Experimental research on A 1.5 MW, 110 GHz gyrotron

Megawatt gyrotrons have a variety of applications including electron cyclotron heating (ECH) of plasmas in fusion devices. High efficiency operation is necessary to minimize the prime power required and to ensure good reliability of the device over its lifetime. To achieve high power and efficiency at the required frequencies, the gyrotrons must utilize large, overmoded cavities that face severe mode competition. It is important to understand the start-up scenario of the gyrotron, that is the sequence of modes excited during the voltage rise, since, under such conditions, small changes in operational parameters can affect the final operating state of the gyrotron. The start-up scenario had previously been examined using the numerical code MAGY and showed that higher-order modes would be excited and different start-up scenarios could yield a different final operating state [1,2].