Download - ECE Diagnostic on the HSX Stellarator
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ECE Diagnostic on the HSX Stellarator
K.M.Likin, C.Domier*, J.N.Talmadge, D.T.Anderson, F.S.B.Anderson,
A.F.Almagri, S.P.Gerhardt, J.M.Canik
University of Wisconsin, Madison, USAUniversity of Wisconsin, Madison, USA
*University of California, Davis, USA *University of California, Davis, USA
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IntroductionA single spatial channel conventional radiometer is used for
detection of the electron cyclotron emission (ECE) from the HSX plasma. The HSX plasma built-up followed by is made by microwave power (up to 200 kW) at 28 HGz that corresponds to the second harmonic of ce at 0.5 T. The experiments are carried out under
(0.5 – 3)*1012 cm-3 of the mean plasma density and (0.4 – 1) keV of the central electron temperature [1].
To evaluate the optical depth of HSX plasma, the spatial resolution and the radiation temperature profile the ray tracing code developed for ECRH in the HSX geometry has been modified so that it can serve the ECE diagnostic [2]. Both emission and absorption terms are taken into consideration. The available HSX ports have been examined to place the ECE antenna for the optimum sight. The wave beam width, its divergence and the sight angle can be adjusted to get maximum optical depth and spatial resolution.
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ECE in the Box Port
1.4 1.45 1.5
-0.2
-0.1
0
0.1
0.2
Z, m
R, m
Mod |B| and plasma boundary
1.4 1.45 1.5
-0.2
-0.1
0.0
0.1
0.2
R,m
Z,m
Bo = 0.5 Tne(0) = 31012 cm-3;
Ray traces
Advantages:
• Good access to the plasma
• Small wave beam refraction
• Good spatial resolution
• Measurements at both low and high field sides
Disadvantages
• Low optical depth under a moderate electron temperature
= 0 degs.
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Optical Depth in the Box PortAntenna at = 0o
Te(0) = 0.4 keV
0.00
0.10
0.20
0.30
0.40
0.00 0.20 0.40 0.60 0.80 1.00reff.
P, a.u.
27 GHz = 0.6
29 GHz = 0.5
30 GHz = 0.2
31 GHz = 0.1
26 GHz = 0.3
25 GHz = 0.1
Antenna at = 0 degs., Te(0) = 0.4 keV
0.00
0.10
0.20
0.30
1.38 1.40 1.42 1.44 1.46 1.48 1.50 1.52
R, m
P, a.u.
27 GHz = 0.6
29 GHz = 0.5
30 GHz = 0.2
31 GHz = 0.1
26 GHz = 0.3
25 GHz = 0.1
Radiated power profile and optical depth at different frequencies versus the major radius (a,b) and effective plasma radius (c,d) under Bo = 0.5 T; ne(0) = 31012 cm-3;ne(r) = ne(0)*(1- r2); Te(r) = Te(0)*exp(-
2*r2)
Antenna at = 0 degs., Te(0) = 1.0 keV
0.00
0.20
0.40
0.60
1.38 1.40 1.42 1.44 1.46 1.48 1.50 1.52
R, m
P, a.u.
27 GHz = 1.7
29 GHz = 1.1
30 GHz = 0.5
31 GHz = 0.2
26 GHz = 0.9
25 GHz = 0.2
Antenna at = 0o
Te(0) = 1.0 keV
0.00
0.20
0.40
0.60
0.00 0.20 0.40 0.60 0.80 1.00reff.
P, a.u.
27 GHz = 1.7
26 GHz = 0.9 30 GHz
= 0.5
29 GHz = 1.1
25 GHz = 0.231 GHz
= 0.2
a) c)
b) d)
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Inward ResonanceCentral resonance
0.00
0.10
0.20
0.30
1.38 1.40 1.42 1.44 1.46 1.48 1.50 1.52R, m
P, a.u.
27 GHz = 0.6
29 GHz = 0.5
30 GHz = 0.2
31 GHz = 0.1
26 GHz = 0.3
25 GHz = 0.1
Central resonance
0.00
0.10
0.20
0.30
0.40
0.00 0.20 0.40 0.60 0.80 1.00reff.
P, a.u.
27 GHz = 0.6
29 GHz = 0.5
30 GHz = 0.2 31 GHz
= 0.1
26 GHz = 0.3
25 GHz = 0.1
Inward resonance
0.00
0.10
0.20
0.30
1.38 1.40 1.42 1.44 1.46 1.48 1.50 1.52R, m
P, a.u.
