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K2CsSb Cathode Development

Description: K{sub 2}CsSb is an attractive photocathode for high current applications. With a quantum efficiency of >4% at 532nm and >10% at 355nm, it is the only cathode to have demonstrated an average current of 35mA in an accelerator environment We describe ongoing cathode development work. for the energy recovery linac being constructed at BNL Several cathodes have been created on both copper and stainless steel substrates, and their spatial uniformity and spectral response have been characterized… more
Date: October 1, 2008
Creator: Smedley, J.; Rao, T. & Wang, E.
Partner: UNT Libraries Government Documents Department
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Table top, pulsed, relativistic electron gun with GV/m gradient

Description: We present the design and performance characteristics of a compact high voltage pulser with 150 ps rise time, 0.2 to 2 ns adjustable flat top and up to 1 MV amplitude on a 80 Ohm load or up to 0.5 W on a 20 Ohm load, at 1 Hz repetition rate. Combination of a laser triggered SF{sub 6} and a liquid cap is used to form the fast rising pulse and maintain a low jitter between the laser, external trigger, and the high voltage pulsed output. The dark current and breakdown studies with this pulse appli… more
Date: October 1, 1996
Creator: Srinivasan-Rao, T. & Smedley, J.
Partner: UNT Libraries Government Documents Department
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Measurement of the Secondary Emission Yield of a Thin Diamond Window in Transmission Mode.

Description: The secondary emission enhanced photoinjector (SEEP) is a promising new approach to the generation of high-current, high-brightness electron beams. A low current primary electron beam with energy of a few thousand electron-volts strikes a specially prepared diamond window which emits secondary electrons with a current two orders of magnitude higher. The secondary electrons are created at the back side of the diamond and drift through the window under the influence of a strong electrical field. … more
Date: May 16, 2005
Creator: Chang, X.; Rao, T.; Smedley, J. & AL., ET
Partner: UNT Libraries Government Documents Department
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Relativistic electron beams from cathodes at 1 GV/m gradient

Description: In the past decade, there has been extensive research in the development of low emittance, high brightness electron injectors for linear collider and free electron laser applications. RF injectors with a few nC charge in a few ps, with an emittance of {approximately}1--5 {pi}mm mrad are operational in a number of facilities. In these devices, a laser beam irradiates a photocathode embedded in an RF cavity. The photoelectrons released by the laser are immediately accelerated to relativistic velo… more
Date: May 1, 1998
Creator: Srinivasan-Rao, T.; Smedley, J. & Schill, J.
Partner: UNT Libraries Government Documents Department
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A 10-Hz Terawatt Class Ti:Sapphire Laser System: Development and Applications

Description: We developed a two stage Ti:Sapphire laser system to generate 16 mJ/80fs laser pulses at the pulse repetition rate of 10 Hz. The key deriver for the present design is implementing a highly efficient symmetric confocal pre-amplifier and employing a simple, inexpensive synchronization scheme relying only on a commercial digital delay-generator. We characterized the amplified pulses in spatial-, spectral-, and temporal-domains. The laser system was used to investigate various nonlinear optical pro… more
Date: January 12, 2010
Creator: Sharma, A. K.; Smedley, J.; Tsang, T. & Rao, T.
Partner: UNT Libraries Government Documents Department
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Responsivity of Diamond X-ray Photodiodes Calibrated at NSLS

Description: Single crystal, high purity synthetic diamond is used as photoabsorption and carrier transport medium in x-ray photodiodes. While the thermal / mechanical robustness and high x-ray transmission of diamond make such devices attractive for synchrotron instrumentation, state-of-the-art quality material and electrical interfaces further make such detectors feasible. The present work develops methodology for attaining calculable responsivity (photocurrent yield) over a wide range of photon energies … more
Date: September 27, 2009
Creator: Keister,J.W.; Smedley, J.; Muller, E. M. & Bohon, J.
Partner: UNT Libraries Government Documents Department
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Photocathodes for the Energy Recovery Linacs.

Description: This paper presents an overview of existing and emerging technologies on electron sources that can service various Energy Recovering Linacs under consideration. Photocathodes that can deliver average currents from 1 mA to 1 A, the pros and cons associated with these cathodes are addressed. Status of emerging technologies such as secondary emitters, cesiated dispenser cathodes, field and photon assisted field emitters and super lattice photocathodes are also reviewed.
Date: March 19, 2005
Creator: Rao, T.; Burrill, A.; Chang, X. Y.; Smedley, J. & Al., Et
Partner: UNT Libraries Government Documents Department
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Emittance Measurements with a Pulsed Power Photo Injector

Description: This paper describes measurements of beam spot size and emittance of electron beams from a pulsed power photo-injector operating at 150keV output energy. In these measurements, electron bunches with charge up to 20 pC were created by a 300 fs pulse duration Ti: Sapphire laser system illuminating a polished copper cathode. Images of the electron beam were captured at two locations downstream from a solenoid focusing magnet. The focal spot size was studied as a function of bunch charge and accele… more
Date: May 12, 2003
Creator: Smedley, J.; Srinivasan Rao, T.; Tsang, T.; Farrell, J. P. & Batchelor, K.
Partner: UNT Libraries Government Documents Department
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Photoemission Properties of Lead.

