Kazufumi Hara

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.

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.

A Liquid Helium Transfer Line System for Superconducting RF Cavity

A liquid helium transfer line system was designed and constructed for a prototype 3-cell superconducting cavity (SCC) which was Installed in the TRISTAN Accumulator Ring (AR) for electron beam acceleration test. The liquid helium transfer system, about 20 m long, consisting of three helium lines (supply, return and bypass) and two liquid nitrogen lines (supply and return), connects the helium refrigerator or liquid helium dewar at ground level and the SCC cryostat in the underground AR tunnel through a narrow service channel. The operational modes (cooldown, liquefier and refrigerator cooling mode) can be selected by valves in the transfer line system. The system worked very well and the SCC was cooled and tested successfully.

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.

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.