IPAC2012 - List of Authors (Wisniewski, E.E.)

Paper	Title	Page
MOPPR068	Design and Development of the Diagnostic System for 75 MeV Electron Drive Beam for the AWA Upgrade	942
	J.G. Power, S.P. Antipov, M.E. Conde, W. Gai, C.-J. Jing, W. Liu, E.E. Wisniewski, Z.M. Yusof ANL, Argonne, USA
	Funding: Work supported by High Energy Physics, Office of Science, US DOE We report on the development of the diagnostic system for the ongoing upgrade to the Argonne Wakefield Accelerator (AWA) facility where the electron drive beam energy will be increased from 15 to 75 MeV. The facility will produce a wide dynamic range of drive bunch train formats ranging from a single microbunch of 100 pC to bunch trains of up to 32 bunches spaced by 769 ps with up to 100 nC per bunch. In addition to standard diagnostics, this drive bunch train format poses two challenges for the diagnostic system: (i) the close spacing of the drive bunches, 769 ps, makes resolving the individual pulses difficult and (ii) the dynamic range of the bunch charge varies by x1000. A critical parameter of the drive bunch train for the wakefield accelerator is the charge along the train. To measure this, we are planning to use a 15 GHz digital oscilloscope to read either a BPM or Bergoz FCT. To handle the large dynamic range of charge, the imaging system will make use of GigE Vision cameras and a distributed system of motorized lenses, with remote control of focus, zoom, and aperture, which are operated through terminal servers and RS232 controllers.

TUPPD069	Schottky-Enabled Photoemission and Dark Current Measurements - Toward an Alternate Approach to Fowler-Nordheim Plot Analysis	1563
	E.E. Wisniewski, W. Gai, J.G. Power ANL, Argonne, USA H. Chen, Y.-C. Du, Hua, J.F. Hua, W.-H. Huang, C.-X. Tang, L.X. Yan, Y. You TUB, Beijing, People's Republic of China A. Grudiev, W. Wuensch CERN, Geneva, Switzerland E.E. Wisniewski Illinois Institute of Technology, Chicago, Illinois, USA
	Field-emitted dark current, a major gradient-limiting factor in RF cavities, is usually analyzed via Fowler-Nordheim (FN) plots. Traditionally, field emission is attributed to geometrical perturbations on the bulk surface whose field enhancement factor (beta) and the emitting area (A) can be extracted from the FN plot. Field enhancement factors extracted in this way are typically much too high (1 to 2 orders of magnitude) to be explainable by either the geometric projection model applied to the measured surface roughness or by field enhancement factors extracted from Schottky-enabled photoemission measurements. We compare traditional analysis of FN plots to an alternate approach employing local work function variation. This is illustrated by comparative analysis of recent dark current and Schottky-enabled photoemission data taken at Tsinghua S-band RF gun. We conclude by describing a possible experimental plan for discrimination of variation of local work function vs. local field enhancement.

TUPPD070	Kelvin Probe Studies of a Cesium Telluride Photocathode for the AWA Photoinjector	1566
	E.E. Wisniewski, K.C. Harkay, Z.M. Yusof ANL, Argonne, USA L.K. Spentzouris, J. Terry, D.G. Velazquez, E.E. Wisniewski Illinois Institute of Technology, Chicago, Illinois, USA
	Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (>1%), is sufficiently robust in a photoinjector, and has a long lifetime. This photocathode is grown in-house for the new Argonne Wakefield Accelerator (AWA) to produce high charge per bunch (~50 nC). Here, we present a study of the "work function" of a 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 surprising effect of UV exposure on the work function, and the puzzling behavior of the work function during and after photocathode rejuvenation via heating.

