Yuuji Kojima

RF systems for the KEK B-Factory

This paper describes the design features and operational status of the RF systems for the KEK B-Factory (KEKB). Two types of new RF cavities have been developed to store very high-intensity beams with many short bunches. The design and performance of the cavities and other critical components, such as the input couplers and HOM dampers, are reported. The configuration of the RF systems is given and descriptions of various control loops are made, including a direct RF feedback loop and a 0-mode damping loop. The effects of transient beam loading due to a bunch gap on bunch phase modulations were simulated and measured. The development of a superconducting crab cavity, which is a component of luminosity upgrade strategy, is also presented.

Cryogenic System for the Tristan Superconducting RF Cavities: Performance Test and Present Status

The cryogenic system for the TRISTAN superconducting RF cavities (SCC) was constructed and commissioned successfully. Sixteen 5-cell SCC in 8 cryostats were installed in the TRISTAN electron-positron collider at KEK. The cryostats were connected to the helium refrigerator (4 kW at 4.4 K) through a helium transfer line (total length about 330 m) and cooled by pool boiling liquid helium. It took about 3 days to cool down the 16 SCC, a total cold mass of about 8000 kg, from room temperature to liquid helium temperature and 1 day to fill the liquid helium up to about 830 L in each SCC cryostat. The liquid helium level and the pressure fluctuation due to the RF losses in the cryostats were automatically controlled by liquid supply valves and the compensation heaters in the cryostats respectively. The performance test, the present equipment status of the cryogenic system and the six months of operational experience are described.

Upgrading of TRISTAN by superconducting RF system

The energy upgrade of TRISTAN by a superconducting RF system is progressing. Sixteen five-cell 508 MHz cavities made of niobium have been installed and started to operate in November 1988. Superconducting cavities have raised the energy of e/sup -/e/sup +/ to 30.4 GeV from 28.5 GeV with a normal conducting RF system. Construction, vertical tests, horizontal tests and three months of operational experience are described.<<ETX>>

Fabrication and Testing of 1-M-Long SSC Model Dipole Magnets

A series of fifteen 5-cm-aperture, 1-m-long, SSC model dipole magnets with various types of cable have been designed and fabricated at the National Laboratory for High Energy Physics (KEK). These magnets have been quench tested in a 4.2-K vertical cryostat and a 1.8-K pressurized-superfluid cryostat. In order to improve the quench characteristics of the magnets, we have carried out modifications of the coil end and splice design. We will describe the basic features of the magnet design, the various fabrication steps of the magnets, and results of quench tests.

Cryogenic System for TRISTAN Superconducting RF Cavities: Description and Operating Experience

Publisher Summary A large scale helium refrigeration system was constructed and operated for about 7 years for superconducting RF accelerating cavities (SCC) in TRISTAN electron positron collider at National Laboratory for High Energy Physics (KEK). The 32 x 5 cell 508 MHz SCC in 16 cryostats were installed in TRISTAN electron-positron collider at KEK for further upgrading of the beam energy, from 27 GeV to 32 GeV. This chapter provides a short description of the main components of the cryogenic system together with the operating experience gained during the commissioning and 7 years operation. The total number of failures in the cryogenic system during about 7 years operation was 85. The experience in long operation of the large cryogenic system shows the compressor is the key component and the regular maintenance of the system including utilities is essential to attain the system reliability.

STF-2 Cryomodule Performance and New Input Coupler RD for ILC

The high power test for STF-2 cryomodule with twelve cavities has completed successfully in 2015. It became clear the average accelerating gradient was 30.3 MV/m, eight cavities achieved above 31.5 MV/m as the ILC specification, and three cavities had the significant performance degradation by heavy field emission due to the additional clean room work in the STF tunnel. As the following next steps, there are the LFD (Lorenz Force Detuning) measurement, LFD compensation by piezo, and long run for check of stable operation at high gradient. In the long run around 32 MV/m, each cavity without degradation showed the stable operation with the successful LFD compensation by piezo and RF feedback system. On the other hand, from the view point of plug-compatibility for the input coupler in the ILC, new STF input couplers with 40mm of input port were re-designed, fabricated and high-power-tested successfully. Moreover, for the lower cost study, another input couplers with coating-free ceramic was also tested in the collaboration of CERN and KEK. In this presentation, the detailed results for STF-2 Cryomodule test and 40mm input couplers are reported.

Magnetic Field Measurement of Superconducting Dipolemagnets with Harmonic Coil and Hall Probe

Magnetic field measurements and field analyses of 1-m long superconducting dipole magnets fabricated at the National Laboratory for High Energy Physics (KEK) have been carried out using a harmonic coil with the bucking scheme.1 Conditions of the data acquisition are optimized to achieve the accurate and efficient measurements. Not only in the steady state of the magnet excitation by constant currents, but also on the way the excite current increases until the magnet quenches the field measurements have been tried, and the results are discussed in this paper on the possibility of the “on-the-fly” measurement using a harmonic coil. Some results on the so-called remnant field of the magnets measured with a Hall probe are also described.

Cryogenic System for the Tristan-Ar Superconducting RF Cavities

The cryogenic system for two 508 MHz 5-cell superconducting RF cavities in two cryostats was designed and constructed in the TRISTAN accumulation ring at KEK for the reliability study of the SCC and the cryogenic system. Two superconducting cavities, mounted in parallel cryostats and having a total cold mass of about 2000 kg, were cooled down from room temperature and refigerated by pool boiling liquid helium. Various beam tests were performed.