Description: In this paper we present a study of the photoemission properties of lead at several UV wavelengths, including a study of the damage threshold of electroplated lead under laser cleaning. A quantum efficiency in excess of 0.1% has been achieved for a laser cleaned, electroplated lead sample with a laser wavelength of 193 nm. Niobium cathodes have been measured for comparison, and lead is found to be a superior photoemitter for all measured wavelengths.
Date: July 5, 2004
Creator: Smedley, J.; Rao, T.; Warren, J.; Sekutowicz, J.; Lefferts, R. & Lipski, A.
Partner: UNT Libraries Government Documents Department
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A novel, high gradient, laser modulated, pulsed electron gun

Description: This paper describes a high current, fast pulsed, laser excited, electron gun to operate at energies between 1 and 5 MeV. The authors present the design of the high voltage pulse generator, and the laser system, the experimental results obtained with copper cathode in fields > 1 GV/m and diode geometry optimized for the highest brightness using computer simulations. This electron source will generate an electron beam of brightness approaching 10{sup 16} A/m{sup 2} rad{sup 2}, which is 2 orders … more
Date: September 1, 1998
Creator: Batchelor, K.; Dudnikov, V.; Farrell, J.P.; Srinivasan-Rao, T. & Smedley, J.
Partner: UNT Libraries Government Documents Department
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Optimization of gun parameters for a pulsed power electron gun

Description: Extensive simulation work has been done to identify the optimal parameters for a pulsed power electron gun. PBGUNS, an electrostatic beam optics code, was used to optimize the electrode shape and the beam spatial distribution, including modeling the focusing effect of a curved cathode surface. MAFIA, a particle-in-a-cell code, was used to investigate those aspects that required time dependence, such as longitudinal energy spread. The range of agreement between the two codes was also investigate… more
Date: July 1998
Creator: Srvinivasan-Rao, T.; Smedley, J.; Batchelor, K.; Farrell, J. P. & Dudnikova, G.
Partner: UNT Libraries Government Documents Department
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Dark current measurements at field gradients above 1 GV/m

Description: In this paper, the authors report the results of dark current studies on copper cathodes and stainless steel anodes held at a field gradient > 1 GV/m. The field emission current is , 1 A for fields less than 1 GV/m. As the field is increased, the dark current increases rapidly to 150 A for applied fields of {approximately} 1.7 GV/m. Fowler-Nordheim plots in this range of applied fields indicate a field enhancement factor of 10--20 for a copper cathode with a work function of 4.6 eV.
Date: July 1998
Creator: Srinivasan-Rao, T.; Smedley, J.; Schill, J.; Batchelor, K. & Farrell, J. P.
Partner: UNT Libraries Government Documents Department
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Comparison of electrostatic and time dependent simulation codes for modeling a pulsed power gun

Description: This paper is a result of a group of simulations used to determine the optimal parameters for a pulsed power electron gun. As electrostatic codes such as PBGUNS tend to be cheaper, easier to use, and have less stringent computational requirements than time dependent codes such as MAFIA, it was desirable to determine those regimes in which the electrostatic codes agree with time dependent models. It was also necessary to identify those problems that required time dependence, such as longitudinal… more
Date: June 1, 1998
Creator: Srinivasan-Rao, T.; Smedley, J.; Batchelor, K.; Farrell, J. P. & Dudnikova, G.
Partner: UNT Libraries Government Documents Department
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Performance Data of a Pulsed Power Photo Injector

Description: There has been a lot of interest in compact sources of high brightness, relativistic electron beams. One approach for developing such a source is to apply a high gradient that remains constant during the generation and acceleration of the electron beam. In this paper, we describe high voltage pulse generators that deliver up to 5 MV with 1 ns pulse duration. These devices are synchronizable to an external trigger with jitter of {approx}0.5 ns and can establish gradients in excess of 1 GV/m betw… more
Date: November 12, 2002
Creator: Smedley, J.; Srinivasan - Rao, T.; Tsang, T.; Farrell, J. P. & Batchelor, K.
Partner: UNT Libraries Government Documents Department
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Thermal Emittance Measurement Design for Diamond Secondary Emission

