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We report the measurement of small losses in transmission line (TL) components intended for high-power millimeter-wave applications. Measurements were made using two different low-power techniques: a coherent technique using a vector network analyzer (VNA) and an incoherent technique using a radiometer. The measured loss in a 140 GHz 12.7 mm diameter TL system, consisting of 1.7 m of circular corrugated waveguide and three miter bends, is dominated by the miter bend loss. The measured loss was 0.3 ± 0.1 dB per miter bend using a VNA; and 0.22 ± 0.1 dB per miter bend using a radiometer. Good agreement between the two measurement techniques implies that both are useful for measuring small losses. To verify the methodology, the VNA technique was employed to measure the extremely small transmission loss in a 170 GHz ITER prototype TL system consisting of three lengths of 1 m, 63.5 mm diameter, circular corrugated waveguide and two miter bends. The measured loss of 0.05 ± 0.02 dB per miter bend may be compared with the theoretical loss of 0.027 dB per miter bend. These results suggest that low-power testing of TL losses, utilizing a small, simple TL system and a VNA, is a reliable method for evaluating performance of low-loss millimeter-wave TL components intended for use in high-power applications.

A 250-GHz corrugated transmission line with a directional coupler for forward and backward power monitoring has been constructed and tested for use with a 25-W continuous-wave gyrotron for dynamic nuclear polarization (DNP) experiments. The main corrugated line (22-mm internal diameter, 2.4-m long) connects the gyrotron output to the DNP probe input. The directional coupler, inserted approximately midway, is a four-port crossed waveguide beamsplitter design. Two beamsplitters, a quartz plate and ten-wire array, were tested with output coupling of 2.5% (-16dB) at 250.6 GHz and 1.6% (-18dB), respectively. A pair of mirrors in the DNP probe transferred the gyrotron beam from the 22-mm waveguide to an 8-mm helically corrugated waveguide for transmission through the final 0.58-m distance inside the NMR magnet to the sample. The transmission-line components were all cold tested with a 248/spl plusmn/4-GHz radiometer. A total insertion loss of 0.8 dB was achieved for HE/sub 11/-mode propagation from the gyrotron to the sample with only 1% insertion loss for the 22-mm-diameter waveguide. A clean Gaussian gyrotron beam at the waveguide output and reliable forward power monitoring were achieved for many hours of continuous operation.

A radiometric method for resolving emissivity e and temperature T in thermal emission measurements is presented. Thermal radiation from a viewed source is split by a beamsplitter between a radiometer and a mirror aligned to return a part of the thermal radiation back to the source. The ratio of the thermal signal with and without a return reflection provides a measurement of the emissivity without need of any other probing sources. The analytical expressions that establish this relationship are derived taking into account waveguide/optic losses and sources between the radiometer and viewed sample. The method is then applied to thermal measurements of several refractory materials at temperatures up to 1150 °C. A 137 GHz radiometer is used to measure the emissivity and temperature of an alumina brick, an Inconel 690 plate, and two grades of silicon carbide. Reasonable temperature agreement is achieved with an independent thermocouple measurement. However, when the emissivity approaches zero, as in the case ...

This work focuses on the accuracy of the mode content measurements in an overmoded corrugated waveguide using measured radiated field patterns. Experimental results were obtained at 250 GHz using a vector network analyzer with over 70 dB of dynamic range. The intensity and phase profiles of the fields radiated from the end of the 19 mm diameter helically tapped brass waveguide were measured on planes at 7, 10, and 13 cm from the waveguide end. The measured fields were back propagated to the waveguide aperture to provide three independent estimates of the field at the waveguide exit aperture. Projecting that field onto the modes of the guide determined the waveguide mode content. The three independent mode content estimates were found to agree with one another to an accuracy of better than ±0.3%. These direct determinations of the mode content were compared with indirect measurements using the experimentally measured amplitude in three planes, with the phase determined by a phase retrieval algorithm. The phase retrieval technique using the planes at 7, 10, and 13 cm yielded a mode content estimate in excellent agreement, within 0.3%, of the direct measurements. Phase retrieval results using planes at 10, 20, and 30 cm were less accurate due to truncation of the measurement in the transverse plane. The reported measurements benefited greatly from a precise mechanical alignment of the scanner with respect to the waveguide axis. These results will help to understand the accuracy of mode content measurements made directly in cold test and indirectly in hot test using the phase retrieval technique.

