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All systems comprising the Japan Proton Accelerator Research Complex (J-PARC), namely, the 400 MeV linac, 3-GeV rapid-cycling synchrotron, and 50-GeV synchrotron, were completed in 2009 and are now being used to supply high-power proton beams to secondary particle users. In order to minimize maintenance and shorten the pump-down and conditioning period, an ultra-high vacuum of 10 −5 Pa or lower is required for the vacuum system. Here we present a review of the surface processing methods employed and the results of outgassing measurements for the components used in the vacuum system made from the following materials: electroformed copper, alumina ceramic, titanium, and stainless steel. The vacuum performance of these materials during accelerator operation is also reported.

We developed an electroformed copper lining for RF cavities. The pure copper lining with mirror-finish surface was produced by electropolishing the machined surface of an electroformed copper layer obtained from an acid copper sulfate bath containing no organic additives. The copper lining was successfully applied to large RF cavities for the Japan Hadron Facility being constructed by the High Energy Accelerator Research Organization. Dramatic rise in accelerating performance was achieved by this new lining.

Aluminum is one of the candidate materials of the vacuum chamber and components in the ultra-large scale integration device production facilities, because of high thermal conductivity and minimizing weight. For that purpose, their surface must be smooth and passivated so as to have a low outgassing rate. An electropolishing method to obtain a mirror-finish and pit-free smooth surface has been developed by controlling the flow of the electrolytic fluid during polishing. The polished surface, which shows an average roughness of 0.03 μm was found to be covered with an oxide film of 200 nm thick as determined by Auger electron spectroscopy, indicating a chemically stable surface. The outgassing rate measurement using a conduction-modulation method shows the value of 10−10 Pa m3 s−1 m−2, after baking treatment at 150 °C.

It was success to develop alumina ceramics vacuum ducts for the 3GeV-RCS of J-PARC at JAERI. This duct has titanium flanges and exterior RF shield to reduce duct impedance. The longitudinal duct impedance was sufficient small for stable beam acceleration from impedance measurement by coaxial method. The temperature of titanium flange became 45 Co due to eddy current heating under dipole magnet operation. This duct is usable for the 3GeV-RCS of J-PARC.

We apply a new copper lining with a high purity and a high electric conductivity to normal-conducting RF cavities for an electron-positron super B factory, in which four-times more beam current is required to be stored than in the present KEK B factory (KEKB). The lining is produced first by electroplating in an acid copper sulfate bath without brightener nor other organic additives, where the current is periodically reversed (“PR process”). Then the copper surface is electropolished to make it smoother. There are two differences between our application and the previous one to the accelerator components for J-Parc. The first one is the lining thickness; our target of 120 µ m is much thinner. The second one is that we have no mechanical polishing on the electroplated surface before electropolishing. In this paper, results of the quantitative estimations of the quality factor on the electroplated pillbox test cavity are reported together with microscale investigations of the copper surfaces.

The effects of copper deposits produced by three kinds of electroforming techniques on the breakdown characteristics in vacuum were compared. The electroforming was performed in (i) an acid sulfate bath with brighteners, (ii) a pyrophosphate bath, and (iii) an acid copper sulfate bath with periodic reverse electrolysis and electropolishing. Vacuum degassed oxygen-free copper was used as the substrate material. Electrical breakdown characteristics measured by repetitive breakdowns by applying impulse voltages revealed that the breakdown fields at the first application of voltage in vacuum were 13.4, 10.0, and 40.8 MV/m for the electrodes processed in the first, second and third baths, respectively. In addition an excellent conditioning effect was achieved without in situ electrode surface cleaning.

A new type microwave dummy-load using SiC ceramic, which has an indirect water cooling structure, was successfully operated with up to 50-MW of rf power at a 1-/spl mu/s pulse width and 50-pps repetition rate in the S-band frequency. The input VSWR obtained was less than 1:1.1 at the maximum rf power. The vacuum pressure in the rf-load raised from the base pressure of 1/spl times/10/sup -6/ Pa with no rf power to 2/spl times/10/sup -6/ Pa at the maximum rf-power; and there was found to be no special outgassing from the SiC-ceramics.

In order to avoid the eddy-current effect due to a rapid-cycling magnetic field in the J-PARC proton synchrotron ring (348 m in circumference), several tens of ceramic chambers (3.5-m long and 500 mm in diameter, at their maximum) are to be installed. The 99.7% alumina ceramic ducts of sub-meter in length, having racetrack and circular cross-sections were sintered and jointed by braze. Several chambers of rectangular and racket-shape cross sections were also produced. A TiN film of 15 nm thick was formed inside the chambers for suppressing secondary electron emission, and electroformed copper stripes were plated outside for lowering the beam-impedance. The course of the production process, including polishing, metallizing and brazing to a titanium flange is reported. Outgassing rates were also measured for a few of the chambers by a conductance-modulation method.

