Development of a tritium compatible mass spectrometer.

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Tritium exposure gives rise to considerable increase in the noise of mass spectrometers. To avoid this imparirment and apply the mass spectrometer to tritium handling system for D-T burning fusion devices, we developed a tritium compatible quadrupole mass spectrometer equipped with tritium decontamination devices< Possible parts of the mass spectrometer were coated with gold to reduce the adsorption of tritium.It was observed that the noise level and width of the mass spectrometer increased with tritium exposure: namely, the noise level and width increased to 1E-9 and 5E-11 Amp., respectively, owing to cumulative tritium exposure of 0.1 Torr.sec. The increase in the noise level was about 100 times and that in the width was about 30 times of the initial one. It was confirmed that the increase in the noised due to the tritium adsorbed on the surfaces of inner wall of the vacuum system, quadrupole and detector itself: the tritium in gasphase playd only a minor role. The noise level and width could not be effectivly reduced by simple evacuation at room temperature. On the other hand, it was revealed that photon irradiation by halogen lamp caused to reduce both of the noise level and width to 2E-10 and 1.5E-11 Amp., respectively. They were about 1/15 or those of a conventional quadrupole mass spec- trometer after decontamination with similar procedures. The photon irradiation by mercury lamp acted similarly. The decontamination is not due to thermal effect but to photon induced desorption. These results indicate the mass spectrometer developed in the present study is compatible to carrier free tritium because the tritium contamination can be removed in-situ by photon irradiation to reduce the nose of the mass speqtrometer, although the improvement of the pumpling system and photon irradiation device should be required.