A Microwave Detector Based on an MCT Photodiode for Subthermonuclear Plasma Research

摘要

A microwave detector including a single-element infrared (IR) photodiode mounted in a cooled Dewar and a preamplifier is developed. An IR photodiode of the n{sup}+-p type is created on the basis of mercury-cadmium telluride (HgCdTe or MCT) heteroepitaxial structures grown by means of molecular beam epitaxy. A special profile of MCT structures throughout the MCT layer thickness ensures a low series resistance of less than 10 Ω. and a high quantum efficiency at a level of 0.65 without any antireflection coating. For the spectral range of 8 to 12 μm, IR photodiodes are characterized by a low threshold power of 3.8·10{sup}(-13) W·Hz{sup}(-1/2) and 10{sup}(-19) W·Hz{sup}(-1) in the direct and heterodyne regimes, respectively. The cooled Dewar maintains the operating temperature of the IR photodiode in the interval of 77 to 80 K for 8. The preamplifier operates in a frequency range up to 1 GHz. With the use of this microwave detector, a method is developed for detection of intensity of a CO{sub}2 laser beam on plasma fluctuations caused by heating by a relativistic electron beam (REB). At high REB intensities, dips of the turbulence signal with a duration of several nanoseconds are observed, which is interpreted as a collapse of Langmuir waves.