PAC2013 - List of Authors (Rao, T.)

Paper	Title	Page
MOPBA21	Modeling Localized States and Band Bending Effects on Electron Emission Ion from GaAs	225
	D.A. Dimitrov, Y. Choi, C. Nieter Tech-X, Boulder, Colorado, USA I.V. Bazarov, S.S. Karkare, W.J. Schaff Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA I. Ben-Zvi, T. Rao, J. Smedley BNL, Upton, Long Island, New York, USA
	Funding: The authors wish to acknowledge the U.S. Department of Energy (DOE) and the National Science Foundation for funding under grants DOE DE-SC0006246, NSF DMR-0807731, and DOE DE-SC0003965. High acceptor doping of GaAs and (Cs, O) or (Cs, F) surface coating leads to downward band bending terminating with effective negative electron affinity surface. The periodicity breaking at the surface together with the formed potential leads to one or more localized states in the band bending region together with effective Fermi level pinning. We report results on how to calculate the band bending potential, the Fermi level pinning, and localized states as functions of GaAs p-doping density, surface density of states, and temperature. We also consider how these surface properties affect electron emission.

TUPSM06	The Cathode Preparation Chamber for the DC High Current High Polarization Gun	640
	O.H. Rahman, I. Ben-Zvi, D.M. Gassner, A.I. Pikin, T. Rao, E.J. Riehn, B. Sheehy, J. Skaritka, E. Wang, Q. Wu BNL, Upton, Long Island, New York, USA I. Ben-Zvi Stony Brook University, Stony Brook, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. A compact cathode preparation chamber for the high current high polarization gun for the proposed eRHIC project has been designed and assembled at Brookhaven National Laboratory. This preparation chamber will be used to activate GaAs photocathodes to be used in the Gatling gun. The chamber is capable of achieving XHV on a consistent basis. Bulk GaAs samples were activated in this chamber with standard QE for the respective wavelength. In this paper, we discuss the design of this vacuum system, the heat cleaning and the activation procedure for the GaAs sample which will eventually be followed for the Gatling gun.

TUPSM08	Beam Dynamics of Funneling Multiple Bunches Electrons	646
	E. Wang, I. Ben-Zvi, D.M. Gassner, W. Meng, O.H. Rahman, T. Rao, E.J. Riehn, J. Skaritka BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The proposed electron ion collider (eRHIC) at Brookhaven National Laboratory requires a polarized electron source with high average current, short bunch length, and small emittance. The-state-of-the-art single polarized electron photocathode is far from delivering the required 50mA current due to ion back-bombardment limiting the cathode’s lifetime and surface charge limit. In our funneling gun design, currently under construction, the electron bunches, generated from 20 photocathodes in a 220 kV DC gun, funnel to a single common beam axis. This article details our design of a high-average-current polarized electron gun’s optics, and presents our simulation of beam dynamics and combiner design. We also report the progress of funneling gun construction here.

THPAC12	Preparation and Investigation of Antimony Thin Films for Multi-Alkali Photocathodes	1163
	X. Liang, K. Attenkofer, T. Rao, S.G. Schubert, J. Smedley, E. Wang, Q. Wu BNL, Upton, Long Island, New York, USA I. Ben-Zvi, M. Ruiz-Osés Stony Brook University, Stony Brook, USA J. Jordan-Sweet IBM T. J. Watson Center, Yorktown Heights, New York, USA H.A. Padmore, J.J. Wong LBNL, Berkeley, California, USA
	Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DEAC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713. Multialikali antimonide cathodes provide high visible light quantum efficiency, with low thermal emittance and are excellent candidate materials for high average current next generation ERLs or high repetition rate FELs. Although these materials have some excellent characteristics, control of the growth mode of the thin film and ultimately the surface roughness is difficult and will effect the emittance that can be obtained in high gradient fields. To complement our growth studies of crystalline phases using x-ray diffraction studies, here we use the technique of grazing incidence small angle x-ray scattering (GI-SAXS) and atomic force microscopy (AFM) to measure the roughness as a function of film thickness. In this study, we demonstrate these techniques as applied to the growth of Sb, for a range of thicknesses, temperatures and growth rates, and show the wide range of moprphologies that can be formed with relatively minor changes in deposition conditions.

