Takashi Momose

Observations of dust trapping phenomena in the TRISTAN accumulation ring and a study of dust removal in a beam chamber

Using a gamma‐ray detector and a television camera system for synchrotron light, high‐energy bremsstrahlung and horizontal growth of the synchrotron light source were observed when sudden decrease in the electron‐beam lifetime occurred due to dust trapping in the electron beam. Two types of beam current losses were found; one was a continuous beam current loss, and the other was a short‐term beam current loss. High‐energy bremsstrahlung at a location was observed in a short time and after that, the bremsstrahlung was not detected in spite of the occurrence of dust trapping phenomena. The fact suggests motions of the trapped dust particles in the longitudinal directions. Materials collected in the beam chamber are dust particles from ion pumps and dust particles made during the beam chamber processing for welding. Most of the collected dust particles were less than 2 mm in size and surfaces of some dust particles were melted with the electron beam. Simple analysis was carried out for the conditions necessa...

Quick acquisition of clean ultrahigh vacuum by chemical process technology

Baking of vacuum system for removing adsorbed water is essential and important treatment to shorten pumping time and obtain clean UHV. Removing adsorbed water by chemical treatment, based on the decomposition and dissociation of O–H bond of the adsorbed water, was examined as an alternative method of rapidly attaining UHV conditions. Several experiments have been done using typical water decomposing gases, which are organic silane compounds, dichloro‐propane and halogen gases, introduced and exposed to the vacuum chamber made of an aluminum alloy. In these gases, dichloro‐propane gas exposed in vacuum chamber at a temperature of 50–100 °C and pressure (0.01–40 Torr) particularly shortens the pumping time to 1/4–1/500 of the time required without dichloro‐propane treatment to obtain less than 10−8 Torr. For the exposure conditions of dichloro‐propane gas at 70 °C and 0.1 Torr, a quadrupole mass spectrometer showed no remaining dichloro‐propane gas and reaction products within 0.5 h after pumping started. T...

Surface analysis of carbon on ozone treated metals

To reduce gas desorption, especially dynamic gas desorption, of ultrahigh vacuum materials, it is necessary to reduce carbon on the surface and in the rear surface layer which deteriorates dynamic gas desorption coefficient. To eliminate carbon, an ozone treatment was applied to metal surfaces. The surfaces of aluminum, copper, and stainless steel without any treatment were exposed to 250 ppm ozone using air with flow rates of 1 l/min for 24 or 48 hours. The samples were shown to decrease carbon levels, especially on Cu and Al surfaces, as detected by Auger electron spectroscopy (AES). In addition, no carbon was detected in the rear surface layers as detected by sputter profiling. The detectability of AES is on the order of 10−2 monolayers or approximately 3×1013 carbon atoms/cm2. The thickness of the oxidized layer was 6.3, 8.1, and 3.0 times the native oxide layer for Cu (120 A), Al (170 A), and stainless steel (60 A), respectively. X‐ray photoelectron spectroscopy shows (1) the ratio (O/Al) is 1.5 for ...

Motions of trapped dust particles around the electron beam in the TRISTAN accumulation ring

High‐energy bremsstrahlung synchronized with the electron beam in the TRISTAN accumulation ring was observed accompanied by a sudden decrease in the electron beam lifetime which occurred due to dust trapping in the electron beam. The bremsstrahlung observed with gamma‐ray detectors was obviously different from that caused by interactions between residual gases and the electron beam. Other bremsstrahlung observations showed a trapped dust particle passing through the periphery of the electron beam in the bending magnetic field; the transit time through the periphery of the electron beam was 0.15 ms; the half period of the horizontal oscillation perpendicular to the orbit of the electron beam was about 200 ms and the period of the vertical oscillation was 1 s. Simultaneous observation at two adjacent gamma‐ray detectors showed that a trapped dust particle in the bending magnetic field moved in a longitudinal direction at the average speed of about 0.191 m/s. These observations coincide with the results base...

Vacuum gauge self-compensating external environment in the SPring-8 storage ring

Some Bayard–Alpert gauges mounted on crotch chambers in the SPring-8 storage ring have indicated negative pressures at stored electron beam currents more than 5 mA. Simple measurements have shown that the negative pressure indications of these vacuum gauges are caused by influx of photoelectrons to their collectors. In order to measure the pressure in such a vacuum environment, the authors propose a vacuum gauge which self-compensates for photoelectrons from the external vacuum environment. The gauge has an added correcting electrode which detects the photoelectron current, only from the external environment, and then compensates to show the real pressure from the measured ion current of the gauge collector.

