High Harmonic Fast Wave Experiments on TST-2 Y. Takase, A. Ejiri, S. Kainaga, H. Kasahara 1) , R. Kumazawa 1) , T. Masuda, H. Nuga, T. Oosako, M. Sasaki, Y. Shimada, F. Shimpo 1) , J. Sug iyama, N. Sumitomo, H. Tojo, Y. Torii, N. Tsujii, J. Tsujimura, T. Y amada 2) 12th International Workshop on Spherical Torus 2006 Chengdu 11-13 October 2006 University of Tokyo, Kashiwa, 277-8561 Japan 1) National Institute for Fusion Science, Toki, 509-5292 Japan 2) Kyushu University, Kasuga, 816-8580 Japan
High Harmonic Fast Wave Experiments on TST-2. Y. Takase, A. Ejiri, S. Kainaga, H. Kasahara 1) , R. Kumazawa 1) , T. Masuda, H. Nuga, T. Oosako, M. Sasaki, Y. Shimada, F. Shimpo 1) , J. Sugiyama, N. Sumitomo, H. Tojo, Y. Torii, N. Tsujii, J. Tsujimura, T. Yamada 2). - PowerPoint PPT Presentation
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High Harmonic Fast Wave Experiments on TST-2
Y. Takase, A. Ejiri, S. Kainaga, H. Kasahara1), R. Kumazawa1), T. Masuda,
H. Nuga, T. Oosako, M. Sasaki, Y. Shimada, F. Shimpo1), J. Sugiyama,
N. Sumitomo, H. Tojo, Y. Torii, N. Tsujii, J. Tsujimura, T. Yamada2)
12th International Workshop on Spherical Torus 2006 Chengdu
11-13 October 2006
University of Tokyo, Kashiwa, 277-8561 Japan1)National Institute for Fusion Science, Toki, 509-5292 Japan2)Kyushu University, Kasuga, 816-8580 Japan
• TST-2 spherical tokamak and RF system
• HHFW experiment– Electron heating experiment– Wave diagnostics
• RF magnetic probes• Reflectometry
– Wave measurements• parametric decay• scattering
– TORIC full-wave analysis
• EC start-up experiment
• Plans – 200MHz experiments on TST-2– RF sustainment of high plasmas in UTST
Outline
TST-2 Spherical Tokamak
ECH: 2.45GHz (< 5 kW)HHFW: 21MHz (< 200 kW x 2)
ECH
HHFW
R / a = 0.38 / 0.25 m (A = 1.5)
Bt = 0.3 T / Ip = 0.1 MA
21 MHz Matching/Transmission System
• RF power
400 kW
• Frequency f = 13, 21, 30 MHz (/H ~ 7 at BT = 0.2 T, f = 21 MHz)
• Toroidal wavenumber k = n/R0 = 11, 16, 26 m-1
(n = 4.3, 6, 10)
varied by changing the strap spacing
• Faraday shield angle ~ 30°
currentstraps(0, )
Mo limiters
Faraday shield
Variable k Two-Strap Antenna
Single-pass Absorption Calculation
• Single-pass absorption is greater for double-strap excitation
• Single-pass absorption– increases with ne
– increases with Te
– decreases with Bt
(increases with e )
0.0
2.0
4.0
6.0
8.0
10
0.0 5.0 10 15 20 25 30
ne dependence for single and
double strap excitations
Single strap[%] Double strap[%] Single strap[%] Double strap[%] Single strap[%] Double strap[%]
Sin
gle
pas
s ab
sorp
tion
[%]
Toroidal mode number
Te = 300 eV
BT = 0.2 T
5.0x1019 m-3
1.0x1019 m-3
3.0x1019 m-3
double-strap
single-pass absorption
== 0.18
ELD + TTD
ELD + TTD + CROSS
ELD
ELD + CROSS
Imag ( k⊥)
dxke
)Im(21
Bt = 0.15 T ne = 1.0×1019 m-3
Te = 100 eV n = 10
Single-Pass Absorption Improves with e
• Analysis of HHFW heating scenarios used on TST-2 is being carried out using the TORIC full-wave code.
Bt = 0.2 T, f = 21 MHz, n = 10, ne0 = 2 1019 m-3, Te0 = 0.2 keV
TORIC Full-Wave Calculations
Electron absorption: 100%
• Soft X-ray increased, but density and radiated power did not change electron heating
• Strongest response near plasma center
t (ms)
Ip
nel
Prad
SX (> 200 eV)
360 kW RF
Electron Heating by HHFW
Low
field
sid
eH
igh fi
eld
sid
e
~ R0
180kW360kW
no HHFW
R=0.19m
R=0.26m
R=0.38m
R=0.43m
R=0.54m
Center
PS noise
• Increases in stored energy and visible-SX emission are greater for double-strap excitation
– Consistent with single-pass absorption calculation
Single-Strap vs. Double-Strap Excitation
double-strapsingle-strap
no RF
with RF
Edgeemission
visible-SXemission(A.U.)
PNET = 120 kW PNET = 120 kW
• RF magnetic probes– Sensitive to electromagnetic component
– Plasma edge only
• Reflectometry– Sensitive to electrostatic component
– Can probe the plasma interior
• Both parametric decay instability (PDI) and frequency broadening due to scattering by density fluctuations were observed.– These processes can alter the wavenumber spectrum, and affect bot
h wave propagation and absorption.
