Author: Biswas, J.P.
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MOPLH02 Study of Photocathode Surface Damage due to Ion Back-Bombardment in High Current DC Gun 174
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  • J.P. Biswas
    Stony Brook University, Stony Brook, USA
  • O.H. Rahman, E. Wang
    BNL, Upton, New York, USA
  Funding: This work was supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704, with the U.S. DOE
In high current DC gun, GaAs photocathode lifetime is limited by the ion back-bombardment. While gun operation ions are generated and accelerate back towards the cathode thus remove the activation layer’s material Cesium from the photocathode surface. We have developed an object-oriented code to simulate the ion generation due to dynamic gas pressure and ion trace in the electromagnetic field. The pressure profile varies from cathode position towards the transfer line behind the anode, which signifies the importance of dynamic simulation for ion back-bombardment study. In our surface damage study, we traced the energy and position of the ions on the photocathode surface and performed the Stopping and Range of Ions in Matter(SRIM) simulation to count the number of Cesium atoms removed from the surface due to single bunch impact. Cesium atom removal is directly related to the photocathode Quantum Efficiency(QE) decay. Our new dynamic simulation code can be used in any DC gun to study ion back-bombardment. We have used this new code to better understand the ion generation in prototype BNL 350 KV DC gun, and we have also estimated the normalized QE decay due to ion back-bombardment.
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About • paper received ※ 27 August 2019       paper accepted ※ 03 September 2019       issue date ※ 08 October 2019  
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