Samuel Andreason

Visible bremsstrahlung tomographic diagnostic for the pulsed high density field-reversed configuration experiment

A diagnostic suite for the source section of the pulsed high density field-reversed configuration (FRC) experiment has been constructed to investigate the equilibrium and stability of FRC plasmas. In particular, a visible bremsstrahlung tomographic system has been designed and implemented. Three types of tomographic analyses for FRCs are performed: a Fourier fit method (Cormack-Granetz), a maximum entropy method, and a minimum Fisher method utilizing code developed for the TCV tokamak experiment in Switzerland [Anton et al., Plasma Phys. Controled Fusion 38, 1849 (1996)]. Results from the different methods and end-on imaging from the fast-framing camera are compared showing relative agreement of FRC internal structures between all measurements.

Experimental apparatus for studying rotating magnetic field current drive in plasmas

This article describes the design and operation of an experimental apparatus that was constructed for studying rotating magnetic field (RMF) current drive in plasmas formed in a metal vacuum chamber. The device was designed to enable the study of various RMF coil geometries that are fully enclosed inside the vacuum chamber. To date, the apparatus has been used with three distinct RMF coil geometries, one of which was fully immersed in the RMF-driven plasma.

Plasma resistivity profile measurement from an external radio-frequency magnetic coil

Plasma resistivity is obtained by measuring the change in circuit behavior from a simple loop placed externally to the plasma. The loop is part of a series-driven oscillator that can be tuned over a wide range of frequencies with a very low internal impedance. By varying the frequency, and observing both the detuning and loading of this circuit, the location and resistance of the screening currents can be determined. A two-dimensional resistive magnetohydrodynamic code calculation is performed to obtain both the plasma interaction with the oscillating field as well as the effects of nearby conductors. The plasma resistance in the numerical calculations is adjusted to match the data from the experiment and, in this way, obtain a measure of the plasma resistivity profile.

Internal probe array for the measurement of radial electric field

A multipoint radial electric field probe, paired with a Langmuir triple probe has been operated on a RF sustained field reversed configuration. Langmuir probe measurements confirm the approximation that Te(r)∼constant, allowing for simpler interpretation of the floating potential, and the probe array was implemented with nonemissive, floating probes. Due to the large antenna potentials (multi-kilovolts), the electric field probe was designed taking advantage of the development of inexpensive, multichannel, portable digital storage oscilloscopes. This also made it possible to operate the internal plasma diagnostic with a minimum of electrical design work and fewer calibration issues. The diagnostic was electrically isolated (floated) separate from experiment ground, and has been used to measure transient electric fields as large as 2.5 kV/m.

High Power Pseudospark Switches for Pulsed Power

Summary form only given. Cold cathode thyratrons, or pseudospark switches (PSS), have been developed which combine the best qualities of classical heated cathode thyratrons, spark-gaps and mercury ignitrons. Russian researchers and manufacturers have developed sealed, commercially suitable, high-power closing switches designated as TDI-thyratrons. TDI thyratrons form an internal high density glow discharge and are capable of switching tens of Coulombs per shot. Compared to spark-gaps, PSS enjoy longer service life (up to 2-3 orders), a wider range of operating voltage, high stability of electrical and temporal features, opportunity of parallel operation of several devices into a low impedance common load.