Robert Nietubyć

Experimental station to study the interaction of intense femtosecond vacuum ultraviolet pulses with matter at TTF1 free electron laser

An experimental station to study the interaction of intense femtosecond vacuum ultraviolet pulses generated by the TTF1 free electron laser (FEL) (DESY, Germany) with solids was developed. The vacuum chamber, the sample holder and the detectors had been designed to fulfill strong constraints caused both by the unique properties of the interacting radiation and by TTF1 FEL innovative design. The applied mounting system allowed one to move and rotate the samples precisely with 4degrees of freedom and to heat them up to the maximal temperature of 1000K. In order to accomplish the in situ growth of thin metallic layers on the sample surfaces, evaporation cells had been installed in the vacuum chamber. A time-of-flight apparatus capable of recording both electrons and ions excited on the solid surfaces by the laser pulses had been included in the chamber design. A pulse energy monitor had been placed in the laser beam outside the experimental chamber. A second energy detector had been mounted inside the chambe...

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.

Review and present status of preparation of thin layer lead photocathodes for e - injectors of superconducting RF linacs

Results are reported on using evaporation and UHV arc lead deposition to create thin-layer superconducting Pb photocathodes on niobium wall of electron gun. Evaporated photocathodes were prepared and tested for the first time in 2014. A complete XFEL-type photo-injector with an evaporated photocathode underwent successful quality check at DESY - an acceptable working point was reached. On the other hand poor adhesion to niobium proved to be the most serious shortcoming of the evaporated Pb layers. UHV arc deposition seems to be much more promising in this context as it allows energetic coating. Filtered arc coating lead to creation of uniform, 2 μm thick lead layers with casual spherical extrusions which enhance locally electric field and leads to high dark current. Conditioning in electric field is needed to reduce the field emission effects from these layers to acceptably low value. Using non-filtered UHV lead deposition enabled fast coating up to a thickness above 10 μm. Pb films obtained in this way require further post-processing in pulsed plasma ion beams in a rod plasma injector. In order to reach a sufficiently planar film surface the pulsed heat flow through a lead layer on niobium was modeled and computed.

Recent development in optimization of superconducting thin film lead photocathodes at NCBJ in Świerk

We report the efforts undertaken at NCBJ and some of its collaborating laboratories dedicated to prepare pure and flat lead film coated onto niobium to operate as superconducting photocathodes. Three approaches to lead cathodic arc deposition have been implemented and tested: active plasma flux filtering, passive filtering and unfiltered flux. None of them allowed us to find a proper balance between thickness and surface roughness of a cathode. At that point efforts were taken to establish post-deposition heat treatment of lead film.