THPAC18	Progress on Growth of a Multi-alkali Photocathode for ERL	1181
	E. Wang, S.A. Belomestnykh, I. Ben-Zvi, T. Rao, J. Smedley BNL, Upton, Long Island, New York, USA I. Ben-Zvi, M. Ruiz-Osés Stony Brook University, Stony Brook, USA X. Liang SBU, Stony Brook, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and DOE grant at Stony Brook DE-SC0005713 K2CsSb is a robust photocathode capable of generating electron beams with high peak, high average current and low thermal emittance. During the last two year, a great improvement in the design and fabrication of a reliable deposition system suitable for K2CsSb cathode growth and its insertion into BNL high current ERL SRF gun has been achieved. A standard procedure for the growth of multi-alkali cathodes combined with another procedure to transport these cathodes into the SRF gun was developed. The first cathode growth on a copper insertion was ready to mount into the 704MHz gun. In this article, we will describe the progress of cathode growth and transportation for ERL project. In particular, laser heating and the cathode growth on Ta will be included.

THPAC34	Diamond Amplifier Design and Preliminary Test Results	1211
	T. Xin, S.A. Belomestnykh, I. Ben-Zvi Stony Brook University, Stony Brook, USA S.A. Belomestnykh, I. Ben-Zvi, T. Rao, J. Skaritka, J. Smedley, E. Wang, Q. Wu BNL, Upton, Long Island, New York, USA M. Gaowei, E.M. Muller SBU, Stony Brook, New York, USA
	Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713. Diamond as a large energy gap material can be easily made into a negative electron affinity (NEA) device. Using a few keV primary electrons as input and a few kV bias, the NEA diamond will emit cold electrons into vacuum with a large gain. We had tested and reported the performance of the diamond amplifier in our DC system somewhere else. The best amplification achieved so far was above 170. Next step of the experiment is to test the diamond amplifier in the 112 MHz superconducting RF electron gun. In this report we describe the design and simulations of the diamond amplifier to be tested in our SRF gun, show the finished amplifier containing the DC primary gun and light optics. We also provide preliminary test results of the laser and electron beam transport.

THPAC35	Multipacting Study of 112 MHz SRF Electron Gun	1214
	T. Xin, S.A. Belomestnykh, I. Ben-Zvi Stony Brook University, Stony Brook, USA S.A. Belomestnykh, I. Ben-Zvi, X. Liang, T. Rao, J. Skaritka, E. Wang, Q. Wu BNL, Upton, Long Island, New York, USA C.H. Boulware, T.L. Grimm Niowave, Inc., Lansing, Michigan, USA X. Liang SBU, Stony Brook, New York, USA
	Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713. The 112 MHz quarter wave superconducting electron gun was designed and built as an injector for the coherent electron cooling experiment. Besides that, the gun is suitable for testing various types of photocathodes thanks to its specially designed cathode holder. In recent RF tests of the gun at 4 K, the accelerating voltage reached 0.9 MV CW and more than 1 MV in pulsed mode. During this testing, we observed several multipacting barriers at low electromagnetic field levels. Since the final setup of the gun will be different from the cool down test configuration, we want to understand the exact location of the multipacting sites. We used Track3P to simulate multipacting. The results show several resonant trajectories that might be responsible for the observed barriers, but fortunately no strong multipacting barriers have been found in the cavity.

THPHO06	SRF and RF Systems for CeC PoP Experiment	1310
	S.A. Belomestnykh, I. Ben-Zvi, J.C. Brutus, D. Kayran, V. Litvinenko, P. Orfin, I. Pinayev, T. Rao, B. Sheehy, J. Skaritka, K.S. Smith, R. Than, J.E. Tuozzolo, E. Wang, Q. Wu, W. Xu, A. Zaltsman BNL, Upton, Long Island, New York, USA S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko, M. Ruiz-Osés, T. Xin Stony Brook University, Stony Brook, USA C.H. Boulware, T.L. Grimm Niowave, Inc., Lansing, Michigan, USA Y. Huang Fermilab, Batavia, USA X. Liang SBU, Stony Brook, New York, USA P.A. McIntosh, A.J. Moss, A.E. Wheelhouse STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE. Efforts to experimentally prove a concept of the coherent electron cooling are underway at BNL. A short 22-MeV linac will provide high charge, low repetition rate beam to cool a single ion bunch in RHIC. The linac will consist of a 112 MHz SRF gun, two 500 MHz normal conducting bunching cavities and a 704 MHz five-cell accelerating SRF cavity. The paper describes the SRF and RF systems, the linac layout, and discusses the project status, first test results and schedule.

