Beam Refrigeration by Means of Large Magnetic Fields

Abstract

The resistive loading which an electron beam produces in an adjacent structure can be made to exhibit a very low noise temperature. This is achieved by coupling to the fast cyclotron wave in a large magnetic field; the noise temperature at a given signal frequency is shown to be equal to the cathode temperature times the ratio of signal frequency to cyclotron frequency. An experiment is described in which this ratio is 19. The coupling structure interacts with the fast cyclotron wave but rejects the slow cyclotron wave. A noise temperature of 186°K is measured. In conclusion, it is shown that the large magnetic field required for beam cooling need not extend throughout the tube.