27 GHz = 0.7
29 GHz = 0.3
30 GHz = 0.1
26 GHz = 0.6
25 GHz = 0.2
Inward resonance
0.00
0.10
0.20
0.30
0.40
0.00 0.20 0.40 0.60 0.80 1.00reff.
P, a.u.
27 GHz = 0.7
29 GHz = 0.3
30 GHz = 0.1
26 GHz = 0.6
25 GHz = 0.2
a) c)
b) d)
Radiated power profile versus the major radius (a,b) and versus the effective plasma radius (c,d) under B o = 0.5 T (a,c); Bo = 0.49 T (b,d), respectively;ne(0) = 31012 cm-3; Te(0) = 0.4 keV; ne(r) = ne(0)*(1- r2); Te(r) = Te(0)*exp(-2*r2)
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ECE in the 6” Top Port
1.1 1.15 1.2 1.25 1.3 1.35
0
0.05
0.1
0.15
0.2
0.25
0.3
Z, m
R, m
Mod |B| and plasma boundary
1.1 1.15 1.2 1.25 1.3 1.35
0
0.05
0.1
0.15
0.2
0.25
0.3
R,m
Z,m
Ray traces
Bo = 0.5 T; ne(0) = 31012 cm-3; Advantages:
• Good access to the plasma
• High optical depth
Disadvantages
• High wave beam refraction
• Poor spatial resolution under high plasma densities
• Measurements at down shifted frequency only
= 18.1 degs.
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Optical Depth in the 6” Top Port
Antenna at = 18.1 degs., ne(0) = 1013 cm-3
0.00
0.10
0.20
0.30
1.16 1.18 1.20 1.22 1.24 1.26 1.28 1.30R, m
P, a.u.
27 GHz = 0.3
29 GHz = 0.3
30 GHz = 0.2
26 GHz = 0.2
25 GHz = 0.04
Antenna at = 18.1 degs., ne(0) = 3*1013 cm-3
0.00
0.10
0.20
0.30
0.40
0.50
1.16 1.18 1.20 1.22 1.24 1.26 1.28 1.30
R, m
P, a.u.
27 GHz = 2
26 GHz = 1
25 GHz = 0.14
a)
b)
Radiated power profile and optical depth at different frequencies versus the major radius (a,b) and versus the effective plasma radius (c,d) in the 6” top port under Bo = 0.5 T; ne(r) = ne(0)*(1- r2); Te(0) = 0.4 keV; Te(r) = Te(0)*exp(-2*r2)
Antenna at = 18.1 degs., ne(0) = 3*1013 cm-3
0.00
0.10
0.20
0.30
0.40
0.00 0.20 0.40 0.60 0.80 1.00reff.
P, a.u.
27 GHz = 2
25 GHz = 0.14
26 GHz = 1
Antenna at = 18.1 degs.
ne(0) = 1013 cm-3
0.00
0.10
0.20
0.30
0.40
0.00 0.20 0.40 0.60 0.80 1.00reff.
P, a.u.
27 GHz = 0.3
29 GHz = 0.3
30 GHz = 0.2
26 GHz = 0.2
25 GHz = 0.04
c)
d)
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ECE at the High Field Side
0.9 0.95 1 1.05 1.1 1.15 1.2
0
0.05
0.1
0.15
Z, m
R, m
Mod |B| and plasma boundary Ray traces
Bo = 0.5 T ne(0) = 31012 cm-3
Advantages:
• Small magnetic field gradient
• Moderate optical depth
Disadvantages
• High refraction
• One side measurements at up shifted frequencies
• Small port diameter
= 37.8 degs.
0.9 0.95 1 1.05 1.1 1.15 1.2
0
0.05
0.1
0.15
0.44
0.44
0.44
0.47
0.47
0.47
0.47
0.47
0.5
0.5
0.5
0.5
0.53
0.53
0.53
0.53
0.56
0.56
Z, m
R, m
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Optical Depth at the High Field
Radiated power profile and optical depth versus the major radius (a) and versus the effective plasma radius (b) in the high field side port under Bo = 0.5 T; ne(0) = 31012 cm-3; ne(r) = ne(0)*(1- r2);
Te(0) = 0.4 keV; Te(r) = Te(0)*exp(-2*r2)
Antenna at = 37.8 degs.
0.00
0.10
0.20
0.30
0.40
0.50
1.05 1.10 1.15 1.20 1.25R, m
P, a.u.
29 GHz = 1 30 GHz
= 0.6
31 GHz = 0.1
Antenna at = 37.8 degs.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.00 0.20 0.40 0.60 0.80 1.00reff.
P, a.u.
