Fumihiko Oda

Optical beam transport system at FEL-SUT

Abstract Kawasaki Heavy Industries Ltd. has installed an FEL beam transport system at the IR FEL Research Center of the Science University of Tokyo (FEL-SUT). This system transports the FEL output beam from the FEL machine room to the optical diagnostic room through a vacuum tube. The in-vacuum multi-mirror synchronized system operated from the FEL control room enables the operator to control the multiple mirrors simultaneously on or off axis of the FEL beam and to distribute the FEL output to one of the laboratories. The essential component of the transport system is the passive control optics that is composed of an elliptical and parabolic mirror couple. Once the control optics is aligned, a parallel FEL beam with a good pointing stability is obtained without any active operation to tune the optical system for different wavelengths.

Surface Reaction Enhancement by UV irradiation during Si Etching Process with Chlorine Atom Beam

We investigated the dependence of etching rate on irradiation of photons with a UV lamp during Si etching processes with chlorine atom beam to understand the influence of UV photon irradiation in the plasma etching process. We found that UV from 220 to 380 nm drastically enhanced Si surface reactions with a chlorine atom beam at lamp power densities over 20 mW/cm2. Additionally, we were able to control the Si etching rate by changing the photon irradiation power density. These results led us to speculate that the irradiation of UV photons from 220 to 380 nm generates crystal defects on the Si surface and enhances chemical reactions between Si and chlorine during Cl2 plasma etching processes.

Performance of the KHI FEL device at FEL-SUT

FEL lasing with the saturated power in the wavelength of 4–16mm was achieved by using the KHI (Kawasaki Heavy Industries, Ltd.) FEL device. The macro-pulse length of the electron beam was improved by using the LaB6 cathode instead of the dispenser cathode as a cathode of the OCS RF-gun. The improvement yielded the saturated FEL power with the macro-pulse length of 0.5–1.5ms. The FEL energy was 2–40 mJ. The measured FEL output powers were in agreement with the values which were taken into account Piovella’s theory. r 2002 Elsevier Science B.V. All rights reserved. PACS: 41.60.C

Performance of the thermionic RF gun injector for the linac-based IR free electron laser at the FEL-SUT

Abstract Kawasaki Heavy Industries, Ltd. (KHI) has developed a linac-based compact IR free electron laser device and has installed it in the FEL-SUT (IR FEL Research Center of Science University of Tokyo). The FEL device adopts a combination of a multi-cell RF gun with a thermionic cathode and an α-magnet as an injector. The fundamental design of this RF gun is the π /2 mode standing wave structure. It has two accelerating cells and a coupling cell located on the beam axis, a so-called “on axis coupled structure” (OCS). Characteristics of momentum distribution and micropulse bunch length of the electron beam are compared with beam dynamics simulation results in this paper. We succeeded in obtaining sufficient peak current for FEL lasing with this injector, and the first lasing was achieved on 6 July 2000.

The properties of on-axis coupled structure RF gun

Abstract Kawasaki Heavy Industries Ltd. (KHI) has developed the compact IR FEL device, which adopts a combination of a newly designed RF gun with a thermionic cathode and an α-magnet as an injector. The accelerating mode of the S-band RF gun is a π/2 standing wave mode. The coupling cell is located on the beam axis, the so-called on-axis coupled structure (OCS). The cavity shape was designed by using electromagnetic field analytical codes. The OCS RF gun was manufactured and the electromagnetic properties were measured. The results show good agreement with the simulations.

The on axis coupled structure type RF gun

Abstract The fundamental design of this newly developed RF gun with a thermionic cathode is the π/2 mode standing wave structure. It has two accelerating cells and a coupling cell located on the beam axis, a so-called on axis coupled structure (OCS). This structure offers a stable operation for high beam current, owing to high group velocity and wide bandwidth. It is important to reduce damage onto the cathode caused by back bombardment, especially for long macropulse operation, such as in an FEL injector. Back bombardment, as well as output beam profile was simulated by using the electromagnetic field analytical codes ‘EMSYS’(2D) and ‘MAFIA’(3D). The cavity shape was optimized to reduce back bombardment power without sacrificing beam emittance.

Design and study of FIR FEL device using S-band linac at FEL-SUT

Tokyo University of Science and Kawasaki Heavy Industries, Ltd. (KHI) have completed in 2001 the design and assembly of an FIR-FEL device using an S-band linac based at a spectral range between 300 and 1000 μm. The FEL device was installed into the IR FEL Center at Tokyo University of Science in April 2002. Our optical resonator is composed of a waveguide with a gap of 4.5 mm and two cylindrical mirrors positioned in the waveguide in order to mitigate problems of slippage and diffraction losses.

Observation of theoretical power saturation by the KHI free electron laser device

The saturation of free electron laser (FEL) output power by the KHI-FEL device was achieved on 3rd, October 2000 at the wavelength of 9.3 µm. The FEL device has operated thereafter successfully in the wavelength region between 4.0 and 16.0 µm. The macropulse average FEL power of 37.5 kW, which is the theoretical saturation level, has been obtained at the wavelength of 7.9 µm. The net FEL gain was estimated to be 16%.

Improvement of KHI FEL device at FEL-SUT

FEL lasing with the saturated power in the wavelength of 4-16 µm was achieved by using the KHI (Kawasaki Heavy Industries, ltd.) FEL device. The macro-pulse length of the electron beam was improved by using the LaB6 cathode instead of the dispenser cathode as a cathode of the OCS RF-gun. The improvement yielded to obtain the saturated FEL power. The FEL energy was 2-40mJ. In addition to it, the vertical position (the same direction as the electron beam from the cathode) of the RF-gun cathode was tuned. As a result, the FEL energy was increased to 2-65mJ. The FEL output powers estimated from the FEL energy and the macro-pulse shape were in agreement with the values which were taken into account Piovellas theory.

Numerical study of optical-cavity misalignment effects for a far-infrared FEL

A far-infrared FEL will be newly installed in the IR FEL Research Center at the Science University of Tokyo (FEL-SUT) in 2002. In this study, optical cavity misalignment effects for the far-infrared FEL are researched by using the simulation code that has been developed at Kawasaki Heavy Industries, Ltd. Results show not only cavity losses but also the gain reduction by the tilt and the offset of the mirror and the offset of the electron beam. The required alignment accuracy is also obtained in this study.