MOSS Spectroscopy Applications in Plasma Physics John Howard

MOSS Spectroscopy Applications in Plasma Physics John Howard Plasma Research Laboratory Australian National University

Outline • MOSS spectrometer – Principle – Doppler measurements on H-1 • Polarization Spectroscopy – Zeeman effect and MSE • Spread spectrum FTS • Imaging systems

Fourier Transform Spectroscopy

MOSS Spectrometer Concept Instrument

Advantages of MOSS • High light throughput • High time resolution • Compact, robust MOSS is optimum in the sense that all photons contribute to three independent pieces of information - intensity, shift and contrast. DC Light intensity atan(odd, even) Flow velocity (shift) sqrt(odd 2+even 2) Temperature (contrast)

MOSS Hardware

MOSS spectroscopy on H-1 Lines of sight Central ring conductor Plasma cross section Fringe contrast versus time delay Ar. II 488 nm, Ti=10, (10), 100 e. V Nominal delay for Li. Nb. O 3 ( 25 mm)

L-H Confinement Transitions

Heat Modulation Experiments

Fluctuation Measurements

Polarization Spectroscopy Zeeman Effect. Relative intensity The Zeeman components are spectrally shifted and circularly polarized when viewed parallel to B. The nett circular polarization is a measure of the intensity weighted longitudinal component of the B field. Total lineshap e RHCP Normalized wavelength LHCP

Polarization Spectroscopy By filtering/modulating the polarization state of the plasma light using a spherical quadrature polarimeter, either the coherence (bandwidth) or centre of mass of the spectral line can be varied. The MOSS spectrometer senses these modulations as contrast or phase variations of the interferometer fringes. Spherical quadrature polarimeter

Polarization Spectroscopy Motional Stark Effect. H or D atoms in a heating beam experience an induced electric field E= v x B that generates a complex spectrum. Viewed transverse to E the Stark split s and p components are polarized respectively perpendicular and parallel to E. Combined polarimeter/MOSS system for MSE measurements

Spread Spectrum FTS

Imaging systems Multiple spatial channels can be multiplexed through an imaging MOSS spectrometer while maintaining high light throughput and low instrument temperature. Multiple-crystal modulators can be employed for truly 2 -D spectral imaging: the spectrum at each spatial position is encoded in the temporal frequency domain.

Spread spectrum data at 587 nm He. I Plasma light Calibration laser pulse Laser interferogram time (ms) Power spectrum of interferogram

Conclusion • MOSS spectroscopy is a high throughput alternative to traditional grating spectrometers • Well suited to plasma Doppler and polarization spectroscopy • Fully 2 -D spectral imaging is possible. • Facilitates tomography of scalar (intensity) and vector (velocity) fields in H-1 NF force balance, fluctuation and particle/heat modulation studies