Cavity designs for a space hydrogen maser

MoL and FEA investigations have been performed to optimize parameters in a TE₀₁₁ mode cavity resonator suitable for a space-borne hydrogen-maser. The criteria sought were both minimization of the total volume of the cavity as well as the maximization of the product of the z-component of the magnetic energy filling factor and the cavity TE₀₁₁ mode Q-factor (Q·η). Several designs including a sapphire tube in a Cu cylinder, a sapphire tube in a Cu cylinder with Bragg reflectors, and spherical Cu cavities both empty and sapphire-lined were studied. At 320 K, the simulations resulted in an optimum product Q·η=4.9×10⁴ with an inner cavity radius of 80 mm and unity aspect ratio in a simple sapphire tube design. This represents a 54% improvement over a similar design. The expected increase in the product Q·η with the inclusion of Bragg reflectors was not realized. Moreover the z-component of the magnetic filling factor was greatly reduced due to an increase in the radial component of the magnetic field. The sapphire lined spherical cavity showed no better performance than an equivalent sized empty, Cu cavity. For the empty cavity, the simulations resulted in the product Q·η=4.4×10⁴. The total volume in this case is 33% larger than the optimized sapphire tube resonator.