sideband

T. Shinya

rf magnetic probe array for k measurement grill antenna 1ka
RF Magnetic Probe Array for k Measurement(Grill Antenna, ~ 1kA)
  • Array can be rotated about its axis
    • to distinguish RF polarization
    • to measure wavevector components
  • Dominant kcomponents excited by the antenna are kt 50 m-1, kp 10 m-1.
    • Measured kt≲ 10 m-1 is much smaller (higher kt absorbed?)

a

30 mm

b

(= 0°)

(= 90°)

e

d

c

rotation

radial

translation

k||= 10 m-1 corresponds to n||= 2.4

T. Shinya

slide21

TST-2 Double-Pass Thomson Scattering System

Plasma

YAG laser

Nd:YAG laser

1064nm

Laser energy: 1.6 [J]

Repetition rate: 10 [Hz]

Pulse width: 10 [ns]

[2nd pass]

Brewster Window

P||

B

Nd:YAG Laser

~6m

TST-2

TST-2

Scattering Vector

Beam Dump

Spherical Mirror

Optical isolator

[1st pass]

B

Incident

Laser

Spherical

Mirror

P⊥

Lens

  • Laser beam is focused in the plasma by a lens (f = 2000mm).
  • Optical isolator is used to prevent laser damage by reflected light.

Polychromator

Spherical Mirror

Observer

J. Hiratsuka

slide22

Typical ne and Teprofiles

(OH Plasma)

Thomson scattering

Interferometer

neL time slice

neL [1018 m-2]

ne [1019m-3]

ne profile

Timing of TS measurement

  • Comparison with interferometer
  • Thomson: 5.7 × 1018 [m-2]
  • Interferometer: 4.9 × 1018 [m-2]

Te [eV]

Te profile

reasonable agreement

Major Radius [mm]

J. Hiratsuka

slide23

Electron Temperature Anisotropy

(OH Plasma)

R=220mm (plasma edge)

R=389mm (plasma center)

Assuming Maxwellian velocity distribution, current densities are:

plasma edge: 300kA/m2plasma center: 500kA/m2

(plasma current / plasma cross section ~ 300kA/m2)

J. Hiratsuka

slide24

Time evolution of electron temperature

Center

Evolution of Teanisotropy

Center of Plasma

→ Cooling

Edge

TST-2

Edge of Plasma

→ Heating

Central and edge Te

approach each other

K. Nakamura

multi pass thomson scattering

Half-wave plate

Multi-Pass Thomson Scattering

Polarizer

f = 2500 mm

Mirror #1

Laser pulse is confined between concave mirrors (red line)

TST-2

Pockels Cell

f = 2000 mm

Mirror #2

YAG Laser

Brewster Window

H. Togashi

probe system for turbulence study
Probe System for Turbulence Study

tip1

tip2

tip3

Global mode

30mm

Jdown

Plasma flow, magnetic field, potential, and density fluctuations are measured simultaneously.

Jup

Nonlinear energy transfer direction

Micro-turbulence

coil1

zonal flow

coil2

location

3-axis pickup coil

Bt, Ip

M. Sonehara

poloidal flow and stresses
Poloidal Flow and Stresses
  • Poloidal flow and radial derivative of stress (Te=Ti is assumed).
  • Profiles of poloidal flow and stress derivative are similar.

M. Sonehara

rogowski probe
RogowskiProbe

Langmuir probe

Rogowski coil

3-D pick up coil

Rogowski coil for measuring

the local current was developed.

1-D pickup coil

H. Furui

successful measurement of local current oh plasma
Successful Measurement of Local Current(OH Plasma)
  • Plasma current
  • Local plasma current density
  • Poloidalmagnetic field generated
  • by the plasma current

・ Bp is estimated to be under 20 mT

at the location of the Rogowskicoil.

・ Output voltage of the Rogowski coil

due to Bp is estimated to be under

100 μV.

Local current measurement was

performed successfully with small pickup of magnetic fields.

H. Furui

conclusions
Conclusions
  • ST plasma initiation and Ip ramp-up by waves in the LH frequency range were demonstrated on TST-2.
    • Inductively-coupled combline antenna (FW launch), dielectric-loaded waveguide array (“grill”) antenna (SW launch), and electrostatically-coupled combline antenna (SW launch) were used.
    • Spontaneous formation of the tokamak configuration with closed flux surfaces was observed when the toroidal current in the open field line configuration exceeded a critical level (~ 1 kA in TST-2).
    • Similar Ipwas obtained with different antennas for similar Bv and PRF, but hCD is higher with the ECC antenna because of higher ne.
    • At low Ip ( < 2 kA in TST-2), Ip is dominantly pressure-driven, and is proportional to Bv. In this regime, Ip is independent of the wave type. At higher Ip (> 5 kA in TST-2), Ipbecomes mainly wave-driven. In this regime, control of the current density profile by externally excited waves should become possible.
conclusions1
Conclusions
  • Various diagnostics and RF launchers are being developed.
    • Electrostatically-coupled combline antenna (LHW launch).
    • Hard X-ray spectroscopy and imaging.
    • UV spectroscopy for ion temperature and flow measurements.
    • Electrostatic probes for wave and turbulence measurements.
    • Magnetic probes for wave and current density measurements.
    • Double-pass Thomson scattering for Te anisotropy measurement.
    • Two-fluid equilibrium.
need for power supply upgrade
Need for Power Supply Upgrade

In order to demonstrate ramp-up to higher Ip, power supply upgrade is needed to sustain higher Bt(~ 0.3 T) for longer time (> 0.1 s).

32

near future plans
Near-Future Plans
  • Coil Power Supply Upgrade
    • Sustained high field (Bt = 0.3 T for > 0.1 s) for further Ip ramp-up.
  • Wave/Turbulence Diagnostics
    • Electrostatic probe array
    • Reflectometer / interferometer-polarimeter
  • Plasma diagnostics
    • Multi-pass Thomson scattering
    • EBW emission
    • Current profile measurement by Rogowski probe / magnetic probe
    • Ion flow measurement