R. I. Cutler

Progress Report on the NBS/LOS Alamos RTM

The NBS-Los Alamos 200 MeV Racetrack Microtron (RTM) is being built under a program aimed at developing the technology needed for high-current intermediateenergy CW electron accelerators. In this report we give an overview of the present status of the project. Recent progress includes: (1) completion of testing of the 100 keV chopper-buncher system demonstrating a normalized emittance well under the design goal of 2.6 ¿ mm mrad at currents exceeding the design goal of 600 ¿A; (2) operation of the rf structures comprising the 5 MeV injector linac at power levels up to 50 kW/m, resulting in an accelerating gradient at ß=1 of 2 MV/m (compared to a design goal of 1.5 MV/m). The measured shunt impedance is 82.5 Mn/m; (3) construction and installation of the 30 ton end magnets of the RTM. Field mapping of one magnet has been completed and its uniformity exceeds the design goal of ±2 parts in 104; (4) performance tests (with beam) of prototype rf beam monitors which measure current, relative phase, and beam position in both transverse planes. (5) Installation and initial operation of the primary control system.

NBS-LANL RTM Injector Installation

The injector for the NBS-LANL CW racetrack microtron consists of a 100 KeV electron gun and beam transport line followed by a 5 MeV linac. The function of the gun and transport line, which have been installed at NBS, is to provide a chopped and bunched 100 KeV and up to 0.67 mA dc or pulsed beam of very low transverse emittance for matched insertion into the linac. In this paper the authors present both the design and construction details of the 100 KeV system and the results of preliminary beam tests. The tests conducted thus far show the gun and transport system to be performing well within design specifications.

A High Resolution Wire Scanner Beam Profile Monitor with a Microprocessor Data Acquisition System

A beam profile monitor has been constructed for the NBS-LANL Racetrack Microtron. The monitor consists of two perpendicular 30 ¿m diameter carbon wires that are driven through an electron beam by a pneumatic actuator. A long-lifetime, electroformed nickel bellows is used for the linear-motion vacuum feedthrough. Secondary emission current from the wires and a signal from a transducer measuring the position of the wires are simultaneously digitized by a microprocessor to yield beam current density profiles in two dimensions. The wire scanner is designed for use with both pulsed and cw beams.

Performance of the 100 keV Chopper/Buncher System of the NBS-Los Alamos RTM Injector

The purpose of the chopper/buncher system for the RTM injector is to chop a 100 keV 5 mA dc electron beam into 60/sup 0/-long pulses at 2380 MHz and then bunch these beam pulses to 10/sup 0/ at insertion into the 5 MeV injector linac. These beam manipulations must contribute a minimum increase in the phase space of the beam such that, at the entrance to the injector linac, the transverse emittance is less than 5..pi.. mm-mrad. Phase-shift measurements on the chopped beam indicate that the bunching fields are sufficient to achieve the required longitudinal compression. Beam envelope measurements, using wire scanners on the chopped and bunched beam, show that the emittance remains within design goals.

Performance of an RF Beam Monitor on the NBS-Los Alamos Racetrack Microtron

A prototype rf beam-position, current, and phase monitor has been used on the 100-keV injector beamline of the racetrack microtron (RTM) where performance was measured with the chopped and bunched beam. This monitor works with both a pulsed beam and a cw beam. The pulsed beam consists of beam pulses with a FWHM of 40 ns. The rf beam monitor was tested with beam currents from ~50 to 600 ¿A. The rf beam monitor will be described and its performance will be reported.

Design Of A High-current Injector For The Nist-NRL Free Electron Laser

The electron beam of the NIST-LANL racetrack microtron (RTM) is to be used to drive a free electron laser and for other applications. We have designed a new injector for the RTM to provide the 3.5 ps long, 7-14 pC electron beam pulses required for lasing. The new injector consists of a pulsed, 120 keV thermionic electron gun, a subharmonic chopping and bunching system, and the existing 5 MeV RTM injection linac. It has been designed to produce a continuous train of electron pulses at 5 MeV with a normalized transverse eraittance of 5 mm mrad and a longitudinal emittance of 20 keV deg for 95% of the beam (for 7 pC) at repetition rates of 66.111 or 16.528 MHz. These two frequencies are subharmonics of the fundamental accelerator frequency of 2380 MHz. The new injector will also produce lower-emittance beams at lower peak currents at the fundamental frequency.