31 GHz = 0.1
30 GHz = 0.6
29 GHz = 1
a) b)
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Description of the radiometer
The radiometer is a heterodyne type receiver [5]. Radiation from the plasma, over a frequency range of 25-31 GHz, is collected by a horn antenna (Millitech Model SGH-28, with a nominal 25 dB of gain at the axis) and after a notch filter it applies to a broadband balanced mixer. A Gunn diode (21 mW at 42.5 GHz) is used as a local oscillator. The 11.5-17.5 GHz IF signals from the mixer (4.3-7.5 dB conversion loss) are amplified by a low noise microwave amplifier (model JCA1218-F01, 22 dB gain), bandpass filtered (center frequency may be varied from 11.5 to 17.5 GHz) and amplified once more (model C060180G-4F1, 32 dB gain). Conventional IF modules incorporate wideband detectors which are coupled to two stage (100X gain, 20 kHz) video amplifiers.
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ECE Radiometry
n nce
ce eB me
e
X
Y
Z
Vacuum Vessel
Plasma
R
z
R0
B ~ 1/R
The gyromotion of electrons results in the Electron Cyclotron Emission (ECE) at a series of discrete harmonic frequencies:
2
3 2( ) ( )
8e
B
TI I
c
When the plasma is optically thick, the ECE radiation intensity is the black body intensity:
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Location of the ECE antenna
Pecrh = 50 kW
ECE antenna
MD_5
MD_1
MD_4
MD_6
MD_2MD_3
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Radiometer set-up
12 - 18 GHzHigh Pass
Filter
Amplifier:22 dB gain+10 dBm3 dB NF
27 GHz Low Pass
Filter
Video Amplifier
Video Detector
Amplifier:32 dB gain+18 dBm3.5 dB NF
15.5 GHzBand Pass
Filter
Diode Mixer
Horn Antenna
Gunn diode:42.5 GHz21 mW
Data Acquisition
System
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Gyrotron power leakage test
First test of the notch filter on HSX operation with 50 kW of launched power showed that the gyrotron leakage power through the filter is 3 mW with a peak at the gyrotron leading front (it is greater by factor of 3 in power).
0.795 0.8 0.805 0.81 0.815 0.82 0.825 0.83-0.08
-0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
Time (seconds)
Vo
lts
7/11/02, shot #2
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Low Pass FilterTo reduce the gyrotron leakage power a lowpass filter is suggested to use. The filter consists of a pair of K-band lowpass filters (HP model K362A), in which the cut-off frequency has been lowered by the insertion of carefully cut sections of dielectric strips within the filter, coupled with a K and Ka band transition. Also shown on the Fig. are three shaded areas which represent available IF bandpass filter.
-70
-60
-50
-40
-30
-20
-10
0
24 25 26 27 28
Lowpass Filter Response
Tra
nsm
issi
on
(d
B)
Frequency (GHz)
Gyrotron power leakage through the filter in HSX operation is about 0.8 mW in a lack of absorption and drops down to 0.03 mW when the absorption is high.
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Raw ECE signal and Te
The calibration of the radiometer demonstrated its temperature response to be ~ 400 eV/V.
In terms of a noise level the sensitivity of radiometer is 2 eV
The estimated electron temperature at plasma radius of 0.6 is 250eV.
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Low Plasma Density Discharge
0 2 4 6 8 10-5
0
5
10
HSX Status, Shot:47Main & Aux Current (kAmps), and Coil Ground Current
0 2 4 6 8 10-3
-2
-1
0
Neu
tral
Pre
ssur
e (m
icro
Tor
r)
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.860
0.2
0.4
0.6
0.8
1
11/8/02Density of Last 4 Shots:red(current), magenta, green, blue
time (sec)
1e12
/cm
3
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.860
0.5
1
time (sec)
H
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.860
0.2
0.4
SX
R E
mis
sion
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.86
0
10
20
30
Flu
x Lo
op (
J)
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.860
1
2
time (sec)
EC
H P
ower
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Moderate Plasma Density Discharge
0 2 4 6 8 10-5
0
5
10
HSX Status, Shot:36Main & Aux Current (kAmps), and Coil Ground Current
0 2 4 6 8 10-3
-2
-1
0
Neu
tral
Pre
ssur
e (m
icro
Tor
r)
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.860
0.5
1
1.5
2
2.5
11/8/02Density of Last 4 Shots:red(current), magenta, green, blue
time (sec)
1e12
/cm
3
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.860
1
2
time (sec)
H
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.860
0.1
0.2
0.3
SX
R E
mis
sion
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.86
0
10
20
Flu
x Lo
op (
J)
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.860
1
2
time (sec)
EC
H P
ower
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Raw ECE SignalsLow plasma density
ne = 0.5*1012 cm-3
Moderate plasma density
ne = 1.5*1012 cm-3
0.8 0.81 0.82 0.83 0.84 0.85 0.86 0.87
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Time (seconds)
Vo
lts
11/8/02, shot #47
0.8 0.81 0.82 0.83 0.84 0.85 0.86 0.87
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Time (seconds)
Vo
lts
11/8/02, shot #36
The higher level in radiated power at low plasma density is supposed due to superthermal electron emission.