Paper

Title

Page

Modeling Localized States and Band Bending Effects on Electron Emission Ion from GaAs

225

D.A. Dimitrov, Y. Choi, C. Nieter
Tech-X, Boulder, Colorado, USA
I.V. Bazarov, S.S. Karkare, W.J. Schaff
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
I. Ben-Zvi, T. Rao, J. Smedley
BNL, Upton, Long Island, New York, USA

Funding: The authors wish to acknowledge the U.S. Department of Energy (DOE) and the National Science Foundation for funding under grants DOE DE-SC0006246, NSF DMR-0807731, and DOE DE-SC0003965.
High acceptor doping of GaAs and (Cs, O) or (Cs, F) surface coating leads to downward band bending terminating with effective negative electron affinity surface. The periodicity breaking at the surface together with the formed potential leads to one or more localized states in the band bending region together with effective Fermi level pinning. We report results on how to calculate the band bending potential, the Fermi level pinning, and localized states as functions of GaAs p-doping density, surface density of states, and temperature. We also consider how these surface properties affect electron emission.

TUPSM06

The Cathode Preparation Chamber for the DC High Current High Polarization Gun

640

O.H. Rahman, I. Ben-Zvi, D.M. Gassner, A.I. Pikin, T. Rao, E.J. Riehn, B. Sheehy, J. Skaritka, E. Wang, Q. Wu
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi
Stony Brook University, Stony Brook, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
A compact cathode preparation chamber for the high current high polarization gun for the proposed eRHIC project has been designed and assembled at Brookhaven National Laboratory. This preparation chamber will be used to activate GaAs photocathodes to be used in the Gatling gun. The chamber is capable of achieving XHV on a consistent basis. Bulk GaAs samples were activated in this chamber with standard QE for the respective wavelength. In this paper, we discuss the design of this vacuum system, the heat cleaning and the activation procedure for the GaAs sample which will eventually be followed for the Gatling gun.

TUPSM08

Beam Dynamics of Funneling Multiple Bunches Electrons

646

E. Wang, I. Ben-Zvi, D.M. Gassner, W. Meng, O.H. Rahman, T. Rao, E.J. Riehn, J. Skaritka
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
The proposed electron ion collider (eRHIC) at Brookhaven National Laboratory requires a polarized electron source with high average current, short bunch length, and small emittance. The-state-of-the-art single polarized electron photocathode is far from delivering the required 50mA current due to ion back-bombardment limiting the cathode’s lifetime and surface charge limit. In our funneling gun design, currently under construction, the electron bunches, generated from 20 photocathodes in a 220 kV DC gun, funnel to a single common beam axis. This article details our design of a high-average-current polarized electron gun’s optics, and presents our simulation of beam dynamics and combiner design. We also report the progress of funneling gun construction here.

THPAC12

Preparation and Investigation of Antimony Thin Films for Multi-Alkali Photocathodes

1163

X. Liang, K. Attenkofer, T. Rao, S.G. Schubert, J. Smedley, E. Wang, Q. Wu
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi, M. Ruiz-Osés
Stony Brook University, Stony Brook, USA
J. Jordan-Sweet
IBM T. J. Watson Center, Yorktown Heights, New York, USA
H.A. Padmore, J.J. Wong
LBNL, Berkeley, California, USA

Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DEAC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713.
Multialikali antimonide cathodes provide high visible light quantum efficiency, with low thermal emittance and are excellent candidate materials for high average current next generation ERLs or high repetition rate FELs. Although these materials have some excellent characteristics, control of the growth mode of the thin film and ultimately the surface roughness is difficult and will effect the emittance that can be obtained in high gradient fields. To complement our growth studies of crystalline phases using x-ray diffraction studies, here we use the technique of grazing incidence small angle x-ray scattering (GI-SAXS) and atomic force microscopy (AFM) to measure the roughness as a function of film thickness. In this study, we demonstrate these techniques as applied to the growth of Sb, for a range of thicknesses, temperatures and growth rates, and show the wide range of moprphologies that can be formed with relatively minor changes in deposition conditions.

