Present Status of the Nd:YAG Thomson Scattering System Development for Time

Evolution Measurement of plasma profile on Heliotron J

Takashi Minami, Shohei Arai, Naoki Kenmochi, Hiroaki Yashiro, Chihiro Takahashi, Shinji Kobayashi, Tohru Mizuuchi, Shinsuke Ohshima, Satoshi Yamamoto, Hiroyuki Okada, Kazunobu Nagasaki, Yuji Nakamura,

Kiyoshi Hanatani, Shigeru Konoshima , Fumimichi Sano Institute of Advanced Energy, Kyoto University, Gokasho, Uji 611-0011, Japan

2011.11.3 APFA20112011.11.3 APFA2011

Outline

•Introduction of Heliotron J•Recent results•SMBI Experiments•Plasma startup without ECH

•Nd:YAG Thomson scattering•Introduction•Design overview for collective optics•polychromator•present status of development

•Summary

ITER

FFHR HSR SPPS

Compact Reactor

A steady-state, compact,

high-β helical reactor- No disruptions (currentless operation)- No close conducting wall or

active feedback control of instabilities

(no serious MHD instabilities)- High Qeng (= net Pele. / Poper. )

(at minimum recirculating powers)

- High power density (3~4 MW/m2 under the

development of advanced wall materials)

Heliotron J Project Aims To Develop Attractive Compact Fusion Reactor

Heliotron J Device•Major Radius: R=1.2 m•Plasma Minor Radius: a=0.1-0.2 m•Magnetic Field: B 1.5 T≦•Vacuum iota: 0.3-0.8 with low magnetic shearHeating System:•ECH 0.4MW•NBI 0.8MW•ICRF 0.4MW•Magnetic coil system :

•one l/m=1/4 continuous helical coil•two sets of toroidal coils•three pairs of vertical field coils

Typical plasma parameters; ne=0.2-4 x 1019 m-3

Te=0.3-1 keVTi=150-200 eV

Inner Vertical Coil

Toroidal Coil A

Outer Vertical Coil

Toroidal Coil BHelical Coil

PlasmaVacuum Chamber

SMBI Has Extended Operational Regime• The stored energy reached Wp~4.5 kJ for ECH(~0.35 MW)+NBI(~0.6 MW), about 50% higher than that of conventional

gas-puff fueling. • The optimization study of SMBI-relevant operation scenario is in

progress.

Mizuuchi, Contribution to Plasma Physics 50 (2010) 639

NBI Plasmas Have Been Successfully Started Up By Assist of 2.45GHz 5kW Microwaves

•Plasmas of ne=1x1019 m-3 have been successfully produced 20msec after NBI turn-on with assistance of 2.45GHz 5kW microwaves

•No high-power ECH is applied

•Plasma startup without ECH widely will extend the operation region

•High β experiment•B dependence of confinement•B dependence of high-energy particles

•Extension of configuration•Off-axis 70GHz ECH

Kobayashi, Nucl. Fusion 51 (2011) 062002

Production of Low-Density Plasma and High-Energy Electrons by 2.45GHz Microwaves is Important

No density build-up

• There is no EC resonance for 2.45GHz microwaves• Plasma is successfully started up when ECE intensity exceeds a critical value

Objective for Construction new Nd:YAGThomson

•Previous experiments show the improved confinements phenomena accompany with the transient phenomena. The plasma profile is rapidly changed by the transition.

•Therefore, the time evolution of the plasma profile should be measured to understand the physics of the improved confinement.

•For this purpose, we are developing new Nd:YAG Thomson scattering system for Heliotron J device.

Design of Heliotron J Nd:YAG Thomson system

• Goal: Performance

• Spatial resolution ~1cm

• Spatial channels : 25

• Time intervals of measurement ~10ms (Period of discharge ~200ms,confinement time~1-10ms)

• Range of Te 10eV-10keV

• Range of ne >0.5x1019m-3

• Nd:YAG Laser spec

• 100Hz (50Hz two lasers), 550mJ 10ns pulse by Continuum.inc.

• We have a future plan to improve time interval to ~5ms (2 lasers->4 lasers)

Schematic of YAG Thomson Scattering system

Design of Scattered Light Collective System

Dimeter: 800mm F/2.25

20 度

(mm)

(mm

) Scatter volume imageconcave mirror

Scattered angle:20deg.

25 spatial points->resolution ~10mm Image length:14cmScattered angle: 20degreeLaser Length inside plasma: 25-

30cmMagnification: 0.3-0.5

Large concave mirror is used for large solid angleHigher F number for low aberration

Solid angle and aberration✓Large solid angle: 0.08-0.1str.=>Considerable scattered light can be collected

✓Back scattered light is small due to small backward region.=>Good S/N ratio

✓Aberration (<3mm) is small due to larger F number (Fiber width ~3mm)

✓It is easy to choose optical fiber, because required fiber NA(numerical aperture) is >0.25.

✓Uniform optical characteristic for all spatial points

>80mstr

<3mm

~0.25

6 channel Interference PolychromatorPolychromator

•Wavelength channel 5ch.•Rayleigh channel 1ch.

•Interference filter•Relay lens•Detector•Avalanche photo diode -Hamamatsu photonics: S8890-30,[area: 3Φ]•Bias: High voltage regulator with temperature control•Preamplifier is made by JFET input OP amplifier.

APD

HV regulator

Amplifier performanceSignal response by SPICE Circuit Simulator

ADA4817

Output signalof preamplifier Gate width 60ns-80ns

APD signal

Time

manufacturer Cin(F) G.B.(MHz)

S.R.(V/μs)

Iout(mA)

en(nV/√Hz)

ADA4817 Analog Devices 1.5p 410 870 70 4n

OPA627 Texas Instruments 8p 16 55 45 4.5n

LF356 National Semiconductor 3p 5 12 5 12n

Design for Filter Combination of Polychromator

Filter Combination•Ch1(FIlter1) : 700-845nm•Ch2(FIlter2) : 845-960nm•Ch3(FIlter3) : 960-1025nm•Ch4(FIlter4) : 1025-1050nm•Ch5(FIlter5) : 1050-1060nm

•Te : 10-10keV ne: 3x1019m-3

•Error from bremsstrahlung is below 2% for Te and 3% for ne

•Filter set optimization using modeling code.

>80%

Development of Data Acquisition System for Fast SIgnal

PolychromatoPolychromatorsrs

25x6ch.25x6ch.=150ch.=150ch.

V792 QDCV792 QDC32ch.x532ch.x5

CINOSCINOSControllerControllerMemoryMemory

VMEVMECAMACCAMAC

Heliotron JHeliotron JFedoraFedoraLinuxLinux

Data baseData base

CAEN V79232 Channel Multi-event QDC （ Charge-to-Digital Conversion)VME bus system based on CHS CINOS system

V792

CINOS

Movie:Manufacturing new port on Heliotron J

Outer Port

Inner Port

New Heliotron J port for Nd:YAG Thomson

Window for scattered light(30cm)

Laser injection port

Heliotron J

New Nd:YAG Thomson Scattering Stage

Summary• To investigate the relation between the plasma profile and the

improved confinement on Heliotron J. We develop the new Nd:YAG Thomson scattering system.

• Spatial resolution ~1cm

• Spatial channels : 25

• Time interval of measurement ~10ms

• Range of Te 10eV-10keV

• Range of ne >0.5x1019m-3

• Laser optics, Collection optics for scattered light (Concave mirror, optical fiber bundles), Polychromator (filter combination, relay lens, preamplifier), Data acquisition system are developed.