Shigeki Fukuda

The KEKB injector linac

Abstract An 8-GeV electron/3.5-GeV positron injector for KEKB was completed in 1998 by upgrading the existing 2.5-GeV electron/positron linac. The main goals were to upgrade its accelerating energy from 2.5 to 8 GeV and to increase the positron intensity by about 20 times. This article describes not only the composition and features of the upgraded linac, but also how these goals were achieved, by focusing on an optics design and commissioning issues concerning especially high-intensity single-bunch acceleration to produce positron beams.

Design and evaluation of a compact 50 MW rf source of the PF linac for the KEKB project

Abstract A compact 50 MW rf source, an upgraded version of an existing rf source of the PF linac, has been developed for the KEKB project. The rf pulse-width requirement for the 50 MW klystron is 4 μs in order to be used with SLED-type rf compressors. On the basis of a computer simulation, the existing 30 MW klystron has succeeded to produce more than 51 MW at a 310 kV beam voltage with a 4 μs rf pulse width by optimizing the focusing magnetic field. Based on this result, we have designed and tested a new compact 50 MW klystron, the interaction region of which is the same as that of the 30 MW tube. In order to realize a practically reliable tube, we enlarged the cathode diameter, the gun housing and the insulation ceramic-seal. As a result, we have succeeded in obtaining a 50 MW output power with an rf pulse width of 4 μs and a more than 60 MW output power with an rf pulse width of 2 μs from this klystron. Compatibility between the 30 MW klystron and the 50 MW klystron has been aimed at for a socket assembly, such as a focusing electromagnet and a pulse-transformer assembly, with only a small change. These could lead to a compact rf source, which would save on upgrading costs. We can expect an easy construction method, which could be required to be conducted during an interval of machine operation for the Photon Factory.

Klystron modulator for the KEK 2.5 GeV linac

Abstract The klystron modulator for the KEK 2.5 GeV linac has been designed, constructed and operated. Design philosophy, equipment configuration, results of the performance tests and the present status of the system are described. With careful consideration to reliability and maintainability, 3.5 μs wide pulses with 22.5 kV voltage and 3600 A peak current were successfully generated.

Performance of a high-power klystron using a BI cathode in the KEK electron linac

Fifty-megawatt high-power klystrons in the KEK electron linac have used a larger diameter cathode of 85 mm. Stable operation requires a careful manufacturing process of the cathode and a low-gradient gun design. Therefore, the klystron manufacturing, including a cathode processing, has been improved so as to obtain stable performance. This paper presents the klystron improvements associated with using the BI cathode and klystron operation statistics for the past 17 years.

RF windows used at S-band pulsed klystrons in the KEK linac

Abstract The breakdown of the alumina RF-windows used in high-power klystrons is one of the most serious problems in the development of klystrons. This breakdown results from excess heating of alumina due to multipactor bombardment and/or localized RF dissipation. In order to develop RF windows having high durability for the KEKB klystrons, several kinds of alumina ceramics are being examined, and the breakdown mechanism of RF windows are being considered. An improved RF window installed in a KEKB klystron is also being tested.

Status of the low-level RF system at KEK-STF

RF field stabilities less than 0.3%, 0.3deg are required at the STF low-level rf (LLRF) system. In order to satisfy these requirements, a digital FB system using an FPGA is adopted. A total of eight cavities will be installed in STF- phase 1 and the vector sum control of eight cavity signals will be achieved. The performance of the FB system is examined using electrical cavity simulators prior to the rf operation. Other R&D projects such as the development of a simplified interlock system with an FPGA are also summarized.

Development of a Portable 950 keV X‐band Linac for NDT

We are developing a portable 950 keV X‐band (9.4 GHz) linac X‐ray source for on‐site nondestructive testing of erosion of metal pipes at a petrochemical complex. To develop it, we adopted a compact X‐band 9.4 GHz magnetron of 250 kW for RF generation device. The whole device, including power supply and cooling devices, were also downsized. The dose rate of X‐ray converted in a tungsten target is designed to be 0.2 Gy/min at 1‐m distance. We designed an accelerating tube that uses the π mode for the lower energy part and the π/2 mode cavity for the higher energy. We manufactured the accelerating tube and carried out beam acceleration tests, confirming that the electron beam was accelerated up to 950 keV.

Development of digital low-level RF control system using multi-intermediate frequencies

In a superconducting accelerator, an FPGA-based low-level RF system is adopted and a digital feedback control system is utilized to satisfy the requirement of stability in the accelerating field. A digital low-level RF system using multi-intermediate frequencies has been developed and the stability of the feedback operation is estimated using a cavity simulator based on an FPGA board. In this study, the RF system is examined and the results of estimations that are obtained using the cavity simulator are reported.

Construction and development of an UV free electron laser under the cooperation of Nihon U., KEK, PNC, ETL and Tohoku U.

Abstract The construction and the development of an UV free electron laser at Narashino Campus, Nihon U. have been started under the cooperation of Nihon U., KEK 1 , PNC 2 , ETL 3 and Tohoku U. The project requires a 125 MeV S-band electron linear accelerator to expand the oscillation of FEL to the UV region using fundamental mode. The injection system consists of a thermionic RF-gun with a LaB 6 cathode and a magnet for magnetic bunching. We are studying to reduce the back-bombarding electrons to realize the macropulse length of 20 μs. Electron beams, up to the energy of 125 MeV, are injected into the optical cavity. Changing the accelerating energy and/or undulator parameters, this system will cover the range from infrared to ultraviolet for the applications in the various fields.

Compact 950 keV X-band (9.4GHz) Linac X-ray Source for On-site Nondestructive Evaluation

We are developing a compact X-ray nondestructive evaluation (NDE) system using 9.4 GHz X-band linac with 250 kW magnetron. A conventional 1 MeV X-band machines use a large 1 MW magnetron system. We have chosen the 250 kW magnetron so that the RF heat loss is remarkably reduced. This design yields compactness and portable. This system consists of the X-band magnetron, modulator, thermionic 20 kV electron gun, X-band linac and metal target of X-ray generation. We aim that X-ray spot size is less than 1 mm. We designed the linac structure of the pi mode at low energy parts and the pi/2 mode at high energy parts by using updated commercial software. We finished to measure resonant frequency, and electromagnetic field on axis used by bead-pull method. These devices are to be applied to on-site NDE at petrochemical complex, nuclear- and thermal-power plants. We are also going to test the system at the Nuclear Professional School, the University of Tokyo this year. This paper presents the details of the system and experimental results.