2011 Particle Accelerator Conference - List of Authors (Smedley, J.)

Paper	Title	Page
MOP155	Progress on Diamond Amplified Photo Cathode	382
	E. Wang PKU/IHIP, Beijing, People's Republic of China I. Ben-Zvi, X. Chang, J. Kewisch, E.M. Muller, T. Rao, J. Smedley, Q. Wu BNL, Upton, Long Island, New York, USA T. Xin Stony Brook University, Stony Brook, USA
	Funding: Work supported by Brookhaven science Associates, LLC Contract No.DE-AC02-98CH10886 with the U.S.DOE Two years ago, we obtained an emission gain of 40 from the Diamond Amplifier Cathode (DAC) in our test system. In our current systematic study of hydrogenation, the highest gain we registered in emission scanning was 178. We proved that our treatments for improving the diamond amplifiers are reproducible. Upcoming tests planned include testing DAC in a RF cavity. Already, we have designed a system for these tests using our 112 MHz superconducting cavity, wherein we will measure DAC parameters, such as the limit, if any, on emission current density, the bunch charge, and the bunch length.

MOP207	Diamond X-ray Beam Position Monitors	483
	J. Smedley, A. Heroux, J.W. Keister BNL, Upton, Long Island, New York, USA K. Attenkofer ANL, Argonne, USA J. Bohon Case Western Reserve University, Center for Synchrotron Biosciences, Upton, New York, USA J. Distel LANL, Los Alamos, New Mexico, USA M. Gaowei SBU, Stony Brook, New York, USA E.M. Muller Stony Brook University, Stony Brook, USA
	Funding: The authors wish to acknowledge the support of the U.S. Department of Energy (DOE) under grant DE-FG02-08ER41547. Modern synchrotrons are capable of significant per-pulse x-ray flux, and time resolved pulse-probe experiments have become feasible. These experiments provide unique demands on x-ray monitors, as the beam position, flux and arrival time all potentially need to be recorded for each x-ray pulse. Further, monitoring of “white” x-ray beam position and flux upstream of beamline optics is desirable as a diagnostic of the electron source. We report on a diamond quadrant monitors which provide beam monitoring for a variety of applications, for both white and monochromatic beams. These monitors have a position resolution of 20 nm for a stable beam, are linear in flux over at least 11 orders of magnitude, and can resolve beam motion shot-by-shot at repetition rates up to 6.5 MHz.

WEP161	Modeling and Simulations of Electron Emission from Diamond-Amplified Cathodes	1791
	D.A. Dimitrov, R. Busby, J.R. Cary, D.N. Smithe Tech-X, Boulder, Colorado, USA I. Ben-Zvi, X. Chang, T. Rao, J. Smedley, E. Wang, Q. Wu BNL, Upton, Long Island, New York, USA
	Funding: This work is supported by the U. S. Department of Energy under the DE-SC0004431 grant. Emission of electrons from a diamond-amplified cathode was recently demonstrated. This experiment was based on a promising new concept* for generation of high-current, high-brightness, and low thermal emittance electron beams. The measurements from transmission and emission experiments have shown the potential to realize the diamond-amplified cathode concept. However, the results indicate that the involved physical properties should be understood in greater detail to build diamond cathodes with optical properties. We have already made progress in understanding the secondary electron generation and charge transport in diamond with the models we implemented in the VORPAL computational framework. We have been implementing models for electron emission from diamond and will present results from 3D VORPAL simulations with the integrated capabilities on generating electrons and holes, initiated by energetic primary electrons, propagation of the charge clouds, and then the emission of electrons into diamond. We will discuss simulation results on the dependence of the electron emission on diamond surface properties. * X. Chang et al., Electron Beam Emission from a Diamond-Amplified Cathodes, to appear in Phys. Rev. Lett. (2010). ** I. Ben-Zvi et al., Secondary emission enhanced photoinjector, Rep. C-A/AP/149, BNL (2004).