Experiments to trap dust particles by a wire simulating an electron beam

Motion of trapped dust particles has been previously analyzed using high‐energy bremsstrahlung data obtained during dust trapping in the TRISTAN accumulation ring. Because it is difficult to observe the actual motions of dust particles trapped in an electron beam due to the strong synchrotron light background, we carried out experiments to trap sample dust particles with a Cu wire simulating an electron beam. A negative potential was slowly applied to the wire using a high voltage dc power supply. Motions of dust particles trapped by the wire were recorded with a video camera system. In an experiment using a Cu wire (1.5 mm in diameter) with no magnetic field, the charged dust particle made vertical oscillation about the wire. In another experiment using the same wire but with a vertical magnetic field (0.135 T) simulating a bending magnetic field, both vertical and horizontal oscillating motions perpendicular to the wire were observed. Furthermore, it was found that the dust particle moved in the longitudinal direction of the wire in the bending magnetic field. Therefore, it is expected that charged dust particles trapped by the electric field of the electron beam oscillate vertically where there is no magnetic field in the TRISTAN accumulation ring. It is also expected that trapped dust particles where there is a bending magnetic field oscillate horizontally and vertically as the particle drifts in a longitudinal direction along the ring.

Liquid helium cryopumps with low‐emissivity Al film coatings and low helium consumption

Liquid helium storage‐type cryopumps made in Russia with a special surface treatment were experimentally studied. Pressures of the order of 10−9 Pa were obtained 19.5 h after the pump was filled with liquid helium. The ultimate pressure obtained was 2×10−10 Pa, with no baking, after about 58 days. The temperature of the cryosurface was 4.2 K. The evaporation rate of liquid helium was 8.7×10−10 m3/s (3.1 ml/h). The volume for liquid helium in the pump is about 7 l. The total inner surface area of the cryopump is about 0.23 m2. The Al film coating has an emissivity of 2×10−3 for liquid helium temperature to liquid nitrogen temperature. Its grain size is 2 to 3 μm, with a thickness of no less than 1 μm and a roughness of about 0.16 μm. The 7 l of liquid helium lasted for about three months.

Oxygen discharge cleaning method for aluminum storage ring vacuum chambers

A discharge cleaning method using a dc plasma gun was developed to reduce photon‐induced gas desorption by synchrotron radiation in electron storage rings. Hydrocarbon contaminations adsorbed on the inside surface of a long aluminum vacuum chamber (2.5 m) were removed by an oxygen plasma produced by an arc discharge. The plasma density and electron temperature were about 109 cm−3 and 1 eV, respectively, near the inside wall of the vacuum chamber at a discharge current of 5 A. The discharge cleaning was applied for 1 h to an aluminum vacuum chamber manufactured by the EX‐extrusion process. The results were as follows: (1) measurements with a quadrupole mass spectrometer determined that 6×1019 CO molecules coming from the hydrocarbon contaminations were removed by the discharge cleaning, (2) in situ Auger electron spectroscopy showed that carbon on the surface of an aluminum sample piece was removed within 1 h of discharge cleaning and (3) the photodesorption yield of the chamber with the discharge cleaning...

Inversely operated aluminum alloy distributed ion pump

The distributed ion pump (DIP) for the accumulation ring (AR) for TRISTAN is described. The elements of the DIP are newly designed and fabricated. The cathode consists of titanium (Ti) rods and the anode is five aluminum (Al) plates with punched holes 12 mm in diameter. The unit of the DIP is 50 cm long and 5.3 cm wide. There are 62 holes in the unit. Five units are connected and installed in a bending magnet (B) chamber. Both the cathode and the anode are insulated from the chamber. The insulation makes it possible to measure only the current between the anode and the cathode. Therefore, the insulation enables us to use the DIP as an ultrahigh vacuum gauge. The initial pumping curve shows that the ultimate pressure is 9×10−11 Torr at 2000‐h operation after several conditioning processes were applied. The processes are a higher magnetic field application (4–11 kG), bakings, a higher voltage application (5–12 kV), and argon glow discharge (dc, ac). Pressure improvement of one order was obtained after bakin...

A new distributed ion pump made of aluminum alloy with an aluminum or a titanium cathode in the transposable ring intersecting storage accelerators in Nippon e+e− colliding ring

The characteristics of the distributed ion pump (DIP) for TRISTAN (TMR) which has Al cathodes (Al‐DIP) are described. The test of the Al‐DIP showed a comparable initial pumping curve and pumping speeds (1/2–1/3) to the DIP which has a Ti cathode (Ti‐DIP). But the Al‐DIP in TMR showed a deteriorated pumping action. The reasons for this action were: (i) The surface of Al cathode was covered with a thicker oxide layer than those of the original cathode and of the tested DIP. (ii) The oxide layer was possibly grown in polyethelene envelopes with no desiccant, while the Al‐DIP’s were transported and stocked before DIP assembly. (iii) The residual gases during a test evacuation of the deteriorated DIP in a TMR B chamber were H2 and H2O. (iv) A burst of H2 was observed after the DIP was turned on. An exponential increase of H2 was observed during the operation of DIP alone (before baking). (v) H2 decreased by about two orders after baking. These facts suggest that the H2 decomposed from the water contained in th...