NSTXHHFW
1
R0a
R0 = 0.38 m a = 0.25 mA = R0/a = 1.5Bt = 0.3 TIp = 0.1 MA
Overview of TST-2 Experiment
Y. Takase for the TST-2 Group
The University of Tokyo, Kashiwa 277-8561 Japan
The Second A3 Foresight Workshop on Spherical TorusRoom 105,
Liu-Qing BuildingTsinghua University, Beijing, China6-8 January
2014Motivation and Goal of ResearchEconomically competitive tokamak
reactor may be realized at low aspect ratio (A = R0/a) by
eliminating the central solenoid (CS)
S. Nishio, et al., in Proc. 20th IAEA Fusion Energy Conf.,
FT/P7-35 (Vilamoura , 2004). 2higher Btlower A higher btno CSCS
2002.06.21Start-up and initial ramp-upNoninductive ramp-up
(LH)Transition to self-driven phase
advanced tokamakS. Shiraiwa, et al., Phys. Rev. Lett. 92 (2004)
035001. 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-234Three Antennas used on TST-2
Combline Antennatraveling waveexcites traveling FWIp driven by
SW (LHW)
requires mode conversion from FW to SWexcites traveling SW
travelingwave
traveling waveexcites traveling SW
sharper k spectrum & higher directivityGrill AntennaECC
Antennan|| Dependence of Ip and HX Spectrum(Grill Antenna)
Highest plasma current was obtained for 1.5 < n|| <
4.5
Count rate of high energy photons was lower when n|| >
7.5[kA]n|| 5T. Wakatsuki
Calculated Electric Field (Ez)Ez (Without Plasma)6T.
InadaRamp-up to 12 kA by LHW(ECC Antenna)
IpBvBtFWDREFtransECHnelLCFSlimiter#2 #4 #6 #9AXUVHaTST-2 Shot
983627T. ShinyaScaling of Ip with Bv and BtIp increases with Bv
.Upper bound of Ip increases with Bt .co-drivecounter-drive8T.
ShinyaHigher Ip is obtained with ECCA for the same PRF . Higher ne
is obtained with ECCA. Scaling of Ip with PRF and ne1 A/W9T.
ShinyaComparison of the Current Drive Figure of MeritHigher 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.10IP [kA]CD vs IP CD [1016 A/m2/W ]T.
WakatsukiHard X-ray Spectra for Co/Ctr Current Drive
Directions(Combline 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.
Ip coctr
antennaHX viewHX viewwave11T. Wakatsuki
CoCh1CtrCh2
SBD Be&SBD P.P SBD PP__ SBD Be
1721.51.00.50[kA][j/m^2][1/m^3]Analysis section[ms][ms][ms]
E[keV]:Ch1,Co:Ch2,CtrSimilar co and counter temperatures,but co
flux is larger than counter flux.[a.u.]Hard X-ray Spectra for
Co/Ctr Current Drive Directions(ECC Antenna)12K. Imamura
59 mm5.6 mm675.7 mm31Limiter Vf has a large gradient near the
limiter radius. LCFSRadial Profile of the Floating
Potential(Combline Antenna)13H. KakudaFloating potential (where
Iprobe = 0) is sensitive to the presence of high energy
electrons.R= 585 mmR=700 mmR=125 mmantennaprobewave
IpBtIon Temperature, Toroidal Flow and Poloidal Flow(Grill
Antenna, Ip ~ 6kA)Lower sightlineUpper sightline
Right sightlineLeft sightline
14S. TsudaEmission intensity is small in the poloidal direction
and was comparable to the case of ECH.Measurement was not possible
amount of light is insufficient in the 35-60msec.In a measurable
period of time, as well as when the ECH, poloidal flow was larger
than the toroidal flow
14One-Fluid Equilibrium (EFIT)
Ip = 11 kAbp = 0.9Reconstructed equilibriumVisible light
imagecurrent density profile peaked on the outboard side15A.
Ejiri15Plasma pressure max ~40 Pa (?)Peaked toroidal current
distribution (?)What is plasma sound speed?Large Er shear ion orbit
compressionElectron: largely satisfies pe = -JBIon (outboard):
roughly equal pi, centrifugal, and electrostatic forces balanced by
-JB
Two-Fluid Equilibrium (Initial Result)TST-2 Shot 7546716M. Peng
& A. IshidaFloating Potential Measurement at 200 MHz :ES Probe
with Embedded High Impedance Resistor
1051041030.11101001000[][MHz]Chip resistor 100 kRed broken line
: Sheath impedanceGreen solid line :Ordinary Langmuir ProbeBlack
solid line :Electrostatic Probe witha 100 k Chip ResistorAbsolute
Value of Impedance23452345Electrode 1, 2, 3 With 100 kElectrode 4
Magnetic ProbeElectrode 5Ordinary Langmuir Probe17H. KakudaPhase
Difference and Wavenumber Measurement
Electrode Separation14.2 mm
2318H. KakudaFrequency Spectra Measured by RF Magnetic
Probes(Combline Antenna)
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.
