collective thomson scattering diagnostics of confined fast ions paul woskov 1, s. b. korsholm 1,2,...
TRANSCRIPT
Collective Thomson Scattering Diagnostics of Confined Fast Ions
Paul Woskov1, S. B. Korsholm1,2, H. Bindslev2, J. Egedal1, F.Leipold2, F. Meo2, P. K. Michelsen2, S. Michelsen2, S.K.Nielsen2,
E. Westerhof3, J. W. Oosterbeek4, J. Hoekzema4, F. Leuterer5, D.Wagner5
1MIT Plasma Science & Fusion Center2Risø National Laboratory, Technical University of Denmark3FOM IPP Rijnhuizen4IPP, Forschungszentrum Jülich5Max Planck IPP
ITPA Diagnostics Meeting, Princeton, March 26 - 30, 2007
CTS Diagnostic Features
CTS diagnostics can diagnose the complete fast ion distribution function, f(v, r, t)
spatially resolved time resolved no fundamental limits on energy range
Accessible to plasma core of burning plasmas
Recent experiments in tokamaks have firmly established fast ion CTS
JET (Bindslev et al., PRL 83, 3206, 1999) TEXTOR (Bindslev et al., PRL 97, 205005, 2006)
Principal of CTS Fast Ion Diagnostics
,s sk
,i ik
Electromagnetic scattering off microscopic fluctuations, principally in electron distribution, driven by ion motion when the condition between fluctuation
wavevector (k) and Debye length (D) is given by:
11
Dk
receiver
plasma
laser or gyrotron
Scattering Geometry
In tokamaks
Long wavelength sources required for large scat. angles
mmwaves for > 20
ˆf u u f d k v v v
i sk k k Projection of ion velocities
v along k diagnosed
Tokamak Access for CTS
ECE background restricts access to where the CTS condition (kD)-1 > 1 can be satisfied
Below fundamental ECE resonance, fi < fB
Used at TFTR and proposed for ITER
Between fundamental and first harmonic, fB < fi < 2 fB
Used at JET, TEXTOR, and ASDEX-Up Not accessible in burning plasmas with Te > 10 keV
Above the highest significant harmonic, fi > > fB
Used at JT-60 with CO2 laser for small angle CTS
Used at Alactor C, TCA, and UNITOR for thermal ion CTS with FIR lasers
Illustrative CTS Spectrum
6.7
110 GHz Gyrotron, 160 Scattering Angle
Each ion species and electrons contribute to the total CTS spectrum
The fast ions are distinguished in the CTS spectrum by their large Doppler shift above the electron feature
(kD)-1 = 6.7
Sensitivity to NBI Ions in ASDEX-Up
CTS with 104 GHz Gyrotron, 130 Scattering Angle
100 keV H Beam Te = Ti = 6 keV , ne = 8 x 1019 m-3
Sensitivity to ICRH Ions in ASDEX-Up
CTS with 104 GHz Gyrotron, 130 Scattering Angle
100 KeV H ion Maxwellian Te = Ti = 6 keV , ne = 8 x 1019 m-3
Alphas and Beam Ions in ITER
Alpha particles can be distinguished in the presence of 1 MW D beam ions in ITER
Egedal, Bindslev, Budny and Woskov, NF, 45, 191 (2005)
Alphas and Beam Ions in ITER H-Mode
Ion Density Profiles
Velocity Space Distribution at Scattering Volume
Projected Velocities Along k
k Direction
CTS Spectrum ITER H-Mode
60 GHz Gyrotron
CTS ion signal proportional to ion charge squared
Alphas and Beams in ITER Reverse Shear
Velocity Space Distribution at Scattering Volume
Projected Velocities Along k
k Direction
Ion Density Profiles
CTS Spectrum ITER Reverse Shear
60 GHz Gyrotron
Two Fast Ion CTS Systems Implemented
TEXTOR CTS - OperationalGyrotron 110 GHz
Max. Power 200 kW
Max. Pulse 0.2 sec
Rec. Bandwidth 106.3-113.4 GHz
Channels 42
Scat. Angle 150 - 170
ASDEX-Upgrade CTS - CommissioningGyrotron 105 GHz
Max. Power 800 kW
Max. Pulse 10 sec
Rec. Bandwidth 100-115 GHz
Channels 50
Scat. Angle 84 - 171
• Fast ion measurements being carried out in NBI and ICRH plasmas
• Up to 100 CTS spectra per plasma shot to study ion dynamics
• makes use of new two frequency gyrotrons
• First plasma measurements expected in 2007
TEXTOR CTS
CTS cabinet with DAQ & electronics
CTS quasi-optical transmission line
CTS port
Copper bellow
CTS receiver
Balcony
Liquid N2
Liner
TEXTOR CTS
Steerable mirror 1
