Pengnan Lu

Performance and Application Status of the Superconducting Photoinjector at ELBE

A new SRF gun has been commissioned at the ELBE linac. The gun has an improved 3.5-cell cavity and a superconducting solenoid is integrated. Beam parameter measurements have been carried out with a Cu photocathode.

Highlights on Metallic Photocathodes Used in SRF Gun

For the accelerator-based light sources and the electron colliders, the development of photoinjectors has become a key technology. Especially for the superconducting radio frequency cavity based injector (SRF Gun), the searching for better photocathodes is always a principal technical challenge. To use metallic photocathodes for ELBE SRF Gun is the primary choice to prevent cavity contamination. In this contribution, we will report the investigation of Magnesium (Mg) in ELBE SRF gun, including laser cleaning treatment and the measurement on quantum efficiency, Schottky effect, dark current and damage threshold.

Plug Transfer System for GaAs Photocathodes

The transport and exchange technology of Cs2Te photocathodes for the ELBE superconducting rf photoinjector (SRF Gun) has been successfully developed and tested at HZDR. The next goal is to realize the transport of GaAs photocathodes into the SRF Gun, which will need a new transfer system with XHV 10 mbar. The key component of the setup is the transfer chamber and the load-lock system that will be connected to the SRF Gun. In the carrier, four small plugs will be transported, one of them will be put on the cathode-body and inserted into the cavity. The new transport chamber allows the transfer and exchange of plugs between HZDR, HZB and other cooperating institutes. In HZDR this transfer system will also provide a direct connection between the SRF Gun and the GaAs preparation chamber inside the ELBE-accelerator hall. INTRODUCTION The Rossendorf superconducting RF photo injector (SRF Gun), developed within a collaboration of the institutes HZB, DESY, MBI and HZDR, has been put into operation in 2007. It is designed for medium average beam current and operation in CW mode [1]. The superconducting cavity, the main part of SRF gun, consists of three TESLA cells and one optimized halfcell. The Cs2Te photocathode is inserted in the half cell isolated by a 1mm vacuum gap. CATHODE SYSTEM UPDATE The design of the new transfer system for the SRF gun is shown in Fig. 1. Figure 1: View of new transfer system on the cryomodule. The main difference of the new transfer system to that of the present one is, that the moving object is only the plug and not the entire cathode (Fig. 2). • ELBE SRF Gun has been operated with Cs2Te for medium current up to 400μA • for high current operation in the future GaAs(Cs,O) is considered to be combined with the SRF Gun technology. • SRF Gun is supposed to serve as a test bench for GaAs(Cs, O) Cs Te 2 (Fig. 3). • driven by UV light • UV laser shaping complicated • medium current • 10 -10 -10 mbar NEA-GaAs (Cs, O) [2] • high QE in the visible light • laser pulse shaping easier • polarized electron source • critical vacuum requirement GaAs (Cs,O) will be in-situ activated before the transport into SRF gun through a new transfer system. XHV of less than 1×10 mbar is required. Figure 2: Photocathode of the new Transfer system. Figure 3: Arrangement in the coating chamber. Proceedings of SRF2015, Whistler, BC, Canada TUPB010 Projects/Facilities progress A02-Upgrade plans/status ISBN 978-3-95450-178-6 553 C op yr ig ht

RF Performance Results of the 2nd ELBE SRF Gun

An improved SRF gun (ELBE SRF Gun II) has been installed and commissioned at HZDR. This new gun replaced the first SRF gun of the ELBE accelerator which had been in operation since 2007. The new gun has an improved 3.5-cell niobium cavity those SRF performances have been studied first with a copper cathode. After the replacement by our standard Cs2Tecathode we observed a tremendous degradation of the cavity gradient paired with an increase of field emission. In this contribution we will report on our in-situ investigations to find the origin and the reason for the particle contamination that happened during the first cathode transfer.