K. Hosoyama

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.

Coil bobbin composed of high-strength polyethylene fiber reinforced plastics for a stable high-field superconducting magnet

High-field superconducting solenoid magnets sometimes quench by wire motion induced by electromagnetic force. Fiber reinforced plastic [Dyneema fiber reinforced plastic (DFRP)] pipes composed of high-strength polyethylene fiber by filament winding method could be constructed so as to expand in the circumferential direction when cooled to low temperature with an appropriate selection of winding angle and shape of the pipes. In the case of a superconducting coil fabricated with a DFRP bobbin, it is expected that wire motions in high field are decreased by expansion of the coil bobbin. In this paper, tap voltage between both ends of the coils fabricated with DFRP bobbin and stainless steel (SUS) bobbin were measured with increasing current. The coil using SUS bobbin showed many sharp peaks in tap voltage induced by quick wire motions. In contrast, those using DFRP bobbin showed only a few small peaks. These results suggest that wire motions were constrained by DFRP bobbin. The training effects were observed in both cases.

Coil bobbin composed of high strength polyethylene fiber reinforced plastics for a stable high field superconducting magnet

High field superconducting solenoid magnets sometimes quench by wire motion induced by electro-magnetic force. High strength polyethylene fiber reinforced plastic (DFRP) has a negative thermal expansion coefficient and a low frictional coefficient. DFRP pipes made by filament winding method could be constructed so as to expand in the circumferential direction when cooled to low temperature with an appropriate selection of winding angle and shape of the pipes. In the case of a superconducting coil wound on a DFRP bobbin, it is expected that wire motions in high field are decreased by expansion of the coil bobbin. In this work, sample coils wound on DFRP bobbin and stainless steel (SUS) bobbin were prepared. The sample coil voltages were measured during increasing current in background external field. The coil using SUS bobbin showed many sharp peaks in tap voltage induced by quick wire motions. In contrast, those using DFRP bobbin showed no peaks. These results suggest that the quick wire motions were constrained by DFRP bobbin which had a negative thermal expansion coefficient and a low frictional coefficient.

Development of a High Performance Transfer Line System

High performance transfer lines are key components for design and construction of cryogenic systems for superconducting magnets and cavities. We have developed two types of high performance transfer lines; main transfer lines with liquid helium flow and cold gas return dual path and sub-transfer line with single path, all helium lines in these are guarded by 80K liquid nitrogen cooled thermal shields. We have adopted the aluminum molding made by extrusion for the 80K thermal shields. The structure of the transfer lines was designed to be easy to assemble. The performance of these transfer lines were tested. The heat loss of the main transfer lines at straight section are 0.04W/m and 0.06W/m for supply and return line, respectively.

A Status Report on the Development of 5-cm Aperture, 1-m Long SSC Dipole Magnet at KEK

The design and construction of a series of eleven 5-cm aperture, 1-m long SSC model dipole magnets KEK#1-#11 was started in May 1990. We have paid much attention to the design of magnet end part and developed new-type end spacers1 which have constant perimeter profiles to minimize internal stress of the cables at the coil end. Except for length, these short magnets have the same baseline design and features as the long magnet. We have performed the quench test, ramp rate quench dependence, and AC loss measurement in 1.8K superfluid helium cryostat.3

Cryogenic system for TRISTAN superconducting RF cavities

The superconducting RF cavities (32 × 5 cell) will be installed in TRISTAN electron-positron collider at KEK to upgrade the electron-positron beam energy up to 33 GeV × 33 GeV. Two 5-cell cavities are coupled together, enclosed in a cryostat and cooled by liquid helium pool boiling. Cryogenic system for the superconducting RF cavities was designed. The capacity of helium refrigerator is 4 kW at 4.4 K with liquid nitrogen precooling and two expansion turbines. The present system is designed to be easily upgraded to 6.5 kW without liquid nitrogen with an addition of expansion turbines and compressors.

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.

Status of Solenoid System to Suppress the Electron Cloud Effects at the KEKB

A large number of solenoids have been installed in the KEKB LER to remove the electron cloud. This paper describes recent solenoid winding work and the effect of it on electron cloud effects.

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>>

A NbTi Superconducting Dipole Magnet Installed in a Pressurized Helium II Cooling Bath

A double-bath pressurized helium II cryostat for an accelerator NbTi test dipole was constructed. Heat leakage into the cryostat was 5 W at 1.8 K. The dipole was excited in the cryostat. After several quenchings in pressurized helium II, the dipole achieved a highest central field of 6.75 T with an excitation current of 6.6 kA.