1999 Fiscal Year Final Research Report Summary
Microwave Generation due to Degenerate Interaction of Cherenkov and Cyclotron Beam Modes
| Project/Area Number |
09680456
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
プラズマ理工学
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| Research Institution | Niigata University |
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Principal Investigator |
OGURA Kazuo Niigata University, Department of Electrical and Electronic Engineering, Professor, 工学部, 教授 (40214093)
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| Project Period (FY) |
1997 – 1999
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| Keywords | Microwave / Electron Beam / Plasma / Cherenkov Interaction / Cyclotron Resonance / Degenerate Interaction / Hybrid Mode |
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| Research Abstract |
For a magnetized electron beam, there exist three distinct beam waves, which can contribute microwave generations. They are the slow and the fast cyclotron waves and the beam space charge wave. At zero-magnetic field, the conventional Cherenkov and cyclotron resonance interactions degenerate. This research project has proposed microwave generations due to the degenerate interaction and includes theoretical and experimental studies.
At zero-magnetic field, vertical as well as longitudinal perturbed beam motions should be taken into account. In the degenerate beam interaction of the conventional Cherenkov and cyclotron resonance interactions, surface charge at beam-vacuum boundary plays an essential role. Instabilities due to the degenerate interaction occurs for axisymmetric TM mode and non-axisymmetric HE and EH hybrid modes. In the high current region above 100 A and in the weakly relativistic energy region, the degenerate interaction is superior to the conventional Cherenkov interaction
A large diameter backward wave oscillator (BWO) without guiding magnetic field is demonstrated experimentally. This BWO is simple and compact. Electron beam can propagate without guiding magnetic field due to generation of plasma in ion-focused regime by self-ionization of background gas (helium or nitrogen). The gas pressures, at which microwave generations of the BWO are observed, are 5-10 mTorr and 100-160 mTorr for nitrogen and helium, respectively. The oscillation modes are axisymmetric TM and non-axisymmetric TE modes, which can be explained by the degenerate interaction. The output power of the TM mode is less than 1kW, which corresponds to electronic efficiency less than 0.004 %. The low electronic efficiencies might be ascribed to poor profile control of the large diameter beam.
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