Time-resolved%20Tomographic%20Spectroscopy%20System

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Time-resolved Tomographic Spectroscopy System for
H-1NF
F. Glass J. Howard
Plasma Research Laboratory Australian National
University
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Introduction

• Encouraged by results of a single-view Modulated
  Optical Solid State (MOSS) spectrometer.
• MOSS spectrometer is a robust, compact
  Fourier-transform device.
• The line-integrated measurement leans to
  tomography.
• Several challenges in implementing

-flexible emission collection system. - many
views -gt many spectrometers? - thorough
calibration. - interpretation of measurements
(tomographic inversions).
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Overview

• Goals

- create time-resolved images of emitted
intensity, ion temperature of a poloidal
cross-section. - initial estimates of bluk flow
speeds simultaneously from several directions. -
better estimate of force balance in H-1NF.

• System Design - Light Collection, Light
  Processing, Signal Analysis
• Calibration - spatial response, in-situ, MOSS
  spectrometer.
• Results - first data
• Future Work
• Conclusion

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System Design Light Collection

• Flexible system which optimises light throughput
  and maximises number of channels.
• Five 45 sectioned viewing modules mounted on
  800mm diameter rotatable wheel (200 rotation
  range).
• Each module - 11 parallel views embedded in
  module.
• Total of 55 angularly views channels.

• Each view

• coupling lens 15mm dia. 12.5mm aperture.
• mirror polished stainless steel, 11 different
  angles.
• optical fibre 1mm core dia., teflon jacketed,
  aperture restricted.

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System Design Light Collection

• Stray light reduction diffuse blackened
  stainless steel.
• thin sheet viewing dumps.
• optical fibre apertures.

• Rotation using external stepper motor gear set
  and internal sprocket engaging holes on wheel
  side.

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System Design Light Processing

• Fourier-transform device using optical
  solid-state modulation techniques.
• Measures line intensity, species' temperature
  and flow speed simultaneously.
• Time-resolved measurements on large number of
  channels.

• Input 8x8 array of fibres.
• Detection 8x8 multi-anode photomultiplier
  assembly.
• Issues

-detector cross-talk -instrument calibration
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Calibration Spatial Response

• Need to know where and how much the views are
  seeing.
• -gt tomography
• -gt insitu calibration
• Pre-installation scan
• thin fluorescent tube (3mm dia. 85Mm length)
  translated perpendicular to viewing chord.
• 10-15 locations along length of chord.
• chords scanned individually.
• all scans compiled to a 'generic' scan.
• Response curves characterised by Gaussian fit
  parameters
• -gt profile of height and width parameters.

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Calibration Insitu

• Remove variations between channels in total
  transmission.
• Compensate for any long term variaton.
• Understanding of stray light effects.
• 3 thin fluorescent tubes (3mm dia. 85Mm length)
  installed perpendicular to wheel's viewing plane.

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Calibration Insitu

• Measured calibration

• Simulated calibration

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Calibration MOSS Spectrometer

• Account for spatial variations in
  lithium-niobate crystal birefringence.
• Multi-anode photomultiplier assembly
  'cross-talk'.
• system is field-widened.
• laser light through an initial channel - measure
  intensity and contrast
• measure other channels individually and
  referenced to initial channel.
• Laser pulse -gt per shot baseline.

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Results First Data

• Argon plasma (488nm line).
• 48 active channels.
• Shows transition.

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Future Work

• Initial work on tomographic inversions to be
  completed
• poloidal cross-section images of intensity and
  ion temperature.
• Estimates of bulk flow speeds from several
  directions simultaneously.

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Conclusion

• Designed, manuactured and installed light
  collection and spectrometer sub-systems.
• Performed initial and insitu calibration of
  system.
• Obtained first data using argon discharge.
• Demodulated signals to give intensity and ion
  temperature time-evolution in 5 seperate views of
  plasma.