M. Krasilnikov

Recent Developments at PITZ

The ability to produce high brightness electron beams as required for modern Free Electron Lasers (FELs) has been demonstrated during the first stage of the Photo Injector Test Facility at DESY Zeuthen (PITZ1). The electron source optimization at PITZ1 was successfully completed, resulting in the installation of the PITZ rf gun at the VUV-FEL (DESY, Hamburg). One of the main goals of the second stage of PITZ (PITZ2) is to apply higher gradients in the rf gun cavity in order to obtain smaller beam emittance by faster acceleration of the space charge dominated beams. In order to reach the required gradients a 10 MW klystron has to be installed and the gun cavity has to be conditioned for higher peak power. Another important goal of PITZ2 is a detailed study of the emittance conservation principle by using proper electron beam acceleration with a booster. Further photo injector optimization, including update of the photocathode laser and diagnostic tools, is foreseen as well. Recent progress on the PITZ developments will be reported.

Emission Mechanisms in a Photocathode RF Gun

In photocathode rf guns, emission mechanisms at the photocathode play a crucial role in the overall beam dynamics. An electron beam with a low bunch charge as well as a short laser pulse length allow to study the emission mechanisms with a good phase definition and with a very small influence of the space charge force. This pa per presents experimental and numerical studies toward detailed understanding of the photo emission and secondary emission processes at the Cs2Te cathode.

Dark Current and Multipacting in the Photocathode RF Guns at PITZ

For photocathode rf guns, the amount of dark current depends on the cavity surface as well as on the photocathodes. Smooth conditioning reduces the amount of dark current. Multipacting in the gun cavity changes the surface status of the cathodes and sometimes obstructs the gun operation because of vacuum interlocks. In this paper, dark current and multipacting features of an rf gun are presented including experimental and simulation studies.

Beam-Based Procedures for RF Guns

A wide range of rf photo injector parameters has to be optimized in order to achieve an electron source performance as required for linac based high gain FELs. Some of the machine parameters can not be precisely controlled by direct measurements, whereas the tolerances on them are extremely tight. Therefore, this should be met with beam-based techniques. Procedures for beam-based alignment (BBA) of the laser on the photocathode as well as solenoid alignment have been developed. They were applied at the Photo Injector Test facility at DESY at Zeuthen (PITZ) and at the photo injector of the VUV-FEL at DESY at Hamburg. The field balance of the accelerating mode in the 1 1/2 cell gun cavity is one of the key beam dynamics issues of the rf gun. Since no direct field measurement in the half and full cell of the cavity is available for the PITZ gun, a beam-based technique to determine the field balance has been proposed. A beam-based rf phase monitoring proce dure has been developed as well.