Wave diagnostics on TST-2
φ= -60°
φ= -30°
φ= -55°φ= -65°
φ= -115°
φ= -120°
φ= 155°φ= 150°
φ= 145°
φ= 65°φ= 60°φ= 55°
φ= 30°
φ= 0°
Top viewS.S. enclosure
Slit
Core (insulator)
1-turn loop
Semi-rigid cable
2cm
Direction ofB field to bemeasured
RF Magnetic Probes at 14 Toroidal Locations
toroidal direction
Bz B
φ= 9°
φ= -9°
φ= -125°
B
RF21MHz
eit
One of three sources is used Frequency sweepable VCO for profile measurements Fixed Gunn Osc. (25.85 or 27.44 GHz) for RF measurements
Ep x Bt
Aeit
Aeit+i
I
cos(p+t+RF)
sin(p+t+RF)
VCO6-10GHz
X4
QLO RF
coaxial waveguidescalar horn
Digitizer or Oscilloscope
<250MHz sampling
F.G.
X5
X10
Gunn25.85 or 27.44 GHz
D.C.-3dB
5-20mW
DC-500MHz
24-40GHz100mW
TST-2 Reflectometer System
Window200
TFCoil
TST-2V.V.
Mirror
Mirror
HornAntennas
Microwave Reflectometer
Most probable decay process:
High Harmonic Fast Wave (HHFW)
Ion Bernstein Wave (IBW)+
Ion-Cyclotron Quasi-Mode (ICQM)
Magnetic field dependence
H at outboard edge
Threshold power ~ 20 kW
High power
Lowpower
Parametric Decay: FW IBW + ICQM
Parametric Decay Instability (PDI)
PDI
①
②
probe②
RF probe
1.8 MHz
HHFW250 kW
Time [s]
Reflectometer25.85 GHz (cosine)
Reflectometer25.85 GHz (sine)
RF Probe (dB/dt)Antenna Limiter, P12
Frequency [MHz]
Comparison of RF Probe and Reflectometer Spectra
QMIBW
Comparison of RF Probe and Reflectometer Spectra
Reflectometer (cos)
Reflectometer (sin)
RF Magnetic Probes
f (MHz)
FW ?
IBW
QMIBW
noise (Al reflector)
2510 20
0
-20
-40
-60
-800
P (dB)
0
-20
-40
-60
-80
P (dB)
0
-20
-40
-60
-80
P (dB)
155
PDI becomes stronger as the plasma outer boundary approaches the antenna
Rout
Dependence on Plasma Position
antennalimiter
①
②
③
④
① ②
③ ④
Outboard vs. Inboard Comparison
• Inboard spectrum similar to outboard, but weaker
RF probes
φ= 21°straps
φ= 39°
R=125 R=630mmR=700mm
Z = 0mm
Z = -150mm
port10
①
②③
④
① ②
③ ④
• Broadened spectrum is only weakly dependent on vertical position
midplane B
midplane Bz
Z = 150mm
Inboard Side Spectra
RF probes
Vacuum Plasma
① ①
② ②
Frequency broadening of the pump waveby the plasma is observed.
Possible processes:
• Parametric decay• Scattering by density fluctuations
Frequency Broadening
①
②
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
7.0 7.5 8.0 8.5 9.0
ch1ch4ch3ch2
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
7.0 7.5 8.0 8.5 9.0
ch1ch4
ch3ch2
f (HHFW)Pump wave power
0
0.0005
0.001
0.0015
0.002
0.0025
7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6 8.8 9.0
ch1ch4ch3ch2
Lower sideband power
①
②
③
④
0
0.5
1
1.5
2
2.5
7.0 7.5 8.0 8.5 9.0
R = 195
R = 260
R = 370
SX / SX
Density Dependence Varies with Probe Position
10dBf (HHFW)
• PDI is generally reduced at high density
• Only weak effect on heating
Preliminary
nelnel
• A k|| variable antenna was installed in TST-2, and the RF power capability was increased to 400kW. – Dependence on k|| spectrum (same spectral shape but different k||)
will be studied.– Single-pass absorption is expected to change from 10% to 35% wh
en ne0 = 3.01019 m−3 and Bt = 0.3T.
• In electron heating experiments, soft X-ray emission increased with RF power.– Stored energy increase was larger for double-strap excitation. – More direct measurement of Te is necessary (TS in preparation).
• Analysis of HHFW scenarios used on TST-2 is being carried out using TORIC.
Summary (HHFW Heatng)
• PDI and frequency broadening due to scattering were observed by RF magnetic probes.– The strength of PDI increased as the outer boundary of the plas
ma approached the antenna.
– Density dependence varies with RF probe location.
– Parametric decay became weaker at high densities where single-pass absorption is predicted to become stronger.
– The effect of parametric decay on plasma heating is not clear.
• Initial results of RF wave detection inside the plasma by microwave reflectometry were obtained.– PDI spectrum clearly observed
– Differentiation of ES and EM components may be made.
Summary (RF Measurements)
EBW Heating on TST-2@K (2003)
(dW/dt) indicates Pabs/Pin > 50% when ne in front of antenna is steep enough
Thursday: S. Shiraiwa, et al.,“Study of EBW Heating on TST-2”