TUPPD069	Schottky-Enabled Photoemission and Dark Current Measurements - Toward an Alternate Approach to Fowler-Nordheim Plot Analysis	1563
	E.E. Wisniewski, W. Gai, J.G. Power ANL, Argonne, USA H. Chen, Y.-C. Du, Hua, J.F. Hua, W.-H. Huang, C.-X. Tang, L.X. Yan, Y. You TUB, Beijing, People's Republic of China A. Grudiev, W. Wuensch CERN, Geneva, Switzerland E.E. Wisniewski Illinois Institute of Technology, Chicago, Illinois, USA
	Field-emitted dark current, a major gradient-limiting factor in RF cavities, is usually analyzed via Fowler-Nordheim (FN) plots. Traditionally, field emission is attributed to geometrical perturbations on the bulk surface whose field enhancement factor (beta) and the emitting area (A) can be extracted from the FN plot. Field enhancement factors extracted in this way are typically much too high (1 to 2 orders of magnitude) to be explainable by either the geometric projection model applied to the measured surface roughness or by field enhancement factors extracted from Schottky-enabled photoemission measurements. We compare traditional analysis of FN plots to an alternate approach employing local work function variation. This is illustrated by comparative analysis of recent dark current and Schottky-enabled photoemission data taken at Tsinghua S-band RF gun. We conclude by describing a possible experimental plan for discrimination of variation of local work function vs. local field enhancement.

TUPPD070	Kelvin Probe Studies of a Cesium Telluride Photocathode for the AWA Photoinjector	1566
	E.E. Wisniewski, K.C. Harkay, Z.M. Yusof ANL, Argonne, USA L.K. Spentzouris, J. Terry, D.G. Velazquez, E.E. Wisniewski Illinois Institute of Technology, Chicago, Illinois, USA
	Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (>1%), is sufficiently robust in a photoinjector, and has a long lifetime. This photocathode is grown in-house for the new Argonne Wakefield Accelerator (AWA) to produce high charge per bunch (~50 nC). Here, we present a study of the "work function" of a 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 surprising effect of UV exposure on the work function, and the puzzling behavior of the work function during and after photocathode rejuvenation via heating.

TUPPD071	Development of Cesium Telluride Photocathodes for the AWA Accelerator Upgrade	1569
	Z.M. Yusof, M.E. Conde, W. Gai ANL, Argonne, USA L.K. Spentzouris, E.E. Wisniewski Illinois Institute of Technology, Chicago, Illinois, USA
	Funding: U.S. Department of Energy Office of Science under Contract No. DE-AC02-06CH11357. Cesium telluride photocathodes have been fabricated for the Argonne Wakefield Accelerator (AWA) upgrade. The as-deposited photocathodes have consistently produced quantum efficiency values better than 10% with 254 nm light source and with variation of less than 5% over a circular area of 1.2 inches in diameter. We present various characterizations of the photocathode that have performed, including rejuvenation, lifetime, and performance in the L-band AWA photoinjector.

WEPPP025	A Test-bed for Future Linear Collider Technology: Argonne Wakefield Accelerator Facility (AWA)	2778
	M.E. Conde, D.S. Doran, W. Gai, R. Konecny, W. Liu, J.G. Power, Z.M. Yusof ANL, Argonne, USA S.P. Antipov, C.-J. Jing Euclid TechLabs, LLC, Solon, Ohio, USA E.E. Wisniewski Illinois Institute of Technology, Chicago, Illinois, USA
	Funding: Work supported by the U.S. Department of Energy under contract No. DE-AC02-06CH11357. Research at the AWA Facility has been focused on the development of electron beam driven wakefield structures. Accelerating gradients of up to 100 MV/m have been excited in dielectric loaded cylindrical structures operating in the microwave range of frequencies. Several upgrades, presently underway, will enable the facility to explore higher accelerating gradients, and also be able to generate longer RF pulses of higher intensity. The upgraded 75 MeV drive beam will consist of bunch trains of up to 32 bunches spaced by 0.77 ns with up to 100 nC per bunch. The RF pulses generated by the drive bunches are expected to reach GW power levels, establishing accelerating gradients of hundreds of MV/m.

