**4.6 Collector**

After the electron-beam comes out of the interaction-cavity, the spent electronbeam gets collected in the collector. The kinetic energy of the spent-electron beam (the electron-beam which has already undergone beam-wave interaction) gets dissipated in the collector. Hence, if the electronic-efficiency of a gyrotron is 40%, 60% of the electron beam power gets dissipated in the collector. Since the dissipated power in the collector is very high, the thermal management of collector is a very critical issue. The cut-section view of a typical collector is presented in the **Figure 12**. In some of the high power gyrotrons, a low frequency magnetic sweeping coil is used for sweeping the electron-beam along the length of collector to avoid creation of hot-spots. For the enhancement of overall efficiency of gyrotron, multistage depressed collector (MDC) is used, where the collector is kept at a negative potential with respect to cavity.
