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J. Howard
MOSS spectrometer applications in plasma diagnostics
High Temperature Plasma Diagnostics, Princeton June, 1998
Abstract:
A new electro-optically Modulated Solid-State (MOSS) interferometer
has been constructed for measurement of
the low order spectral moments of line
emission from optically thin radiant media. The instrument,
which is based on the principle of the Fourier transform spectrometer, is
rugged, compact and inexpensive and offers a number of advantages over
conventional grating based spectrometers.
Most importantly, by employing electro-optical
path-length modulation techniques,
the spectral information is obtained using a single photomultiplier tube.
Specifically, the zeroth moment (brightness) is given by the
average signal level, the first moment (shift) by the modulation phase and
the second moment (line width) by the modulation amplitude.
In applications such as Zeeman spectroscopy and MSE,
polarization modulation can
be used to effect a modulation of the centre frequency
and/or coherence of the light which is then
measured by the MOSS spectrometer.
This paper describes a number of applications, including Doppler and
Zeeman spectroscopy and CXRS and MSE for which the MOSS spectrometer
is an inexpensive and powerful alternative to multichannel
grating spectrometers.
POSTER Gzipped PostScript (1280k)
PAPER Gzipped PostScript (490k)
PAPER Acrobat PDF
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J. Howard
Ion temperature and flow during confinement transitions
in the H-1 heliac
Presented at the 1997 Toki conference
on , Toki city, JAPAN '97.
Abstract:
The poster presents results of ion and atom temperature and
flow measurements on the H-1NF heliac obtained using a new
electro-optically modulated solid state (MOSS) spectrometer.
We present the instrument and indicate some possible
applications, including Zeeman, Doppler (CXRS) and MSE spectroscopy.
We show that the instrument measures directly
low order spectral moments of the emission and that these
quantites are related directly and
simply to line integrals of the underlying vector and scalar fields.
Finally, we show some results for discharges showing
transitions from low to high confinement in the H-1NF heliac at ANU
and examine the implications for radial force balance.
Gzipped PostScript (303k)
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J. Howard
Current profile diagnostics for NSTX
Presented at the 1997 Workshop on Current Profile Diagnostics for
NSTX, Princeton, August 1997.
Abstract:
The poster will look at two techniques: standard laser polarimetry and
Zeeman and MSE spectroscopy for current profile diagnostics on NSTX.
Though we mostly focus on spectroscopic techniques, in both cases,
the emphasis is on sensitive methods for
detection and analysis of experimental signals.
Spectroscopy has the advantage that it can be a passive measurement
requiring minimal access. However, light fluxes can be very
low requiring high efficiency instruments.
Laser polarimetry gives line-integrals of the electron
density and density-weighted parallel magnetic field.
An important issue is therefore the inversion/interpretation
of spatially integrated measurements. This is discussed briefly with
reference to tomography of vector fields.
For Zeeman and Doppler spectroscopy, we show that the
low order spectral moments are also related directly and
simply to line integrals of the underlying vector fields.
Gzipped PostScript (410k)
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J. Howard
Course notes for 4th year EE case study on TOMOSS - tomographic MOSS
spectroscopy system for H-1NF
Presented at the University of Canberra Oct. 1998
Abstract:
The course notes consist of five chapters, each separately
down-loadable below.
Beware that not all figures have been completed yet.
Chapter 1 (p 1-20): Controlled Fusion and H-1NF
Gzipped PostScript (3.57M)
Chapter 2 (p 21-44): Plasma Diagnostic Systems
Gzipped PostScript (906K)
Chapter 3 (p 45-60): The MOSS Optical system
Gzipped PostScript (561K)
Chapter 4 (p 61-74): Single channel MOSS spectroscopy on H-1NF
Gzipped PostScript (637K)
Chapter 5 (p 75-89): TOMOSS - The Tomographic MOSS plasma diagnostic system
Gzipped PostScript (504K)
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J. Howard
Optical coherence-based techniques
for motional Stark effect
measurements of magnetic field pitch angle
Plasma Physics and Controlled Fusion (1998)
Abstract:
Motional Stark effect measurement of magnetic field pitch
angle in tokamaks is a mature and powerful technique for
estimating plasma current density in tokamaks.
However, its range of applicability is limited by the
requirement that the $\sigma$ and $\pi$ manifolds be
spectrally sufficiently well separated (high magnetic fields,
high beam energies) to ensure adequate
nett polarization for a successful measurement.
This paper proposes alternative
schemes based on the optical coherence properties of the Stark
multiplet that are somewhat more versatile
than the standard method and better suited to measurements on
low field toroidal confinement devices. An interference
filter is used to transmit the Stark multiplet to a
polarimeter (which uses a single photoelastic plate) that
modulates the light temporal coherence and/or its first
spectral moment. This light is subsequently processed using a
a novel electro-optically modulated solid-state
interferometer that is sensitive to the low order spectral
moments. The modulation of these quantities
conveys information about the
orientation of the light polarization and hence the magnetic
field pitch angle.
See Plasma Physics and
Controlled Fusion, Vol 41, p271-284, 1999
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J. Howard, C. Michael, F. Glass
MOSS Spectrometer Application in Plasma Diagnostics
Abstract:
A new electro-optically Modulated Optical Solid-State
(MOSS) interferometer
has been constructed for measurement of
the coherence of line
emission from plasmas. The instrument,
which is based on the principle of the Fourier transform
spectrometer, has high etendue and is
rugged, compact and inexpensive.
By employing electro-optical
path-length modulation techniques,
the spectral information is obtained using a single photodetector.
This paper describes a number of applications, including
Doppler and polarization spectroscopy
(Zeeman and MSE) for which the MOSS spectrometer
is an inexpensive and powerful alternative to multichannel
grating spectrometers.
POSTER Gzipped PostScript (625k)
Powerpoint presentation (1.15M)
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J. Howard, C, Michael, F. Glass and A. Cheetham
Optical Coherence Techniques for
Plasma Spetcroscopy
Abstract:
A new electro-optically Modulated Optical Solid-State
(MOSS) spectrometer has been constructed for high temporal
resolution measurement of the coherence of line
radiation from plasmas. The instrument is a
polarization interferometer, or Fourier transform
spectrometer, electrooptically modulated about a fixed optical
delay. It has high light throughput compared with
conventional grating based instruments of comparable resolving power
while being compact and robust against alignment errors.
By employing electro-optical path-length modulation techniques,
the spectral information is transferred to the temporal
frequency domain and can be obtained using a single
photodetector. A wide field-of-view MOSS camera has been
developed for imaging apllications, while multiple-delay
variants of the basic single fixed delay instrument have also been
successfully tested.
We discuss applications including
passive Doppler spectroscopy,
charge exchange recombination spectroscopy and
Zeeman and motional Stark effects.
For Doppler tomographic applications,
we show that such time-domain
instruments have certain fundamental advantages, not least of
which is a simple relationship between fringe visibility and
the line-integral of the intensity weighted velocity
distribution function.
PAPER Acrobat PDF (2.4M)
PAPER Gzipped PostScript (2.48M)
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Overhead slides for HTPD presentation:
J. Howard, C, Michael, F. Glass and A. Cheetham
Optical Coherence Techniques for
Plasma Spetcroscopy
Slides 1-4 (50K)
Slides 5,6 (270K)
Slides 7,8 (346K)
Slides 9-12 (639K)
Slides 13-16 (2.07M)
Slides 17-20 (430K)
Slides 21-24 (1.47M)
Slides 25-28 (646K)
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