UCLA's Role in the NSTX Research Program

The National Spherical Torus eXperiment (NSTX) has opened up a wide range of exciting new physics research avenues and plasma operating regimes within the overall US Fusion Energy Science Program. In particular, the study of a high beta, high performance plasma in the unique magnetic geometry of a spherical torus (ST) provides significant insight into transport, stability and wave-particle physics issues which benefit not only the ST concept but fusion science in general. 

UCLA has been an active NSTX team member since 1999 and contributes to both the operation and understanding of the NSTX plasma through application of a range of cross-cutting measurement techniques. UCLA contributes to the NSTX Research program as described below:

• UCLA develops, operates and maintains an array of millimeter-wave plasma measurement systems. These include an array of reflectometers for measurement of density profiles, internal magnetic field, plasma flow, MHD activity, Alfven wave structure, and turbulence characteristics; a 1 mm interferometer/scattering system for study of line-integrated density and low-wavenumber turbulence, and a microwave backscattering system for the study of high-k turbulence. 

• In the research arena UCLA performed the first local measurements of density turbulence spectra and density turbulent correlation length in the core of a spherical torus plasma. In addition, local internal observation of fast-particle driven Alfven modes has led to the first unambiguous identification of nonlinear three-wave interactions between low frequency/low toroidal mode number energetic particle modes and high frequency/high toroidal mode number modes.

• Microwave back-scattering has recently been installed to study short wavelength turbulence (e.g. electron temperature gradient (ETG) driven modes) predicted to dominate the core of NSTX. This approach strongly discriminates against observation of the large amplitude, long wavelength ITG-like turbulence typically observed in fusion plasmas.

•  In the future a radially viewing, polarimetry/interferometry system will be installed to determine current density on axis (i.e. J_o(t)) and study long wavelength magnetic and current fluctuations for both coherent and potentially turbulent modes. This system will provide a wealth of information on both current profile evolution (by providing a constraint in EFIT) and magnetic/current fluctuations.

The technique has been developed and demonstrated by UCLA on the MST reversed field pinch and is now ready for transfer to a high beta ST where magnetic fluctuations are prevalent and potentially play a critical role.

Presentations

Radial and Poloidal Correlation Reflectometry for NSTX:

            S. Kubota
            11th EU-US TTF Workshop, September 4-7, 2006, Marseille, France

Using Microwaves to Study Fast Particle Driven Modes in Burning Plasmas:

Tony Peebles
Burning Plasma Organization Workshop, Oak Ridge, TN December 2005

Coherent & Turbulent Fluctuation Measurements on NSTX Using Millimeter-Wave Reflectometry:

S. Kubota
48th Annual Meeting of Division of Plasma Physics, American Physical Society, October 30-November 3, 2006, Philadelphia, PA

Three-wave Interaction of Fast Ion Driven Modes in NSTX:

N.A. Crocker
Presented at the 47th Annual, APS Division of Plasma Physics Meeting
Denver, CO Oct 24-28, 2005

Millimeter-Wave FM-CW Reflectometry on NSTX:

S. Kubota, W. A. Peebles, X. V. Nguyen

Publications

Three-Wave Interactions between Fast-Ion Modes in the National Spherical Torus Experiment:

N. A. Crocker, W.A. Peebles, S. Kubota, E. D. Fredrickson, S. M. Kaye, B. P. LeBlanc, and J. E. Menard
PRL 97, 045002 (2006)

Fast ion loss in a 'sea-of-TAE':

E.D. Fredrickson, N.N. Gorelenkov, R.E. Bell1, J.E. Menard, A.L. Roquemore, S. Kubota, N.A. Crocker and W. Peebles
Nucl. Fusion 46 (2006) S926-S932

S. Kubota, W. A. Peebles, X. V. Nguyen, N. A. Crocker, A. L. Roquemore
Review of Scientific Instruments 77, 10E926, 2006

Progress toward a practical magnetic field diagnostic for low-field fusion plasmas based on dual mode correlation reflectometry:

M. Gilmore, W. A. Peebles, S. Kubota, X. V. Nguyen and A. Ejiri
Review of Scientific Instruments Volume 74, Number 3, 1469-1472

Automatic profile reconstruction for millimeter-wave frequency-modulated continous-wave reflectometry on NSTX:

S. Kubota, W. A. Peebles, X. V. Nguyen, A. L. Roquemore
Review of Scientific Instruments Volume 74, Number 3, 1477-1480