| AVS 62nd International Symposium & Exhibition | |
| Vacuum Technology | Tuesday Sessions |
| Session VT-TuA |
| Session: | Gas Dynamics and Modeling, Pumping and Outgassing |
| Presenter: | Junichiro Kamiya, Japan Atomic Energy Agency |
| Authors: | J. Kamiya, Japan Atomic Energy Agency N. Ogiwara, Japan Atomic Energy Agency M. Kinsho, Japan Atomic Energy Agency |
| Correspondent: | Click to Email |
The usual way to reduce outgassing from a device in vacuum is to heat up a whole vacuum chamber containing the device. However, the situation, where this method can be applied, is limited due to the heat expansion of the chamber. Especially in accelerators, where the vacuum chambers are connected with nearby beam pipes, this normal bake-out method may not be applied. If a heat source and heat shields are appropriately installed inside the chamber, heat flux is directed to the device. Therefore the device can be baked out without raising the temperature of the vacuum chamber.
One candidate for such bake-out method to be applied is kicker magnets in J-PARC 3GeV synchrotron (RCS), which are installed in large vacuum chambers. The kicker magnets are installed in vacuum to prevent the discharge by high voltage. The kicker magnet mainly consists of Ni-Zn ferrite cores, aluminium electrode plates. The total outgassing rate of the materials is large due to the large surface area. Therefore it is very important to develop a degassing method for the kicker magnets in the beam line because the vacuum quality may become poor after repeated exposures to air for the maintenances. The main outgassing component of those kicker magnet components is water vapour. Therefore the bake-out temperature should be above 100 °C, which is the typical desorption temperature of water vapour from the general surface. In the RCS beam line, 3 and 5 kicker magnets are located in vacuum chambers, whose length is 3 and 5 m, respectively. It is undesirable to use a normal baking method like baking the vacuum chamber of the kicker magnets because the large heat expansion of the vacuum chamber will break nearby equipment such as alumina ceramics pipes. By applying the bake-out method, which is mentioned at the beginning, only the kicker magnet is heated without raising the temperature of the vacuum chamber. In the first stage, we performed the operability assessment of the new degassing method by the calculation with a simple model and the principal experiments using the kicker magnet, which have the same structure as the production kicker magnets in RCS. As a result, the kicker components were heated up above 100 °C by a wide margin, while keeping the temperature rise of the vacuum chamber less than 20 °C. Next, we developed the design of the heater, which has a good maintainability. The small heater of graphite, which is installed through a maintenance port of the vacuum chamber, is designed. The ideal temperature distribution was obtained with this graphite heater. Furthermore, the outgassing of the graphite was suppressed by the heating process.