WEP162	Modeling of Diamond Based Devices for Beam Diagnostics	1794
	D.A. Dimitrov, R. Busby Tech-X, Boulder, Colorado, USA I. Ben-Zvi, J.W. Keister, T. Rao, J. Smedley BNL, Upton, Long Island, New York, USA E.M. Muller Stony Brook University, Stony Brook, USA
	Funding: The authors wish to acknowledge the support of the U.S. Department of Energy (DOE) under grants DE-SC0004584 (Tech-X Corp.) and DE-FG02-08ER41547 (BNL). Beamlines at new light sources, such as the National Synchrotron Light Source II will operate at flux levels beyond the saturation level of existing diagnostics, necessitating the development of new devices. Currently, there is no detector which can span the entire flux range that is possible even in a second generation light source and will become crucial for next generation light sources. One new approach* is a diamond-based detector that will be able to monitor beam position, flux and timing to much better resolution. Furthermore, this detector also has linear response to flux over 11 orders of magnitude. However, the successful development of the detector requires thorough understanding and optimization of the physical processes involved. We will discuss the new modeling capabilities we have been implementing in the VORPAL 3D code to investigate the effects of charge generation due to absorption of x-ray photons, transport, and charge trapping. We will report results from VORPAL simulations on charge collection and how it depends on applied field, charge trapping, and the energy of absorbed photons. *J. W. Keister, J. Smedley, D. A. Dimitrov, and R. Busby, Charge Collection and Propagation in Diamond X-ray Detectors, IEEE Transactions on Nuclear Science, 57, 2400 (2010).

WEP284	Performance Study of K2CsSb Photocathode inside a DC High Voltage Gun	2017
	T. Rao, J. Smedley BNL, Upton, Long Island, New York, USA J.M. Grames, R.R. Mammei, J.L. McCarter, M. Poelker, R. Suleiman JLAB, Newport News, Virginia, USA
	Funding: The authors wish to acknowledge the support of the U.S. Department of Energy (DOE) under grant DE-FG02-08ER41547. In the past decade, there has been considerable interest in the generation of tens of mA average current in a photoinjector. Until recently, GaAs:Cs cathodes and K2CsSb cathodes have been tested successfully in DC and RF injectors respectively for this application. Our goal is to test the GaAs:Cs in RF injector and the K2CsSb cathode in the DC gun in order to widen our choices. Since the multialkali cathode is a compound with uniform stochiometry over its entire thickness, we anticipate that the life time issues seen in GaAs:Cs due surface damage by ion bombardment would be minimized with this material. Hence successful operation of the K2CsSb cathode in DC gun could lead to a relatively robust electron source capable of delivering ampere level currents. In order to test the performance of K2CsSb cathode in a DC gun, we have designed and built a load lock system that would allow the fabrication of the cathode at BNL and its testing at JLab. In this paper, we will present the design of the load-lock system, cathode fabrication, and the cathode performance in the preparation chamber and in the DC gun.

Paper

Title

Page

Progress on Diamond Amplified Photo Cathode

382

E. Wang
PKU/IHIP, Beijing, People's Republic of China
I. Ben-Zvi, X. Chang, J. Kewisch, E.M. Muller, T. Rao, J. Smedley, Q. Wu
BNL, Upton, Long Island, New York, USA
T. Xin
Stony Brook University, Stony Brook, USA

Funding: Work supported by Brookhaven science Associates, LLC Contract No.DE-AC02-98CH10886 with the U.S.DOE
Two years ago, we obtained an emission gain of 40 from the Diamond Amplifier Cathode (DAC) in our test system. In our current systematic study of hydrogenation, the highest gain we registered in emission scanning was 178. We proved that our treatments for improving the diamond amplifiers are reproducible. Upcoming tests planned include testing DAC in a RF cavity. Already, we have designed a system for these tests using our 112 MHz superconducting cavity, wherein we will measure DAC parameters, such as the limit, if any, on emission current density, the bunch charge, and the bunch length.

MOP207

Diamond X-ray Beam Position Monitors

483

J. Smedley, A. Heroux, J.W. Keister
BNL, Upton, Long Island, New York, USA
K. Attenkofer
ANL, Argonne, USA
J. Bohon
Case Western Reserve University, Center for Synchrotron Biosciences, Upton, New York, USA
J. Distel
LANL, Los Alamos, New Mexico, USA
M. Gaowei
SBU, Stony Brook, New York, USA
E.M. Muller
Stony Brook University, Stony Brook, USA

Funding: The authors wish to acknowledge the support of the U.S. Department of Energy (DOE) under grant DE-FG02-08ER41547.
Modern synchrotrons are capable of significant per-pulse x-ray flux, and time resolved pulse-probe experiments have become feasible. These experiments provide unique demands on x-ray monitors, as the beam position, flux and arrival time all potentially need to be recorded for each x-ray pulse. Further, monitoring of “white” x-ray beam position and flux upstream of beamline optics is desirable as a diagnostic of the electron source. We report on a diamond quadrant monitors which provide beam monitoring for a variety of applications, for both white and monochromatic beams. These monitors have a position resolution of 20 nm for a stable beam, are linear in flux over at least 11 orders of magnitude, and can resolve beam motion shot-by-shot at repetition rates up to 6.5 MHz.