Recently the Dutch, Belgian, and North-Rhine Westphalian Fusion Institutes have consolidated their fusion research on the medium-sized tokamak TEXTOR-94 in the so-called Trilateral Euregio Cluster. To aid the new physics program of TEC, a large number of advanced core diagnostics has recently been implemented. In this article we will discuss the reasoning that has led to the choices of the various diagnostics. Furthermore, we will briefly describe the new diagnostics systems. (C) 2001 American Institute of Physics.

Spectral purity of the transmitter source of a collective Thomson scattering (CTS) system is vitally important to insure that measured signals only originate from the plasma and not from stray source light. A number of high power (up to 500 kW), 140 GHz gyrotron tubes used with the Joint European Torus (JET) CTS system have been found to have one or more spurious modes and many harmonics in the output spectrum. The CTS diagnostic receiver system was used to make measurements of the gyrotron spectrum. It was comprised of a homodyne part from MIT for frequency sidebands

The receiver of the Joint European Torus (JET) energetic ion and alpha particle collective Thomson scattering diagnostic is calibrated assuming blackbody emission from the torus vacuum vessel (VV) and using electron cyclotron emission (ECE). The 32 receiver channels are absolutely calibrated with a mechanical chopper in the quasioptical arm of the receiver, alternating the receiver view between the torus vacuum at 320 °C and room temperature. This calibration is noisy due to the small difference between torus and room temperatures. A more accurate relative calibration is achieved with the ECE during plasma shots. The intensity of the ECE is found to be a smooth function of frequency, which enables the combination of the ECE calibration with the VV calibration. The accuracy of the absolute VV calibration is hereby improved to nearly the same standard as the relative ECE calibration. ECE signals measured by the calibrated receiver agree well with standard JET ECE diagnostics. Based on mathematical considerations presented here, noise is injected into the receiver final intermediate frequency stage during VV calibrations to provide more bit transitions for accurate analog-to-digital (AD) conversion of the low level calibration signals. This yields a resolution which is better than 1% of an (AD) step.

Two new types of high frequency (HF) MHD mode activity are observed when a core transport barrier is formed during ion Bernstein wave (IBW) heating in PBX-M. These modes, localized in the core transport barrier, seem to be mainly responsible for the soft saturation in the strength of the core transport barrier. The two types of HF mode activity are determined by the presence or absence of a strong 1/1 mode. The n = m modes are observed with the 1/1 mode, while the n = m - 1 modes are seen when the 1/1 mode is absent. The m numbers of both of these modes vary between 4 and 13. They all seem to be coupled and rotate as a rigid body. The n = m - 1 modes seemed to be narrowly localized on their corresponding rational surface, i.e. q = m/(m - 1). The modes are ballooning-like, and their amplitudes increase with increasing β. Calculations with the CASTOR code show that the n = m - 1 modes are most probably pressure driven tearing modes, but the possibility of kinetic ballooning modes (KBMs) cannot be fully excluded. The n = m modes appear on or around the q = 1 surface, and are localized at the X point of the 1/1 mode island. The frequency offset of the n = m modes, which is too low for a TAE, is shown to be consistent with β-induced toroidal Alfven eigenmodes (BAEs).

A general method using a ray-tracing analysis has been developed to improve the accuracy of surface temperatures measured by pyrometry inside a furnace. This method allows temperature correction for enclosed non-ideal black-body surfaces, having temperature gradients, by taking into account the contributions from the reflected fraction of the pyrometer field-of-view. The development has been made possible by the recent availability of internal furnace scanning pyrometry technology for complete temperature profile measurements inside furnaces. The correction method can be expressed in terms of the solution of a square matrix having a dimension corresponding to the number of spatially resolved points in the temperature profile, with the number of non-zero elements depending on the number of field-of-view reflective surface bounce points used in the analysis. The utility of this method is demonstrated for the correction of 19-point temperature profiles measured inside a dc arc furnace. Reflective contributions from two, three, and four field-of-view surface bounce points are considered. Generally, the lower the surface emissivity and the higher the temperatures, the more bounces needed in the analysis. It is shown that there can be significant corrections to internal furnace temperatures measured by pyrometry when temperature gradients exist.

Here we report on a study of the feasibility of measuring the fast ion phase space distribution in the International Thermonuclear Experimental Reactor (ITER) by collective Thomson scattering (CTS). The study covers the full range of potential probe frequencies from gyrotron based millimeter waves to the infrared of the CO2 laser. It is assessed whether the systems can meet the ITER measurement requirements and which technological developments may be required. The relative merits of the systems are compared. The study reveals that a CTS system based on a 60 GHz probe has the highest diagnostic potential, and is the only system expected to be able to meet all the ITER fast ion measurement requirements with existing or near term technology. With modest additions this system may also provide measurements of the fuel ion ratio.

