Collective Thomson Scattering Diagnostics of Confined Fast Ions

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