poloidaltoroidalpumplower sidebandupper sideband19T. ShinyaRF
Magnetic Probe Array for k Measurement(Grill Antenna, ~ 1kA)
radialtranslationabcderotation30 mm20k|| = 10 m-1 corresponds to
n|| = 2.4 T. ShinyaNd:YAG laser1064nmLaser energy: 1.6
[J]Repetition rate: 10 [Hz]Pulse width: 10 [ns]~6mSpherical
MirrorPolychromatorSpherical MirrorBeam DumpLensNd:YAG
LaserTST-2
Brewster WindowOptical isolatorYAG laserTST-2TST-2 Double-Pass
Thomson Scattering SystemLaser beam is focused in the plasma by a
lens (f = 2000mm).Optical isolator is used to prevent laser damage
by reflected light.21[1st pass][2nd pass]Scattering
VectorP||PIncident LaserBSphericalMirrorObserverPlasmaBJ.
Hiratsuka21Comparison with interferometerThomson: 5.7 1018
[m-2]Interferometer: 4.9 1018 [m-2]Thomson scatteringTypical ne and
Te profiles(OH Plasma)reasonable agreementTiming of TS
measurement
InterferometerneL time slice
ne profile
Te profileneL [1018 m-2]ne [1019m-3]Te [eV]Major Radius [mm]22J.
Hiratsuka
R=220mm (plasma edge)R=389mm (plasma center)Electron Temperature
Anisotropy(OH Plasma)Assuming Maxwellian velocity distribution,
current densities are: plasma edge 300kA/m2plasma center 500kA/m2
(plasma current / plasma cross section ~ 300kA/m2)23J.
Hiratsuka
Time evolution of electron temperature
Central and edge Te approach each otherTST-2Center of Plasma
CoolingEdge of Plasma Heating
Evolution of Te anisotropy
CenterEdge
24K. Nakamura24Multi-Pass Thomson ScatteringTST-2f = 2500 mm
Mirror #1f = 2000 mmMirror #2Pockels CellPolarizerHalf-wave
plateYAG LaserBrewster WindowLaser pulse is confined between
concave mirrors (red line)25H. Togashi25Probe System for Turbulence
StudyPlasma flow, magnetic field, potential, and density
fluctuations are measured simultaneously. coil1Bt , Ip
3-axis pickup coil
tiptip2tip3JupJdowncoil230mm
zonal flowGlobal modeMicro-turbulenceNonlinear energy transfer
directionlocation26M. Soneharathis is the composite probe system
used in the experiment.the size is 30 mm in diameter at the front,
and it has 7 electrodes to measure floating potential or ion
saturation current, probe tip is made of Molybdenum, and encased in
boron nitride.each electrode is 1mm in diameter 5mm in lengththe
two electrodes located in the shadowed area can be used to measure
plasma flow as a mach probe. It also has a 3 axis pickup coil to
measure 3 dimensional magnetic fluctuation simultaneously.this
probe system is inserted at the midplane of the device.
this probe tip can be rotated with rotary stage. ant it is
inserted at the midplane of the device.30mm5mm2mm
----- (2013/02/26 10:25) -----BT,Bp,Ip26Poloidal Flow and
Stresses Poloidal flow and radial derivative of stress (Te=Ti is
assumed).Profiles of poloidal flow and stress derivative are
similar.
27M. SoneharaRogowski Probe
1-D pickup coil3-D pick up coilRogowski coil for measuring the
local current was developed.Langmuir probeRogowski coil28H.
Furui28Successful Measurement of Local Current(OH Plasma) Plasma
current Local plasma current density Poloidal magnetic field
generated by the plasma current Bp is estimated to be under 20 mT
at the location of the Rogowski coil. Output voltage of the
Rogowski coil due to Bp is estimated to be under 100 V.
Local current measurement was performed successfully with small
pickup of magnetic fields.
29H. FuruiConclusionsST 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 Ip was 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), Ip
becomes mainly wave-driven. In this regime, control of the current
density profile by externally excited waves should become
possible.30ConclusionsVarious 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.31Need for Power Supply UpgradeIn 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
32Near-Future PlansCoil Power Supply UpgradeSustained high field
(Bt = 0.3 T for > 0.1 s) for further Ip ramp-up.
Wave/Turbulence DiagnosticsElectrostatic probe
arrayReflectometer / interferometer-polarimeter
Plasma diagnosticsMulti-pass Thomson scatteringEBW
emissionCurrent profile measurement by Rogowski probe / magnetic
probeIon flow measurement33