Paper

Title

Page

Design and Development of the Diagnostic System for 75 MeV Electron Drive Beam for the AWA Upgrade

942

J.G. Power, S.P. Antipov, M.E. Conde, W. Gai, C.-J. Jing, W. Liu, E.E. Wisniewski, Z.M. Yusof
ANL, Argonne, USA

Funding: Work supported by High Energy Physics, Office of Science, US DOE
We report on the development of the diagnostic system for the ongoing upgrade to the Argonne Wakefield Accelerator (AWA) facility where the electron drive beam energy will be increased from 15 to 75 MeV. The facility will produce a wide dynamic range of drive bunch train formats ranging from a single microbunch of 100 pC to bunch trains of up to 32 bunches spaced by 769 ps with up to 100 nC per bunch. In addition to standard diagnostics, this drive bunch train format poses two challenges for the diagnostic system: (i) the close spacing of the drive bunches, 769 ps, makes resolving the individual pulses difficult and (ii) the dynamic range of the bunch charge varies by x1000. A critical parameter of the drive bunch train for the wakefield accelerator is the charge along the train. To measure this, we are planning to use a 15 GHz digital oscilloscope to read either a BPM or Bergoz FCT. To handle the large dynamic range of charge, the imaging system will make use of GigE Vision cameras and a distributed system of motorized lenses, with remote control of focus, zoom, and aperture, which are operated through terminal servers and RS232 controllers.

TUPPD069

Schottky-Enabled Photoemission and Dark Current Measurements - Toward an Alternate Approach to Fowler-Nordheim Plot Analysis

1563

E.E. Wisniewski, W. Gai, J.G. Power
ANL, Argonne, USA
H. Chen, Y.-C. Du, Hua, J.F. Hua, W.-H. Huang, C.-X. Tang, L.X. Yan, Y. You
TUB, Beijing, People's Republic of China
A. Grudiev, W. Wuensch
CERN, Geneva, Switzerland
E.E. Wisniewski
Illinois Institute of Technology, Chicago, Illinois, USA

Field-emitted dark current, a major gradient-limiting factor in RF cavities, is usually analyzed via Fowler-Nordheim (FN) plots. Traditionally, field emission is attributed to geometrical perturbations on the bulk surface whose field enhancement factor (beta) and the emitting area (A) can be extracted from the FN plot. Field enhancement factors extracted in this way are typically much too high (1 to 2 orders of magnitude) to be explainable by either the geometric projection model applied to the measured surface roughness or by field enhancement factors extracted from Schottky-enabled photoemission measurements. We compare traditional analysis of FN plots to an alternate approach employing local work function variation. This is illustrated by comparative analysis of recent dark current and Schottky-enabled photoemission data taken at Tsinghua S-band RF gun. We conclude by describing a possible experimental plan for discrimination of variation of local work function vs. local field enhancement.

TUPPD070

Kelvin Probe Studies of a Cesium Telluride Photocathode for the AWA Photoinjector

1566

E.E. Wisniewski, K.C. Harkay, Z.M. Yusof
ANL, Argonne, USA
L.K. Spentzouris, J. Terry, D.G. Velazquez, E.E. Wisniewski
Illinois Institute of Technology, Chicago, Illinois, USA

Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (>1%), is sufficiently robust in a photoinjector, and has a long lifetime. This photocathode is grown in-house for the new Argonne Wakefield Accelerator (AWA) to produce high charge per bunch (~50 nC). Here, we present a study of the "work function" of a 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 surprising effect of UV exposure on the work function, and the puzzling behavior of the work function during and after photocathode rejuvenation via heating.