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

A graphite helix corrugated waveguide with a miter mirror has been fabricated and used for 135 GHz pyrometer measurements on a high temperature plasma arc furnace. The guide has an internal diameter of 3.81 cm, a length of 123 cm, and a corrugation of 32 grooves/inch. One end of the guide was sealed with a Teflon window having moth eye surfaces to reduce reflections. The room temperature insertion loss of this guide assembly for HE/sub 11/ mode propagation and launch was measured to be 0.5/spl plusmn/0.1 dB. It was used successfully in a high temperature environment where the miter mirror end reached incandescent temperatures in access of 1200/spl deg/C. High temperature graphite surface corrosion typically increased the insertion loss to 1.2/spl plusmn/0.2 dB but did not significantly affect the beam divergence.

Applications of high-power Terahertz (THz) sources require low-loss transmission lines to minimize loss, prevent overheating and preserve the purity of the transmission mode. Concepts for THz transmission lines are reviewed with special emphasis on overmoded, metallic, corrugated transmission lines. Using the fundamental HE(11) mode, these transmission lines have been successfully implemented with very low-loss at high average power levels on plasma heating experiments and THz dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) experiments. Loss in these lines occurs directly, due to ohmic loss in the fundamental mode, and indirectly, due to mode conversion into high order modes whose ohmic loss increases as the square of the mode index. An analytic expression is derived for ohmic loss in the modes of a corrugated, metallic waveguide, including loss on both the waveguide inner surfaces and grooves. Simulations of loss with the numerical code HFSS are in good agreement with the analytic expression. Experimental tests were conducted to determine the loss of the HE(11) mode in a 19 mm diameter, helically-tapped, three meter long brass waveguide with a design frequency of 330 GHz. The measured loss at 250 GHz was 0.029 ± 0.009 dB/m using a vector network analyzer approach and 0.047 ± 0.01 dB/m using a radiometer. The experimental results are in reasonable agreement with theory. These values of loss, amounting to about 1% or less per meter, are acceptable for the DNP NMR application. Loss in a practical transmission line may be much higher than the loss calculated for the HE(11) mode due to mode conversion to higher order modes caused by waveguide imperfections or miter bends.

Instrumentation for making localized, precise relative reflection measurements of metals and superconductors in the terahertz frequency range is demonstrated. The results can be used to determine the surface resistivity of these materials which is of particular importance to development of high‐temperature superconductors. Emission from a commerically available 1000 °C blackbody source was reflected from the materials under test and a reference reflector. The reflected signals were detected by a Schottky diode heterodyne receiver using a CO2‐laser‐pumped 214.5 μm CH2F2 laser as the local oscillator. Double‐sideband bandwidth and receiver noise temperature were 2 GHz and 30 000 K, respectively. The use of a broadband incoherent diagnostic source minimizes instrumentation sensitivity to coherent interference effects. The heterodyne receiver provides for sensitive detection with good spatial and frequency resolution. Unoptimized spatial resolution of four times the diffraction limit was achieved. The potenti...

Corrugated waveguide made with a tap can significantly lower fabrication costs. A 330 GHz, 19 mm i.d., 4.5 m long brass circular waveguide was tapped and tested. Transmission measurements were compared with models that take into account the shape of the corrugation.

Millimeter wave (MMW) radiometry can be used for simultaneous measurement of emissivity and temperature of materials under extreme environments (high temperature, pressure, and corrosive environments). The state-of-the-art dual channel MMW passive radiometer with active interferometric capabilities at 137 GHz described here allows for radiometric measurements of sample temperature and emissivity up to at least 1600 °C with simultaneous measurement of sample surface dynamics. These capabilities have been used to demonstrate dynamic measurement of melting of powders of simulated lunar regolith and static measurement of emissivity of solid samples. The paper presents the theoretical background and basis for the dual-receiver system, describes the hardware in detail, and demonstrates the data analysis. Post-experiment analysis of emissivity versus temperature allows further extraction from the radiometric data of millimeter wave viewing beam coupling factors, which provide corroboratory evidence to the interferometric data of the process dynamics observed. These results show the promise of the MMW system for extracting quantitative and qualitative process parameters for industrial processes and access to real-time dynamics of materials behavior in extreme environments.

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 HE 06 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.

We report amplification of pulses as short as 400 ps in a 1 kW, 140 GHz gyro-TWT amplifier. To our knowledge, this is the first observation of picosecond pulse amplification in a gyro-amplifier. The pulses show measurable broadening due to two distinct phenomena: group velocity dispersion and spectral narrowing due to the finite gain bandwidth. Theoretical analysis is in good agreement with the observed broadening of the pulses. Picosecond pulses are useful for applications in spectroscopy and advanced radar.

