Production And Studies Of Photocathodes For High Intensity Electron Beams

For short, high-intensity electron bunches, alkali-tellurides have proved to be a reliable photo-cathode material. Measurements of lifetimes in an RF gun of the CLIC Test Facility II at field strengths greater than 100 MV/m are presented. Before and after using them in this gun, the spectral response of the Cs-Te and Rb-Te cathodes were determined with the help of an optical parametric oscillator. The behaviour of both materials can be described by Spicer's 3-step model. Whereas during the use the threshold for photo-emission in Cs-Te was shifted to higher photon energies, that of Rb-Te did not change. Our latest investigations on the stoichiometric ratio of the components are shown. The preparation of the photo-cathodes was monitored with 320 nm wavelength light, with the aim of improving the measurement sensitivity. The latest results on the protection of Cs-Te cathode surfaces with CsBr against pollution are summarized. New investigations on high mean current production are presented.Comment: Submission to LINAC2000 conference, Paper number MOB08, 3 pages, 6 figure

Cesium-Telluride Photocathode No. 166

In the CERN photoemission laboratory, a Cs2 Te photocathode has been produced in December 2006. The co-evaporation of Cs and Te onto a copper substrate is observed with two quartz oscillator thickness monitors. The calibration of these monitors and the resulting Cs and Te layer thicknesses are described, and the calculated stoichiometric ratio of the sample is given. The quantum efficiency of cathode No. 166, measured using the cathode in a DC gun, has been found to be 6.2%

Photo-cathodes for the CERN CLIC Test Facility

Since 1993 the CLIC Test Facility (CTF) has used laser-illuminated Tellurium Alkali photo-cathodes as intense electron sources (up to 50 nC in 10 ps), for the Drive Beam of a two-beam accelerator. These cathodes have been produced and tested in our photo­emission laboratory and transported under vacuum to the CTF. They are placed in a 3 GHz RF gun with a 100 MV/m electric field. This RF gun produces a train of 48 pulses, each of 13.4 nC charge and 10 ps length. The CTF Probe Beam has used air­transportable cesium iodide + germanium photo­cathodes in another RF gun, which produces a single pulse of the same duration but with only 1 nC charge. The optical damage threshold in the laser is the main limitation of energy available on the photo­cathode. From an operational point of view, the photo­cathode lifetime is defined to be the time during which the cathode is able to produce the nominal charge with the nominal laser energy. After having recalled the main characteristics of the photo-cathodes tested, this note describes in more detail the performa nce obtained in operation. The possibility of photo-cathode production at the RF gun in a simplified evaporation chamber will also be discussed

The photo-injector option for CLIC: past experiments and future developments

The Compact Linear Collider (CLIC) drive beam requires a long bunch train (92 us) consisting of 42880 bunches with a bunch charge of 17.5 nC in a bunch length of less than 20 ps. This train might be produced by an RF-photo-injector equipped with a Cs-Te cathode. After a short review of experience with such cathodes in the present CLIC Test Facility (CTF2), mainly focused on the production of short trains of high-charge bunches, we will present the scheme foreseen for CLIC and CTF3. The laser will be a diode-pumped MOPA (Master Oscillator Power Amplifier), operating at a repetition rate of 469 MHz for CLIC and 1.5 GHz for CTF3. The specific requirements of an RF-gun for this high-current operation are discussed. New experimental results on the photocathode lifetime at high average current are summarized

OTR FROM NON-RELATIVISTIC ELECTRONS

Abstract OTR EMISSION FROM NON RELATIVISTIC ELECTRONS The CLIC Test Facility 3 (CTF3) injector will provide pulsed beams of high average current; 5A over 1.56µs at 140keV. For transverse beam sizes of the order of 1mm, as foreseen, this implies serious damage to the commonly used scintillating screens. Optical Transition Radiation from thermally resistant radiators represents a possible alternative. In this context, the backward OTR radiation emitted from an aluminium screen by a 80keV, 60nC, 4ns electron pulse has been investigated. The experimental results are in good agreement with the theoretical expectations, indicating a feeble light intensity distributed over a large solid angle. Our conclusions for the design of the CTF3 injector profile monitor are also given. We consider the transition between the vacuum and a material with a relative permittivity ε. The screen is tilted with respect to the beam trajectory ( z r ) by an angle ψ, as shown in figure 1. The OTR emission results from the contribution of the direct ( n r ), the reflected ( ' n r ) and the refracted ( ' n' r ) radiations emitted by the particle. Usin

The transverse and longitudinal beam characteristics of the phin photo-injector at Cern

