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

Paper	Title	Page
WEP035	Intense Sheet Electron Beam Transport in a Periodically Cusped Magnetic Field	1558
	P.B. Larsen, B. Levush, J.A. Pasour NRL, Washington, DC, USA T.M. Antonsen UMD, College Park, Maryland, USA A.T. Burke, J.J. Petillo SAIC, Billerica, Massachusetts, USA K.T. Nguyen Beam-Wave Research, Inc., Union City, USA
	Funding: Acknowledgements: We gratefully acknowledge funding by the Office of Naval Research. We explore periodically cusped magnetic (PCM) fields in the regime of a Ka-Band coupled-cavity travelling wave tube (beam current = 3.5A, voltage = 19.5kV, 10:1 beam aspect ratio). We use finite-element beam optics code MICHELLE to simulate the 3-dimensional beam optics for the beam transport within a PCM field. Realistic 3-dimensional magnetic fields have been considered to determine the practicality of these designs. We present the methodology used to focus and transport a thermal beam from a shielded-cathode, high aspect-ratio electron gun.

WEP160	Inclusion of Surface Roughness Effects in Emission Modeling With the MICHELLE Code	1788
	J.F. DeFord STAAR/AWR Corporation, Mequon, USA N.J. Dionne, S.G. Ovtchinnikov, J.J. Petillo SAIC, Billerica, Massachusetts, USA
	High-brightness electron beams are needed in millimeter-wave tubes and other high-power RF applications. Cathode surface roughness at the micron scale, commonly due to machining or other effects, can lead to broadening of the velocity distribution of electrons downstream, increasing emittance and lowering beam brightness. In this paper we investigate methods of including surface roughness effects in the MICHELLE code. Modeling of typical surface imperfections over an entire cathode is not feasible, since it requires representation of features that are 3 to 5 orders of magnitude smaller than the cathode. Moreover, the actual surface imperfections for a given cathode are unknown without a prohibitive microscopic investigation of the surface, and these details vary between cathodes with the same machining history. To avoid these problems we investigated modifications to emission models that can account for these effects in an average sense, allowing the use of a smooth emission surface in a model while retaining the essential effects of the rough surface on the beam. We present the results of this investigation, along with representative solutions for sample structures. John Petillo, et al., “Recent Developments in the MICHELLE 2D/3D Electron Gun and Collector Modeling Code”, IEEE Trans. Electron Devices Sci., vol. 52, no. 5, May 2005, pp. 742-748.

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).

Paper

Title

Page

Intense Sheet Electron Beam Transport in a Periodically Cusped Magnetic Field

1558

P.B. Larsen, B. Levush, J.A. Pasour
NRL, Washington, DC, USA
T.M. Antonsen
UMD, College Park, Maryland, USA
A.T. Burke, J.J. Petillo
SAIC, Billerica, Massachusetts, USA
K.T. Nguyen
Beam-Wave Research, Inc., Union City, USA

Funding: Acknowledgements: We gratefully acknowledge funding by the Office of Naval Research.
We explore periodically cusped magnetic (PCM) fields in the regime of a Ka-Band coupled-cavity travelling wave tube (beam current = 3.5A, voltage = 19.5kV, 10:1 beam aspect ratio). We use finite-element beam optics code MICHELLE to simulate the 3-dimensional beam optics for the beam transport within a PCM field. Realistic 3-dimensional magnetic fields have been considered to determine the practicality of these designs. We present the methodology used to focus and transport a thermal beam from a shielded-cathode, high aspect-ratio electron gun.

WEP160

Inclusion of Surface Roughness Effects in Emission Modeling With the MICHELLE Code

1788

J.F. DeFord
STAAR/AWR Corporation, Mequon, USA
N.J. Dionne, S.G. Ovtchinnikov, J.J. Petillo
SAIC, Billerica, Massachusetts, USA

High-brightness electron beams are needed in millimeter-wave tubes and other high-power RF applications. Cathode surface roughness at the micron scale, commonly due to machining or other effects, can lead to broadening of the velocity distribution of electrons downstream, increasing emittance and lowering beam brightness. In this paper we investigate methods of including surface roughness effects in the MICHELLE code*. Modeling of typical surface imperfections over an entire cathode is not feasible, since it requires representation of features that are 3 to 5 orders of magnitude smaller than the cathode. Moreover, the actual surface imperfections for a given cathode are unknown without a prohibitive microscopic investigation of the surface, and these details vary between cathodes with the same machining history. To avoid these problems we investigated modifications to emission models that can account for these effects in an average sense, allowing the use of a smooth emission surface in a model while retaining the essential effects of the rough surface on the beam. We present the results of this investigation, along with representative solutions for sample structures.
*John Petillo, et al., “Recent Developments in the MICHELLE 2D/3D Electron Gun and Collector Modeling Code”, IEEE Trans. Electron Devices Sci., vol. 52, no. 5, May 2005, pp. 742-748.

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).