Analysis of the influence of the magnetic field profiles on the high-power gyrotron's magnetic injection gun

In order to improve the performance of the magnetic injection gun(MIG),the beam has the mezzo velocity ratio between 1.5 and 2.0 and transvelocity spread lower than 5%.Three kinds of the magnetic field:the sin function magnetic field,the conic function one and the tanh function one, are discussed. Each kind of field distribution was changed and the simulation shows that:if sin or conic function field is used ,the beam performance can be improved by changing the flat region length,i.e.,moving the turning point near the end of the control anode ,then the velocity ratio will be maximum;if the tanh one is adopted ,and the field angle is in the range 9°to 70°,when the field angle increases,the velocity ratio increases as well as the trans velocity spread remains stable.