We report the first experimental studies of picosecond pulse amplification and broadening in a gyrotron amplifier. These studies allow investigation of the amplification process in a new physical regime, where wave dispersion and finite gain bandwidth play a major role. The experiments were performed on a 140 GHz gyro-traveling wave tube (Gyro-TWT) operating in a higher order mode of a confocal waveguide. We observed significant pulse broadening for pulses shorter than 1 ns when the operating point of the amplifier was close to the waveguide cut-off. For example, a 580 ps pulse at 137.30 GHz, a frequency near cutoff, was measured to be broadened by 100 %, while pulses at higher frequency, further from cutoff, showed much smaller broadening. The results of these experimental studies show that for the picosecond pulse amplification necessary in applications such as Electron Paramagnetic Resonance (EPR), the operating point of the gyro-TWT should be chosen to be at least a few percent above the cut-off to avoid pulse distortion.

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 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 mn mode basis set should be used to describe the fields in the corrugated waveguide. The HOM content greatly affects the propagation of HE 11 content in a miter bend, with a large emphasis placed on the percentage of HOMs and the phase difference between HE 11 and each HOM. By considering LP modes, a complete basis set is used to investigate the HOM effects on HE 11 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 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 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.

Mode conversion in miter bends and polarizers is the main contributor of loss in the transmission lines (TLs) for the ITER 170 GHz ECH system, which should transport one megawatt of power with the smallest possible loss. Previous loss estimates assumed that the power in the TL was carried by a pure HE11 mode; however, in practice, there is significant power in higher order modes (HOMs). It is shown that the mode conversion loss of the power in an HE11 mode at a miter bend is greatly altered by the presence of even a small proportion of HOMs in the TL, and is a strong function of both the magnitude of the HOM and its phase relative to that of the HE11 mode. The resulting total loss in the ITER transmission lines is expected to be very different from the loss previously predicted using single mode theory.

A new multifrequency electron cyclotron resonance heating system is under construction for the Axially Symmetric Divertor Experiment (ASDEX) Upgrade tokamak experiment. For the first time in a fusion device, this system employs multifrequency gyrotrons that are step-tunable in the range 105-140 GHz. In its final stage the system will consist of four gyrotrons with a total power of 4 MW and a pulselength of 10 s. The first two gyrotrons, working at 105 and 140 GHz, were installed and tested. Transmission line elements such as corrugated waveguides, polarizer mirrors and vacuum windows are designed to cope with this frequency band. The system includes fast steerable launchers at the front end that will allow for localized feedback-controlled power deposition in the plasma.

The transmission lines (TLs) for ITER electron cyclotron heating require extremely low losses, since the 24 MW of power generated by the 170 GHz gyrotrons should be delivered to the plasma with an efficiency of 83% or more. We are developing cold-test techniques to precisely measure the losses in the TL components for ITER, before installation. Experimental results on the measurement of the loss in some TL systems with coherent and incoherent techniques are presented and compared. We report a preliminary measurement of loss in the prototype TL components for the ITER 170 GHz transmission line.

Gyrotrons operating in the millimeter and submillimeter wavelength ranges are the promising sources for applications that are requiring good spectral characteristics and a wide range of output power. We report the precise measurement results of gyrotron spectra. Experiments were conducted using a 140-GHz long-pulse gyrotron that is developed for the dynamic nuclear polarization/nuclear-magnetic-resonance spectroscopy at the Massachusetts Institute of Technology. Transient downshift of the frequency by 12 MHz with a time constant of 3 s was observed. After reaching equilibrium, the frequency was maintained within 1 ppm for over 20 s. The coefficient of the frequency change with cavity temperature was -2.0 MHz/K, which shows that fine tuning of the gyrotron frequency is plausible by cavity-temperature control. Frequency pulling by the beam current was observed, but it was shown to be masked by the downward shift of the gyrotron frequency with temperature. The linewidth was measured to be much less than 1 MHz at 60 dB relative to the carrier power [in decibels relative to carrier (dBc)] and 4.3 MHz at 75 dBc, which is the largest dynamic range to date for the measurement of gyrotron linewidth to our knowledge.

