Collective Thomson Scattering Study using Gyrotron in LHD

Collective Thomson Scattering Study using Gyrotron in LHD Shin KUBO, Masaki NISHIURA, Kenji TANAKA, Takashi SHIMOZUMA, Yasuo YOSHIMURA, Hiroe IGAMI, Hiromi TAKAHASHI, Takashi MUTOH National Institute for Fusion Science Namiko TAMURA, Dept. Energy Science & Technology, Nagoya Univ. Yoshinori TATEMATSU, Teruo SAITO Research Center for Development of FIR Region, Univ. of Fukui

Contents ECRH System in LHD --> Potential as a diagnostic tool Collective Thomson Scattering Receiver Preliminary results Scattering Volume and CTS spectrum Sub-Tera Hz Gyrotron Development Future Plan Summary

ECRH System

Design of the Antenna System of ECRH in LHD Two sets of upper antennas from 5.5U and 9.5 U port for 82.7GHz and 168GHz Two 84 GHz Antenna from 1.5 L port All antennas can focus and deposit the power within r<0.2 for R ax =3.53m,B=2.951 T Antenna Scan Range U antenna R=-3.2-3.8m, t=±0.2m on mid plane L antenna R=-3.0-4.2m,t= ±1.5m

Elliptical Gaussian Beam Focusing Scheme 168GHz from Waveguides Beam Waveguide mouth 84GHz Beam Bi-focal Mirror mid-plane Focusing Mirror Focusing Mirror Steering Mirror Focusing Mirror Steering Mirror 6

Hot test of beam steering/focusing Errors of steering for tor/rad-directions notably affect deposition profile Beam steering/focusing were checked in vacuum vessel of LHD by using Kapton film and IR-camera.

ECRH Beam as a Scattering Probe Beam Well defined beam for heating is also suitable for probe beam for scattering measurement. High power density, High Frequency Modulation Good S/N Ratio Controllable Scattering Cross Section Position Scattering Angle Promising Candidate for Density Fluctuation Measurement Structure study of micro-turbulence Wave detection EC wave, LH wave, IC wave, Alfven wave Collective Thomson Scattering Ion temperature measurement Alpha particle distribution study

Collective Scattering using ECRH System 9

Collective Scattering Condition θ =10 deg θ =90 deg 3 10

LHD ECH Antenna Configuration (2008) 1.5L Antenna out 84 GHz in 84 GHz 1.25 inch corrugated WG 2-O Antenna right 77 GHz left 168 GHz 3.5 inch corrugated WG 3.5 inch corrugated WG 9.5U Antenna out 82.7 GHz in 77 GHz 3.5 inch corrugated WG 5.5U Antenna out 82.7 GHz in 168 GHz 11

LHD ECH Antenna used for probe and receiving beams 1.5L Antenna out 84 GHz in 84 GHz 1.25 inch corrugated WG 2-O Antenna right 77 GHz left 168 GHz 3.5 inch corrugated WG 3.5 inch corrugated WG 9.5U Antenna out 82.7 GHz in 77 GHz 3.5 inch corrugated WG 5.5U Antenna waist size 0.015 m out 82.7 GHz 3 waist size 0.02 m 0.8 MW/5s, 0.24 in MW/CW 168 GHz 12

Present ECRH System in LHD Two sets of transmission line/ antenna are installed on the ports. 9.5U, 5.5U 1.5L and 2O 13

Proposed Scattering Probe/ Receiving transmission Line A set of transmission line/ antenna on the 9.5U port is used for CTS. A line which 77GHz 1MW power available is used for probe beam 14

