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Yusof, Z

Publications and source records attributed to Yusof, Z.

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Kelvin probe studies of cesium telluride photocathode for the AWA photoinjector

Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (> 1%), is robust in a photoinjector, and long lifetime. This photocathode is fabricated in-house for a new Argonne Wakefield Accelerator (AWA) beamline to produce high charge per bunch ({approx}50 nC) in a long bunch train. We present some results from a study of the work function of cesium telluride photocathode using the Kelvin Probe technique. The study includes an investigation of the correlation between the quantum efficiency and the work function, the effect of photocathode aging, the effect of UV light exposure on the work function, and the evolution of the work function during and after photocathode rejuvenation via heating.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Generation of Picosecond Electron-Bunch Trains with Variable Spacing Using a Multi-Pulse Photocathode Laser

We demonstrate the generation of a train of electron bunches with variable spacing at the Argonne Wakefield Accelerator. The photocathode ultraviolet laser pulse consists of a train of four pulses produced via polarization splitting using two alpha-BBO crystals. The photoemitted electron bunches are then manipulated in a horizontally-bending dogleg with variable longitudinal dispersion. A downstream vertically-deflecting cavity is then used to diagnose the temporal profile of the electron beam. The generation of a train composed of four bunches with tunable spacing is demonstrated. Such a train of bunch could have application to, e.g., the resonant excitation of wakefield in dielectric-lined structures. We have presented preliminary measurements on a simple technique to generate a train of electron bunches with variable separation. In the initial experiment appreciable density modulation down to wavelengths of {approx}1.8 mm (corresponding to a temporal separation of {approx}6 ps) were achieved for a total charge of 0.5 nC. Finding ways to reach smaller separations is being explored with the help of numerical simulations and will be presented elsewhere.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Recent Experiment on Wakefield Transformer Ratio Enhancement at AWA

One technique to enhance the transformer ratio beyond the ordinary limit of 2 in a collinear wakefield acceleration scheme is to use a ramped bunched train (RBT). The first experimental demonstration has been reported in [1]. However, due to the mismatch between the beam bunch length and frequency of the accelerating structure, the observed transformer ratio was only marginally above 2 in the earlier experiment. We recently revisited this experiment with an optimized bunch length using the laser stacking technique at Argonne Wakefield Accelerator (AWA) facility. A transformer ratio of 3.4 has been measured using two drive bunches. Attempting to use four drive bunches met with major challenges. In this article, measurement results and data analysis from these experiments are presented in detail.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Dielectric-Based Wakefield Power Extractor

In the Two Beam Accelerator (TBA), wakefield power extractors which extract high power RF from a high current beam are used to power high gradient accelerating structures. A dielectric-based Wakefield Power Extractor (DWPE) is one option in addition to the metallic structures considered previously, like the CLIC PETS (Power Extraction and Transfer Structure). 7.8 GHz and 26 GHz DWPE prototypes have been successfully built and tested at the Argonne Wakefield Accelerator (AWA) facility. We are currently designing an X-band version for a potential application with the CLIC beam. In this article, we report on test results of the 26 GHz DWPE and the preliminary design of the X-band structure. Future plan and possible difficulties in the development of DWPEs are also discussed.

43 PARTICLE ACCELERATORS↗