Seiji Hiroki

Detection of a 10−4 helium peak in a deuterium atmosphere using a modified high‐resolution quadrupole mass spectrometer

This paper describes how a small helium (4He) peak can be separated from a large adjacent deuterium (D2) peak using a modified quadrupole mass spectrometer (QMS). This QMS utilized a condition of the second stability zone (zone II) in the Mathieu diagram. The minimum detectable peak ratio of 4He to D2 was 10−4 when a mass scan line was set close to the upper tip, and was 10−3 when the scan line was adjusted to the lower tip. The ion transmission rates simulating the peaks were calculated for the upper and lower zone conditions. It was found that a longer peak tail occurs when an unstable orbit has mainly a cosh function. From the experimental and theoretical data, it is concluded that the upper zone condition is the most suitable for realizing a high‐resolution peak.

Development of TiC coated wall materials for JT-60

Abstract Development of titanium carbide (TiC, 20 μm thick) coated wall materials has been carried out for JT-60. Application of TiC coatings onto molybdenum and Inconel 625 substrates requires a deposition temperature below 950°C and 600°C respectively, because recrystallization of molybdenum and age hardening of Inconel 625 occur above these temperatures. Through this process of coating we developed a new type plasma CVD(TP-CVD method) for molybdenum and a new type PVD(HCD-ARE method) for Inconel 625 which could successfully reduce the deposition temperature to 900°C and 500°C, respectively. The TiC coated wall samples were characterized by AES, ESCA, X-ray diffractometer, EPMA, SEM, metallography, tensile tests, thermal shock tests, and others techniques. As a results of the above measurements, it was demonstrated that the characteristics of those TiC coated walls satisfy the requirements arising from JT-60 operation conditions.

Separation of helium and deuterium peaks with a quadrupole mass spectrometer by using the second stability zone in the Mathieu diagram

4He+ and D2+ have been separated with a conventional quadrupole mass spectrometer by using the second stability zone in the Mathieu diagram. The minimum resolving power needed for the separation of 4He+ and D2+ is 161. A resolution of 320 defined by the full width at half maximum was attained at an ion energy of 14.6 eV in the experiment.

Development of a quadrupole mass spectrometer using the second stable zone in Mathieu’s stability diagram

A quadrupole mass spectrometer (QMS) utilizing the second stable zone in Mathieu’s stability diagram was developed. The system performance was experimentally compared with the conventional QMS using the first stable zone. The peak shapes obtained were sharper and the tail components arising from adjacent peaks were less than those of the conventional QMS, although the analyzable range was limited to lower mass and the attenuation in sensitivity was about 1/50. This improved QMS is usable in detecting very small peaks adjoining large ones.

Effect of a pre-filter on the sensitivity of a highresolution quadrupole mass spectrometer

The effect of a pre-filter on the sensitivity of a high-resolution quadrupole mass spectrometer (QMS) has been experimentally studied. The high-resolution QMS uses the condition of a higher stable zone in the Mathieu stability diagram where the higher zone is defined as zone II having a center of a = 2.83 and q = 3.02 in the a-q plane. The pre-filter of a short auxiliary quadrupole was added in front of a main quadrupole and only an r.f. voltage was applied. A helium peak intensity (mass 4 at 50% peak resolution of 40) increased by a factor of two compared with that without the pre-filter, when an r.f. voltage ratio of the pre-filter to the main quadrupole was roughly 0.2. An ion orbit analysis is used to support the experimental result.

High-resolution mass spectrometric analysis of gases released from graphite during sequential helium and deuterium glow discharge cleanings

The amounts of helium (4He) and deuterium (D2) retention/release on a graphite wall during sequential 4He and D2 glow discharge cleanings have been evaluated using the high-resolution quadrupole mass spectrometer. A large amount of D2 was retained on the graphite wall and/or released from the wall during these discharges. At a wall temperature of 300°C, the total amount of 4He released during a 15 min D2 glow discharge was much smaller than the amount of D2 retained on the wall. Thermal desorption experiments showed that the graphite sample, exposed to the 4He glow discharge, retained a very small amount of 4He which desorbed at around 150°C.

Sensitive helium leak detection in a deuterium atmosphere using a high-resolution quadrupole mass spectrometer

Abstract In fusion machines, realizing a high-purity plasma is a key to improving the plasma parameters. Thus, leak detection is a necessary part of reducing the leak rate to a tolerable level. However, a conventional helium ( 4 He) leak detector is useless in fusion machines with a deuterium (D 2 ) plasma, because retained D particles on the first walls release D 2 for a long period and the released D 2 interferes with the signals from the leaked 4 He due to the near identical masses of 4.0026 u ( 4 He) and 4.0282 u (D 2 ). A high-resolution quadrupole mass spectrometer (HR-QMS) that we have recently developed, can detect a 4 He + population as small as 10 −4 peak in a D 2 atmosphere. Thus, the HR-QMS has been applied to detect 4 He leaks. To improve the minimum detectable limit of 4 He leak, a differentially pumped HR-QMS analyzer was attached to a chamber of the 4 He leak detector. In conclusion, the improved 4 He leak detector could detect 4 He leaks of the order of 10 −10 Pa · m 3 /s in a D 2 atmosphere.

Applicability of the rf-only mode in a quadrupole mass spectrometer for direct analysis of keV ions

This paper describes an applicability of a quadrupole mass spectrometer (QMS) for direct analysis of high energy ions up to 3 keV without decelerating fields. The QMS uses an rf-only mode in which only an rf voltage is applied to the quadrupole, although the conventional QMS applies the coincident dc and rf voltages to the quadrupole. On the rf-only mode, the rf voltage is determined by a small triangular stability zone in the Mathieu stability diagram, where the point a = 0 and q = 7.547 in the a-q plane centers on the bottom of the triangle zone and the resolution of 104 is expected. The mass spectrum for air of 3 keV ion beams was obtained on the rf-only mode, where the O2 peak indicated the half-height resolution of 48. It was concluded that the rf-only mode is applicable for direct analysis of keV energy order ions, although further research to eliminate the conventional q < 0.9 related large peak is essential and the elimination will be realized using the pre-filter.

Influence of the fringing field length on the separated 4He/D2 peak shape of a high-resolution quadrupole mass spectrometer

Abstract The influence of the fringing field length on the separated 4He/D2 peak shape was experimentally studied by using a high-resolution quadrupole mass spectrometer (QMS) that adopts the second stability zone (zone II) in the Mathieu diagram. The fringing fields arise on the inlet and outlet of the quadrupole, where the traveling ions receive the confused static and dynamic forces. Therefore, the fringing field length strongly influences the performance of the high-resolution QMS. The inlet and outlet fringe lengths were changed by moving an ion source and a detector, respectively. It was concluded that the resolution, sensitivity and peak disturbance were improved by decreasing the inlet and outlet fringe lengths.

Development of a QMS with a ceramic single-piece quadrupole

Abstract A novel quadrupole mass spectrometer (QMS) has been developed by using a ceramic single-piece quadrupole. The quadrupole was made of silicon nitride (Si3N4). The four hyperbolic surfaces were coated with metal thin films of about 10 μm to form electrodes. Mass spectra were successfully obtained by using the conditions of the second stable zone in the mathieu diagram. It seems that there are no differences in sensitivity and resolution between the two QMSs with a ceramic quadrupole and a conventional metal one of the same dimensions.