Plasma and Fusion Research

Volume 16, 2401028 (2021)

Regular Articles

Experimental Study on Microwave Generation due to Merged Instability in F-Band Surface Wave Oscillator
Keiichiro RACHI, Kazuo OGURA, Yuta ANNAKA1), Mao AOKI and Tsubasa KATO
Graduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan
Faculty of Engineering, Niigata University, Niigata 950-2181, Japan
(Received 1 December 2020 / Accepted 10 January 2021 / Published 5 March 2021)


A surface wave oscillator (SWO) is driven by an electron beam to generate intense microwaves. The electron beam possesses slow space-charge (SSC) and slow cyclotron (SC) modes that interact with the surface wave leading to microwave generation. The beam current and external magnetic field affect the relationship between SSC and SC modes. The SSC mode gradually approaches the SC mode when the beam current increases. Meanwhile the SC mode gradually approaches the SSC mode when the magnetic field decreases. The two modes merge in a low magnetic field and high beam current. In this work, we experimentally examine the operation of an F-band SWO in the low magnetic field region. The output power decreases with low beam current when magnetic field decreases. Meanwhile, the SWO maintains its power level with high beam current even though the magnetic field decreases to around 0.4 T. The merged instability enables a sustained power level in the low magnetic field region.


surface wave oscillator, merged instability, intense terahertz radiation, slow cyclotron instability, Cherenkov instability

DOI: 10.1585/pfr.16.2401028


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