SENSITIVE HELIUM LEAK DETECTION IN A DEUTERIUM ATMOSPHERE USING A HIGH-RESOLUTION QUADRUPOLE MASS-SPECTROMETER

In fusion machines, realizing a high-purity plasma is a key to improvi ng the plasma parameters. Thus, leak detection is a necessary part of reducing the leak rate to a tolerable level. However, a conventional h elium (He-4) leak detector is useless in fusion machines with a deuter ium (D-2) plasma, because retained D particles on the first walls rele ase D-2 for a long period and the released D-2 interferes with the sig nals from the leaked He-4 due to the near identical masses of 4.0026 u (He-4) and 4.0282 u (D-2). A high-resolution quadrupole mass spectrom eter (HR-QMS) that we have recently developed, can detect a He-4(+) po pulation as small as 10(-4) peak in a D-2 atmosphere. Thus, the HR-QMS has been applied to defect He-4 leaks. To improve the minimum detecta ble limit of He-4 leak, a differentially pumped HR-QMS analyzer was at tached to a chamber of the He-4 leak detector. In conclusion, the impr oved He-4 leak defector could defect He-4 leaks of the order of 10(-10 ) Pa . m(3)/s in a D-2 atmosphere. Copyright (C) 1996 Elsevier Science Ltd.