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Vacuum Electronics Research at The University of Michigan

Vacuum Electronics Research at The University of Michigan. Profs. Ron Gilgenbach, Y.Y. Lau and Mary Brake Nuclear Engineering & Radiological Sciences Dept. University of Michigan Ann Arbor, MI 48109-2104 funded by the AFOSR. OUTLINE. motivation research topics recent results

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Vacuum Electronics Research at The University of Michigan

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  1. Vacuum Electronics Research at The University of Michigan Profs. Ron Gilgenbach, Y.Y. Lau and Mary Brake Nuclear Engineering & Radiological Sciences Dept. University of Michigan Ann Arbor, MI 48109-2104 funded by the AFOSR

  2. OUTLINE • motivation • research topics • recent results • future planned research

  3. U. Michigan Research Topics • initial studies have begun on a small scale (expanded program begins Jan. 1, 2000) • crossed field devices: noise and mode stability experiments • theoretical research on intermodulation and noise in microwave tubes • microwave plasma cleaning/ processing of tubes

  4. Motivation: Crossed Field Amplifier Applications in DoD Systems (96-97) • System CFA Tube • AEGIS SFD-261/262 and L-4707/4708 • PATRIOT L-4927A • TPS-32 L-4829 • TPS-63 VXL-1169, L-4806 • APS-116 SFD-251, L-4764 • APS-137 L-4764A • MK-92 SFD-233G, L-4810 • SPS-48C SFD-267, L-4717, VXS-1247/1247F, L-4716/4718 • SPS-48E L-4719 • HAWK-PAR L-4939/4940 • ARSR-1&2 L-4953 • AEGIS (Israel) L-4891 • HADR (Ger., Nor.) L-4756 • FLORIDA (Swit.) L-4822 • E2-C L-4934 • TPN-19/GPN-22 L-4764 • AR-320 (UK) L-4756A • APS-145 VXL-1910 (in development)

  5. magnetron experiments • beginning with oven magnetrons (most efficient sources known); e.g. Toshiba 2M229, 700-900 W @ 4kV, 0.3A • investigate noise and out-of-band mode generation (source of EM pollution) • investigate mode hopping in startup- regime • explore the existence of “quiet-states” (W.C. Brown, 1988 Raytheon Tech. Rep.)

  6. magnetron experiments (continued) • utilize time-frequency-analysis to examine the spectrum of magnetrons • investigate the connection of noise to “excess” cathode emission current • modeling of magnetron by Phillips Lab Scientists (Luginsland and Spencer)

  7. Microwave-tube related theory efforts at U of Michigan • 1) Intermodulation in klystrons and in TWTs (Work in progress) • 2) Low frequency emission noise from thermionic cathodes (scaling law synthesized for flicker noise power relative to shot noise power) • 3) Low frequency ion noise in linear beam tubes (many observed features, such as sensitivity to B-field, to cathode voltages, etc., explained by simple theory.) Methods to reduce this low frequency phase noise proposed.

  8. theoretical research (continued) • 4. Time-frequency analysis: Novel technique studied for reduction of interference in time-frequency analysis of tubes that display mode competition. • 5. Crossed-field-device output characterization: Time frequency analysis being applied to various crossed-field device output, from microwave oven magnetron to CFA's. Noise in crossed-field geometry continues to be investigated. • 6. Cathode processes: Processes that affect cathode life and cathode noise (e.g., changes in emission due to evaporation and ion backbombardment) being analyzed.

  9. MICROWAVE PLASMA DISCHARGE CLEANING • can clean from the inside of tube • can match microwave frequency to tube type • no electrode impurities added to system • remote cleaning & cleans non-symmetric parts • - high density processing plasma (> 10E12- 10e14 /cc) Vs. RF plasmas (~10E9 - 10E10 or ICP =10E12) • in principle, no limitation to plasma column length, depends upon the power capability • inexpensive sources of 1 kW power at 2.45 GHz

  10. SURFACE WAVE EXCITED PLASMAS • Electromagnetic surface waves can sustain long plasma columns • wave is excited at one end of a long tube containing a gas (~1 Torr to 750 Torr) • EM wave travels along a plasma column it sustains (from the power that is carried by the wave) and these media constitute the wave's sole propagating structure

  11. INITIAL MICROWAVE PLASMA CLEANING STUDIES • Microwave resonant cavity • Fixed cavity inside diameter of 17.8 cm • Sliding short adjusts the length of the cavity to obtain specific electromagnetic modes (14.5 cm to ~9.5 cm • Tuning stub , which applies the microwave power to the cavity, is placed very close to the glass tube containing the gas/ plasma

  12. LOW FREQUENCY ION NOISE IN TWT* Professor Y.Y. Lau Nuclear Engineering & Radiological Sciences Dept. University of Michigan Ann Arbor, MI 48109-2104 *In collaboration with Dave Chernin and Wally Manheimer during sabbatical in 1999

  13. A Comparison of Flicker Noise and Shot Noise on a Hot Cathode* Professor Y.Y. Lau Nuclear Engineering & Radiological Sciences Dept. University of Michigan Ann Arbor, MI 48109-2104 *In collaboration with K. Jenson and B. Levush during sabbatical in 1999

  14. CONCLUSIONS • The University of Michigan will contribute to the MURI-1999 Program in: • crossed-field device science • intermodulation and noise • tube processing techniques • time-frequency signal analysis

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