D. Y. Rhee

Microwave plasma continuous emissions monitor for trace‐metals in furnace exhaust

A microwave plasma continuous emissions monitor has been successfully demonstrated for sensitive (<1 ppb), real time measurements of trace metals in furnace exhaust. The instrument uses a robust, up to 1.5 kW, 2.45 GHz microwave plasma sustained in a portion of the undiluted furnace exhaust flow for atomic emission spectroscopy. The waveguide device is constructed of refractory materials compatible with high‐temperature environments (≳500 °C) and is flange mountable into the inside of the furnace exhaust duct. Fused quartz fiber optics in close proximity to the plasma flame transmit the UV through visible emission (190–690 nm) to three spectrometers for simultaneous monitoring of several metals. This instrument has been used for continuous monitoring for a 49 h period with 0.5 s time resolution on a dc graphite electrode arc furnace during a soil vitrification test. Results are presented for chromium, manganese, and iron emissions during soil loading operations.

Active millimeter-wave pyrometer

A 135 GHz heterodyne receiver with a rotatable graphite waveguide/mirror system has been implemented on a waste remediation direct‐current arc furnace for internal surface temperature measurements. The linear temperature measurement range extends from <1° to approximately 15,000 °C relative to ambient with a simultaneous capability to monitor surface reflectivity with the local oscillator leakage. Reliable and robust operation on a continuous 24 h basis in a smoky, dirty furnace environment is demonstrated for a total of five furnace runs reaching a maximum temperature of 2200 °C. Complete temperature profile measurements with approximately 5 cm spatial resolution clearly documented thermal gradients on the slag melt surface and refractory walls and ceiling for all operating regimes of the furnace. The unique active probing capability of this instrument provided additional real‐time information on melt surface turbulence, changing furnace wall emissivity, and millimeter‐wave optic losses inside the furnace.

Design of a third‐harmonic electron cyclotron emission diagnostic for ballooning mode fluctuations in PBX‐M

A third‐harmonic electron cyclotron emission diagnostic using ultrawide bandwidth (≊40 GHz) heterodyne receivers centered on 120 GHz with 14 channels per radial view is described for localized, long wavelength (5≲λ≲50 cm), fast time response (≊1 μs) fluctuation studies in the PBX‐M tokamak. The optically gray emission signal will have a γne/ne+(3/β)Te/Te dependence on temperature and density fluctuations where γ≤1 and 1≤β≤3 depending on local optical depth. Electron temperature fluctuation sensitivity is estimated to be 0.2%≤Te/Te ≤2.9% depending on local optical depth and fluctuation frequency in the 0.1–1 MHz range. Spatial resolution of approximately 3 cm radially and 5 cm vertically are estimated for 2 keV plasmas with low suprathermal electron emission.

Gyrotron collective Thomson scattering from plasma fluctuations in a Tara axicell

Collective Thomson scattering in the Tara Tandem Mirror axicell at MIT was accomplished with a 137-GHz, approx.0.4-kW, 75-ms pulsed gyrotron. Ion cyclotron waves, ion Bernstein wave harmonics, and other plasma fluctuations possibly due to microinstabilities and magnetohydrodynamic (MHD) activity have been observed during ion cyclotron resonance frequency (ICRF) heating. The observation of ion Bernstein waves may be due to an enhanced ion thermal fluctuation spectrum in an ICRF heated plasma.

Calculated collective Thomson scattered spectra from tokamak plasma with non‐Maxwellian ions

Theoretical scattered spectra from energetic ions in tokamak plasmas (TFTR and Alcator C‐Mod) are calculated. A new numerical code that calculates the collective Thomson scattered spectrum with a completely arbitrary distribution function was developed to model scattered spectra in ICRF heated and DT burning plasmas. Calculated spectra for nonthermal minority He3 ions in ICRF heated plasmas along with results from Maxwellian distributions are shown.

ITER millimeter-wave CTS diagnostic option

Localized alpha-particle velocity distribution and density, ion temperature, DT fuel ratio, and internal magnetic field pitch angle can all be potentially diagnosed by a collective Thomson scattering system. Relativistic electron cyclotron calculations and TORAY ray tracing for 6 tesla ITER parameters indicate that 90 GHz is an optimum frequency for this diagnostic. With 400 kW at the plasma and a 90/spl deg/ scattering angle, signal to noise ratios approaching 100 are possible for 0.5% n/sub e/, alpha-particle fractions and 100 ms integration times. A millimeter wave system would be robust and adaptable to the ITER environment and access.

Localized magnetic field pitch angle measurements by collective Thomson scattering

A novel new method is proposed to measure the internal magnetic field pitch angle in tokamaks by measuring the frequency of the lower hybrid resonance in the collective Thomson scattered spectrum. The resonance frequency has a dependence of 1.2 and 2.0 GHz/deg pitch angle for ITER and C‐MOD‐like plasma parameters, respectively, using a submillimeter‐wave diagnostic source. Sensitivity to other plasma parameters such as electron density, temperature, energetic ion fraction, and magnetic field is shown to be weak.

Development of high‐power millimeter and submillimeter wavelength collective Thomson scattering diagnostics for energetic ion measurements in tokamaks

High‐power, large‐angle (≳10°), collective Thomson scattering diagnostics can provide localized density and velocity distribution data of confined alpha particles, ICRH simulated alpha particles, and ions related to ICRH and neutral beam energy deposition. Millimeter‐wave gyrotron systems are under development for TFTR and JET. Scattering with a submillimeter gyrotron is being investigated for Alcator C‐Mod. Major design issues include plasma accessibility, scattering angle, orientation to magnetic field, spectra of non‐Maxwellian velocity distributions, signal‐to‐noise ratio, refraction, electron cyclotron emission, and beam and viewing dumps.

Performance evaluation of the TFTR gyrotron CTS diagnostic for alpha particles

A large‐angle, 60‐GHz collective Thomson scattering (CTS) diagnostic system for localized measurements of DT alpha‐particle velocity distribution and fraction is being implemented on TFTR. Calculations of expected CTS spectra, signal‐to‐noise ratio per receiver channel, and estimated error in determining the temperature and fraction of alpha particles are being carried out. The experimental spectra are simulated by adding noise to the theoretical calculation by a Monte Carlo technique. Error analysis is then performed by using a relative intensity calibrated nonlinear curve fitting code to calculate the desired plasma parameters (Ti, Tα, nα/ni). Simulation results indicate that expected background emission of 20 eV during Supershot in TFTR poses no problem to the experiment. Also short integration times (<10 ms) can be used to resolve the energetic ion features, thus offering a possibility for the study of temporal evolution of energetic ion velocity distribution during a single plasma shot.

Characteristics of gyrotron scattering system for α particle diagnostics in TFTR (abstract)

In D‐T plasmas, the understanding of the physics of confined α particles is extremely valuable for the future fusion plasma device. Among the various proposed α diagnostics, an X‐mode collective Thomson scattering system employing a high‐power gyrotron source (P≂200 kW, f=60 GHz, pulse length ≂0.5 s, and modulation frequency=10–25 kHz) is being designed for TFTR. The detailed description of the gyrotron source, transmission lines, optical designs, beam and viewing dump design, and receiver system will be presented in this paper. In particular, the test results of the beam and viewing dump indicate that the stray light can be reduced by 60 dB. The background emission level (∼20 eV) near 60‐GHz range during high Q discharge may also be reduced with beam and viewing dump further. The optical system is designed to measure the radial profile of α particles and to orient the incident wavevector (k0) to test the electromagnetic effects of the scattered spectrum. Prior to the study of α physics in D‐T plasmas, th...