The surface erosion yield of substoichiometric titanium carbide coating and sintered titanium carbide bulk have been measured at normal incidence for 4He+ in the energy range 0.5 to 2.5 MeV by scanning electron microscopy. The erosion, such as multi-layer exfoliation, was observed on the irradiation surface area. The projected ion ranges were depended on the impinging helium-ion energy and agreed fairly well with the theoretical values. It was observed that the erosion yields of the sample strongly depended on the irradiation energy. We discuss these results on the substoichiometric carbon compositions and then estimate the erosion rate of 3.5 MeV 4He+-ion bombardment for titanium carbide from measurements with various high-energy, helium-ion irradiations.

In order to investigate plasma-surf ace interactions, a surface analysis station and its attachment devices, a vacuum suitcase and a high temperature test stand have been designed and constructed. Silicon samples were transferred into the JIPP T-IIU torus by a driving shaft of the surface analysis station and set in the scrape-off layer. After exposure to the plasma with 200 kW ICRH during several tens of shots, the samples were drawn out to be observed by in situ AES in the analysis chamber of the surface analysis station. Spatial profiles of impurities and deuterium in the scrape-off layer were obtained by AES and NRA. The decrease of C and D as well as the increase of O are found on the ion side sample by these analyses. Based on these data, the role of the vacuum suitcase and the high temperature test stand in relation to the surface analysis station is briefly mentioned.

It has become important recently to study plasma impurities in an actual tokamak machine from the standpoint of the material development for the next-step fusion reactors. In order to study the behaviour of plasma impurities in the tokamak machine, experiments of sampling impurities and analyses of the sampled impurities by RBS and ISS were performed. In the sampling experiments, specimens, which sample the impurities implanted in them during plasma exposure, were set in the scrape-off layer in the JIPP T-II tokamak. Exposed spceimens were then observed by RBS and ISS, and spatial distributions and depth profiles of impurity elements in specimens were obtained. Some impurities, C, O, Fe, Mo, Ta and Ti, were identified in the specimens, and they were considered to originate from residual gases, the torus wall, sample holders and the limiter. From depth profiles analysed by ISS, it was found that most impurity atoms implanted in sampling specimens during plasma exposure are present within a short range of the specimen surface. Our results, as the first attempt, will contribute towards the studied of plasma behavior.

Preparation of high current steady state ion source, fabrication of linac tanks by coating method, and development of high power high frequency power tube are described. The first one is the application of bombarded cathode to ion source with rather high operating pressure of 150 Pa, and the second is an application of coating technique primarily developed for tokamak divertor plate to linac cavity. Copper coating onto aluminium substrate is prepared and the measurements of the change of Q-value with coating thickness of 10 ∼ 30 μm is performed. The development of high power high frequency tube of 500 MHz frequency range for continuous operation is also described.

A coating experiment of a TiB 2 compound on a polycrystalline Mo substrate has been carried out using the magnetron sputter method. The substrate surface must be carefully prepared in order to obtain a defect-free coating with good adhesion properties. This has been found by ISS, AES, and SEM analysis of the TiB 2 coating. The surface composition of the TiB 2 coating, as determined by AES, is the same as that of the hot pressed TiB 2 cathode rod. The sputtering yields of the films for an Ar + ion of 1 keV are measured by the weight-loss method, and the average value obtained is 0.56 atoms/ion.

It was experimentally demonstrated that high power irradiation of ions on metal surfaces is possible by using a `Plasma Anode' for electron beam generation. The irradiation power of 600 keV protons was 50 MWcm-2 which is comparable with the pulse power loading of a CTR tokamak first wall at a strong major disruption. The damage of the 304 stainless steel irradiated in this way was different from that due to usual ion irradiation at lower power levels.

Noble gas ion scattering is applied to surface analysis of a stainless steel (SS) sample. The scattering experiments have been carried out in UHV system with a sputter ion pump and a Ti sublimation pump. In the scattering spectra, two predominant signals are observed. These are due to scattered ion current from oxygen atom on the SS surface and the composition atoms (such as Cr, Fe, Ni) of SS. The sorption dependency by oxygen atom and the primary ion energy dependency of the relative signal ratio are discussed by comparing with the experimental results (He+ → O/Ni) reported by E. Taglauer and W. Heiland [1]. Shadowing effect is observed for oxygen over 0.7 Langmuir. It is concluded that, from the obtained energy spectra for the SS sample under various cleaning conditions, surface concentration of oxygen atom distributes from 0.1 to several Langmuir.