ABSTRACT
Due to their excellent photoemissive properties, especially low thermal emittance and high sensitivity in the green wavelength, multi-alkali antimonide photocathodes, in particular, cesium-potassium-antimonide, emerged as prominent photoemissive materials for the electron sources of high-repetition-rate FEL applications. To explore its feasibility of operating in a high-gradient RF gun, DESY collaborated with INFN LASA to develop multi-alkali photocathode materials. In this report, we describe the recipe of K-Cs-Sb photocathodes, which were grown on a Mo substrate by varying the foundational Sb layer thickness using sequential deposition techniques. This report also illustrates the information regarding the film thickness, substrate temperature, deposition rate, and its possible effects on the photocathode's properties. In addition, the influence of temperature on the cathode degradation is also summarized. Furthermore, in the framework of density functional theory (DFT), we investigated the electronic and optical properties of the K2CsSb material. The optical properties, such as dielectric function, reflectivity, refracting index, and extinction coefficient, were evaluated. The correlation between the calculated and measured optical properties, such as reflectivity, provides a better and more efficient strategy to rationalize and understand the photoemissive material's properties.
ABSTRACT
At the Photo Injector Test facility at DESY in Zeuthen (PITZ), an R&D platform for electron FLASH and very high energy electron radiation therapy and radiation biology is being prepared (FLASHlab@PITZ). The beam parameters available at PITZ are worldwide unique. They are based on experiences from 20â¯+â¯years of developing high brightness beam sources and an ultra-intensive THz light source demonstrator for ps scale electron bunches with up to 5 nC bunch charge at MHz repetition rate in bunch trains of up to 1â¯ms length, currently 22â¯MeV (upgrade to 250â¯MeV planned). Individual bunches can provide peak dose rates up to 1014 Gy/s, and 10â¯Gy can be delivered within picoseconds. Upon demand, each bunch of the bunch train can be guided to a different transverse location, so that either a "painting" with micro beams (comparable to pencil beam scanning in proton therapy) or a cumulative increase of absorbed dose, using a wide beam distribution, can be realized at the tumor. Full tumor treatment can hence be completed within 1â¯ms, mitigating organ movement issues. With extremely flexible beam manipulation capabilities, FLASHlab@PITZ will cover the current parameter range of successfully demonstrated FLASH effects and extend the parameter range towards yet unexploited short treatment times and high dose rates. A summary of the plans for FLASHlab@PITZ and the status of its realization will be presented.
Subject(s)
Electrons , Neoplasms , Humans , RadiobiologyABSTRACT
Particle-beam-driven plasma wakefield acceleration (PWFA) enables various novel high-gradient techniques for powering future compact light-source and high-energy physics applications. Here, a driving particle bunch excites a wakefield response in a plasma medium, which may rapidly accelerate a trailing witness beam. In this Letter, we present the measurement of ratios of acceleration of the witness bunch to deceleration of the driver bunch, the so-called transformer ratio, significantly exceeding the fundamental theoretical and thus far experimental limit of 2 in a PWFA. An electron bunch with ramped current profile was utilized to accelerate a witness bunch with a transformer ratio of 4.6_{-0.7}^{+2.2} in a plasma with length â¼10 cm, also demonstrating stable transport of driver bunches with lengths on the order of the plasma wavelength.
