Tohru Sugawara

Axisymmetric optical system for quasi-optical gyrotron

An analysis is carried out with a profile of hollow Gaussian radiation beam propagating in an optical system composed of coaxial annular curved mirrors. The result will be a useful tool in designing an axisymmetric quasi-optical gyrotron oscillator (ASQUOTRON).

Quasi-optical waveguide-mode converters using a pair of phase correction mirrors

This paper describes a quasi-optical method for the conversion of modes transmitted through highly oversized circular waveguides. A waveguide-mode is radiated once from a waveguide cut in the form of a radiation beam, which is then properly shaped by two curved mirrors and directed back into the waveguide. The curved mirror shapes are iteratively and automatically determined for given propagation distances using the design technique for phase correction mirrors. The proposed method gives favorable results in designing a waveguide expander/reducer, a TE01-TE02 mode converter, and a TE01-HE11 mode converter.

Design of a 1-MW, CW coaxial gyrotron with two Gaussian beam outputs

The design of a 170 GHz, 1 MW-CW gyrotron for electron cyclotron heating of nuclear fusion plasmas is presented. The designed gyrotron incorporates a coaxial cavity to reduce mode competition, and a coaxial electron gun to support the cavity inner conductor. A new mode converter splits the generated wave into two beams and radiates them in different directions. The radiated beams are transmitted to two output windows through two mirror systems, being transformed into Gaussian-like beams. A single-stage depressed collector improves the overall efficiency of the gyrotron and reduces the heat flux to the collector surface.

Magnetic Suppression of Secondary Electron Emission from the Negative Electrode in a Beam Direct Energy Converter

A method is described for suppressing secondary electron emission from the negatively biased electrode of a beam direct energy converter by surrounding it with magnetic field lines. Experiments in a positive ion beam converter with a magnetically protected suppressor have shown that the secondary electrons generated by ion bombardment are successfully prevented from leaving the suppressor. It is also found that backscattered ions from the positive electrode occupy a noticeable portion of the loss currents generated in a converter with a copper electrode.

Experimental study of a quasi-optical cavity with slotted output mirror

This paper describes an experimental study of a quasi-optical cavity to be used in qyrotrons. The cavity configuration was designed so that its output wave could pass into a quasi-optical transmission line. The test cavity was coaxially composed of a pair of annular mirrors, one of which was a curved conical mirror and the other was a plane mirror having a radial slot array for wave output. A mode excited in the cavity at 56.4 GHz was observed by detecting the radiation wave that leaked out through the slotted mirror. It was shown that the present slotted mirror served as a partially and uniformly transparent mirror to radiate the output wave with the same mode as in the cavity.

A 120 GHz Axisymmetric Quasi Optical Gyrotron

An axisymmetric quasi-optical gyrotron was designed, constructed, and operated. Its cavity resonator was composed of a conical mirror and a plane slotted mirror. The observed oscillation frequencies were in a range from 114 to 123 GHz. Output waves were transmitted quasi-optically to a water load. The measured output power was more than 20 kW at a frequency of 120 GHz.

Multimode Analysis of A Dual Electron-Beam Quasi-Optical Gyrotron

A multimode analysis has been carried out to clarify growing frequencies of a 1-MW, 150-GHz dual electron-beam quasi-optical gyrotron oscillation, with a cavity resonator composed of two coaxial annular mirrors. The results show that the gyrotron can be operated at a single frequency with a fundamental mode in the azimuthal direction for the present range of parameters. Its achievable efficiency is 40% when the magnetic field of the cavity is shifted after the operation mode is grown up.

DESIGN CONSIDERATIONS OF NEUTRAL BEAM INJECTION SYSTEM FOR AN IGNITION TOKAMAK

A reference design of 20 MW - 150 keV neutral beam injector unit is presented after discussion of problems of ion source, neutralizer and residual ion beam handling from the standpoint of system integration. A direct converter of residual ion beams deflected magnetically from the neutral beamline is proposed.