Influence of Growth Method on K3Sb Photocathode Structure and Performance

Future high brightness photoelectron sources delivering gt;100 mA average current call for a new generation of photocathodes. Materials which qualify for this purpose should exhibit low intrinsic emittance, long lifetime and high quantum efficiency at photon energies in the visible range of the spectrum to relax drive laser requirements. A combination of material science techniques are used to determine the influence of the growth parameters on structure and performance of photocathode materials . In situ XRR, XRD and GiSAXS measurements were performed at the synchrotron radiation sources, NSLS and CHESS. The growth of K3Sb, a precursor material of one of the prime candidates CsK2Sb, was studied intensively to optimize this intermediate growth step in terms of quantum efficiency and roughness. Three methods, a layer by layer type and a super lattice type were examined. K3Sb exists in two crystallographic phases, namely cubic and hexagonal. The cubic phase exhibits a higher quantum efficiency at 532 nm than the hexagonal phase and transforms more easily into CsK2Sb, tuning this phase is believed to be one of the key parameters in the CsK2Sb growt

Results from Beam Commissioning of an SRF Plug Gun Cavity Photoinjector

Superconducting rf photo electron injectors SRF photoinjectors hold the promise to deliver high brightness, high average current electron beams for future light sources or other applications demanding continuous wave operation of an electron injector. This paper discusses results from beam commissioning of a hybrid SRF photoinjector based on a Pb coated plug and a Nb rf gun cavity for beam energies up to 2.5MeV at Helmholtz Zentrum Berlin HZB . Emittance measurements and transverse phase space characterization with solenoid scan and slitmask methods will be presente

Emittance Measurements of a Superconducting High Frequency Electron Gun

Synchrotron light sources are of vital importance to modern spectroscopy and surface science. Due to their unique properties combination of uniformly high brightness and brilliance over a wide frequency range, synchrotron light sources nd broad application in solid state surface science, chemistry, biology and life science[1]. In a linear accelerator based light source, the properties of the electron beam that emits synchrotron radiation are largely de ned at the rst stages of beam production and acceleration. Especially, for prospected future light sources, such as X Ray Free Electron Lasers FELs and Energy Recovery Linacs ERLs , initial beam parameters are key factors of performance because no damping as in storage rings occurs. In an e ort to explore research and development areas required for future ERL design and operation, the demonstration facility BERLinPro will be built at Helmholtz Zentrum Berlin. It will demonstrate feasibility of the ERL concept in a parameter scale envisaged for X ray facilities. The superconducting radio frequency SRF photo electron gun is one promising concept to deliver electron beams of the desired quality of ultra low emittance below 1mmmrad and high average current in the order of 100 mA. Gun 0.2 is a demonstration project to explore the generation of a low current beam from a photoinjector where cathode, cavity and solenoid are all superconducting. Cavity operation at high gradients was demonstrated, albeit at low beam loading and a low duty cycle. In order to investigate and understand the in uence of gun design, cathode preparation and operational parameters on the beam quality it is important to have reliable and accurate beam diagnostics available. The focus of this work was thus to employ the available diagnostic beam line of the current gun demonstrator to characterize the transverse phase space of the beam and measure the emittance at various beam settings and operation conditions. Slit mask and solenoid scanning techniques are applie

Characterization of a Superconducting Pb Photocathode in a SRF Gun Cavity

Photocathodes are a limiting factor for the next generation of ultra high brightness photoinjector driven accelerators. We studied the behavior of a superconducting Pb cathode in the cryogenic environment of a superconducting rf gun cavity related to the quantum efficiency, its spatial distribution and the work function. Cathode surface contaminations can modify the performance of the photocathodes as well as the gun cavity. We discuss the possibilities to remove these contamination

On the structural composition and stability of Fe N C catalysts prepared by an intermediate acid leaching

The development of highly active and stable non noble metal catalysts NNMC for the oxygen reduction reaction ORR in proton exchange membrane fuel cells PEM FC becomes of importance in order to enable cost reduction. In this work, we discuss the structural composition as derived from Fe 57 Mö bauer spectroscopy and X ray dif fraction, catalytic performance determined by a rotating ring disk electrode RRDE technique and stability evaluation of our Fe N C catalysts prepared by an intermediate acid leaching IAL . The advantage of this IAL is given by a high density of active sites within the catalyst, as even without sulphur addition, an iron carbide formation and related disintegration of active sites are inhibited. In addition, our accelerated stress tests illustrate better stability of the sulphur free IAL catalyst in comparison to the sulphur added on

High resolution surface analysis of Si roughening in dilute ammonium fluoride solution

The initial stages of porous Si formation on Si 111 in dilute ammonium fluoride solution are analysed by photoelectron spectroscopy PES using synchrotron radiation. PES in the por Si formation regime shows no contradiction to a recent dissolution model. The contribution from a Si 2p surface core level shift shows that 0.4 ML of the surface is still H terminated after interruption of the conditioning process at the first photocurrent maximum. A higher oxidised species found with EB 103.2 eV is attributed to a precipitate, expected from the reaction mechanism and from theoretical calculations using density functional theory DFT . The roughening upon por Si formation is monitored by in situ AFM measurements. A RMS roughness parameter of 2.6 nm is calculated