Abstract
Advanced technical solution for the design of a low perveance electron gun with a high quality beam dedicated to high power Ka-band klystrons is presented in this paper. The proposed electron gun can be used to feed linear accelerating structures at 36 GHz with an estimated input power of 20 MW, thus achieving an effective accelerating electric field in the (100–150) MV/m range. Additionally, in the framework of the Compact Light XLS project, a short Ka-band accelerating structure providing an integrated voltage of at least 15 MV, has been proposed for bunch-phase linearization. For the klystron, a very small beam dimension is needed and the presented electron gun responds to this requirement. An estimate of the rotational velocity at beam edge indicates that the diamagnetic field due to rotational currents are small compared to the longitudinal volume. A detailed analysis of how this has been achieved, including compression of the beam, rotation in the magnetic field, and analysis of the subsequently generated diamagnetic field has been discussed.
Highlights
The new generation of high-gradient linear accelerators is extremely demanding in order to produce high-brightness electron beams
(2) Define an optimal electrostatic beam compression ratio and the maximum electric field on the focusing electrode: By solving the Poisson’s equation in spherical coordinates and with the help of the electrostatic lens effect, which is a bridge between light and charged-particle optics, we can find the potential distribution between cathode and anode and it is possible to optimize the geometry of the electron gun in order to have a high electrostatic beam compression ratio and a low electric field strength on the focusing electrode
It will be demonstrated that the diamagnetic field effect is negligible due to the fact that the rotation frequency is much smaller than Larmor frequency and that the beam radius is far away from the Brillouin limit
Summary
The new generation of high-gradient linear accelerators is extremely demanding in order to produce high-brightness electron beams. In the framework of the Compact Light XLS project [4], a short ultra-high gradient linearizer working on the third harmonic (∼36 GHz) of the bunched electron beam and generated by a high-voltage DC gun (up to 480 kV) operating with an accelerating gradient of ∼150 MV/m (i.e., 15–20 MV integrated voltage range) is requested [6,7] To meet these requirements, a 36-GHz pulsed Ka-band RF power source with a pulse length of 100 ns and a repetition frequency in the (1–10) Hz range with an output power of (50–60) MW is necessary [1,2,3,8,9,10,11,12,13]. The analytical results for calculation of the electron gun dimensions have been compared with numerical estimations
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