MTX/ELF II (Microwave Tokamak Experiment/ Electron Laser Facility II) Microwave Power Measurements and Calibration for the 2-GW, 140-GHZ, ELF II Free-Electron Laser (FEL).

摘要

We have developed techniques for measuring the power and frequency of the Electron Laser Facility (ELF) II free-electron laser (FEL) used for plasma heating experiments on the Microwave Tokamak Experiment (MTX). We also have designed a multichannel, 140-GHz receiver capable of measuring FEL power levels from 10 mW to 0.1 (mu)W within an accuracy of (plus minus)1 dB with a 50-dB dynamic range and a 2-ns response time. By using calibrated attenuators, we can measure power levels from 10 GW to 0.1 (mu)W. We sample the microwave output of the FEL in a microwave load tank by using WR-8 or WR-28 stub waveguide antennas. Microwave turning mirrors are used to guide the microwave beam down an evacuated beam tube to the MTX. Stub, WR-8, fundamental-mode, waveguide antennas are used for beam detection on the microwave turning mirrors. Orthogonal, WR-8, stub waveguides are machined into the surfaces of the mirrors and used as directional couplers to measure forward and reflected power from the FEL. The microwave power is then transported to the microwave receiver via a low-loss, over-moded, WR-28 waveguide. A movable modes probe in the microwave load tank is used to scan across the microwave beam to determine the modes content of the beam. Frequency stability of the FEL is measured with a fast, frequency-modulation detector (FFMD) capable of measuring frequency shifts and modulation on a 2- to 4-ns time frame. 2 refs., 14 figs.