Description: Thermal emittance is a very important characteristic of cathodes. A carefully designed method of measuring the thermal emittance of secondary emission from diamond is presented. Comparison of possible schemes is carried out by simulation, and the most accessible and accurate method and values are chosen. Systematic errors can be controlled and maintained at small values, and are carefully evaluated. Aberration and limitations of all equipment are taken into account.
Date: June 25, 2007
Creator: Wu, Q.; Ben-Zvi, Ilan; Burrill, A.; Chang, X.; Kayran, D.; Rao, T. et al.
Partner: UNT Libraries Government Documents Department
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Diamond Secondary Emitter

Description: We present the design and experimental progress on the diamond secondary emitter as an electron source for high average power injectors. The design criteria for average currents up to 1 A and charge up to 20 nC are established. Secondary Electron Yield (SEY) exceeding 200 in transmission mode and 50 in emission mode have been measured. Preliminary results on the design and fabrication of the self contained capsule with primary electron source and secondary electron emitter will also be presente… more
Date: October 9, 2005
Creator: Ben-Zvi, Ilan; Rao, T.; Burrill, A.; Chang, X.; Grimes, J.; Rank, J. et al.
Partner: UNT Libraries Government Documents Department
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Superconducting Photocathodes.

Description: We present the results of our investigation of lead and niobium as suitable photocathode materials for superconducting RF injectors. Quantum efficiencies (QE) have been measured for a range of incident photon energies and a variety of cathode preparation methods, including various lead plating techniques on a niobium substrate. The effects of operating at ambient and cryogenic temperatures and different vacuum levels on the cathode QE have also been studied.
Date: October 9, 2005
Creator: Smedley, J.; Rao, T.; Warren, J.; Sekutowicz, Langner, J.; Strzyzewski, P.; Leffers, R. et al.
Partner: UNT Libraries Government Documents Department
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R&D ERL: Photocathode Deposition and Transport System

Description: The purpose of the photocathode deposition and transport system is to (1) produce a robust, high yield multialkali photocathode and (2) have a method of transporting the multialkali photocathode for insertion into a super conducting RF electron gun. This process is only successful if a sufficient quantum efficiency lifetime of the cathode, which is inserted in the SRF electron gun, is maintained. One important element in producing a multialkali photocathode is the strict vacuum requirements of … more
Date: January 1, 2010
Creator: Pate, D.; Ben-Zvi, Ilan; Rao, T.; Burrill, R.; Todd, R.; Smedley, J. et al.
Partner: UNT Libraries Government Documents Department
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Progress on Lead Photocathodes for Superconducting Injectors.

Description: We present the results of our investigation of bulk lead, along with various types of lead films, as suitable photocathode materials for superconducting RF injectors. The quantum efficiency of each sample is presented as a function of the photon energy of the incident light, from 3.9 eV to 6.5 eV. Quantum efficiencies of 0.5% have been obtained. Production of a niobium cavity with a lead-plated cathode is underway.
Date: May 16, 2005
Creator: Smedley, J.; Rao, T.; Sekutowicz, J.; Kneisel, P.; Langner, J.; Strzyzewski, P. et al.
Partner: UNT Libraries Government Documents Department
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Diamond Amplified Photocathodes

Description: High-average-current linear electron accelerators require photoinjectors capable of delivering tens to hundreds of mA average current, with peak currents of hundreds of amps. Standard photocathodes face significant challenges in meeting these requirements, and often have short operational lifetimes in an accelerator environment. We report on recent progress toward development of secondary emission amplifiers for photocathodes, which are intended to increase the achievable average current while … more
Date: November 26, 2007
Creator: Smedley, J.; Ben-Zvi, Ilan; Bohon, J.; Chang, X.; Grover, R.; Isakovic, A. et al.
Partner: UNT Libraries Government Documents Department
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Recent Progress on the Diamond Amplified Photo-Cathode Experiment.

Description: We report recent progress on the Diamond Amplified Photo-cathode (DAP). The use of a pulsed electron gun provides detailed information about the DAP physics. The secondary electron gain has been measured under various electric fields. We have achieved gains of a few hundred in the transmission mode and observed evidence of emission of electrons from the surface. A model based on recombination of electrons and holes during generation well describes the field dependence of the gain. The emittance… more
Date: June 25, 2007
Creator: Chang,X.; Ben-Zvi, Ilan; Burrill, A.; Grimes, J.; Rao, T.; Segalov, Z. et al.
Partner: UNT Libraries Government Documents Department
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