Theory, Design and Operation of a Compact Cerenkov Free-Electron Laser

Microwave radiation is extensively used in various elds of research and applications. An important example is the selective heating of materials. In particular, the so-called millimetre-wave radiation, which covers the wavelength range between 1 mm and 10 mm, has several advantages compared to radiation from standard microwave magnetrons, at a wavelength of about 12 cm. For example, in most technical ceramics dielectric absorption and, therefore, heating is stronger at higher microwave frequencies. Also, with higher frequency the heating radiation can be focused to smaller volumes which, together with a smaller penetration depth, becomes useful for applications which require spatially selective heating, e.g., plasma production and metal sintering. However, current research into applications of millimetre-waves lacks a suitable source that provides appreciable output powers within the millimetre-wave range and, at the same time, offers the simplicity and compactness which is required for industrial applicability. The objective of this thesis is to demonstrate that C erenkov Free-Electron Lasers (CFELs) are a promising route towards such compact microwave sources with high-power and millimetrewave output. The CFEL has already proven its general potential as wavelength tunable, highfrequency and high-power source in previous designs reported in literature, although at the expense of bulky constructions. The main aim here is to show that CFELs can actually be realized with a much reduced size such as, for example, a table-top device. The main obstacle to the realization of a compact device is that, to date, CFELs have required a rather strong electron current with a high kinetic energy to successfully bring the laser above threshold and into oscillation. Such electron beams cannot be generated in a compact setup. Here we demonstrate that CFELs can be brought into oscillation also with a much weaker electron beam current and with a much reduced kinetic energy. For this, we have theoretically and experimentally investigated a compact design of CFEL which should operate with a relatively small electron beam current of less than 1 A, and relatively low kinetic energy of less than 100 keV.