Summary form only given. A critical need exists for confined fast ion diagnostics in tokamak fusion experiments, particularly for fusion product alpha particles in ITER and future fusion burning experiments. To develop this diagnostic capability and in support of current fast ion plasma physics research, collective Thomson scattering (CTS) diagnostics have been implemented at TEXTOR and ASDEX Upgrade (AUG) tokamaks using available gyrotron infrastructure with the addition of sensitive scattered signal receiver systems. At TEXTOR a 180 kW, 110 GHz gyrotron and a 42 channel. 6 GHz bandwidth heterodyne receiver has achieved up to 100 CTS scattered spectra per plasma shot with 4 ms time and 10 cm spatial resolution. Large scattering angles (~160deg) with steerable optics enable observation of fast ion spatial and field orientation anisotropies. Studies of fast ion dynamics behavior with neutral beam injection (NBI) and ion cyclotron heating have commenced, resulting in unique observations of fast ions redistributions during sawteeth and slow down after NBI turn off. At AUG a 1 MW, 105 GHz mode of a two-frequency gyrotron with a 50 channel, 10 GHz bandwidth receiver is becoming operational for CTS diagnostics with resolutions similar to TEXTOR. Precise gyrotron frequency measurements, notch filter timing, transmission line alignments, and receiver field of view mappings inside the tokamak have been accomplished using novel beam profile instrumentation. AUG-CTS commissioning progress will be presented. Plasma measurements in AUG are expected to provide new insights into fast ion physics and to further validate gyrotron CTS as a fast ion diagnostic tool for ITER.

A new multifrequency electron cyclotron resonance heating (ECRH) system is currently under construction at the ASDEX Upgrade tokamak experiment. This system will, for the first time in a fusion device, employ multifrequency gyrotrons, step-tunable in the range 105 to 140 GHz. In its final stage the system will consist of four gyrotrons with a total power of up to 4 MW and a pulse length of 10 s. The variable frequency will significantly extend the operating range of the ECRH system both for heating and current drive. The matching optics unit includes a set of phase-correcting mirrors for each frequency as well as a pair of broadband polarizer mirrors. The transmission line consists of nonevacuated corrugated HE 11 waveguides with inner diameter of 87 mm and has a total length of∼70 m. A fast steerable launcher enables the steering of the beam over the whole plasma cross section poloidally. The first two-frequency gyrotron has been installed recently. It is equipped with a single-disk diamond window. The next gyrotrons will be step-tunable with two additional frequencies between 105 and 140 GHz. They will require a broadband output window, which will be either a Brewster or a double-disk window.

We report microsecond pulse and CW results of a gyrotron operating near 460 GHz and 230 GHz at the second electron cyclotron harmonic and fundamental, respectively. Peak power levels of up to 70 W at the fundamental and 3 W at the second harmonic have been obtained in operation at up to 13 kV and 150 mA. The gyrotron has been operated continuously to achieve 3 W CW at the second harmonic. The gyrotron was also demonstrated as a wideband continuous frequency tunable oscillator by magnetically exciting fundamental higher order longitudinal modes. The gyrotron oscillator can be used for dynamic nuclear polarization (DNP) studies in conjunction with a 700 MHz (/sup 1/H), 16.5 T nuclear magnetic resonance (NMR) spectrometer.

Diagnostics of materials in high-temperature, optically inaccessible environments can be reliably achieved with millimeter-wave methods and components. A 137 GHz heterodyne receiver using a thermal return reflection (TRR) technique and ceramic waveguides tested to 1500/spl deg/C have been used to demonstrate the capability to measure temperature, emissivity, viscosity, and salt layer formation in laboratory and pilot scale melter tests.

The operating characteristics of a 140-GHz 14-W long pulse gyrotron are presented. The device is being used in dynamic nuclear polarization enhanced nuclear magnetic resonance (DNP/NMR) spectroscopy experiments. The gyrotron yields 14 W peak power at 139.65 GHz from the TE(0,3) operating mode using a 12.3-kV 25-mA electron beam. Additionally, up to 12 W peak has been observed in the TE(2,3) mode at 136.90 GHz. A series of mode converters transform the TE(0,3) operating mode to the TE(1,1) mode. Experimental results are compared with nonlinear simulations and show reasonable agreement. The millimeter-wave output beam was imaged in a single shot using a pyroelectric camera. The mode patterns matched reasonably well to theory for both the TE(0,1) mode and the TE(1,1) mode. Repeatable mode patterns were obtained at intervals ranging from 0.8 s apart to 11 min apart at the output of the final mode converter.

A 250 GHz HE/sub 11/ corrugated transmission line with a sampling directional coupler for multiwatt CW gyrotron radiation has been successfully implemented for dynamic nuclear polarization experiments. A second transmission line at 460 GHz is being built. Trade offs between smooth walled dielectric and corrugated waveguides are evaluated.

