Characteristics of an Ammonia Beam Maser

Design, construction and operating characteristics of an ammonia beam-type maser are described with particular emphasis on the J =3, K =2 line. The maser with an eight-pole focuser of 40 cm length starts oscillation on the 3, 2 line at a focuser voltage of 5.6 kV when the maximum available source flux of about 1.2×10 18 molecules per second is used. Threshold conditions of oscillation as functions of the focuser voltage, lengths of the focuser and of the cavity are calculated the theory on the Maxwell velocity distribution. The observed frequency-change with the cavity tuning and with the focuser voltage is compared with theory in some detail. The effect of traveling wave component in the cavity and the pulling due to cavity tuning are calculated. It is shown that the frequency shift with the focuser voltage becomes very small, when the beam flux is reduced.