S.V. Miginsky

HIGH AVERAGE CURRENT 2-MEV ELECTRON ACCELERATOR FOR A HIGH-POWER FREE-ELECTRON LASER

Abstract A high average current CW RF electron accelerator has been developed for the free electron laser programs at KAERI. The accelerator is composed of a 300-keV electron gun, one RF bunching cavity, and two RF acceleration cavities. The kinetic energy of the electron beam is 1.5 MeV nominally and 2 MeV at maximum. The duration of a pulse is 350 ps and its repetition rate is variable from a single pulse to 22.5 MHz. The peak current is 6 A, and the average current, at the maximum repetition rate, is 45 mA. The resonant frequency of the RF cavities is 180 MHz. The energy gain of an RF acceleration cavity is 0.6 MeV nominally and 0.85 MeV at maximum. The total RF power supplied into the RF cavities is 262 kW. A millimeter-wave FEL driven by the 2-MeV accelerator is under design. The 2-MeV accelerator will be used as an injector of a high-average-power infrared FEL.

A compact far infrared free electron laser

Abstract The Korean Atomic Energy Research Institute and the Budker INP developed a design and manufactured the main parts of a free electron laser with emission power of one watt in the infrared region of 25 to 30 microns including 10-cm microtron. After the commissioning of microtron, beamline and undulator electron beams were transmitted through the undulator and by using a special code microtron electron beam, performance parameters were measured and computed.

Commissioning of the accelerator-recuperator for the FEL at the Siberian Center for Photochemical Research.

A 100 MeV eight-turn accelerator-recuperator intended to drive a high-power infrared free-electron laser (FEL) is currently under construction in Novosibirsk. The first stage of the machine includes a one-turn accelerator-recuperator that contains a full-scale RF system. It was commissioned successfully in June 2002.

Beam characterization at the KAERI UED beamline

The UED (ultrafast electron diffraction) beamline of the KAERI’s (the Korea Atomic Energy Research Institute’s) WCI (World Class Institute) Center has been successfully commissioned. We have measured the beam emittance by using the quadrupole scan technique and the charge by using a novel measurement system we have developed. In the quadrupole scan, a larger drift distance between the quadrupole and the screen is preferred because it gives a better thin-lens approximation. A high bunch-charge beam, however, will undergo emittance growth in the long drift caused by the space-charge force. We present a method that mitigates this growth by introducing a quadrupole scan with a short drift and without using the thin-lens approximation. The quadrupole in this method is treated as a thick lens, and the emittance is extracted by using the thick-lens equations. Apart from being precise, our method can be readily applied without making any change to the beamline and has no need for a big drift space. For charge measurement, we have developed a system consisting of an in-air Faraday cup (FC) and a preamplifier. Tests performed utilizing 3.3-MeV electrons show that the system was able to measure bunches with pulse durations of tens of femtoseconds at 10 fC sensitivity.

Frequency multiplying oscillator with an electron beam accelerated in a drift space

In a uniform acceleration region, the behavior of a velocity-modulated electron beam has been analyzed using a particle-in-cell code. By making use of one of the accelerated harmonic components of the velocity-modulated electron beam, we demonstrate a frequency multiplying oscillator for a compact THz emitter, which employs multiple electron beams and a higher order mode resonator to modulate the electron beam without an additional driving source.

A project of accelerator-recuperator for Novosibirsk high-power FEL

The first stage of the Novosibirsk high-power free-electron laser (FEL) was commissioned in 2003. It is driven by a CW energy recovery linac. The next step will be the full-scale machine, a four-track accelerator-recuperator based on the same RF accelerating structure. This upgrade will permit to get shorter wavelengths in the infrared region and increase the average power of the FEL by several times. The scheme and some technical details of the project are set out. The installation will be a prototype for future multiturn accelerator-recuperators.

Status of the free electron laser for the Siberian centre for photochemical research

Abstract A high-power infrared free electron laser is under construction in Novosibirsk. As the full-scale machine seems to be complicated and quite expensive, the project was divided into two stages so that the first-stage machine can be assembled and commissioned as soon as possible. Main features of the project and the current status are described.

A Compact THz FEL at KAERI: the Project and the Status

A new compact THz free electron laser driven by a microtron is being developed recently at KAERI. It uses a hybrid electromagnetic undulator. A novel scheme of injection/extraction/outcoupling is developed. The machine is partially assembled and commissioned. Characteristic features and current state are described in the paper.

Waveguide-Mode Terahertz Free Electron Lasers Driven by Magnetron-Based Microtrons

We have developed small-sized terahertz free-electron lasers by using low-cost and compact microtrons combining with magnetrons as high-power RF sources. We could stabilize the bunch repetition rate by optimizing a modulator for the magnetron and by coupling the magnetron with an accelerating cavity in the microtron. By developing high-performance undulators and low-loss waveguide-mode resonators having small cross-sectional areas, we could strengthen the interaction between the electron beam and the THz wave inside the FEL resonators to achieve lasing even with low-current electron beams from the microtron. We used a parallel-plate waveguide in a planar electromagnet undulator for our first THz FEL. We try to reduce the size of the FEL resonator by combining a dielectric-coated circular waveguide and a variable-period helical undulator to realize a table-top THz FEL for applying it to the security inspection on airports.