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A method of producing very high resistivity surface conduction on ceramic accelerator components using metal ion implantation

Description: An important technique used for the suppression of surface flashover on high voltage DC ceramic insulators as well as for RF windows is that of providing some surface conduction to bleed off accumulated surface charge. The authors have used metal ion implantation to modify the surface of high voltage ceramic vacuum insulators to provide a uniform surface resistivity of approximately 5 x 10{sup 10} Q{sup 2}. A vacuum arc ion source based implanter was used to implant Pt at an energy of about 135 MeV to doses of up to more than 5 x 10{sup 16} ions cm{sup 2} into small ceramic test coupons and also into the inside surface of several ceramic accelerator columns 25 cm I. D. by 28 cm long. Here they describe the experimental set-up used to do the ion implantation and summarize the results of their exploratory work on implantation into test coupons as well as the implantations of the actual ceramic columns.
Date: May 1, 1997
Creator: Liu, F.; Brown, I.; Phillips, L.; Biallas, G. & Siggins, T.
Partner: UNT Libraries Government Documents Department

Dramatic Reduction of DC Field Emission from Large Area Electrodes by Plasma-Source Ion Implantation

Description: Field emission from the electrodes of practical electron guns is one of the principal phenomena limiting the operating voltage of these guns. There is substantial interest in developing photoemission cathode based DC electron guns operating with cathode field strengths and cathode-anode voltages well beyond the present state-of-the-art. These electron sources could provide high brightness, high average current beams for energy recovering superconducting linear accelerators, for applications in next generation light sources, electron cooling, and electron-ion colliders. We have studied the effect of plasma-source ion implantation on the field emission behavior of large area stainless steel electrodes. Our apparatus allows operation of disc-shaped electrode pairs with 100 cm{sup 2} uniform field areas to 125 kV. The cathode electrode is biased at high voltage, and the anode is electrically isolated, permitting measurement of the field emission current from the cathode. The electrode pairs were either mechanically polished, or implanted with nitrogen ions. Two separate ion implanted electrodes have shown negligible field emission at 20 MV/m, and emission between 0.5 and 1.7 pA/cm{sup 2} at 30 MV/m during multi-hour runs at high field. These electrodes showed very little conditioning effect.
Date: June 1, 2001
Creator: Sinclair, C.K.; Dylla, H.F.; Siggins, T.L.; Manos, D. & Verhaus, T.J.
Partner: UNT Libraries Government Documents Department

A kilowatt average power laser for sub-picosecond materials processing

Description: The performance of laser pulses in the sub-picosecond range for materials processing is substantially enhanced over similar fluences delivered in longer pulses. Recent advances in the development of solid state lasers have progressed significantly toward the higher average powers potentially useful for many applications. Nonetheless, prospects remain distant for multi-kilowatt sub-picosecond solid state systems such as would be required for industrial scale surface processing of metals and polymers. The authors present operational results from the world's first kilowatt scale ultra-fast materials processing laser. A Free Electron Laser (FEL) called the IR Demo is operational as a User Facility at Thomas Jefferson National Accelerator Facility in Newport News, Virginia, USA. In its initial operation at high average power it is capable of wavelengths in the 2 to 6 micron range and can produce {approximately}0.7 ps pulses in a continuous train at {approximately}75 MHz. This pulse length has been shown to be nearly optimal for deposition of energy in materials at the surface. Upgrades in the near future will extend operation beyond 10 kW CW average power in the near IR and kilowatt levels of power at wavelengths from 0.3 to 60 microns. This paper will cover the design and performance of this groundbreaking laser and operational aspects of the User Facility.
Date: November 1, 1999
Creator: Benson, Stephen V.; Neil, George R.; Bohn, C.; Biallas, G.; Douglas, D.; Dylla, F. et al.
Partner: UNT Libraries Government Documents Department

