NAPAC2019 - List of Authors (Rahman, O.H.)

Paper	Title	Page
MOPLM06	High Voltage Design of a 350 kV DC Photogun at BNL	102
	W. Liu, O.H. Rahman, E. Wang BNL, Upton, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. Brookhaven National Laboratory is constructing a 350 kV DC high voltage photogun to provide spin-polarized electron beam for the proposed eRHIC facility. The photogun employs a compact inverted-tapered-geometry ceramic insulator that extends into the vacuum chamber and mechanically holds the cathode electrode. By operating at high voltage, the photogun will provide lower beam emittance, thereby improving the beam transmission through the injector apertures, and prolong the operating lifetime of the photogun. However, high voltage increases the field emission, which can result in high voltage breakdown and even lead to irreparable damage of the ceramic insulator. This work describes the methods to minimize the electric field near the metal-vacuum-insulator interface, and to avoid high voltage breakdown and ceramic insulator damage. The triple point junction shields are designed. The simulated electric field, field emission and beam transportation will be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2019-MOPLM06
About •	paper received ※ 19 August 2019 paper accepted ※ 31 August 2019 issue date ※ 08 October 2019
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MOPLH02	Study of Photocathode Surface Damage due to Ion Back-Bombardment in High Current DC Gun	174
SUPLE16	use link to see paper's listing under its alternate paper code
	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2019-MOPLH02
About •	paper received ※ 27 August 2019 paper accepted ※ 03 September 2019 issue date ※ 08 October 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

High Voltage Design of a 350 kV DC Photogun at BNL

102

W. Liu, O.H. Rahman, E. Wang
BNL, Upton, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
Brookhaven National Laboratory is constructing a 350 kV DC high voltage photogun to provide spin-polarized electron beam for the proposed eRHIC facility. The photogun employs a compact inverted-tapered-geometry ceramic insulator that extends into the vacuum chamber and mechanically holds the cathode electrode. By operating at high voltage, the photogun will provide lower beam emittance, thereby improving the beam transmission through the injector apertures, and prolong the operating lifetime of the photogun. However, high voltage increases the field emission, which can result in high voltage breakdown and even lead to irreparable damage of the ceramic insulator. This work describes the methods to minimize the electric field near the metal-vacuum-insulator interface, and to avoid high voltage breakdown and ceramic insulator damage. The triple point junction shields are designed. The simulated electric field, field emission and beam transportation will be presented.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2019-MOPLM06

About •

paper received ※ 19 August 2019 paper accepted ※ 31 August 2019 issue date ※ 08 October 2019

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPLH02

Study of Photocathode Surface Damage due to Ion Back-Bombardment in High Current DC Gun

174

SUPLE16

use link to see paper's listing under its alternate paper code

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.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2019-MOPLH02

About •

paper received ※ 27 August 2019 paper accepted ※ 03 September 2019 issue date ※ 08 October 2019

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)