Transcript No Slide Title

MAST
EBW Experiments on MAST
V. Shevchenko1, G. Cunningham1, A. Gurchenko2, E. Gusakov2,
A. Saveliev2, A. Surkov2, F. Volpe1
1EURATOM/UKAEA
2Ioffe
Fusion Association, Culham Science Centre, Abingdon,Oxon, OX14 3DB, UK
Institute, Politechnikheskaya 26, 194021, St. Petersburg, Russia
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
MAST
Introduction
EC harmonics are usually obscured by cut-offs in ST
80
Shot #2942
Long-term goals
 NBCD is considered as a main
source to sustain steady state
current in ST plasma
 EBW can provide a critical offaxis current drive to sustain ST
plasma in equilibrium
 EBW H&CD can also assist
plasma start-up
60
Frequency, GHz
 CTF or ST Power Plant will not
allow the use of a central solenoid
70
fU hybrid
fpe
50
fU cut-off
fL cut-off
40
4fce
3fce
30
2fce
20
fce
10
0
20
40
60
80
100
120
140
Major Radius, cm
Midplane topology of cut-offs and resonances
in MAST (H-mode)
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
MAST
Antenna Configuration for O-X-B Conversion
30
30
25
25
Plasma
ne
Poloidal angle, deg
LH O-mode
Poloidal angle, deg
1.0
0.10
20
0.50
15
0.90
10
5
0
0
Btotal
a)
RH O-mode
sin2f=N2||,opt=Y/(Y+1), Y=ce/
5
10
15
20
Toroidal angle, deg
25
30
1.0
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0
0.90
0.80
20
0.70
0.50
0.60
15
10
0.50
0.10
0.40
0.30
0.20
0.10
5
0
0
0
b)
5
10
15
20
25
30
Toroidal angle, deg
O-X-B mode (N|| < 0) conversion window calculated for the 60 GHz launcher
located 22.5 cm below the midplane in MAST: a) high density ELM-free Hmode, b) high density L-mode plasma. Contours indicate 10% steps in
conversion efficiency, i.e. 0.5 means 50% mode conversion efficiency etc.
• O-X-B conversion is possible when ce < RF < pe
• Angular width of mode conversion cone depends on ne
• Launch plane is determined by Btot and ne at the plasma edge
• Angle between ne and optimal direction depends only on | Btot | in the layer where RF = pe
• Btot at the plasma edge is the most crucial parameter for the optimal launch configuration
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
MAST
EBW Modelling in MAST
1.0
80
# 7798, 0.24 sec
0.9
0.8
0.7
0.6
r/a
Frequency, GHz
60
40
0.5
0.4
0.3
20
0
0.2
fpe
fUHR
n fce
1ce
0.2
like O/X
0.1
0.0
0.4
0.6
0.8
1.0
15
1.2
Major Radius, m
Midplane topology of cut-offs and resonances in sawtoothing
H-mode plasma, shot #7798 in MAST.
16
17
18
19
20
21
22
23
24
25
f, GHz
Power deposition radius against frequency within the range of
fundamental EC resonance. 40 cm above midplane launch, N|| < 0.
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
EBW Emission in MAST
MAST
40
Frequency, GHz
From Ruby TS
and EFIT
30
20
Ip, MA
1.0
shot #7798
0.5
Plasma Current
1.2
Frequency, GHz
ITF, kA
RLCFS, m
0.0
Plasma Size
1.1
90
Toroidal Field
80
0.0
0.1
0.2
0.3
0.4
Time, s
EBW emission spectrogram measured in sawtoothing H-mode
plasma, shot #7798. Red areas correspond to higher emission
intensity. ECRF power was injected at 0.21 - 0.24 s, ITF = 91 kA.
EBW emission spectrogram in ELM-free H-mode plasma at optimised
TF (ITF = 83 kA), shot #11156. ECRF power (0.5 MW) was injected at
0.22 - 0.29 s.
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
MAST
EBW Steerable Launcher in MAST
21 mirrors
7 beams
200 kW each
60 GHz
•
•
•
Final polarisation can be chosen from linear to circular
Resultant beam divergence is less than +/-2.5o (w = 25 mm)
Poloidal steering range of +/-13o, toroidal +/-24o, accuracy of 0.5o
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
MAST
Plasma Targets for EBWH
EBW deposition
100
100
100
shot #9265, 0.30 s
Frequency, GHz
shot #11420, 0.27 s
shot #10897, 0.18 s
80
80
60
60
60
40
40
40
20
20
20
0
0.2
80
Fpe
Fce
Fuh
Fuc
Flc
c)
b)
a)
0
0.4
0.6
0.8
1.0
1.2
Major Radius, m
1.4
ELM-free H-mode
0.2
0.4
0.6
0.8
1.0
1.2
Major Radius, m
1.4
Sawtoothing H-mode
0
0.2
0.4
0.6
0.8
1.0
1.2
Major Radius, m
1.4
Ohmic H-mode
• O-X-B mode conversion window is
broad (about ± 5° at 50% efficiency).
Relaxed launch configuration.
•Mode conversion window is moderate
(about ± 3° at 50% efficiency). Relatively
stringent to launch parameters.
•Mode conversion window is narrow
(about ± 1.5° at 50% efficiency). Very
stringent to launch parameters
• EBW absorption is expected to be
very peripheral, r/a ~ 0.8. Non-linear
effects can be observed.
• EBW absorption is more central, can
reach r/a ~ 0.6. Heating effects can be
observed.
• EBW absorption can reach
transiently r/a ~ 0.4. Heating effects
must be detectable.
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
MAST
Lower Hybrid Probe Head
50 mm
 Can be moved to a specified distance from the plasma in the midplane
 Allows axial rotation ± 45o
 Loop (20x40 mm2) & L shape antennas
 76-545MHz spectrum analyser with 10 MHz resolution
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
MAST
LH, a.u.
4
4
255 ms
285 ms
290 ms
Plasma Density
2
3
0
1
0
1
LHE signal, mW
P, MW
D, a.u. <ne>, 1019m-3
Parametric Effects in ELM-free H-mode
D Signal
RF Power
0
2
1
2
1
LH Signal, 134 MHz
0
0
0.0
MAST #11420
0.1
Time, s
0.2
0.3
100
200
300
400
500
Frequency, MHz
• A strong emission enhancement around 134 MHz has been observed during RF injection.
• This emission was identified as LH emission originating in the X-B mode conversion layer
near UHR at 60 GHz
• Parametric Decay (subject to ~80 kW RF power threshold at UHR) indicates the mode
conversion is no less than 50%
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
600
MAST
Parametric Decay Threshold

