High-power infrared free electron laser driven by a 352 MHz superconducting accelerator with energy recovery

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Abstract

A high-average power infrared free electron laser driven by a 40 MeV energy recovery superconducting accelerator is being developed at the Korea Atomic Energy Research Institute. The free electron laser is composed of a 2-MeV injector, two superconducting acceleration cavities, a recirculation beamline, and an undulator. Each accelerator module contains two 352-MHz 4-cell superconducting cavities and can generate an acceleration gain of 20 MeV. The 2-MeV injector has been completed, and generates stably an average current of 10 mA. One of the 20 MeV superconducting accelerator modules has been installed, cooled down to 4.5 K, and RF-tested. An average power of 1 kW at the wavelengths of 3–20 μm is expected.

Introduction

There are several potential applications of tunable high-average power free electron lasers (FELs) in nuclear industry. For example, it is possible to separate stable isotopes such as silicon (Si29), carbon (C11), oxygen (O18), etc., by using selective multi-photon dissociation of molecules. Tunable ultraviolet FELs are useful in separating long-lifetime elements from nuclear spent fuels using selective photochemical reactions. In these applications, few tens of kilowatts in average power of radiation at a reasonably low cost is needed. One of the best ways of generating high-average power FEL radiation at low cost is using superconducting accelerator with energy recovery.

After successful development of a millimeter-wave FEL driven by a 0.4-MeV electrostatic accelerator [1], and an infrared FEL driven by an 8-MeV microtron accelerator [2], and being encouraged by the pioneering demonstration of energy recovery FELs by the Jefferson Laboratory [3], and JAERI [4], the Korea Atomic Energy Research Institute (KAERI) started a project for the development of a high-power infrared FEL driven by a 40-MeV superconducting accelerator with energy recovery. This paper describes design concept of the FEL and the results of the first stage of the project.

Section snippets

Schematic layout of the FEL

The KAERI infrared FEL is composed of a 300-keV electron gun, a 2-MeV pre-accelerator, two 20-MeV 352-MHz superconducting acceleration cavities, an undulator unit, and an energy recovery beamline. Schematic layout of the FEL is shown in Fig. 1, and design parameters of the FEL are listed in Table 1.

2-MeV injector

The 2-MeV injector [5] is composed of a 300-keV electron gun, one RF bunching cavity, and two normal-conducting RF acceleration cavities. The kinetic energy of the electron beam is 1.5 MeV nominally,

Undulator

An upgraded version of the high-precision electromagnetic undulator assisted by permanent magnets [9] will be used in the high-power infrared FEL. This type of undulator is very compact in its structure, cost-effective, and generates high magnetic field with very high precision. The field strength changes depending on the electric current through main coil. Fig. 5 shows a schematic of the undulator.

Summary

A high-average power infrared free electron laser driven by a 40 MeV energy recovery superconducting accelerator is being developed at KAERI. The 2-MeV injector has been completed, and generates stably an average current of 10 mA. The 2-MeV electron beam has been transported successfully to the entrance of the superconducting cavity. One of the superconducting cavities from CERN has been installed and cooled down to its operating temperature, 4.5 K. Two 50-kW 352-MHz RF generators have been

Acknowledgements

The superconducting cavities used in this project has been donated by CERN. Authors thank to CERN for donation. Many parts of the accelerator has been fabricated on contract base by the Budker Institute of Nuclear Physics, Novosibirsk. The authors thank to the members for their contributions.

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