Receiver Setting Configuration 15

Attached Receiver System 16

f0+df+fs plasma Heterodyne Receiver for Collective Thomson Scattering in LHD (2008) Notch filter BPF Isolator pin SW Att. WG SW fixed local oscillator stability < 10 MHz Mixer fl=78 GHz Filtek HPF A1 Two way divider 2 measure port monitor port Two way divider 1 Four way divider A2 low freq. high freq. A3 500-200 900-200 1300-200 1700-200 1900-100 2100-100 2300-100 2500-100 A1: Cernex CBLU1103030-01 A2: Cernex CBLU1103050-01 A3: Amplitek apt4_sn104331 Diodes Video Amps. (x1000) ECRH Transmission line (corrugated waveguide) gyrotron df~200mhz f0+df power monitor

Filter Combination Local Oscillator 74 GHz Filter combination Center freq. IF 3 GHz sensitive low freq. IF for high energy ions narrow band dense near center freq. IF for bulk ion wide band sparse at peripheral IF for high energy ions

Actual Receiver Configuration Horn Antenna Notch Filter PIN Switch Waveguide Switch From 77 GHz Gyrotron Waveguide for Probe Beam Mixer Local Oscillator Filters Splitters IF Amps.

Actual Filter Combination During the first trial of CTS measurement, the local oscillator of 74 GHz was damaged, and switched tentatively to 78 GHz Courtesy of Dr. T. Tokuzawa

Actual Filter Combination and Calibration with Liq N2 Background, calib. Ch.1,4,5 double side band Ch.2,3,6-8 lower side band CTS component All channel lower side band Ch2,3 almost notched 10 0 2009.01.23 ΔT=210 deg. lock-in factor=3.0 Cal. Factor(V/eV) 10-1 10-2 Effect of Notch Filter 10-3 0 1 2 3 4 5 6 7 8 9 Channel

78GHz local combination Measured Notch Filter Characteristics Courtesy of Prof. A. Mase Filter Characteristics Courtesy of Prof. Y. Nagayama Dr. T. Yoshinaga Mr. D. Kuwabara

Actual Measurement Configuration B=2.75 T R=3.6 m rho=0.7±0.2 k ~ perpendicular

Preliminary Results 25

Fundamental ECRH plasma (double side band factor) B=2.75T, R=3.6m Fundamental ECRH Plasma Noise well suppressed Spikes at every modulation turn-on, off due to spurious mode oscillation from gyrotron removable by pin switch

Expanded in time (#91758)

CTS #91758 (double side band factor) B=2.75T, R=3.6m Fundamental ECRH Plasma Noise well suppressed Spikes at every modulation turn-on, off due to spurious mode oscillation from gyrotron removable by pin switch

Analysis ECRH plasma Decomposition of scattering component from heating/heat wave component is necessary

Method of analysis Raw data of several modulation periods are rearranged in time relative to the turn on/off time These rearranged data are fitted with the function δa corresponds to background increments/ decrements due to heating (change in slope) δb corresponds to increment/decrement due to scattered signal over background (stepwise change)

Example of deduced raw signal change

Spectrum change in time

Example of deduced scattered power spectrum

Receiver Improvements 36

Heterodyne Receiver for Collective Thomson Scattering in LHD (2009) Filters 32 channel Video Amp. (x100) fixed local oscillator stability < 10 MHz Power Amps 0.5<f<4GHz A4 A4 A D C f0+df+fs plasma Notch filter Isolator Att. WG SW fl=74 GHz Mixer LPF f<6ghz Low NF Amps A3 A4 A4 A D C BPF pin SW n 5th-Harmonic Mixer HPF f>0.3ghz A1 A2 0.5<f<18GHz A4 A4 A D C HPF * A3 fl1-ndf A5 A5 Error Amp Voltage Controlled Oscillator Att HPF 2<f<8GHz A4 A4 A D C n Harmonic Mixer ECRH Transmission line (corrugated waveguide) power monitor gyrotron df~200mhz f0+df

Increased IF bands local frequency = 74.00 GHz

IF filter characteristics

Scattering Volume Key to confirm scattering signal confirmation Necessary for absolute calibration 40

Beam Cross Section Controlled by beam steering Max cross section at ρ=0.75 probing beam receiving beam Zero cross section probing beam receiving beam ρ=1.0 ρ=0.1 9.5U in 77GHz injection 9.5U out receiving

