Papers by Philip Adderley
Bunched-beam electron cooling is a key feature of all proposed designs of the future electron-ion... more Bunched-beam electron cooling is a key feature of all proposed designs of the future electron-ion collider, and a requirement for achieving the highest promised collision luminosity. At the Jefferson Lab Electron Ion Collider (JLEIC), fast cooling of ion beams will be accomplished via so-called 'magnetized cooling' implemented using a recirculator ring that employs an energy recovery linac. In this contribution, we describe the production of magnetized electron beam using a compact 300 kV DC high voltage photogun with an inverted insulator geometry, and using alkali-antimonide photocathodes. Beam magnetization was assessed using a modest diagnostic beamline that includes YAG view screens used to measure the rotation of the electron beamlet passing through a narrow upstream aperture. Magnetization results are presented for different gun bias voltages and for different laser spot sizes at the photocathode, using 532 nm lasers with DC and RF time structure. Photocathode lifetim...
AIP Conference Proceedings, 2008
Ion back-bombardment is the dominant mechanism that limits the operating lifetime of DC high volt... more Ion back-bombardment is the dominant mechanism that limits the operating lifetime of DC high voltage GaAs photoelectron guns. In this work, an electrically isolated anode electrode was used to distinguish the QE damage contributions of ions produced within the cathode/anode gap and those produced downstream of the anode. This new anode design provides a means to suppress QE decay due to ionized gas in the beam line.
Physical Review Special Topics - Accelerators and Beams, 2013
Two K 2 CsSb photocathodes were manufactured at Brookhaven National Lab and delivered to Jefferso... more Two K 2 CsSb photocathodes were manufactured at Brookhaven National Lab and delivered to Jefferson Lab within a compact vacuum apparatus at pressure $10 À11 Torr. These photocathodes were evaluated using a dc high voltage photogun biased at voltages up to 200 kV, and illuminated with laser light at wavelengths 440 or 532 nm, to generate dc electron beams at currents up to 20 mA. Some conditions produced exceptionally large photocathode charge lifetimes, without measurable quantum efficiency decay, even from the center of the photocathode where operation using GaAs photocathodes is precluded due to ion bombardment. Under other conditions the charge lifetime was poor due to extensive ion bombardment under severely degraded vacuum conditions, and as a result of localized heating via the laser beam. Following beam delivery, the photocathodes were evaluated using a scanning electron microscope to determine surface morphology.
Physical Review Special Topics - Accelerators and Beams, 2012
The field emission characteristics of niobium electrodes were compared to those of stainless stee... more The field emission characteristics of niobium electrodes were compared to those of stainless steel electrodes using a DC high voltage field emission test apparatus. A total of eight electrodes were evaluated: two 304 stainless steel electrodes polished to mirrorlike finish with diamond grit and six niobium electrodes (two single-crystal, two large-grain, and two fine-grain) that were chemically polished using a buffered-chemical acid solution. Upon the first application of high voltage, the best large-grain and single-crystal niobium electrodes performed better than the best stainless steel electrodes, exhibiting less field emission at comparable voltage and field strength. In all cases, field emission from electrodes (stainless steel and/or niobium) could be significantly reduced and sometimes completely eliminated, by introducing krypton gas into the vacuum chamber while the electrode was biased at high voltage. Of all the electrodes tested, a large-grain niobium electrode performed the best, exhibiting no measurable field emission (< 10 pA) at 225 kV with 20 mm cathode/anode gap, corresponding to a field strength of 18:7 MV=m.
The Energy Citations Database (ECD) provides access to historical and current research (1948 to t... more The Energy Citations Database (ECD) provides access to historical and current research (1948 to the present) from the Department of Energy (DOE) and predecessor agencies.
Ion pumps are common vacuum pumps on DC high voltage photoguns and baked-accelerator beamlines. C... more Ion pumps are common vacuum pumps on DC high voltage photoguns and baked-accelerator beamlines. Commercial ion pump power supplies provide a measure of the electrical current drawn by the pump, but typically have resolution to only ~0.1 uA, which corresponds to pressure ~10-9 Torr, a value considerably higher than the minimum pressure required by photoguns and nearby beamline. This submission describes a very sensitive in-house-built ion pump power supply with current monitoring capability good to less than 1 nA, and corresponding pressure in the low-minus10-11 Torr range. Besides providing ``free'' pressure monitoring on a scale equivalent to the best available commercial pressure gauges, the ion pump power supply also serves as a sensitive diagnostic for detecting field emission from the photogun cathode electrode and bad electron beam orbits that could diminish photogun operating lifetime. Since its inception, this ion pump power supply has become an invaluable tool for o...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007
A vacuum system with pressure in the low ultra-high vacuum (UHV) range is essential for long phot... more A vacuum system with pressure in the low ultra-high vacuum (UHV) range is essential for long photocathode lifetimes in DC high voltage GaAs photoguns. A discrepancy between predicted and measured base pressure in the CEBAF photoguns motivated this study of outgassing rates of three 304 stainless steel chambers with different pretreatments and pump speed measurements of non-evaporable getter (NEG) pumps. Outgassing rates were measured using two independent techniques. Lower outgassing rates were achieved by electropolishing and vacuum firing the chamber. The second part of the paper describes NEG pump speed measurements as a function of pressure through the lower part of the UHV range. Measured NEG pump speed is high at pressures above 5 Â 10 À11 Torr, but may decrease at lower pressures depending on the interpretation of the data. The final section investigates the pump speed of a locally produced NEG coating applied to the vacuum chamber walls. These studies represent the first detailed vacuum measurements of CEBAF photogun vacuum chambers.
Journal of Physics: Conference Series, 2008
Ultimate pressure of a well-designed vacuum system very much depends on pretreatments, processing... more Ultimate pressure of a well-designed vacuum system very much depends on pretreatments, processing and procedures . Until now much attention has been paid to minimizing hydrogen outgassing from the vacuum chamber wall materials, however, procedures and processing deserve further scrutiny. For reducing the gas load, high sensitivity helium leak detection techniques with sensitivities better than 1×10 -12 Torr l/sec should be used. Effects that are induced by vacuum instrumentation need to be reduced in order to obtain accurate pressure measurements. This paper presents the current status of the CEBAF DC photogun. This state of the art technology is driving the need for Extreme High Vacuum (XHV). We also present sensitive helium leak detection techniques with RGA's, vacuum gauge and RGA calibration procedures, metal sponges for cryosorption pumping of hydrogen to XHV, low cost surface diffusion barriers for reducing the hydrogen gas load and clean assembly procedures. Further, alternative backing pump systems based on active NEGs [3] for turbo molecular pumps are also discussed.
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Papers by Philip Adderley