The NIST/NRL Free-Electron Laser Facility

A free-electron laser (FEL) user facility is being constructed at the National Institute of Standards and Technology (NIST) in collaboration with the Naval Research Laboratory. The FEL, which will be operated as an oscillator, will be driven by the electron beam of the racetrack microtron (RTM) that is nearing completion. Variation of the electron kinetic energy from 17 MeV to 185 MeV will permit the FEL wavelength to be tuned from 200 nm to 10 pm. Performance will be enhanced by the high brightness, low energy spread, and continuous-pulse nature of the RTM electron beam. We are designing a new injector to increase the peak current of the RTM. A 3.6-m undulator is under construction, and the 9-m optical cavity is under design. The FEL will emit a continuous train of 3-ps pulses at 66 MHz with an average power of 10-200 W, depending on the wavelength, and a peak power of up to several hundred kW. An experimental area is being prepared with up to five stations for research using the FEL beam. Initial operation is scheduled for 1991.

Design of a high-current injector for the NIST-NRL free electron laser

Abstract The electron beam of the NIST-LANL racetrack microtron (RTM) is to be used to drive a free electron laser and for other applications. We have designed a new injector for the RTM to provide the 3.5 ps long, 7–14 pC electron beam pulses required for lasing. The new injector consists of a pulsed, 120 keV thermionic electron gun, a subharmonic chopping and bunching system, and the existing 5 MeV RTM injection linac. It has been designed to produce a continuous train of electron pulses at 5 MeV with a normalized transverse emittance of 5 mm mrad and a longitudinal emittance of 20 keV deg for 95% of the beam (for 7 pC) at repetition rates of 66.111 or 16.528 MHz. These two frequencies are subharmonics of the fundamental accelerator frequency of 2380 MHz. The new injector will also produce lower-emittance beams at lower peak currents at the fundamental frequency.

NIST-NRL free-electron laser facility

A free-electron laser facility (FEL) is being constructed at the National Institute of Standards and Technology (NIST) in collaboration with the Naval Research Laboratory (NRL) . The FEL will be driven by the electron beam from the NIST racetrack microtron (RTM). The anticipated performance of the FEL is: (1) wavelength variability from 200 run to 10 tim; (2) continuous train of 3-ps pulses at 66 MHz; and (3) average power of 10 W to 200 W. This excellent performance will be achieved primarily because of the unique characteristics of the RTM. This accelerator will provide a continuously pulsed electron beam with high brightness and low energy spread at energies from 17 MeV to 185 MeV. For FEL operation high peak current is required and a new injector for this purpose has been designed. The undulator for the project is 3.64-m long with 130 periods and a peak field of 0.54 T. The construction of the undulator is nearly complete and delivery is expected shortly. The 9-m optical cavity has been designed and is under construction. An experimental area is being prepared for FEL users which will have up to six stations. Initial operation of the FEL is scheduled for 1991. The NIST-NRL FEL will provide a powerful, tunable light source for research in biomedicine, materials science , physics , and chemistry.

The NIST-NRL Free-Electron-laser Facility

A free-electron-laser facility (FEL) is being constructed at the National Institute of Standards and Technology (NIST) in collaboration with the Naval Research Laboratory (NRL). The NIST-NRL FEL will provide a powerful, tunable light source for research in biomedicine, materials science, physics and chemistry. Anticipated performance of the FEL is: (1) wavelength variability from 200 nm to 10 /spl mu/m, (2) continuous train of 3 ps pulses at 66 MHz, and (3) average power of 10 to 200 W. This excellent performance will be achieved primarily because of the unique characteristics of the electron source, the NIST-LANL racetrack microtron (RTM). The RTM will provide a continuously pulsed electron beam with high brightness and low energy spread at energies from 17 to 185 MeV. Construction of the RTM is nearing completion, and a new injector to increase the peak current has been designed. A 3.64 m undulator is under construction, and the 9 m optical cavity is being designed. An experimental area is being prepared for FEL users, which will have up to five stations. Initial operation of the FEL is scheduled for 1991.