137 GHz heterodyne receiver measurements with hollow ceramic HE/sub 11/ waveguides are being applied to nuclear waste glass melt monitoring of temperature, emissivity, and surface fluctuations/flow in both laboratory and engineering scale melters at temperatures as high as 1500/spl deg/C. New insights are being provided on molten glass/salt interaction and glass pour dynamics.

Recently, dynamic nuclear polarization enhanced nuclear magnetic resonance (DNP/NMR) has emerged as a powerful technique to obtain significant enhancements in spin spectra from biological samples. For DNP in modern NMR systems, a high power continuous-wave source in the submillimeter wavelength range is necessary. Gyrotrons can deliver tens of watts of CW power at submillimeter wavelengths and are well suited for use in DNP/NMR spectrometers. To date, 140 GHz and 250 GHz gyrotrons are being employed in DNP spectrometer experiments at 200 MHz and 380 MHz at MIT. A 460 GHz gyrotron, which has operated with 8 W of CW output power, will soon be installed in a 700 MHz NMR spectrometer. High power radiation with good spectral and spatial resolution from these gyrotrons should provide NMR spectrometers with high signal enhancement through DNP. Also, these tubes operating at submillimeter wavelengths should have important applications in research in physics, chemistry, biology, materials science and medicine.

Collective Thomson scattering (CTS) diagnostic systems for measuring fast ions in TEXTOR and ASDEX Upgrade are described in this article. Both systems use millimeter waves generated by gyrotrons as probing radiation and the scattered radiation is detected with heterodyne receivers having 40 spectral channels at TEXTOR and 50 spectral channels at ASDEX Upgrade. The antenna patterns of probe and receiver, both steerable, determine size and location of the measuring volume, and the direction of the resolved fast ion velocity. With overmoded transmission lines, consisting of waveguides and quasioptical mirrors, the antenna patterns depend on the alignment of the entire transmission line. Alignment is aided by visible laser beams relayed by small optical mirrors, inserted in the quasioptical mirrors.

A 60 GHz gyrotron collective Thomson Scattering alpha particle diagnostic has been implemented for the D-T period on TFM. Gyrotron power of 0.1-1 kW in pulses of up to 1 second can be launched in X-mode. Efficient corrugated waveguides are used with antennaes and vacuum windows of the TFTR Microwave Scattering system. A multichannel synchronous detector receiver system and spectrum analyzer acquire the scattered signals. A 200 Megasample/sec digitizer is used to resolve fine structure in the frequency spectrum. By scattering nearly perpendicular to the magnetic field, this experiment will take advantage of an enhancement of the scattered signal which results from the interaction of the alpha particles with plasma resonances in the lower hybrid frequency range. Significant enhancements are expected, which will make these measurements possible with gyrotron power less than 1 kW, while maintaining an acceptable signal to noise ratio. We hope to extract alpha particle density and velocity distribution functions from the data. The D and T fuel densities and temperatures may also be obtainable by measurement of the respective ion cyclotron harmonic frequencies.

A radiometric method for resolving the emissivity, /spl epsiv/, and temperature, T, in thermal emission measurements is derived and experimentally demonstrated. The viewed source's own emission is utilized as an incoherent probe beam by means of a beamsplitter and return mirror. Measurements of several refractory materials at 137 GHz to 1500/spl deg/C were carried out.

summary form only given. A microwave induced plasma device is being developed for sensitive continuous emission monitoring of trace metals in furnace exhausts using atomic emission spectroscopy. The plasma is created in air at atmospheric pressure, and maintained by a 1.5 kW, 2.45 GHz microwave source. A diagnostic system, consisting of a fiber optic cable, lenses, a spectrometer, and a linear Si diode detector array, provides information about the light emitted from the plasma with a maximum resolution of 0.01 nm in the range of 190-600 nm. In this work we describe the experimental setup for the temperature profile reconstruction, the conceptual method for data analysis and some preliminary results.

A Lower Hybrid Current Drive system is being constructed jointly by Plasma Science and Fusion Center (PSFC) and Princeton Plasma Physics Laboratory (PPPL) for installation on the Alcator C-Mod tokamak, with the primary goal of driving plasma current in the outer region of the plasma. The Lower Hybrid (LH) system consists of 3 MW power at 4.6 GHz with a maximum pulse length of 5 seconds. Twelve klystrons will feed an array of 4-vertical and 24-horizontal waveguides mounted in one equatorial port. The coupler will incorporate some compact characteristics of the multijunction power splitting while retaining full control of the toroidal phase. In addition a dynamic phase control system will allow feedback stabilization of MHD modes. The desire to avoid possible waveguide breakdown and the need for compactness have resulted in some innovative technical solution which will be presented.

