Radially resolved measurements of plasma rotation and flow-velocity shear in the Maryland Centrifugal Experiment

Abstract

In diagnosing the Maryland Centrifugal Experiment (MCX) [R. F. Ellis et al., Phys. of Plasmas 8, 2057 (2001)], earlier spectroscopic measurements of averaged plasma rotation velocities have been upgraded to include radial distributions, using a five-channel fiber-optic collection system. Detailed information from each view is now possible with an 8-times increase in spectral resolution, by using a 2m spectrograph and a 2400lines∕mm grating. Inversion of the integrated chordal radiation into a radial dependence of local emissions is performed by two methods: (a) an iterative simulation beginning with assumed emissions in five axially concentric cylindrical zones followed by summation along the five viewing chords, and (b) inversion of a combination of dual Abel-type matrices. The radial profiles of the absolute velocities derived cover a range from 20to70km∕s for both C+ and C++ impurity ions. Previous apparent differences in velocities between ions from a single chordal observation are now explained by the measured radial dependence of velocities and relative emissions. An important result is the first direct and quantitative measurement on MCX of a radial shear in rotational flow velocity as large as 9×105s−1, 9 times a threshold of 1×105s−1 for magnetohydrodynamic stability. Stark-broadened hydrogen Balmer-series spectral lines provide both a value for electron density of Ne=(8.5±1.5)1014cm−3 and supporting data for radial particle distributions.

Sub-Alfvénic velocity limits in magnetohydrodynamic rotating plasmas

“…In addition, there was evidence of some arcing. In previous MCX experiments [15][16][17][18]21 with various different insulator systems, there has always been strong carbon deposition without any accompanying degradation of the system, and arcs have been found to be isolated events. In this sense, the present experimental standards are consistent with previous experimental standards on MCX, and the results obtained in this campaign can be viewed with some confidence.…”

“…By comparing the relative intensity of spectral lines, an upper bound of the electron temperature was found at T e = 10 eV. 16 An important plasma parameter is the plasma momentum confinement time . This can be calculated using a simple zero-dimensional ͑0-D͒ model.…”

Evaluation of an Oxygen Transport Coefficient in the Aditya Tokamak Using the Radial Profile of O4+ Emissivity and the Importance of Atomic Data Used Therein

“…From the recorded spectra, the chord integrated brightness was obtained by integrating the fitted curve of the spectral line using a Gaussian profile. The radial emissivity profiles were obtained using an Abel-like matrix inversion technique [19] from the chord integrated brightness of O 4+ emissions. The details of this conversion have been described in the references [15,20].…”

Diamagnetism of rotating plasma

“…At the speeds observed ($100 km/s), drift orbit theory would predict the rotation speeds of CIII and H ions should be similar on account of the E Â B drift independence of ion mass and that curvature and gradient drifts are much smaller. 14 The first order correction to the E Â B drift, however, is of the order of q L /a, proportional to the carbon Larmor radius and inversely proportional to a radial scale a. This correction is dependent on mass and charge.…”