I.N. Bogatu

Design and fabrication of a multi-purpose soft x-ray array diagnostic system for KSTAR

A multi-purpose soft x-ray array diagnostic system was developed for measuring two-dimensional x-ray emissivity profile, electron temperature, Ar impurity transport, and total radiation power. A remotely controlled filter wheel was designed with three different choices of filters. The electron temperature profile can be determined from the ratio of two channels having different thickness of Be layer, and the Ar impurity concentration transport can be determined from a pair of Ar Ross filters (CaF(2) and NaCl thin films). Without any filters, this diagnostic system can also be used as a bolometer.

Electron cyclotron resonance charge breeder ion source simulation by MCBC and GEM

Numerical simulation results by the GEM and MCBC codes are presented, along with a comparison with experiments for beam capture dynamics and parameter studies of charge state distribution (CSD) of electron cyclotron resonance charge breeder ion sources. First, steady state plasma profiles are presented by GEM with respect to key experimental parameters such as rf power and gas pressure. As rf power increases, electron density increases by a small amount and electron energy by a large amount. The central electrostatic potential dip also increased. Next, MCBC is used to trace injected beam ions to obtain beam capture profiles. Using the captured ion profiles, GEM obtains a CSD of beam ions. As backscattering can be significant, capturing the ions near the center of the device enhances the CSD. The effect of rf power on the beam CSD is mainly due to different steady states plasmas. Example cases are presented assuming that the beam ions are small enough not to affect the plasma.

Soft x-ray virtual diagnostics for tokamak simulations

The numerical toolset, FAR-TECH Virtual Diagnostic Utility, for generating virtual experimental data based on theoretical models and comparing it with experimental data, has been developed for soft x-ray diagnostics on DIII-D. The virtual (or synthetic) soft x-ray signals for a sample DIII-D discharge are compared with the experimental data. The plasma density and temperature radial profiles needed in the soft x-ray signal modeling are obtained from experimental data, i.e., from Thomson scattering and electron cyclotron emission. The virtual soft x-ray diagnostics for the equilibriums have a good agreement with the experimental data. The virtual diagnostics based on an ideal linear instability also agree reasonably well with the experimental data. The agreements are good enough to justify the methodology presented here for utilizing virtual diagnostics for routine comparison of experimental data. The agreements also motivate further detailed simulations with improved physical models such as the nonideal magnetohydrodynamics contributions (resistivity, viscosity, nonaxisymmetric error fields, etc.) and other nonlinear effects, which can be tested by virtual diagnostics with various stability modeling.

C60-fullerene composite plasma jets formation and acceleration for application to disruption mitigation and magneto-inertial fusion

We present the progress on the development of a new idea of using high-Mach number high-density composite plasma jets from coaxial plasma guns for disruption mitigation in tokamak¹ and magneto-inertial fusion² (MIF). The key element of the idea is the solid state pulsed power source with TiH<inf>2</inf> (or TiDT) grains and C<inf>60</inf> micron size powder³. Very fast injection of the molecular gas mixture provided by hydrogen release and sublimation of C<inf>60</inf> into the plasma gun is achieved by a special filter grid with supersonic Laval nozzles. The estimations based on the physical models of TiH2 grains heating, C<inf>60</inf> powder sublimation, molecular gas injection, mass separation, and plasma slug acceleration will be detailed. For disruption mitigation, our calculations show that the plasma gun is able to provide the required impurity mass¹ (∼1–2 g) and the ram pressure to penetrate the tokamak hot plasma and to overcome the confining magnetic field pressure. Core tokamak plasma penetration can be achieved and impurity mass delivered in less than 1 ms, as required by ITER tokamak. The magnetized target fusion (MTF) plasma for MIF is created by injecting two high-Mach number (M≫5) high-density (≫1017 cm⁻³) plasma jets composed of fuel (D-T) and “pusher” (C<inf>60</inf>/C) along the axis of a pulsed magnetic (∼1–2 T) mirror into a metallic cylindrical liner. The high-density (∼10¹⁸ cm⁻³) cylindrical MTF created by head-on collision and stagnation in the magnetic field is compressed radially by the Z-pinch of the liner and prevented to expand axially by the incoming C<inf>60</inf>/C end-plugs. We estimated that, due to the much longer MTF axial dimension (∼30 cm) as compared to other inertial confinement fusion plasmas, the electron thermal conduction time to the C<inf>60</inf>/C end-plugs is longer than liner implosion time.