Study of efficiency enhancement through magnetic field profiling in cyclotron autoresonance maser

Phase control and the increase of the available free energy are two basic mechanisms that enhance the efficiency of a cyclotron autoresonance maser (CARM) device through linearly tapering the externally applied magnetic field. Based on these two mechanisms, a nonlinearly profiled magnetic field, as formed by adding a positively three-quarter sine profile onto a uniform magnetic field, applied on CARM is proposed in this study. Numerical results show that applications of the nonlinearly profiled magnetic field can raise the efficiency of CARM to around 50% over a wide range of frequency detunings. The reduction of efficiency sensitivity to the beam velocity spread can also be achieved for the increase of the available free energy with the use of the nonlinearly profiled magnetic field. Furthermore, the nonlinearly profiled magnetic field is also far more effective and practical than the linearly tapered magnetic field in efficiency enhancement.