J. Fugitt

First Lasing of the Jefferson Lab IR Demo FEL

As reported previously [1], Jefferson Lab is building a free-electron laser capable of generating a continuous wave kilowatt laser beam. The driver-accelerator consists of a superconducting, energy-recovery accelerator. The initial stage of the program was to produce over 100 W of average power with no recirculation. In order to provide maximum gain the initial wavelength was chosen to be 5 mu-m and the initial beam energy was chosen to be 38.5 MeV. On June 17, 1998, the laser produced 155 Watts cw power at the laser output with a 98% reflective output coupler. On July 28th, 311 Watts cw power was obtained using a 90% reflective output coupler. A summary of the commissioning activities to date as well as some novel lasing results will be summarized in this paper. Present work is concentrated on optimizing lasing at 5 mu-m, obtaining lasing at 3 mu-m, and commissioning the recirculation transport in preparation for kilowatt lasing this fall.

Jefferson Lab. FEL user facility

Jefferson Labs IR Demo FEL Facility includes an associated 600 m2 user facility containing six separate laboratory areas. In the summer of 1999 we began delivery of beam int two of these labs as part of our commissioning of the FEL optical transport and laser safety systems. The high average power capability in the mid-IR, along with an ultrafast high PRF temporal structure makes this laser a unique source for both applied and basic research. While commissioning, we conducted several test, primarily of laser-materials interactions that take advantage of the unique characteristics of this FEL. An overview of the FEL facility and its current performance, along with a synopsis of current and future experiments, will be presented.

A status report on the development of a high power UV and IR FEL at CEBAF

Previously the authors presented a design for a kilowatt demonstration industrial UVFEL. Progress has been made in resolving several design issues identified in that work. More exact simulations of the injector have resulted in a better estimate of the injector performance. A more compact lattice has been designed meeting the design requirements for the UV FEL, and a new design point has been studied which greatly increases the threshold for longitudinal instabilities. A stability analysis of the RF control system has found that only minor modifications from the existing CEBAF controls will be necessary to allow them to be used with a high current, energy-recovery accelerator. Designs for the optical cavity length and figure control systems have been conceptualized and a model of the corner-cube resonator is being built and tested. Finally, three-dimensional simulations of the FEL have been carried out which show that the laser should exceed its minimum design goals for average power.

Design of a high charge CW photocathode injector test stand at CEBAF

A 10 MeV high-charge CW electron injector test stand has been designed for the CEBAF UV FEL driver accelerator. It consists of a 500 kV DC photocathode gun, a 1500 MHz room-temperature buncher, a modified CEBAF cryounit (quarter cryomodule) with an SRF accelerating gradient of /spl sim/10 MV/m, two solenoids in the 500 kV region and an achromatic, non-isochronous injection transport line delivering 10 MeV beam to the driver accelerator. Experimental work is in progress toward establishing design system performance.

Kilowatt average-power laser for subpicosecond materials processing

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. We present operation results from the worlds 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.

Accelerator design for the high-power industrial FEL

We have developed a conceptual design for an industrial-use kilowatt UV and IR FEL driven by a recirculating, energy-recovering 200 MeV, 1-5 mA superconducting rf (SRF) electron accelerator. In this paper we describe the accelerator design of this FEL. The accelerator consists of a 10 MeV injector, a 96 MeV SRF linac with a two-pass transport which accelerates the beam to 200 MeV, followed by energy-recovery deceleration through two passes to the dump. Technical challenges include high-intensity injector development, multi-pass energy-recovery operation, SRF modifications and control for FEL operation, development of tuneable, nearly-isochronous, large-acceptance transports, and matching of the beam to the FEL wiggler. An overview of the accelerator design is presented.

A high-average-power FEL for industrial applications

CEBAF has developed a comprehensive conceptual design of an industrial user facility based on a kilowatt UV (150-1000 nm) and IR (2-25 micron) FEL driven by a recirculating, energy-recovering 200 MeV superconducting radio-frequency (SRF) accelerator. FEL users-CEBAFs partners in the Laser Processing Consortium, including AT&T, DuPont, IBM, Northrop-Grumman, 3M, and Xerox-plan to develop applications such as polymer surface processing, metals and ceramics micromachining, and metal surface processing, with the overall effort leading to later scale-up to industrial systems at 50-100 kW. Representative applications are described. The proposed high-average-power FEL overcomes limitations of conventional laser sources in available power, cost-effectiveness, tunability and pulse structure.

A Proposed High-Power UV Industrial Demonstration Laser at CEBAF

The Laser Processing Consortium, a collaboration of industries, universities, and the Continuous Electron Beam Accelerator Facility (CEBAF) in Newport News, Virginia, has proposed building a demonstration industrial processing laser for surface treatment and micro-machining. The laser is a free-electron laser (FEL) with average power output exceeding 1 kW in the ultraviolet (UV). The design calls for a novel driver accelerator that recovers most of the energy of the exhaust electron beam to produce laser light with good wall-plug efficiency. The laser and accelerator design use technologies that are scalable to much higher power. The authors will describe the critical design issues in the laser such as the stability, power handling, and losses of the optical resonator, and the quality, power, and reliability of the electron beam. They will also describe the calculated laser performance. Finally progress to date on accelerator development and resonator modeling will be reported.

Proposed high-power UV industrial demonstration laser at CEBAF

The Laser Processing Consortium, a collaboration of industries, universities, and the Continuous Electron Accelerator Facility in Newport News, Virginia, has proposed building a demonstration industrial processing laser for surface treatment and micro-machining The laser is a free-electron laser with average power output exceeding 1 kW in the ultraviolet. The design calls for a novel driver accelerator that recovers most of the energy of the exhaust electron beam to produce laser light with good wall-lug efficiency. The laser and accelerator design use technologies that are scalable to much higher power. We will describe the critical design issues in the laser such as the stability, power handling, and losses of the optical resonator, and the quality, power, and reliability of the electron beam. We will also describe the calculated laser performance. Finally progress to date on accelerator development and resonator modeling will be reported.

RF system modeling for the high average power FEL at CEBAF

High beam loading and energy recovery compounded by the use of superconducting cavities, which requires tight control of microphonic noise, place stringent constraints on the linac RF system design of the proposed high average power FEL at CEBAF. Longitudinal dynamics imposes off-crest operation, which in turn implies a large tuning angle to minimize power requirements. Amplitude and phase stability requirements are consistent with demonstrated performance at CEBAF. A numerical model of the CEBAF RF control system is presented and the response of the system is examined under large parameter variations, microphonic noise and beam current fluctuations. Studies of the transient behavior lead to a plausible start-up and recovery scenario.