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Summary form only given. The levitated dipole experiment (LDX) is investigating a levitated dipole magnetic configuration as an alterative confinement concept for fusion plasmas. A 1.1 MA, 68 cm mean diameter, 560 kg superconducting coil (F-coil) is floated for up to 3 hours between cryogenic recoolings by a 280 kA levitating coil during which time plasmas are pulsed by electron cyclotron breakdown and heating (ECH). Up to a total of 15 kW ECH power from three sources at 2.45 (2.5 kW), 6.4 (2.5 kW), and 10.5 GHz (10 kW) are pulsed to sustain plasmas for up to 14 s with a slowly decaying afterglow detectable for over 20 s. Electron densities in the range of 10[superscript 11] cm[superscript -3] with highly peaked profiles (~1/r[superscript 4]) are diagnosed with a 4-channel 60 GHz interferometer. Significant hot electron synchrotron emission has been observed with two heterodyne radiometers, at 137 and 165 GHz, 3 GHz double sideband (DBS) each and noise temp, of 3000 and 2000 K DBS, respectively. The receivers' field of view (FOV) where combined by a 4-port corrugated Al waveguide beamsplitter (quartz) block and transmitted in HE[subscript 11] mode by a 35 mm dia., 1.1 m long ceramic waveguide to a quartz vacuum widow (>95% trans, at 137 & 165 GHz) located below the F-coil. About 9 dB attenuation was necessary in the waveguide to avoid receiver saturation. The radiometer views were directed vertically upward 28 cm from the dipole axis in X-mode orientation. A 2.3 m distance from window to plasma peak resulted in 1/e[superscript 2] plasma FOV diameters of 29 and 24 cm at 137/165 GHz, respectively. Equivalent blackbody temperatures at 137/165 GHz as high as 620/410 eV were observed at the vacuum window during sustained plasma operation, dropping to about 110/60 eV within 1 s at the start of the afterglow and then deceasing exponentially to 0.2/0.1 eV about 24 s later. These are lower limits for the actual peak plasma emission because the receiver FOVs aren't uniformly, United States. Dept. of Energy

Millimeter waves are ideally suited for sensing and diagnosing materials, devices, and processes that are broadly important to energy, environment, and national security. Thermal return reflection (TRR) techniques that detect and use thermal emission as a probe to diagnose materials and systems make possible accurate noncontact thermal analysis measurements that can resolve emissivity and temperature simultaneously. Scientific basis of TRR, 2-D and potentially 3-D measurements, and applications of TRR are discussed.

An experimental study of picosecond pulse amplification in a gyrotron-traveling wave tube (gyro-TWT) has been carried out. The gyro-TWT operates with 30 dB of small signal gain near 140 GHz in the HE06 mode of a confocal waveguide. Picosecond pulses show broadening and transit time delay due to two distinct effects: the frequency dependence of the group velocity near cutoff and gain narrowing by the finite gain bandwidth of 1.2 GHz. Experimental results taken over a wide range of parameters show good agreement with a theoretical model in the small signal gain regime. These results show that in order to limit the pulse broadening effect in gyrotron amplifiers, it is crucial to both choose an operating frequency at least several percent above the cutoff of the waveguide circuit and operate at the center of the gain spectrum with sufficient gain bandwidth., National Institute of Biomedical Imaging and Bioengineering (U.S.) (Contract No. EB001965), National Institute of Biomedical Imaging and Bioengineering (U.S.) (Contract No. EB004866), National Institutes of Health (U.S.)

The ITER transmission lines (TLs) must be designed to deliver 20 MW from a 24 MW, 170 GHz gyrotron system. Miter bends are the main source of loss for these highly overmoded, corrugated, cylindrical waveguide TLs. Previous estimates have used only a pure HE[subscript 11] mode for the analysis of the loss due to a miter bend, however higher order modes (HOMs) must be considered for a practical analysis. For the linearly-polarized, Gaussian-like beam from a gyrotron, the LP[subscript mn] mode basis set should be used to describe the fields in the corrugated waveguide. The HOM content greatly affects the propagation of HE[subscript 11] content in a miter bend, with a large emphasis placed on the percentage of HOMs and the phase difference between HE[subscript 11] and each HOM. By considering LP modes, a complete basis set is used to investigate the HOM effects on HE11 loss in a miter bend. We also present a new conservation theorem relating the power centroid offset and propagation angle due to any two LP[subscript mn] modes propagating in the corrugated waveguide.

The design and experimental study of a 140 GHz, 1 kW gyro-traveling wave tube (Gyro-TWT) operating in the HE[subscript 06] mode of a confocal waveguide is presented. A combination of quasioptical gain sections with dielectric loaded severs enables high gain operation with mode selectivity. A nanosecond-scale 120 mW pulse driver at 140 GHz was demonstrated. This input driver pulse will be amplified by the Gyro-TWT and the resulting output high-power short pulse will be transmitted to an EPR spectrometer probe. A quasioptical mode converter utilized to transform the higher order operating confocal mode into a Gaussian-like beam was designed and cold tested. The simulated and measured Gaussian beam patterns of the output mode converter are in good agreement., National Institute of Biomedical Imaging and Bioengineering (U.S.) (Contract EB001965), National Institutes of Health (U.S.)

The design and experimental study of a 140 GHz, 1 kW gyro-traveling wave tube (Gyro-TWT) operating in the HE[subscript 06] mode of a confocal waveguide is presented. A combination of quasioptical gain sections with dielectric loaded severs enables high gain operation with mode selectivity. A nanosecond-scale 120 mW pulse driver at 140 GHz was demonstrated. This input driver pulse will be amplified by the Gyro-TWT and the resulting output high-power short pulse will be transmitted to an EPR spectrometer probe. A quasioptical mode converter utilized to transform the higher order operating confocal mode into a Gaussian-like beam was designed and cold tested. The simulated and measured Gaussian beam patterns of the output mode converter are in good agreement., National Institute of Biomedical Imaging and Bioengineering (U.S.) (Contract EB001965), National Institutes of Health (U.S.)

We applied millimeter wave radiometry for the first time to monitor water-freezing and ice-melting dynamics in real-time non-contact. The measurements were completed at a frequency of 137 GHz. Small amounts (about 2 mL) of freshwater or saltwater were frozen over a Peltier cooler and the freezing and melting sequence was recorded. Saltwater was prepared in the laboratory that contained 3.5% of table salt to simulate the ocean water. The dynamics of freezing-melting was observed by measuring the millimeter wave temperature as well as the changes in the ice or water surface reflectivity and position. This was repeated using large amounts of freshwater and saltwater (800 mL) mimicking glaciers. Millimeter wave surface level fluctuations indicated as the top surface melted, the light ice below floated up indicating lower surface temperature until the ice completely melted. Our results are useful for remote sensing and tracking temperature for potentially large-scale environmental applications, e.g., global warming.