Comparison of the calculated and measured stability of a NbTi cable-in-conduit conductor
Calculated curves of cable-in-conduit conductor (CICC) energy stability margins vs. current are compared to experimental curves obtained at Oak Ridge National Laboratory for NbTi single triplex conductors. The conductors ranged in length from 1.8 m to 4.8 m, and had no imposed helium flow. The initiating heat pulse was applied for 16.7 ms over the entire conductor length. The calculated stability curves display the large decrease in energy margin from the low current and high energy margin "well-cooled" stability region, to the high current and low energy margin "ill-cooled" region that was determined experimentally. The calculated "limiting current" of 250 A (boundary between the ill-cooled and well-cooled regions) also agrees with experiment. The multi-valued stability margins measured for lengths of 3.1 and 3.8 m could not be obtained by the computer model. Excluding the multiple stabilities, the calculated margins are generally 30% lower than the experimental values. The decrease in energy margin in the ill-cooled region was found to be due to the low critical to operating temperature difference (2.2 K at 250 A). This prevents an initiating pulse in the ill-cooled region from being able to generate significant Joule heating without quenching, limiting the energy margin.<<ETX>>
Heating-induced flows in cable-in-conduit conductors
Abstract The flow and pressure transients induced in stagnant supercritical helium in a pipe are calculated by energy transfers typical of those associated with the recovery of cable-in-conduit conductors (∼ 50–200 mJ cm−3 in 10–20 ms) are calculated. Pressure surges of several atmospheres accompanied by fluid flow velocities of several meters per second are possible. These strong induced flows are probably the mechanism of recoverey of cable-in-conduit conductors cooled by initially stationary helium.
DESIGN CONSIDERATION TO PPM KLYSTRONS FOR INDUSTRIAL LINAC
Toshiba has been developing the C-band and X-band Periodic Permanent Magnet (PPM) focused klystron in collaboration with KEK and manufactured prototypes for the JLC project. [1] The PPM klystron has an advantage to enhance the total efficiency as a result of eliminating the electric power for the focusing magnet. From experience on the development the PPM focused klystrons for the JLC project, we plan to apply the PPM focused klystron to the medical and industrial linac. The periodic magnet focusing scheme has some technical difficulties such as stop band voltage. To design the PPM klystron for the medical and industrial linac, it is necessary to give heed to electron beam instability; so that the tube parameters of the PPM focused klystrons have some constraints. The size of the accelerator system is substantially reduced if a PPM focused klystron is used. The majority of medical and industrial linacs use frequencies of S-band range. We discuss the availability of the S-band PPM focused klystron in this paper.