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ECH Absorption
ne = 0.5*1012 cm-3
In the QSH magnetic field configuration the heating microwave power is absorbed with high efficiency (about 90%) in a few passes through the plasma column.
The absorption of heating microwave power is measured with a set of microwave diodes installed around the machine. The raw signals are shown in the following figures.
0.8 0.81 0.82 0.83 0.84 0.85 0.860
1
2
3
4
5
6
7
8
Time (seconds)
Vo
lts
11/8/02, shot #47
MD4
MD5
MD6
0.8 0.81 0.82 0.83 0.84 0.85 0.860
1
2
3
4
5
6
7
8
Time (seconds)
Vo
lts
11/8/02, shot #24
MD4
MD5
MD6
ne = 3*1012 cm-3ne = 1.5*1012 cm-3
0.8 0.81 0.82 0.83 0.84 0.85 0.860
1
2
3
4
5
6
7
8
Time (seconds)
Vo
lts
11/8/02, shot #36
MD4
MD5
MD6
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Inward Resonance Discharge
0 2 4 6 8 10-5
0
5
10
HSX Status, Shot:39Main & Aux Current (kAmps), and Coil Ground Current
0 2 4 6 8 10-4
-2
0
Neu
tral
Pre
ssur
e (m
icro
Tor
r)
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.860
0.5
1
1.5
2
2.5
11/8/02Density of Last 4 Shots:red(current), magenta, green, blue
time (sec)
1e12
/cm
3
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.860
1
2
time (sec)
H
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.860
0.1
0.2
0.3
SX
R E
mis
sion
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.86
0
10
20
Flu
x Lo
op (
J)
0.79 0.8 0.81 0.82 0.83 0.84 0.85 0.860
1
2
time (sec)
EC
H P
ower
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Off-axis ResonanceCentral resonance
Bo = 0.5 T
The radiated temperature drops under off-axis heating because of flattening of electron temperature profile and reduction of superthermal electron population.
Resonance shifted inward
Bo = 0.49 T
0.8 0.81 0.82 0.83 0.84 0.850
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Time (seconds)
Vo
lts
11/8/02, shot #39
0.8 0.81 0.82 0.83 0.84 0.85 0.86
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Time (seconds)
Vo
lts
11/8/02, shot #37
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ECE Signal Decay
0.847 0.848 0.849 0.85 0.851 0.852 0.853 0.854
0
0.05
0.1
0.15
0.2
0.25
0.3
Time (seconds)
Vo
lts
11/8/02, shot #36
After the heating microwave power turn-off the decay rate of radiated temperature is about 1.7 msec. while the plasma density is slightly increased.
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Plasma Temperature Profile
Taking the real plasma density profile and assuming some electron temperature profile one can find an optical depth running the ray tracing code. For mean plasma density of 1.5*1012 cm-3 and the central electron temperature of 300 eV the optical depth is 0.5. Taking into account this value the electron temperature has been estimated for two spatial locations (the data were taken at 27 GHz and 26.2 GHz using two different band pass filters ).
0
100
200
300
0 0.2 0.4 0.6 0.8 1
reff
eV
TeTrad
Temperature profile:
Te(r) = Te(0)*exp(-3*r2)
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Conclusion1. Optical depth and radiated power profile in the HSX plasma
can be evaluated with the ray tracing code in 3-D geometry.
2. Three different locations for ECE antenna have been examined. The best access to the plasma is on the box port while an ECE antenna in the 6” top port can be a challenger as well.
3. The notch and low pass filters have been tested on a gyrotron power leakage and it was found that the low pass filter has the suitable attenuation at 28 GHz.
4. The radiometer has been calibrated with a hot load at the UC-Davis and installed at the HSX.
5. First measurements exhibit about 270 eV of electron temperature at the plasma radius of 0.2 at ne = 1.5*1012 cm-3
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References.
1. D.Anderson. HSX: Helically Symmetric Experiment. Progress Report and Renewal Proposal. 2001.
2. K.Likin, B.D.Ochirov. Sov.J.Plasma Phys. 18 (1992), 42.
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