TUPPD069

Schottky-Enabled Photoemission and Dark Current Measurements - Toward an Alternate Approach to Fowler-Nordheim Plot Analysis

1563

E.E. Wisniewski, W. Gai, J.G. Power
ANL, Argonne, USA
H. Chen, Y.-C. Du, Hua, J.F. Hua, W.-H. Huang, C.-X. Tang, L.X. Yan, Y. You
TUB, Beijing, People's Republic of China
A. Grudiev, W. Wuensch
CERN, Geneva, Switzerland
E.E. Wisniewski
Illinois Institute of Technology, Chicago, Illinois, USA

Field-emitted dark current, a major gradient-limiting factor in RF cavities, is usually analyzed via Fowler-Nordheim (FN) plots. Traditionally, field emission is attributed to geometrical perturbations on the bulk surface whose field enhancement factor (beta) and the emitting area (A) can be extracted from the FN plot. Field enhancement factors extracted in this way are typically much too high (1 to 2 orders of magnitude) to be explainable by either the geometric projection model applied to the measured surface roughness or by field enhancement factors extracted from Schottky-enabled photoemission measurements. We compare traditional analysis of FN plots to an alternate approach employing local work function variation. This is illustrated by comparative analysis of recent dark current and Schottky-enabled photoemission data taken at Tsinghua S-band RF gun. We conclude by describing a possible experimental plan for discrimination of variation of local work function vs. local field enhancement.

TUPPD070

Kelvin Probe Studies of a Cesium Telluride Photocathode for the AWA Photoinjector

1566

E.E. Wisniewski, K.C. Harkay, Z.M. Yusof
ANL, Argonne, USA
L.K. Spentzouris, J. Terry, D.G. Velazquez, E.E. Wisniewski
Illinois Institute of Technology, Chicago, Illinois, USA

Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (>1%), is sufficiently robust in a photoinjector, and has a long lifetime. This photocathode is grown in-house for the new Argonne Wakefield Accelerator (AWA) to produce high charge per bunch (~50 nC). Here, we present a study of the "work function" of a 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 surprising effect of UV exposure on the work function, and the puzzling behavior of the work function during and after photocathode rejuvenation via heating.

TUPPD071

Development of Cesium Telluride Photocathodes for the AWA Accelerator Upgrade

1569

Z.M. Yusof, M.E. Conde, W. Gai
ANL, Argonne, USA
L.K. Spentzouris, E.E. Wisniewski
Illinois Institute of Technology, Chicago, Illinois, USA

Funding: U.S. Department of Energy Office of Science under Contract No. DE-AC02-06CH11357.
Cesium telluride photocathodes have been fabricated for the Argonne Wakefield Accelerator (AWA) upgrade. The as-deposited photocathodes have consistently produced quantum efficiency values better than 10% with 254 nm light source and with variation of less than 5% over a circular area of 1.2 inches in diameter. We present various characterizations of the photocathode that have performed, including rejuvenation, lifetime, and performance in the L-band AWA photoinjector.

WEPPP025

A Test-bed for Future Linear Collider Technology: Argonne Wakefield Accelerator Facility (AWA)

2778

M.E. Conde, D.S. Doran, W. Gai, R. Konecny, W. Liu, J.G. Power, Z.M. Yusof
ANL, Argonne, USA
S.P. Antipov, C.-J. Jing
Euclid TechLabs, LLC, Solon, Ohio, USA
E.E. Wisniewski
Illinois Institute of Technology, Chicago, Illinois, USA

Funding: Work supported by the U.S. Department of Energy under contract No. DE-AC02-06CH11357.
Research at the AWA Facility has been focused on the development of electron beam driven wakefield structures. Accelerating gradients of up to 100 MV/m have been excited in dielectric loaded cylindrical structures operating in the microwave range of frequencies. Several upgrades, presently underway, will enable the facility to explore higher accelerating gradients, and also be able to generate longer RF pulses of higher intensity. The upgraded 75 MeV drive beam will consist of bunch trains of up to 32 bunches spaced by 0.77 ns with up to 100 nC per bunch. The RF pulses generated by the drive bunches are expected to reach GW power levels, establishing accelerating gradients of hundreds of MV/m.