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Light Source Photocathode Performance and Development


EMSL Project ID
45795

Abstract

Accelerator photocathode technology must be advanced to meet the needs of fourth generation light sources. The ultimate output characteristics and cost of next-generation ultraviolet or x-ray sources, whether based on free electron laser (FEL) or storage ring designs, is heavily dependent upon photocathode brightness and emittance characteristics. Novel photocathode designs could potentially reduce light source construction costs enormously -- by a factor of two or more -- by significantly simplifying downstream accelerator or FEL design. The international light source community recognizes the need for a more scientific approach to new photocathode development and is in the initial stages of addressing this issue. The fields of materials science, solid-state photochemistry, surface chemistry and analysis can make an immediate and timely contribution to this essential activity.

Photocathode materials and designs must be highly robust, under pulsed or continuous laser irradiation, and tolerant to a variety of high field accelerator operating conditions. Existing photocathode designs degrade in use leading to lower electron bunch intensity, higher emittance, the need for frequent replacement, and consequently, expensive machine downtime. Several photocathode degradation processes are suspected including ion back bombardment, photochemistry of surface adsorbed species, and irradiation induced surface and bulk defect formation. At present, no consensus exists within the user community as to the mechanisms of photocathode damage. Better understanding of photocathode degradation mechanisms could lead to improved emission properties and greater durability (longer operating lifetime). Existing photocathode materials range from metallic (e.g., copper) to semiconducting (e.g., GaAs) with various structures, dopants, and surface preparations. Photocathode emission requirements include high electron yield (intensity) and low thermal emittance (spatial dispersion) at high repetition rate. The exact details regarding electron bunch dynamics change significantly with accelerator type and a variety of robust new photocathode materials and designs need to be developed. The goal of this project is to conduct research necessary to develop new photocathode designs required by next generation light sources. To achieve this goal, we have combined PNNL expertise in materials science, surface chemistry, photophysics and surface analysis with FEL photocathode expertise from scientific staff at Jefferson Lab (JLab).

Project Details

Project type
Exploratory Research
Start Date
2011-08-30
End Date
2012-09-02
Status
Closed

Team

Principal Investigator

Wayne Hess
Institution
Pacific Northwest National Laboratory

Team Members

Archana Pandey
Institution
Michigan Technological University

Kenneth Beck
Institution
Environmental Molecular Sciences Laboratory

Theva Thevuthasan
Institution
Environmental Molecular Sciences Laboratory

Scott Chambers
Institution
Pacific Northwest National Laboratory

Related Publications

Shutthanandan V, Z Zhu, ML Stutzman, F Hannon, C Hernandez-Garcia, MI Nandasiri, SVNT Kuchibhatla, S Thevuthasan, and WP Hess. 2012. "Surface Science Analysis of GaAs Photocathodes Following Sustained Electron Beam Delivery." Physical Review Special Topics - Accelerators and Beams 15(6):063501. doi:10.1103/PhysRevSTAB.15.063501
Vilayur Ganapathy S, A Devaraj, RJ Colby, A Pandey, T Varga, V Shutthanandan, S Manandhar, PZ El-Khoury, AN Kayani, WP Hess, and S Thevuthasan. 2013. "Subsurface Synthesis and Characterization of Ag Nanoparticles Embedded in MgO." Nanotechnology 24(9):Article No. 095707. doi:10.1088/0957-4484/24/9/095707