A collective Thomson scattering diagnostic is being implemented at JET to diagnose the velocity distribution and density of alpha particles and energetic ions. This diagnostic consists of a number of major subsystems including: a high‐power 140‐GHz gyrotron, a 32‐channel 12‐GHz bandwidth heterodyne receiver, efficient corrugated waveguide systems, variable polarizers, and in vacuum beam steering mirrors. Proper calibration of these subsystems for signal level losses, positioning, and polarization is imperative for the successful operation of the diagnostic and to facilitate the interpretation of the scattered data. A low‐power Gunn oscillator was used to verify the polarization rotation induced by the seven miter bends in the receiver transmission line. The full bandwidth receiver front end losses, including the sapphire tokamak vacuum window, were initially calibrated by using the hot tokamak vessel wall as a blackbody source at approximately 310 °C. Background ECE measurements will be presented.

A compact microwave plasma device that can be attached to a stack for near in situ atomic emission spectroscopy, with a real-time span calibration injector for accuracy, is under development for continuous metals monitoring. It uses a commercially available 2.45 GHz, 1.5 kW microwave source to generate a plasma in an undiluted, isokinetic sustained in a shorted waveguide, which together with a short sample line is maintained at high temperature (>150 C) to avoid condensation. Relative to other plasma based CEMs the microwave plasma has a significant advantage to continuously operate reliably in large volumes (- 50 cm3) of fast flowing (> 14 1/minute, up to 40 ft/sec) air or undiluted stack exhaust. A pneumatic nebulizer attached to the sample line can momentarily, on command, inject a known trace concentration of metals to provide a real-time span calibration whenever needed. Novel grating spectrometers using low cost detectors have been used for simultaneous multiple metals monitoring with continuous rapid signal acquisition making possible the observation of discreet particles. Since the particles are observed as plasma induced sources of light, the usual limits on monitoring discreet submicron particles by conventional external light instruments are not encountered. Detection limits for Be, Cr, and Pb of < 3 ug/m3 have been shown for one minute signal averaging in plasmas with 6% water content. A one minute detection limit for Hg of < 1 ug.m3 has been recently achieved in ambient laboratory air plasmas using a dedicated spectrometer. Lower detection limits are possible with longer signal integration time. Pasting testing on an EPA research incinerator demonstrated the capability for monitoring metal concentrations with a relative accuracy of 20% to EPA method 29.

A 1.5-kW 2.45-GHz magnetron source has been used to reliably sustain large electrodeless plasmas at atmospheric pressure in a shorted waveguide without a resonator. Working gases have been air, nitrogen, and heated off gases of sulfur containing ores and coal in nitrogen. Various colorful plasmas of value to environmental monitoring and processing applications are generated depending on the composition of the working gas.

Currently, a new multi-frequency ECRH system is under construction at the ASDEX Upgrade tokamak experiment. This system employs, for the first time in a fusion device, multi-frequency gyrotrons, step-tunable in the range 105–140 GHz. The first two gyrotrons, working at 105 and 140 GHz, were installed and tested. The matching optics unit includes a set of phase correcting mirrors for each frequency as well as a pair of broadband polarizer mirrors. The transmission line consists of non-evacuated corrugated HE11 waveguides with an inner diameter (ID) of 87 mm and has a total length of about 70 m. Transmission losses were deducted from calorimetric measurements both at the beginning and at the end of the transmission line at both frequencies and are in reasonable agreement with theory. Two transmission lines are completed so far and first plasma experiments with the new system have started. The first gyrotron Odissey-1 is currently being equipped with a broadband chemical vapour deposition (CVD) diamond Brewster output window and will become a step-tunable gyrotron with the additional frequencies 117 and 127 GHz. A tunable double-disc CVD-diamond window will be mounted at the torus. The system includes fast steerable launchers at the front end that will allow very localized feedback controlled power deposition in the plasma.

The potential for submillimeter-wave laser relative reflectivity measurements with an accuracy of better than 10 -4 (corresponding to a potential for relative measurements of surface resistivity with an accuracy better than 10 -2 Ohms per square) has been investigated. An experimental arrangement to minimize the effects of changes in laser output and detector drift to levels, necessary to obtain this accuracy has been demonstrated. This was accomplished by simultaneous measurement with a reference detector to reduce short-term fluctuations and rapid sampling to account for longer term drift. Systematic error due to reproducibility of alignment with sample changes limited the present preliminary results to an overall accuracy of approximately 10 -2 This achieved level of accuracy is sufficient for measurements of present state-of-the-art thin film high T c superconductors at 77 K, an example of which is presented here.

