2011 Particle Accelerator Conference - List of Authors (Jensen, K. L.)

Paper	Title	Page
THP204	Corrections to Quantum Efficiency Predictions for Low Work Function Electron Sources	2504
	K. L. Jensen NRL, Washington, DC, USA D.W. Feldman, E.J. Montgomery, P.G. O'Shea UMD, College Park, Maryland, USA J.J. Petillo SAIC, Billerica, Massachusetts, USA
	Funding: Funding by the Joint Technology Office and the Office of Naval Research. The Three-Step Model of Spicer, or the analogous Moments-based models, can be used to predict photoemission from metals and cesiated metals. In either, it is a convenient approximation to neglect electrons that have undergone scattering. Using Monte Carlo to follow scattered electrons, we assess the utility of the approximation particularly for low work function (cesiated) surfaces.

THP205	Modeling the Performance of a Diamond Current Amplifier for FELs	2507
	K. L. Jensen, B. Pate, J.L. Shaw, J.E. Yater NRL, Washington, DC, USA J.J. Petillo SAIC, Billerica, Massachusetts, USA
	Funding: We gratefully acknowledge funding by the Joint Technology Office and the Office of Naval Research. A diamond current amplifier concept can reduce demands made of photocathodes under development for high performance Free Electron Lasers (FELs) by augmenting the charge per bunch (i.e., increasing the apparent QE of the photocathode) by employing secondary emission amplification in a diamond flake. The characteristics of the bunch that emerges from the diamond flake is dependent on properties of the diamond (e.g., impurity concentrations) and the conditions under which it is operated (e.g., voltage drop, space charge, temperature). A study of the electron bunches produced by an incident 3-5 keV beam striking a very thin diamond and its transport under bias subject to scattering and space charge forces is considered. The quantities of greatest interest are then the yield, the transit time, emittance, and the rise/fall characteristics of the emerging bunch. These are simulated using Monte Carlo techniques, the application of which shall be described as it applies to the initial generation of the secondary electrons followed by their scattering and transport in the presence of band bending and space charge. J.E. Yater, et al., IEEE IVNC (2009); J. L. Shaw, et al., ibid. **K.L. Jensen, et al. J. Appl. Phys. 108, 044509 (2010).

THP208	Development of Alkali-Based High Quantum Efficiency Semiconductors for Dispenser Photocathodes	2510
	E.J. Montgomery, D.W. Feldman, S.A. Khan, P.G. O'Shea, P.Z. Pan, B.C. Riddick UMD, College Park, Maryland, USA K. L. Jensen NRL, Washington, DC, USA
	Funding: This work is supported by the Office of Naval Research. Photocathodes as electron beam sources can meet the stringent requirements of high performance FELs, but exhibit a lifetime-efficiency tradeoff. High quantum efficiency (QE) cathodes are typically semiconductors, well described by recently enhanced theory. Cesium dispenser technology, proven to extend lifetime of tungsten cathodes, can be extended to high QE via the development of semiconductor coatings which are suitable for rejuvenation. Rejuvenation occurs via controlled cesium diffusion through a sintered substrate to resupply the surface (as described by models of pore and surface diffusion). Compatible coatings must be thermally stable materials with a cesium-based surface layer. Following standard fabrication processes**, we discuss alkali antimonides and alkali aurides as cesium dispenser photocathode coatings and analyze future prospects. We also describe improvements to experimental techniques. K.L. Jensen et al., (this conference) Moody et al., J. Appl. Phys. 102(10), 2010 B.C. Riddick et al., (this conference) *P.Z. Pan et al., (this conference) ***S.A. Khan et al., (this conference)

Paper

Title

Page

Corrections to Quantum Efficiency Predictions for Low Work Function Electron Sources

2504

K. L. Jensen
NRL, Washington, DC, USA
D.W. Feldman, E.J. Montgomery, P.G. O'Shea
UMD, College Park, Maryland, USA
J.J. Petillo
SAIC, Billerica, Massachusetts, USA

Funding: Funding by the Joint Technology Office and the Office of Naval Research.
The Three-Step Model of Spicer, or the analogous Moments-based models, can be used to predict photoemission from metals and cesiated metals. In either, it is a convenient approximation to neglect electrons that have undergone scattering. Using Monte Carlo to follow scattered electrons, we assess the utility of the approximation particularly for low work function (cesiated) surfaces.

THP205

Modeling the Performance of a Diamond Current Amplifier for FELs

2507

K. L. Jensen, B. Pate, J.L. Shaw, J.E. Yater
NRL, Washington, DC, USA
J.J. Petillo
SAIC, Billerica, Massachusetts, USA

Funding: We gratefully acknowledge funding by the Joint Technology Office and the Office of Naval Research.
A diamond current amplifier concept can reduce demands made of photocathodes under development for high performance Free Electron Lasers (FELs) by augmenting the charge per bunch (i.e., increasing the apparent QE of the photocathode) by employing secondary emission amplification in a diamond flake*. The characteristics of the bunch that emerges from the diamond flake is dependent on properties of the diamond (e.g., impurity concentrations) and the conditions under which it is operated (e.g., voltage drop, space charge, temperature)**. A study of the electron bunches produced by an incident 3-5 keV beam striking a very thin diamond and its transport under bias subject to scattering and space charge forces is considered. The quantities of greatest interest are then the yield, the transit time, emittance, and the rise/fall characteristics of the emerging bunch. These are simulated using Monte Carlo techniques, the application of which shall be described as it applies to the initial generation of the secondary electrons followed by their scattering and transport in the presence of band bending and space charge.
*J.E. Yater, et al., IEEE IVNC (2009); J. L. Shaw, et al., ibid.
**K.L. Jensen, et al. J. Appl. Phys. 108, 044509 (2010).

THP208

Development of Alkali-Based High Quantum Efficiency Semiconductors for Dispenser Photocathodes

2510

E.J. Montgomery, D.W. Feldman, S.A. Khan, P.G. O'Shea, P.Z. Pan, B.C. Riddick
UMD, College Park, Maryland, USA
K. L. Jensen
NRL, Washington, DC, USA

Funding: This work is supported by the Office of Naval Research.
Photocathodes as electron beam sources can meet the stringent requirements of high performance FELs, but exhibit a lifetime-efficiency tradeoff. High quantum efficiency (QE) cathodes are typically semiconductors, well described by recently enhanced theory*. Cesium dispenser technology, proven to extend lifetime of tungsten cathodes**, can be extended to high QE via the development of semiconductor coatings which are suitable for rejuvenation. Rejuvenation occurs via controlled cesium diffusion through a sintered substrate to resupply the surface (as described by models of pore*** and surface**** diffusion). Compatible coatings must be thermally stable materials with a cesium-based surface layer. Following standard fabrication processes*****, we discuss alkali antimonides and alkali aurides as cesium dispenser photocathode coatings and analyze future prospects. We also describe improvements to experimental techniques.
*K.L. Jensen et al., (this conference)
**Moody et al., J. Appl. Phys. 102(10), 2010
***B.C. Riddick et al., (this conference)
****P.Z. Pan et al., (this conference)
*****S.A. Khan et al., (this conference)