Publications of Proceedings for the RF 2005 7th Workshop on High Energy Density and High Power RF

The University of California, Davis hosted the High Energy Density and High Power RF 7th Workshop on High Energy Density and High Power RF in Kalamata, Greece, 13-17 June, 2005. The Proceedings cost was supported by these funds from the U.S. Department of Energy. The Proceedings was published through the American Institute of Physics

Highly efficient frequency triplers in the millimeter wave region incorporating a back-to-back configuration of two varactor diodes

This paper reports on the recent development of monolithic frequency tripler array employing a back-to-back configuration of varactor diodes. Even harmonic idler circuits are unnecessary in this design. Furthermore, no external dc bias is required. The arrangement results in highly efficient, easily-fabricated and inexpensive frequency triplers

Far-infrared imaging of tokamak plasma

A 20-channel interferometer has been developed which utilizes a linear, one-dimensional microbolometer array to obtain single-shot density profiles from the UCLA Microtor tokamak plasma. The interferometer has been used to study time-dependent phenomena in the plasma density profile. Observations of the sawtooth instability clearly show the growth of the m=0 mode from a localized oscillation (r=1 cm) on axis to an oscillation of the entire plasma. Also, measurements during the initial startup phase of the discharge show evidence of hollow density profiles. In addition, a simultaneous measurement of the poloidal magnetic field has been developed which provides 20 channels of polarimetry. Interferometry and polarimetry both use the same imaging system and the spatial resolution of both measurements has been tested using plastic and crystal-quartz test objects. The signal-to-noise ratio for the polarimeter has also proved adequate for the expected Faraday rotation angle (alphamax=7°, Ip=70 kA, n=5×10^13 cm^−3)

Millimeter and submillimeter wave technology developments for the next generation of fusion devices

There is increasing demand for compact watt-level coherent sources in the millimeter and submillimeter wave region. The approach that we have taken to satisfy this need is to fabricate two-dimensional grids loaded with oscillators, electronic beam steerers, and frequency multipliers for quasioptical coherent spatial combining of the outputs of a large number of low-power devices

Monolithic millimeter-wave diode grid frequency multiplier arrays

Monolithic diode frequency multiplier arrays, including barrier-N-N(+) (BNN) doubler, multi-quantum-barrier-varactor (MQBV) tripler, Schottky-quantum-barrier-varactor (SQBV) tripler, and resonant-tunneling-diode (RTD) tripler arrays, have been successfully fabricated with yields between 85 and 99 percent. Frequency doubling and/or tripling have been observed for all the arrays. Output powers of 2.4-2.6 W (eta = 10-18 percent) at 66 GHz with the BNN doubler and 3.8-10 W (eta = 1.7-4 percent) at 99 GHz with the SQBV tripler have been achieved

Observations of Reduced Electron Gyroscale Fluctuations in National Spherical Torus Experiment H-Mode Plasmas with Large E X B Flow Shear

Electron gyroscale fluctuation measurements in National Spherical Torus Experiment H-mode plasmas with large toroidal rotation reveal fluctuations consistent with electron temperature gradient (ETG) turbulence. Large toroidal rotation in National Spherical Torus Experiment plasmas with neutral beam injection generates ExB flow shear rates comparable to ETG linear growth rates. Enhanced fluctuations occur when the electron temperature gradient is marginally stable with respect to the ETG linear critical gradient. Fluctuation amplitudes decrease when the ExB flow shear rate exceeds ETG linear growth rates. The observations indicate that ExB flow shear can be an effective suppression mechanism for ETG turbulence.X1129sciescopu

Monolithic millimeter-wave diode array beam controllers: Theory and experiment

In the current work, multi-function beam control arrays have been fabricated and have successfully demonstrated amplitude control of transmitted beams in the W and D bands (75-170 GHz). While these arrays are designed to provide beam control under DC bias operation, new designs for high-speed electronic and optical control are under development. These arrays will fill a need for high-speed watt-level beam switches in pulsed reflectometer systems under development for magnetic fusion plasma diagnostics. A second experimental accomplishment of the current work is the demonstration in the 100-170 GHz (D band) frequency range of a new technique for the measurement of the transmission phase as well as amplitude. Transmission data can serve as a means to extract ('de-embed') the grid parameters; phase information provides more complete data to assist in this process. Additional functions of the array beam controller yet to be tested include electronically controlled steering and focusing of a reflected beam. These have application in the areas of millimeter-wave electronic scanning radar and reflectometry, respectively

Interferometric fir phase imaging of a tokamak plasma

Multichannel phase imaging of dielectric objects has been demonstrated in the laboratory using a microbolometer detector array and 400 GHz carcinotron radiation cource. The application of this imaging system to perform single shot measurements of electron density profiles in a tokamak plasma is described. The primary advantages are increased spatial resolution together with a much simpler optical system

DC and millimeter-wave performance of watt-level barrier-intrinsic-n+ diode-grid frequency multiplier fabricated on III-V compound semiconductors

This paper reports the fabrication and millimeter-wave performance of a new class of monolithic metal-semiconductor heterostructure devices, the Barrier- Intrinsic-N+ (BIN) diode-grid frequency multipliers, which are fabricated on III-V compound semiconductors. This work also involves the measurement of the DC and low frequency electrical properties of the BIN diode-grid frequency multiplier. In addition, a new analytical model which accurately describes the structure has been developed and is presented for the first time

Phase imaging systems for measurement of plasma density contours

During recent years, there has been considerable interest in obtaining spatially localized time resolved density measurements in fusion plasmas. However, the study of such phenomena requires many channels of information on a scale much finer than available with current discrete chordal view multichannel interferometers. These problems can be overcome by imaging an expanded probe beam occupying the entire plasma port crosssection onto a linear detector array [1], thereby significantly reducing the number of optical components and hence the cost and complexity of the system compared with a comparable discrete chord multichannel interferometer. Other more fundamental advantages of the imaging technique include compensation for phase errors due to plasma refraction, whilst the diffraction limited system resolution (typically ≃ 1cm for FIR probe wavelengths) allows the use of many detector channels for high spatial sampling rates. and hence accurate reconstruction of the density profiles