K.C.D. Chan

Initial performance of Los Alamos Advanced Free Electron Laser

Abstract The Los Alamos compact Advanced Free Electron Laser (AFEL) has lased at 4.7 and 5.2 μm with a 1-cm period wiggler and a high-brightness electron beam at 16.8 and 15.8 MeV, respectively. The measured electron beam normalized emittance is 1.3 π mm mrad at a peak current of 100 A, corresponding to a beam brightness greater than 2 × 10 12 A/m 2 rad 2 . Initial results indicate that the AFEL small signal gain is ∼ 8% at 0.3 nC (30 A peak). The maximum output energy is 7 mJ over a 2-μs macropulse. The AFEL performance can be significantly enhanced by improvements in the rf and drive laser stability.

Experimental study of proton-beam halo induced by beam mismatch in LEDA

We report measurements of transverse beam halo in mismatched proton beams in a 52-quadrupole FODO transport channel following the 6.7-MeV LEDA RFQ. Beam profiles in both transverse planes are measured using beam-profile diagnostic devices that consist of a movable carbon filament for measurement of the dense beam core, and scraper plates for the halo measurement. The gradients of the first four quadrupoles can be independently adjusted to mismatch the RFQ output beam into the beam-transport channel.

Performance of the high brightness linac for the advanced free-electron laser initiative at Los Alamos☆

Abstract The AFEL accelerator has produced beams of 1 nC with peak currents greater than 100 A and a normalized, rms emittance less than 2π mm mrad. The 1300 MHz standing-wave accelerator uses on-axis coupling cells. The electron source is a photoinjector with a CsK 2 Sb photocathode. The photoinjector is an integral part of a single 11-cell accelerator structure. The accelerator operates between 12 and 18 MeV. The beam emittance growth in the accelerator is minimized by using a photoinjector, a focusing solenoid to correct the emittance growth due to space charge, and a special design of the coupling slots between accelerator cavities to minimize quadrupole effects. This paper describes the experimental results and compares those results with PARMELA simulation. The simulation code PARMELA was modified for this effort. This modified version uses SUPERFISH files for the accelerator cavity fields, MAFIA files for the fields due to the coupling slots in the accelerator cells, and POISSON files for the solenoid field in the gun region.

Los Alamos advanced free-electron laser

Abstract Los Alamos researchers are building a free-electron laser (FEL) for industrial, medical, and research applications. This FEL, which will incorporate many of the new technologies developed over the last decade, will be compact, robust, and user-friendly. Electrons produced by a photocathode will be accelerated to 20 MeV by a high-brightness accelerator and transported by permanent-magnet quadrupoles and dipoles. The resulting electron beam will have an excellent instantaneous beam quality of 10πmm mrad in transverse emittance and 0.3% in energy spread at a peak current up to 300 A. Including operation at higher harmonics, the laser wavelength extends from 3.7 μm to 0.4 μm.

Measurements of halo generation for a proton beam in a FODO channel

An experimental effort has been undertaken to investigate the production of halo particles in a proton beam having significant space charge forces. The LEDA RFQ was used to inject a pulsed 6.7 MeV 15-75 mA beam into a linear FODO channel. Four matching quads at the input of this 52-quadrupole transport line were used to generate specific mismatch oscillations, believed to be a key mechanism in the generation of beam halo. A suite of diagnostics that provide beam profile measurements over a wide dynamic range enabled a detailed comparison of measurements with theoretical models.

Recent results from the Los Alamos free electron laser

Abstract Accelerator improvements have been made that allow beams to be produced with higher charge, better pulse shape, and better emittance and energy spread. Record levels of efficiency and optical power have resulted. We could achieve higher levels except for problems with mirror damage at these power levels and growth of emittance and energy spread caused by wakefield effects.

Progress update on the Low-Energy Demonstration Accelerator (LEDA)

As part of the linac design for the accelerator production of tritium (APT) project, we are assembling the first approximately 20 MeV portion of this cw proton accelerator. Primary objective of this low-energy demonstration accelerator (LEDA) is to verify the design codes, gain fabrication knowledge, understand LEDAs beam operation, and be able to better predict costs and operational availability for the full 1700 MeV APT accelerator. This paper provides an updated report on this past years progress that includes beam tests of the 75 keV injector, fabrication of the 6.7 MeV radio-frequency quadrupole (RFQ), preparation of the facility, procurement and assembly of the RF system, and detailed design and documentation of many pieces of support equipment. First tests with the 6.7 MeV, 100 mA, cw beam from the RFQ are scheduled for late 1998. References are given to many detailed papers on LEDA at this conference.

INEX simulations of the Boeing FEL system

Abstract The INEX (integrated numerical experiment) numerical model is applied to the 0.6 μm FEL oscillator at the Boeing laboratory in Seattle, WA. This sytem consists of a 110 MeV L-band rf linac, a beam transport line from the accelerator to the entrance of the wiggler, the 5.0 m THUNDER variable-taper wiggler, and a near-concentric two-mirror optical oscillator. Many aspects of the model for the electron beam accelerator and transport line agree with experimental measurements. Predictions for lasing performance are compared with data obtained in May and June 1989, using a mild-tapered wiggler. We obtain good agreement with the achieved extraction efficiency, while ID pulse simulations reproduce the observed sideband instability.

Linear accelerator for tritium production

For many years now, Los Alamos National Laboratory has been working to develop a conceptual design of a facility for accelerator production of tritium (APT). The APT accelerator will produce high energy protons which will bombard a heavy metal target, resulting in the production of large numbers of spallation neutrons. These neutrons will be captured by a low‐Z target to produce tritium. This paper describes the latest design of a room‐temperature, 1.0 GeV, 100 mA, cw proton accelerator for tritium production. The potential advantages of using superconducting cavities in the high‐energy section of the linac are also discussed and a comparison is made with the baseline room‐temperature accelerator.

In-situ proton irradiation and measurement of superconducting RF cavities under cryogenic conditions

The Accelerator Production of Tritium (APT) Project is investigating using a superconducting linac for the high-energy portion of the accelerator. As this accelerator would be used to accelerate a high-current (100-mA) CW proton beam up to 1700 MeV, it is important to determine the effects of stray-beam impingement on the superconducting properties of 700-MHz Nb cavities. To accomplish this, two 3000-MHz elliptical niobium cavities were placed in a cryostat, cooled to nominally 2 K in sub-atmospheric liquid helium, and irradiated with 798-MeV protons at up to 490-nA average current. The elliptically shaped beam passed through the equatorial regions of both cavities in order to maximize sensitivity to any changes in the superconducting surface resistance. Over the course of the experiment, 6/spl times/10/sup 16/ protons were passed through the cavities. After irradiation, the cavities were warmed to 250 K, then recooled to investigate the effects of a room-temperature annealing cycle on the superconducting properties of the irradiated cavities. A detailed description of the experiment and the results shall be presented. These results are important to employing superconducting RF technology to future high-intensity proton accelerators for use in research and transmutation technologies.