Operating Characteristics of an Ammonia Beam Maser

This paper describes the operating characteristics of an ammonia beam maser. The simple theory for the operation is expanded to predict the angular distribution of the molecules coming from the beam collimator and the effect of the focuser on the velocity distribution of the molecules entering the cavity. Experimental results for the operation of the cavity in the TM001 and TM012 mode show the effects of the variation in beam current and cavity tuning on the frequency and amplitude of oscillation. Relating these results to the theory with the help of measurements of the beam flux density demonstrates the importance of molecular collisions and the beam divergence. Three methods of locating line center are examined, and it is shown that the line centers obtained in each case may be varied over a range of at least 5 parts in l08 by changing the operating parameters.