Fast ion physics will play an important role on ITER where confined alpha particles will affect plasma dynamics and overall confinement. Fast ion collective Thomson scattering (CTS) using gyrotrons has the potential to meet the need for measuring the spatially localized velocity distributions of confined fast ions in ITER. Currently, CTS experiments are performed at TEXTOR using a 150 kW, 0.2 s, 110 GHz gyrotron and a receiver upgraded at the Ris phi National Laboratory. The gyrotron and receiver optics have also been upgraded for rapid scanning during a plasma shot. The receiver consists of a nine-mirror quasioptical transmission line including a universal polarizer and a 42-channel data acquisition system, which allows complete coverage of the double sideband scattered spectrum for localized (similar to 10 cm) time resolved (4 ms) measurements of the ion velocity distribution. At ASDEX Upgrade (AUG) a similar 50-channel CTS receiver has been installed. This CTS system will use the 105 GHz frequency of a dual frequency gyrotron. The gyrotron is presently being commissioned. CTS campaigns are scheduled for the summer of 2006 with a probe power of up to 1 MW for 10 s. This report presents the alignment of the quasioptical transmission line, calibration, and gyrotron tuning of the TEXTOR and AUG CTS systems. We will also review the progress on the design of the proposed fast ion CTS diagnostic for ITER. It is envisaged that scattered radiation from two 60 GHz probe beams launched from the low field side midplane port will be received by two arrays of receivers located on the low and high field sides of the plasma. This geometry will allow the ion velocity distribution near perpendicular and near parallel to the magnetic field to be measured in ten or more spatial locations covering the full plasma cross section. The temporal resolution can be significantly better than the required 100 ms. (c) 2006 American Institute of Physics.

High resolution frequency measurements of the 110 GHz gyrotron at TEXTOR and the 105 GHz mode of the two-frequency gyrotron (Odissey-1) at ASDEX Upgrade (AUG) have been made in support of fast ion collective Thomson scattering diagnostics. Measurements were done by harmonic heterodyne methods using both fast Fourier transform spectroscopy with digital oscilloscopes and fast scanning spectrum analyzers. Accurate frequencies were obtained with a frequency counter. At TEXTOR, at 180 kW forward power the starting frequency was 109.970 +/- 0.005 GHz and chirped down as much as 27 MHz depending on the duty factor. At AUG, at 500 kW forward power the frequency started at 104.786 GHz and chirped down 104 MHz, with 90% of the chirp occurring in the first 100 ms. Plasma perturbation of the TEXTOR gyrotron was observed when both ion cyclotron resonance heating antennas and neutral beam injection were operating, producing modulation at 29 and 58 MHz in the gyrotron output. Each gyrotron was observed to have an instrumental measurement limited linewidth of 120 kHz full width at half maximum. (c) 2006 American Institute of Physics.

Localized measurements of internal magnetohydrodynamic (MHD) activity in the Princeton Beta Experiment-Modification (PBX-M) have been made using a heterodyne radiometer. The radiometer measures third harmonic optically gray electron cyclotron emission (ECE) from the center to the outer edge of the plasma on eight radially localized frequency channels from 112–128 GHz. The radiometer uses a focusing Gaussian optics system, which provides a vertical resolution of approximately 6 cm throughout the plasma. The radial resolution of the diagnostics is limited by the relativistic broadening to approximately 2–3 cm. Long wavelength (k

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...

Conventional superconducting materials used at liquid helium temperatures have been employed to greatly reduce ohmic power loss in microwave cavities. If suitable high temperature superconductor surfaces can be developed, it could be possible to alleviate constraints due to relatively low energy gaps and limits due to critical fields, and operate at more convenient temperatures with larger thermal margins. These features could be used to improve performance of present superconducting microwave cavity devices. They may also facilitate new applications and device designs at millimeter-wave and far infrared frequencies. Possible cavity and waveguide applications are described. Sensitivity of RF surface resistance to boundaries and nonaligned grains in the material and to small amounts of nonsuperconducting material may be an obstacle to development. Moreover, critical RF fields can be limiting for high power applications. An additional problem is the adverse effect of D.C. magnetic fields.

We present a novel technique for the measurement of surface resistivity using whispering gallery modes in an open cylindrical resonator. Preliminary results for copper at 140 GHz and application to high Tc superconductors will be presented.