UHR
2
1 3 11 12 5 4 1 3
f
Teff Te B
P W 
W

3 
 2 10  2 3 1 3

2
13
13 6 

  cm 
L4 3
 cm T GHz eV 
where Teff =Te + 4Ti
ρ is the radius of the heating beam
L is the inhomogeneity scale: L-1 = grad(ne)/ne + 2(ωce/ωpe)2grad(B)/B
For typical MAST parameters: f = 60 GHz, Ti ≈ Te = 140eV, B =0.38 T, L = 3 cm
PUHR*/(πρ2)  260 W/cm2
PUHR* ≈ 80 kW
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
for ρ ≈ 10 cm
Sawtoothing H-mode Ray-tracing Modelling
MAST
Z, cm
UHR
C
100
1.0
50
P/Pmax
0.8
0
-50
0.6
UHR
0.4
0.2
-100
0.0
50
100
150
200
250
3000.0
R, cm
Poloidal projection of EBW ray-tracing results
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
0.2
350
0.4
0.6
0.8
r/a
EBW power deposition profile
1.0
EBWH in Sawtoothing H-mode Plasma
80
7 kJ (~0.25 MW)
70
Plasma Energy, kJ
60
Before RF
injection
During RF
injection
60 kJ (~3 MW)
50
40
400
RF Power, kW
250 kW
300
200
100
0
0.20
EBW radiative temperature measured from 2ωce
during ELM-free intervals at optimal magnetic field.
0.25
b)
a)
0.30
0.35
Time, s
Average heating result. Shots #9262, #9263, #9267.
 EBW emission has been used to optimise magnetic field and launch angles
 EBE has a maximum when O-mode cut-off is about 2/3 of the gap between 5ωce and 6ωce
 mode coupling is strongly modulated by sawteeth and ELMs
 heating effect is better seen after averaging over a few shots
 no parametric decay has been observed in this scenario
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
MAST
MAST
EBE in High Density Ohmic H-mode
100
#10897
Outer plasma radius, m
EBE
ECE
3ce
2ce
4ce
ECE
#10638
Frequency, GHz
80
Fpe
Fce
Fuh
Fuc
Flc
60
40
20
EBE
4ce
3ce
#10639
0
0.2
EBW emission (60.5 GHz) in high density Ohmic H-mode
during plasma compression
0.4
0.6
0.8
1.0
Major Radius, m
1.2
Resonance topology for high density Ohmic H-mode
As the plasma boundary moves into the higher magnetic field during compression,
EBE comes first from 4ωce, then from 3ωce and finally from 2ωce
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
1.4
MAST
Launcher Aiming in Ohmic H-mode
1.0
f=60.5GHz, f = -7deg
f=60.5GHz,  = -5.6deg
1.0
0.8
BXO-EBWSignal (a.u.)
BXO-EBWSignal (a.u.)
0.8
0.6
0.4
0.2
0.0
-11
-10
-9
-8
-7
-6
-5
Toroidal angle (deg)
0.6
0.4
0.2
0.0
-7
-6
-5
Poloidal angle (deg)
Angular window for O-X-B mode conversion measured at 60.5 GHz
EBE has been used to optimise the launch configuration for EBWH at 3ωce
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
-4
SXR Signal During EBWH
MAST
P, MW
SXR, a.u.
Plasma outer radius
0.8
SXR Signal
0.4
D signal
0.0
60 GHz EBE signal
0.4
RF Power
0.2
SXR differential signal
20
<nel>, 10 m
-2
0.0
3
2
Plasma Density
1
0
0.0
RF power
0.1
0.2
0.3
Time, s
SXR signal in the RF heated shot (red) and reference shot (black)
SXR signal from the RF heated shot with subtracted reference signal
SXR signal was doubled during RF pulse
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
Plasma Energy Increase During EBWH
Plasma Energy
RF Power
Plasma Density
D signal
Plasma energy (EFIT) during RF injection. Shots: #10704, #10706, #10707, #10709.
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
MAST
Electron Temperature Increase During EBWH
Electron temperature profiles measured by Thomson scattering in RF
heated (red) and ohmic (blue) plasmas at 0.18 s.
MAST
Electron temperature profiles measured by Thomson scattering in RF
heated (red) and ohmic (blue) plasmas at 0.20 s.
Electron Temperature increased by 10-15% due to RF injection
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
Conclusions
MAST
Proof-of-principle studies of the O-X-B scheme have been conducted on MAST at
60 GHz. Antenna aiming was performed using EBW emission measurements and
mode coupling modelling:
• In ELM-free H-mode only peripheral absorption is possible but the mode coupling