THPAC18

Progress on Growth of a Multi-alkali Photocathode for ERL

1181

E. Wang, S.A. Belomestnykh, I. Ben-Zvi, T. Rao, J. Smedley
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi, M. Ruiz-Osés
Stony Brook University, Stony Brook, USA
X. Liang
SBU, Stony Brook, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and DOE grant at Stony Brook DE-SC0005713
K2CsSb is a robust photocathode capable of generating electron beams with high peak, high average current and low thermal emittance. During the last two year, a great improvement in the design and fabrication of a reliable deposition system suitable for K2CsSb cathode growth and its insertion into BNL high current ERL SRF gun has been achieved. A standard procedure for the growth of multi-alkali cathodes combined with another procedure to transport these cathodes into the SRF gun was developed. The first cathode growth on a copper insertion was ready to mount into the 704MHz gun. In this article, we will describe the progress of cathode growth and transportation for ERL project. In particular, laser heating and the cathode growth on Ta will be included.

THPAC34

Diamond Amplifier Design and Preliminary Test Results

1211

T. Xin, S.A. Belomestnykh, I. Ben-Zvi
Stony Brook University, Stony Brook, USA
S.A. Belomestnykh, I. Ben-Zvi, T. Rao, J. Skaritka, J. Smedley, E. Wang, Q. Wu
BNL, Upton, Long Island, New York, USA
M. Gaowei, E.M. Muller
SBU, Stony Brook, New York, USA

Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713.
Diamond as a large energy gap material can be easily made into a negative electron affinity (NEA) device. Using a few keV primary electrons as input and a few kV bias, the NEA diamond will emit cold electrons into vacuum with a large gain. We had tested and reported the performance of the diamond amplifier in our DC system somewhere else. The best amplification achieved so far was above 170. Next step of the experiment is to test the diamond amplifier in the 112 MHz superconducting RF electron gun. In this report we describe the design and simulations of the diamond amplifier to be tested in our SRF gun, show the finished amplifier containing the DC primary gun and light optics. We also provide preliminary test results of the laser and electron beam transport.

THPAC35

Multipacting Study of 112 MHz SRF Electron Gun

1214

T. Xin, S.A. Belomestnykh, I. Ben-Zvi
Stony Brook University, Stony Brook, USA
S.A. Belomestnykh, I. Ben-Zvi, X. Liang, T. Rao, J. Skaritka, E. Wang, Q. Wu
BNL, Upton, Long Island, New York, USA
C.H. Boulware, T.L. Grimm
Niowave, Inc., Lansing, Michigan, USA
X. Liang
SBU, Stony Brook, New York, USA

Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713.
The 112 MHz quarter wave superconducting electron gun was designed and built as an injector for the coherent electron cooling experiment. Besides that, the gun is suitable for testing various types of photocathodes thanks to its specially designed cathode holder. In recent RF tests of the gun at 4 K, the accelerating voltage reached 0.9 MV CW and more than 1 MV in pulsed mode. During this testing, we observed several multipacting barriers at low electromagnetic field levels. Since the final setup of the gun will be different from the cool down test configuration, we want to understand the exact location of the multipacting sites. We used Track3P to simulate multipacting. The results show several resonant trajectories that might be responsible for the observed barriers, but fortunately no strong multipacting barriers have been found in the cavity.

THPHO06

SRF and RF Systems for CeC PoP Experiment

1310

S.A. Belomestnykh, I. Ben-Zvi, J.C. Brutus, D. Kayran, V. Litvinenko, P. Orfin, I. Pinayev, T. Rao, B. Sheehy, J. Skaritka, K.S. Smith, R. Than, J.E. Tuozzolo, E. Wang, Q. Wu, W. Xu, A. Zaltsman
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko, M. Ruiz-Osés, T. Xin
Stony Brook University, Stony Brook, USA
C.H. Boulware, T.L. Grimm
Niowave, Inc., Lansing, Michigan, USA
Y. Huang
Fermilab, Batavia, USA
X. Liang
SBU, Stony Brook, New York, USA
P.A. McIntosh, A.J. Moss, A.E. Wheelhouse
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE.
Efforts to experimentally prove a concept of the coherent electron cooling are underway at BNL. A short 22-MeV linac will provide high charge, low repetition rate beam to cool a single ion bunch in RHIC. The linac will consist of a 112 MHz SRF gun, two 500 MHz normal conducting bunching cavities and a 704 MHz five-cell accelerating SRF cavity. The paper describes the SRF and RF systems, the linac layout, and discusses the project status, first test results and schedule.