Volume 77, Issue 10, October 2006
Index of content:
- NUCLEAR PHYSICS, FUSION AND PLASMAS
77(2006); http://dx.doi.org/10.1063/1.2356851View Description Hide Description
Time-resolved two-dimensional (2D) velocity maps have been derived for fluctuation measurements in the edge plasma of the National Spherical Torus Experiment (NSTX). The maps have been derived from time sequences of 2D images recorded with the gas puff imagingdiagnostic. A hybrid technique combining optical flow and local pattern matching has been implemented to overcome the individual limitations of each when used with data of limited temporal and/or spatial resolution. Local flowvelocities of up to and average poloidal flowvelocities of up to are found. Results are compared to previous velocity extraction techniques and NSTX results.
77(2006); http://dx.doi.org/10.1063/1.2354568View Description Hide Description
A laser interferometer provides detailed time resolved information about the spatial distribution of the plasma density of field reversed configurations (FRC’s) produced by the FRX-L experiment at Los Alamos National Laboratory. This experiment is an effort to produce a magnetized plasma with closed field lines suitable for compression by a solid metal liner imploded by the Shiva Star capacitor bank at the Air Force Research Laboratory. The interferometer probes a fanned array of eight chords through the FRC midplane, measuring the line integrated free electron density via its effect on optical phase shift relative to eight reference beams as a function of time. The reference beams are given nominally identical optical paths, except that they are folded for compactness and given an higher optical frequency by use of a Bragg cell beam splitter. After the beams are recombined, interference results in electromagnetic beat waves with dynamic phase shifts equal to those of the corresponding optical probes. Quadrature mixing of the electronically monitored light is then performed with rf components. Noteworthy features of the interferometer’s design are the unique compact folding scheme of the reference paths, inclusion of a fused quartz tube in the reference path similar to that of the FRC’s vacuum vessel to compensate for cylindrical lensing, and transmission of the interfering light via optical fibers to a rf shielded room for processing. Extraneous contributions to the phase shift due to vibration resulting from the system’s pulsed magnetic field, and dynamic refractive changes in or near the fused quartz tube wall (possibly due to radiation heating) are corrected for.
77(2006); http://dx.doi.org/10.1063/1.2362720View Description Hide Description
This article presents an experimental system that controls the automatic measuring procedure for the electromagnetic and optical diagnosis of a surface wave discharge by using a LABVIEW virtual instrument. The system also processes the measured data to determine some parameters that characterize the plasma, based on previously developed techniques. The structure of the system is implemented in such a way that permits the diagnosis of the surface wave discharges in both continuous and pulsed modes. The system has been tested and validated in a cylindrical discharge but it can be used to carry out measurement in a coaxial configuration too.
77(2006); http://dx.doi.org/10.1063/1.2214695View Description Hide Description
Alcator C-Mod’s lower hybrid current drive (LHCD) system allows the exploration of advanced tokamak (AT) regimes at densities relevant to ITER and fusion reactors. The location of the LHCD is critical to AT performance and may be inferred by measuring the nonthermal bremsstrahlung emission in the hard x-ray(HXR) region. A pinhole camera using an array of 32 CdZnTe detectors is used to image energies in the range. Detectors and pulse processing electronics are integrated into a compact and modular package making extensive use of printed circuit board and surface mount technology. The system also makes use of fast digitization and software signal processing techniques. An ambient environment of neutrons, gammas, and high rf power requires careful shielding. Shielding is studied using the neutron and photon transport code MCNP. The design of the diagnostic is presented along with background measurements in lieu of LHCD fast electrons. Background measurements are then compared to advanced modeling results to predict the power threshold for meaningful HXR data for a H-mode target plasma.