efficiency was proven to be high. Lower Hybrid emission (subject to ~80 kW RF
power threshold at UHR) indicates the mode conversion is no less than 50%.
• Some evidence of EBW heating was observed in the sawtoothing H-mode target
plasma. Total plasma energy shows 10% increase during RF pulse.
• In high density Ohmic H-mode the mode conversion window is very narrow.
However, after careful antenna alignment using EBW plasma emission at 60 GHz
10% electron temperature increase has been measured during RF power injection.
EBW heating has therefore clearly been observed via the O-X-B mode
conversion process
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
Further Plans
MAST
Conduct EBW assisted plasma start-up experiments with the recently installed 28 GHz,
200 kW start-up system.
As seen in experiments EBW emission is strongly anisotropic. Angular co-ordinates of
maximum EBE intensity are predominantly determined by the magnetic field pitch angle
at the plasma edge. The magnetic field pitch angle experiences strong variations during
the plasma shot due to L-H transitions, sawteeth and other plasma activities. To study
the dynamics of the magnetic pitch angle we are planning to:
• Upgrade the FSR with a remotely controlled spinning mirror
• Make a real time angular scan over the range, expected due to pitch angle variations.
Real time measurements of EBW emission angular dependence should give us a direct
estimate of the magnetic pitch angle  potential q-profile diagnostic.
It would allow more accurate predictions of launch parameters for EBWH experiments
and to clarify the edge plasma physics during L-H transition, ELM-free H-mode etc.
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
MAST
28 GHz EBW Assisted Plasma Start-up
Beam pattern
200
Central rod
Grooved area
40
EBW-mode beam
X-mode beam
30
B
IP
T
Z, cm
10
0
O-mode beam
-10
-20
I, kA (with trapping)
X-mode beam
50
20
19
-3
19
-3
ne=0.8 10 m
ne=0.2 10 m
150
100
50
-30
UHR
-40
-50
0
EC
R
10
20
30
40
50
60
R, cm
70
80
90
0
0.0
100 110
Vessel wall
Ray-tracing modelling (poloidal view) of the EBW CD plasma initiation.
The RF beam pattern, as measured at low power, is well within the
grooved area of the graphite mirror-polariser.
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
0.2
0.4
0.6
0.8
1.0
Te, keV
Modelling results. EBW driven current (trapping effects included) in
the range of plasma temperatures and densities. Input power 150
kW, 28 GHz.
MAST
28 GHz Antenna Mock-up Assembly
In-vessel mirrors of the 28 GHz launcher
Mock-up assembly of the launcher (upside-down)
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
Spinning Mirror Principle
Tilted spinning mirror for angular scan of EBW emission (red ellipses).
Inclination of the contours of BXO conversion efficiency (colour ellipses) 
Inclination of field lines at cutoff location  q-profile
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
MAST
Replacement Mirrors
Manual replacement of mirrors of different tilt
1.5o
3o
1Kg
4.5o
1.1Kg
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
0.9Kg
MAST
Spinning Mirror Set-up on MAST
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China
MAST
Summary
MAST
• A dedicated complex of high power RF heating systems, EBW diagnostics,
and modeling tools has been developed at Culham in order assess the
potential of EBW assisted plasma start-up, EBW heating and CD in MAST.
• EBE measurements provide a powerful tool for EBW heating optimisation
• Proof-of-principle (60 GHz) EBWH experiments confirm modelling predictions
• Real time angular EBE measurement is a potential q-profile diagnostic
• 28 GHz EBW plasma start-up/assist system has been installed on MAST
• Low frequency (~18 GHz) 1 MW EBW system is considered for MAST
V.Shevchenko et al, ISTW 2006, 11 -13 October 2006, Chengdu, China