CC waveguide
Receiver Optics inside TEXTOR
ASDEX-Upgrade CTS
MOU box supporting frames
Quasi-optical CTS transmission line
Towards the tokamak
CTS receiver and electronics cabinet
Gyrotron 1 MOU box
ASDEX-Upgrade CTS
MOU Box #2 Optics CTS Receiver
Moveable Mirror
Polarizer Plates
Exit to CTS Receiver
MOU Box #1
MOU Box #2
CTS Receiver
CTS Horn
From Tokamak
TEXTOR CTS Measurements
ECE
ECE+CTS
ICRH co-NBI
Frq/GHz
CTS
Shot # 100477 with ICRH and NBI
• Gyrotron modulated 2 ms on / 2 ms off
• Signal from off times (blue) used to determine background (green) to subtract from on times (red) to obtain CTS signal
Establishing CTS Beam Overlap
1.2 1.4 1.6 1.8 2 2.2 2.4-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
R / m
z / m
Probe
CTS receiver
Scattering volume
• Receiver scanned in toroidal direction during Ohmic shot # 100467
• Receiver and probe beams go through overlap for a variation of 5 in toroidal angle
• Corresponds to scat. volume width of 4 cm perpendicular to figure
k to B angle 110
Observations of NBI Fast Ion Anisotropy
NBI 1
NOTCH FILTER
B
vcts
45
B
vcts
80
Shot # 97982
Shot # 97984
NBI 1
NOTCH FILTER
Other Ion CTS Observations at TEXTOR
Sawteeth fast ion dynamics localized in space and orientation, and to lower ion velocities1
NBI fast ion relaxation after turn off in good agreement with Fokker-plank modeling1
1 Binslev et al., PRL 97, 205005, 2006
Toroidal rotation of thermal ion population observed
Requirements for CTS to Work Understood
Low background electron cyclotron emission (ECE)
Spectrally narrow, clean, and stable probe beam radiation
Sensitive, wideband receiver with deep notch filter for stay light rejection
Receiver robust against gain compression
Well defined, overlapping probe and receiver beams
Gyrotron Spectral Adjustments
Channel (frequency)
Initial Spectrum
Channel (frequency)
Tim
e (s
ec)
Noise level
Probe signal
Gain Compression
110 GHz TEXTOR gyrotron adjusted for clean spectrum
P(gyro) = 100%
5%
5%
5%
5%
100%
100%
100%
100%
Gyrotron Frequency Gyrotron FrequencyAfter Tuning
6.5 GHz 6.5 GHz
Careful gyrotron operating parameter adjustment achieves clean spectrum for CTS.
Precision Gyrotron Frequency Measurements
ASDEX-Up Gyrotron Measurements
Modulated
Continuous Precision Gyrotron Frequency Measurements Allow:
• Optimization of receiver notch filters
• Optimization of receiver blocking switch
• Improved data analysis
• Higher frequency resolution measurements
• Bulk ion feature• Plasma rotation• Ion Bernstein waves (fuel ratio)• Other plasma resonances
Gain Compression
N+CTS N CTSG GS P P
det CTSP P
N+CTS Ndet CTS
SS
GP P
N+CTS N CTSGS P P
N NS G P
Without Gain Compression
With Gain Compression
Sp
ect
ral p
ow
er
de
nsi
ty (
eV
)
200
300
400
500
600
109.62 GHz
2.4 2.45 2.5 2.55 2.6 2.65
50
150
250
350 109.38 GHz
Time (s)
200
250
300
350
400 109.54 GHz
Red: gyrotron on, Blue: off
det CTS N CTS
GP
GPP P
Compensation Strategies
• Multiplex IF with narrow central band (TEXTOR 2.56 GHz, ASDEX-UP 1.0 GHz)
• Use stiff IF amplifiers (Higher output power compression point)
• Carefully characterize receiver electronics (Eliminate cross talk)
Beam Alignment and Mapping
Mini-rig
Beam
Mini-rig
Beam
Distance [cm]
Dis
tanc
e [c
m]
Distance [cm]
Dis
tanc
e [c
m]
• Receiver view profile measurements insure well defined view with no side lobes.
• Locate view position to help facilitate obtaining overlap with gyrotron probe beam
Micro-rig
Summary
CTS diagnostics can make possible a complete determination of the fast ion distribution function f (v, r, t) in burning plasmas
Experiments at TEXTOR and ASDEX-Upgrade are proving fast ion CTS diagnostics
Practical requirements for making fast ion CTS work in burning plasmas are understood and tractable
A basis for a CTS confined alpha particle diagnostic has been established