WEP161

Modeling and Simulations of Electron Emission from Diamond-Amplified Cathodes

1791

D.A. Dimitrov, R. Busby, J.R. Cary, D.N. Smithe
Tech-X, Boulder, Colorado, USA
I. Ben-Zvi, X. Chang, T. Rao, J. Smedley, E. Wang, Q. Wu
BNL, Upton, Long Island, New York, USA

Funding: This work is supported by the U. S. Department of Energy under the DE-SC0004431 grant.
Emission of electrons from a diamond-amplified cathode was recently demonstrated*. This experiment was based on a promising new concept** for generation of high-current, high-brightness, and low thermal emittance electron beams. The measurements from transmission and emission experiments have shown the potential to realize the diamond-amplified cathode concept. However, the results indicate that the involved physical properties should be understood in greater detail to build diamond cathodes with optical properties. We have already made progress in understanding the secondary electron generation and charge transport in diamond with the models we implemented in the VORPAL computational framework. We have been implementing models for electron emission from diamond and will present results from 3D VORPAL simulations with the integrated capabilities on generating electrons and holes, initiated by energetic primary electrons, propagation of the charge clouds, and then the emission of electrons into diamond. We will discuss simulation results on the dependence of the electron emission on diamond surface properties.
* X. Chang et al., Electron Beam Emission from a Diamond-Amplified Cathodes, to appear in Phys. Rev. Lett. (2010).
** I. Ben-Zvi et al., Secondary emission enhanced photoinjector, Rep. C-A/AP/149, BNL (2004).

WEP162

Modeling of Diamond Based Devices for Beam Diagnostics

1794

D.A. Dimitrov, R. Busby
Tech-X, Boulder, Colorado, USA
I. Ben-Zvi, J.W. Keister, T. Rao, J. Smedley
BNL, Upton, Long Island, New York, USA
E.M. Muller
Stony Brook University, Stony Brook, USA

Funding: The authors wish to acknowledge the support of the U.S. Department of Energy (DOE) under grants DE-SC0004584 (Tech-X Corp.) and DE-FG02-08ER41547 (BNL).
Beamlines at new light sources, such as the National Synchrotron Light Source II will operate at flux levels beyond the saturation level of existing diagnostics, necessitating the development of new devices. Currently, there is no detector which can span the entire flux range that is possible even in a second generation light source and will become crucial for next generation light sources. One new approach* is a diamond-based detector that will be able to monitor beam position, flux and timing to much better resolution. Furthermore, this detector also has linear response to flux over 11 orders of magnitude. However, the successful development of the detector requires thorough understanding and optimization of the physical processes involved. We will discuss the new modeling capabilities we have been implementing in the VORPAL 3D code to investigate the effects of charge generation due to absorption of x-ray photons, transport, and charge trapping. We will report results from VORPAL simulations on charge collection and how it depends on applied field, charge trapping, and the energy of absorbed photons.
*J. W. Keister, J. Smedley, D. A. Dimitrov, and R. Busby, Charge Collection and Propagation in Diamond X-ray Detectors, IEEE Transactions on Nuclear Science, 57, 2400 (2010).

WEP284

Performance Study of K2CsSb Photocathode inside a DC High Voltage Gun

2017

T. Rao, J. Smedley
BNL, Upton, Long Island, New York, USA
J.M. Grames, R.R. Mammei, J.L. McCarter, M. Poelker, R. Suleiman
JLAB, Newport News, Virginia, USA

Funding: The authors wish to acknowledge the support of the U.S. Department of Energy (DOE) under grant DE-FG02-08ER41547.
In the past decade, there has been considerable interest in the generation of tens of mA average current in a photoinjector. Until recently, GaAs:Cs cathodes and K2CsSb cathodes have been tested successfully in DC and RF injectors respectively for this application. Our goal is to test the GaAs:Cs in RF injector and the K2CsSb cathode in the DC gun in order to widen our choices. Since the multialkali cathode is a compound with uniform stochiometry over its entire thickness, we anticipate that the life time issues seen in GaAs:Cs due surface damage by ion bombardment would be minimized with this material. Hence successful operation of the K2CsSb cathode in DC gun could lead to a relatively robust electron source capable of delivering ampere level currents. In order to test the performance of K2CsSb cathode in a DC gun, we have designed and built a load lock system that would allow the fabrication of the cathode at BNL and its testing at JLab. In this paper, we will present the design of the load-lock system, cathode fabrication, and the cathode performance in the preparation chamber and in the DC gun.