| AVS 55th International Symposium & Exhibition | |
| Vacuum Technology | Tuesday Sessions |
| Session VT-TuA |
| Session: | Vacuum Gauging and Calibration |
| Presenter: | M. Kuroiwa, Tokyo Electronics Co., Ltd., Japan |
| Authors: | M. Kuroiwa, Tokyo Electronics Co., Ltd., Japan S. Fujii, Tokyo Electronics Co., Ltd., Japan N. Matsumoto, Tokyo Electronics Co., Ltd., Japan M. Sasaki, Tokyo Electronics Co., Ltd., Japan N. Ogiwara, Japan Atomic Energy Agency Y. Hikichi, Japan Atomic Energy Agency |
| Correspondent: | Click to Email |
Turbomolecular pumps (TMPs) are used for not only rough pumping but also evacuation during beam operation. The backing pressure of the TMPs is always monitored with Pirani gauges. The control unit for the gauge has been newly designed, as the unit should be placed far from the gauge head which is located in a high level of radiation and electrical noise. We have adopted the combination of the constant current method with four-point probe method. Thus, with these techniques the output has been confirmed experimentally to be independent of the cable length, and less influenced by the noise. Generally the constant current method is not so suitable for measuring the higher pressure than that with constant temperature method, because the change in the output voltage so drastically decreases increasing the pressure over than about 100 Pa. As we have to measure the pressure up to about 1000 Pa precisely in order to monitor the backing pressure of TMPs, we have carried out the experiment about the change in the output as a function of the current. And, we have confirmed that the higher pressure can be measured when the higher current is passed. For example, we can measure the pressure less than 20 Pa at 50 mA, and the pressure ranging from 20 Pa to 1000 Pa at 90 mA, respectively. Thus the current is controlled in such a way that the set value is increased with the increasing pressure in several stages. On the other hand, to minimize radiation exposure during maintenance, it is necessary for the gauge head to have high toughness against the vibration and abrupt air inlet etc. Thus we tried to use W wire as the filament instead of Pt wire. However W wire would be unstable characteristic in high temperature status (over the 300C). It had might be affected by oxidation. So we have investigated other material for the filament. Now we have got good data by using W wire with gold coating 30 micrometer in a diameter. 30mA, 10ohm. Still we continue to have investigation to get more toughness and good condition for filament.