First operation of an FEL in same-cell energy recovery mode

Description: The driver for Jefferson Lab's kW-level infrared free-electron laser (FEL) is a superconducting, recirculating accelerator that recovers 75% of the electron-beam power and converts it to radio frequency power. As reported in FEL'98, the accelerator operated ''straight-ahead'' to deliver 38 MeV, 1.1 mA cw current for lasing at wavelengths in the vicinity of 5 microns. The waste beam was sent directly to a dump, bypassing the recirculation loop. Stable operation at up to 311 W cw was achieved in this mode. The machine has now recirculated cw average current up to 4.6 mA and has lased cw with energy recovery up to 1,720 W output at 3.1 microns. This is the first FEL to ever operate in the ''same-cell'' energy recovery mode. Energy recovery offers several advantages (reduced RF power and dramatically reduced radio-nuclide production at the dump) and several challenges will be described. The authors have observed heating effects in the mirrors which will be described. They will also report on the additional performance measurements of the FEL that have been performed and connect those measurements to standard models.
Date: September 1, 1999
Creator: Neil, G.R.; Benson, S.; Biallas, G.; Bohn, C.L.; Douglas, D.; Dylla, H.F. et al.
Partner: UNT Libraries Government Documents Department

Sustained Kilowatt Lasing in a Free-Electron Laser with Same Cell Energy Recovery

Description: TJNAF recently commissioned its high-average-power infrared free-electron laser (FEL). It incorporates a superconducting accelerator that recovers about 75% of the electron-beam power and converts it to radio-frequency power. In achieving first lasing, the accelerator operated straight-ahead to deliver 38 MeV, 1.1 mA cw average current through the wiggler for lasing at wavelengths near 5 {micro}m. The waste beam was then sent directly to a dump. Stable operation at up to 311 W cw was achieved in this mode. Using a transport loop to send the waste electron beam back to the linac for energy recovery, the machine recently lased cw at up to 1720 W average power at 3.1 {micro}m, for which the electron-beam energy and average current were 48 MeV and 4.4 mA, respectively.
Date: September 1, 1999
Creator: Neil, G.R.; Benson, S.; Biallas, G.; Bohn, C.L.; Douglas, D.; Dylla, H.F. et al.
Partner: UNT Libraries Government Documents Department

Status of the Jefferson Lab IR/UV High Average Power Light Source

Description: Jefferson Lab is in the process of building an upgrade to our Free-Electron Laser Facility with broad wavelength range and timing flexibility. The facility will have two cw free-electron lasers, one in the infrared operating from 1 to 14 microns and one in the infrared operating from 0.25 to 1 micron [1]. In addition, there will be beamlines for Thompson-backscattered femtosecond X-rays, and broadband THz radiation. The average power levels for each of these devices will exceed any other available sources by at least 2 orders of magnitude. Timing of the available laser pulses can be continuously mode-locked at least 4 different (MHz) repetition rates or in macropulse mode with pulses of a few microseconds in duration with a repetition rate of many kHz. The status of the construction of this facility and a review of its capabilities will be presented.
Date: September 2002
Creator: Neil, G. R.; Benson, S. V.; Biallas, G.; Boyce, J.; Dillon-Townes, L. A.; Douglas, D. et al.
Partner: UNT Libraries Government Documents Department


Description: A key technology issue of energy recovery linac (ERL) devices for high-power free-electron laser (FEL) and fourth generation light sources is the demonstration of reliable, high-brightness, high-power injector operation. Three ongoing programs that target up to 0.5 Ampere photocathode injector performance with required EFU brightness, are described. The first is a DC gun and superconducting RF (SRF) booster cryomodule. Such a 748.5 MHz device is being assembled and will be tested up to 100 mA at the Thomas Jefferson National Accelerator Facility (JLAB) beginning in 2006. The second approach is a high-current normal-conducting RF (NCRF) injector. A 700 MHz gun will undergo thermal test in late 2005 at the Los Alamos National Laboratory (LANL), which when equipped with a suitable cathode, would be capable of exceeding 0.5 Ampere operation. Finally, a half-cell 703.75 MHz SRF gun with a diamond amplifier and other cathodes, will be tested to 0.5 Ampere at the Brookhaven National Laboratory (BNL) in 2007. The status and projected performance for each of these injector projects is presented.
Date: May 16, 2005
Partner: UNT Libraries Government Documents Department