Optimization of Cathodic Arc Deposition and Pulsed Plasma Melting Techniques for Growing Smooth Superconducting Pb Photoemissive Films for SRF Injectors

Superconducting photoinjectors have a potential to be the optimal solution for moderate and high current cw operating free electron lasers. For this application, a superconducting lead (Pb) cathode has been proposed to simplify the cathode integration into a 1.3 GHz, TESLA-type, 1.6-cell long purely superconducting gun cavity. In the proposed design, a lead film several micrometres thick is deposited onto a niobium plug attached to the cavity back wall. Traditional lead deposition techniques usually produce very non-uniform emission surfaces and often result in a poor adhesion of the layer. A pulsed plasma melting procedure reducing the non-uniformity of the lead photocathodes is presented. In order to determine the parameters optimal for this procedure, heat transfer from plasma to the film was first modelled to evaluate melting front penetration range and liquid state duration. The obtained results were verified by surface inspection of witness samples. The optimal procedure was used to prepare a photocathode plug, which was then tested in an electron gun. The quantum efficiency and the value of cavity quality factor have been found to satisfy the requirements for an injector of the European-XFEL facility

Amorphous and nanocrystalline Fe85Zr7B6Cu2\mathrm{Fe_{85}Zr_7B_6Cu_2} alloys

Local atomic order around Fe and Cu atoms in Fe85Zr7B6Cu2 amorphous and crystalline alloys annealed for 1 h at temperatures 420°C, 460°C, 480°C, 500°C and 570°C were studied by X-ray absorption. It was found that, in the as-quenched alloy, both Fe and Cu atoms are in an amorphous environment. For Fe atoms we have observed a systematic increase of a body centered cubic (bcc) type of ordering with increasing temperature of anneal and bcc Fe crystallites growing at temperatures higher than 460°C. In contrast, for Cu atoms, we have observed face centered cubic (fcc) ordering in all the annealed alloys and that Cu nanocrystallites started to grow at a temperature of 420°C, while the Fe atoms remained in an amorphous matrix

Coating in Ultra-High Vacuum Cathodic-Arc and Processing of Pb Films on Nb Substrate as Steps in Preparation of Nb-Pb Photocathodes for Radio-frequency, Superconducting e− ^− Guns

A photocathode composed of a Pb layer deposited on Nb substrate is an attractive solution proposed for fully superconducting, radio frequency electron gun to be used in the linear accelerator of the European X-ray free electron laser (Eu-XFEL) operating at Deutsches Elektronen Synchrotron (DESY) and in other, similar devices. Much effort has been put in development of deposition and post-processing of Pb films as superconducting photoemitters. These works led to a satisfactory solution based on lead deposition in a cathodic-arc followed by ex-situ smoothing of the obtained film through its re-melting with a pulsed plasma ion beam. Pb layers obtained by different procedures have been tested for their morphology, microstructure, dark current emission, quantum efficiency and impact on SRF e$^−$ gun performance

Deposition and Optimization of Thin Lead Layers for Superconducting Accelerator Photocathodes

A combination of a ultra high vacuum arc deposition system and a recrystallization method was used to optimize the smoothness and thickness of thin-layer lead cathodes for superconducting niobium electron injectors. A non-filtered arc system was chosen to deposit Pb films on niobium. The films then underwent melting and recrystallization by treating them with pulsed argon ion beams in a rod plasma injector