High-speed-driven FM microwave IMPATT sources for reflectometric diagnostic equipment

M. Moresco; Roberto Cavazzana; F. Chino; A. Sardella; Eic Spada

doi:10.1117/12.224239

13 October 1995 High-speed-driven FM microwave IMPATT sources for reflectometric diagnostic equipment

M. Moresco, Roberto Cavazzana, F. Chino, A. Sardella, Eic Spada

Proceedings Volume 2558, Millimeter and Submillimeter Waves II; (1995) https://doi.org/10.1117/12.224239
Event: SPIE's 1995 International Symposium on Optical Science, Engineering, and Instrumentation, 1995, San Diego, CA, United States

Abstract

Microwave FM reflectometry is largely used in thermonuclear fusion experiments to measure the electron density profile. The presence of density fluctuations has a strong influence on the reliability of the data. Large disturbances on the beat signal appear when its frequency is near to the fluctuation frequency. This effect has been observed also in our reflectometric diagnostic even if the modulating frequency used is the highest commercially available (80.0 GHz/msec). In order to reduce the fluctuations effect we have investigated the feasibility of operating the Impatt sources at a higher sweep rate (4000 GHz/msec). To do that we have measured the frequency response and the power response at different sweep speed for our W band sources observing reliable performances and good stability when not limited by thermal management problems. An extensive time resolved spectrum analysis has been done to discover nonlinear effects due to current crowding or local hot spot in the diode. On the basis of this characterization we have designed a high speed current driver tailored to the Impatt sources and able to work well above the requested response time, embodying DC bias control and protection circuit. The driver, based on low cost commercial components, implements microwave frequency range and offset control through a digital interface providing large flexibility on the diagnostic setup.

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M. Moresco, Roberto Cavazzana, F. Chino, A. Sardella, and Eic Spada "High-speed-driven FM microwave IMPATT sources for reflectometric diagnostic equipment", Proc. SPIE 2558, Millimeter and Submillimeter Waves II, (13 October 1995); https://doi.org/10.1117/12.224239

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KEYWORDS

Diodes

Diagnostics

Microwave radiation

Fermium

Frequency modulation

Oscillators

Plasma

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