Maser electron cyclotron resonance in vacuum and plasma with REB

The problem of beam space charge in microwave generator with REB is discussed. The intense REB is injected in plasma and the degree of space charge neutralization is measured. The stimulated cyclotron radiation of spiral beam in vacuum and in plasma is observed. The microwave power in plasma is more than the power in vacuum by a factor of about one hundred. This fact is explained by neutralization of beam space charge in plasma. The investigation of maser electron cyclotron resonance in vacuum is described in the last part of the report. We hope to make this maser with plasma and to increase the microwave power.