International audienceThe laser driven RF photo-injectors are recent candidates for high-brightness, low-emittance electron sources. One of the main beam dynamics issues for a high brightness electron source is the optimization of beam envelope be- havior in the presence of the space charge force in order to get low emittance. Within the framework of the second Joint Research Activity PHIN of the European CARE pro- gram, a new photo-injector for CTF3 has been designed and installed by collaboration between LAL, CCLRC and CERN. Beam based measurements have been made dur- ing the commissioning runs of the PHIN 2008 and 2009 including measurements of the emittance, using multi-slit technique. The demonstration of the high charge and the stability along the long pulse train are between the goals of this photo-injector study as also being important issues for CTF3 and the CLIC drive beam. In this work the photo-injector will be described and the first beam mea- surement results will be presented and compared with the PARMELA simulations

Assessment of Predictors of Early Postoperative Complications After Primary Robotically Assisted Roux-En-Y Gastric Bypass: A Multicenter, Retrospective Cohort Study

BACKGROUND: Robotic Roux-en-Y gastric bypass (RRYGB) is performed in an increasing number of bariatric centers worldwide. Previous studies have identified a number of demographic and clinical variables as predictors of postoperative complications after laparoscopic Roux-en-Y gastric bypass (LRYGB). Some authors have suggested better early postoperative outcomes after RRYGB compared to LRYGB. The objective of the present study was to assess potential predictors of early postoperative complications after RRYGB. METHODS: A retrospective analysis of two prospective databases containing patients who underwent RRYGB between 2006 and 2019 at two high volumes, accredited bariatric centers was performed. Primary outcome was rate of 30 day postoperative complications. Relevant demographic, clinical and biological variables were entered in a multivariate, logistic regression analysis to identify potential predictors. RESULTS: Data of 1276 patients were analyzed, including 958 female and 318 male patients. Rates of overall and severe 30 day complications were 12.5% (160/1276) and 3.9% (50/1276), respectively. Rate of 30 day reoperations was 1.6% (21/1276). The overall gastrointestinal leak rate was 0.2% (3/1276). Among various demographic, clinical and biological variables, male sex and ASA score \u3e2 were significantly correlated with an increased risk of 30 day complication rates on multivariate analysis (OR 1.68 and 1.67, p=0.005 and 0.005, respectively). CONCLUSION: This study identified male sex and ASA score \u3e2 as independent predictors of early postoperative complications after RRYGB. These data suggest a potentially different risk profile in terms of early postoperative complications after RRYGB compared to LYRGB. The robotic approach might have a benefit for patients traditionally considered to be at higher risk of complications after LRYGB, such as those with BMI \u3e50. The present study was however not designed to assess this hypothesis and larger, prospective studies are necessary to confirm these results

The electron accelerator for the AWAKE experiment at CERN

The AWAKE collaboration prepares a proton driven plasma wakefield acceleration experiment using the SPS beam at CERN. A long proton bunch extracted from the SPS interacts with a high power laser and a 10 m long rubidium vapour plasma cell to create strong wakefields allowing sustained electron acceleration. The electron bunch to probe these wakefields is supplied by a 20 MeV electron accelerator. The electron accelerator consists of an RF-gun and a short booster structure. This electron source should provide beams with intensities between 0.1 and 1 nC, bunch lengths between 0.3 and 3 ps and an emittance of the order of 2 mm mrad. The wide range of parameters should cope with the uncertainties and future prospects of the planned experiments. The layout of the electron accelerator, its instrumentation and beam dynamics simulations are presented

The PHIN photoinjector for the CTF3 Drive beam

A new photoinjector for the CTF3 drive beam has been designed and is now being constructed by a collaboration among LAL, CCLRC and CERN within PHIN, the second Joint Research Activity of CARE. The photoinjector will provide a train of 2332 pulses at 1.5 GHz with a complex timing structure (sub-trains of 212 pulses spaced from one another by 333 ps or 999 ps) to allow the frequency multiplication scheme, which is one of the features of CLIC, to be tested in CTF3. Each pulse of 2.33 nC will be emitted by a Cs2Te photocathode deposited by a co-evaporation process to allow high quantum efficiency in operation (>3% for a minimum of 40 h). The 3 GHz, 2 1/2 cell RF gun has a 2 port coupler to minimize emittance growth due to asymmetric fields, racetrack profile of the irises and two solenoids to keep the emittance at the output below 20 p.mm.mrad. The laser has to survive very high average powers both within the pulse train (15 kW) and overall (200 W before pulse slicing). Challenging targets are also for amplitude stability (<0.25% rms) and time jitter from pulse to pulse (<1ps rms). An offline test in a dedicated line is foreseen at CERN in 2007