Efficient 34 GHz second-harmonic peniotron with cusp gun drive Dressman, L.J.; McDermott, D.B.; Hirata, Y. ...
Infrared and Millimeter Waves, Conference Digest of the 2004 Joint 29th International Conference on 2004 and 12th International Conference on Terahertz Electronics, 2004,
2004
Conference Proceeding
A 34 GHz peniotron, operating in the fundamental-mode of a slotted circuit, is under construction at UC Davis. The device is designed for second-harmonic interaction with the axis-encircling beam ...produced by a Northrop Grumman cusp gun. Recent efforts have concentrated on improving the magnetic field design and beam quality. Consequently, the cryogenic magnet of the initial design has been replaced with conventional coils and pole pieces. Measurement of the new magnet indicates that design goals for the magnetic field have been achieved and simulation of the beam predicts greatly improved quality.
A multichannel 280-GHz collective scattering system has been employed to investigate electron gyro-scale density fluctuations in National Spherical Torus Experiment (NSTX) plasmas. The longitudinal ...scattering volume length, which is the spatial resolution of the scattering measurement, was calculated in tokamak geometry since the targeting wavenumber is greatly affected by the configuration of the magnetic field. An absolute power calibration was performed to determine the power response of the detection system. The results of the scattering length calculation and the power calibration were applied to estimate the density fluctuation levels from the scattering signals measured on NSTX plasmas.
High efficiency Ka-band second-harmonic peniotron Dressman, L.J.; McDermott, D.B.; Hirata, Y. ...
ICOPS 2000. IEEE Conference Record - Abstracts. 27th IEEE International Conference on Plasma Science (Cat. No.00CH37087),
2000
Conference Proceeding
Summary form only given. A second-harmonic peniotron has been designed for high efficiency and immunity to mode competition from gyrotron interactions. A peniotron experiment at Tohoku University ...recently achieved an electron efficiency of 70% at the third harmonic, but since the cavity was only critically coupled, the device efficiency was a more modest 35%. In order to achieve high device efficiency, the UC Davis peniotron will employ an overcoupled interaction cavity. To ensure stability from competing gyrotron interactions, the peniotron will operate in the lowest order mode of a slotted four-vane circuit, the /spl pi//2 mode. The cavity is strongly diffraction coupled with a circuit efficiency of 84%. The 33 GHz, slotted second-harmonic peniotron with a 70 kV, 3.5 A, v/spl perp//v/sub z/=1.5, /spl Delta/v/sub z//v/sub z/=10%, axis-encircling electron beam is predicted to yield 130 kW with an electron efficiency of 63% and a device efficiency of 52%. The device is being constructed at UC Davis and will be driven by a recently developed Northrup Grumman Cusp gun.
Ka-band second-harmonic cusp-gun gyro-TWT Harriet, S.B.; Mcermott, D.B.; Hirata, Y. ...
ICOPS 2000. IEEE Conference Record - Abstracts. 27th IEEE International Conference on Plasma Science (Cat. No.00CH37087),
2000
Conference Proceeding
Summary form only given, as follows. A 30 GHz second-harmonic sliced smooth-bore TE/sub 21/ gyro-TWT with a cusp gun has been designed to double the efficiency of our previous 200 kW, 12% efficient, ...MIG TE/sub 21//sup (2)/ gyro-TWT. The new circuit is also sliced to destroy the odd-order azimuthal modes, but the axis-encircling electrons are no longer be confined to the maxima and minima of the linearly polarized mode. The 70 kV, 3.5 A, v/spl perp//v/sub z/=1.2, /spl Delta/v/sub z//v/sub z/=8%, axis-encircling electron beam is produced by a cusp gun delivered by Northrop Grumman. The single-stage amplifier is predicted by our large-signal simulation code to generate 50 kW at 30 GHz with 20% efficiency, 30 dB saturated gain and 3% constant-drive bandwidth. Linear theory has been used to determine the threshold start-oscillation beam current for absolute instability and the critical section lengths for the potential harmonic gyro-BWO interactions.
Sc 2 O 3 -doped W powder for use in high current density thermionic cathodes has been made by the sol-gel method with different particle sizes. Sc 2 O 3 -W matrix cathodes have been prepared from ...these powders, and have shown excellent emission properties. A space charge limited current density of 80 A/cm 2 at 1150°C, 50 A/cm 2 at 1050°C have been obtained by using 500 nm Sc 2 O 3 -doped W powders. Life testing is ongoing with a continuously pulsed loading of 50 A/cm 2 at 1050°C after 5448 hours. The maximum current density of the cathode made from 1-2 micro size S c2 O 3 -doped W powder can reach 106 A/cm 2 at 1150°C.
A millimeter wave imaging diagnostic for simultaneous density and temperature fluctuation measurements has been developed for operation on the TEXTOR Tokamak. The system is based on the quasi-optical ...imaging of the radiation from the plasma onto state-of-the-art millimeter wave mixer/receiver arrays. The temperature (fluctuation) measurements are based on the observation of electron cyclotron emission from a 2D plasma area with 8/spl times/16 sample volumes of about 1 cm/sup 3/. The density fluctuation measurements are based on active probing by means of reflectometry. In this case reflections from 16 sample volumes, arranged along the cutoff surfaces are diagnosed. The combined millimeter wave imaging diagnostic offers distinct advantages above the commonly used non-imaging diagnostics.
The ASPERA-3 experiment onboard the Mars Express spacecraft revealed, near the wake boundary of Mars, a spatially narrow, strip-like plasma structure composed of magnetosheath-like electrons and ...planetary ions. The peak electron energy often exceeds the peak energy at the bow shock that indicates a significant heating (acceleration) during the structure formation. It is shown that this structure is formed during efficient plasma penetration into the martian magnetosphere in the region near the terminator. The penetration of sheath electrons and their gradual heating (acceleration) is accompanied by a change of the ion composition from a solar wind plasma to a planetary plasma dominated by oxygen ions. A possible mechanism of plasma inflow to the magnetosphere is discussed.
Experimental second-harmonic axis-encircling beam gyro-TWT amplifier Harriet, S.B.; McDermott, D.B.; Luhmann, N.C.
2007 Joint 32nd International Conference on Infrared and Millimeter Waves and the 15th International Conference on Terahertz Electronics,
2007-Sep.
Conference Proceeding
A novel Ka-Band TE 21 second-harmonic gyro- TWT amplifier with a large-orbit axis-encircling beam from a Northrop Grumman Cusp gun has been fabricated and is being tested at UCD. The device is ...predicted to produce 50 kW with 20% efficiency, 30 dB saturated gain and 3% bandwidth.