SN ratio of CTS Scattering power from Gyrotron to Receiver Γ: geometrical factor r e : classical electron radius n e : electron density dω: band width r R : beam radius λ s0 : wavelength of scattered radiation S(k,ω): scattering form factor Probe beam Scattered beam

Scattered Power 43

U-antenna for 168 GHz used for 77 GHz Scattering final focus mirror 77 77 bi-focal mirror 77 GHz 168 GHz Beam evolution is recalculated with the 168 GHz antenna mirror configuration radiated from the same waveguide mouth for 77 GHz beam Resultant beam sizes on the midplane are 20 mm in radial 99 mm in toroidal If the configuration of the mirrors and optical axis are the same,i. e. cosφ and ρ are kept, relation between Rin and Rout are defined by even for different frequency, or beam size

Scattering using Gaussian Beam 45

Cross Volume of Gaussian Beam 46

Surface of Cross Volume 47

Cross Volume and resolution 48

Scattering using Gaussian Beam Scattering Length 49

Scattered intensity and effective scattering length well scale top center bottom Scattered spectrum are fitted with offset-gaussian to subtract ECE background Intensity ratio of the scattered power well scales to the calculated effective scattering length 50

Comparison of Exp. / Cal. Spectrum Scattered Power (ev) 1000 100 10 Calculated CTS spectrum scattered radiation Measured data are used for calculation. T e =0.6keV T Ar =0.7keV n e =2.5x10 19 m -3 n fast =0.1x10 19 m -3 T i =0.7keV is better fitting than T i =2keV. Measured data seems to have an offset of +0.1GHz. P(3.6,0,0), R(3.6,0,0) 1-3 -2-1 0 1 2 3 Vsc=153.3cm 3 frequency (GHz) 51

Sub-Tera Hz Gyrotron Development 52

FIR FU f i > 4f ce suppression of ECE CTS in LHD 400 GHz band is one choice. Salpeter Parameter R along scattered wave path (m) Linked with slide 15

FIR FU Vk = 57 kv Achieved 50 kw From Notake PRL paper More than 50 kw at 349 GHz and about 40 kw at 390 GHz have been achieved. These are highest powers as second harmonic oscillation of gyrotron. Oscillation efficiency decreases for large beam current possibly due to degradation of the quality of the electron beam.

Future Plan Establish Calibration/Analysis procedure Scattering Volume CTS spectrum and reduction of ion/fast ion temperature Calibration including polarizer/waveguide coupling Multi receiver / fast volume scan Precise background subtraction Simultaneous measurement in 2-D velocity space Expansion in real/velocity space Sub-Tera Hz Gyrotron Application to CTS

LHD ECH Antenna used for probe and receiving beams 1.5L Antenna out 84 GHz in 84 GHz 1.25 inch corrugated WG 3.5 inch corrugated WG 9.5U Antenna out 82.7 GHz in 77 GHz 2-O Antenna right 77 GHz left 168 GHz waist size 0.03 m 0.8 MW/5s, 0.24 MW/CW 3.5 inch corrugated WG 3.5 inch corrugated WG 5.5U Antenna out 77 GHz 3 in 168 GHz 57

ECRH Horizontal Antenna for parallel component 2 sets of Focusing Mirror Symmetric Gaussian Beam 35 mm waist size at plasma center Steering Plane Mirror Toroidally +/- 30 degree Poloidally +/- 10 degree

Summary Started CTS utilizing ECRH system in LHD 77GHz ( P~1MW) Gaussian beam is used as a probe. Injection ECRH antenna is used as a receiver. Backward, perpendicular 8/32 channel receiver system is attached to ECRH transmission line 3 s, 50 Hz modulated injection at 0.7 MW Preliminary results with 8/32 channel show promising CTS signals 32 channel Higher reliability in ion velocity distribution reduction Examining possible use of horizontal antennas Backward, parallel components Sub-THz gyrotron developed for CTS in LHD