Hajime Ishimaru

Design of the vacuum system for KEKB

Abstract The construction of a new asymmetrical collider with 3.5 GeV positron beam and 8 GeV electron beam has started at KEK. The collider consists of two rings with the circumference of 3 km intersecting at the colliding point. The vacuum ducts deal with intense heat from synchrotron radiation because of a high design current, 2.6 A for a positron and 1.1 A for an electron. As a result of the compact design dimensions for a bunch, the requirement for smoothness of the inner surface is tight. We adopt copper as a material for the vacuum chambers of KEKB. Acid etch or chemical polishing is applied to clean the extruded surface. Using NEG strips as the main pump, a pumping speed is designed as 100 l s −1 m −1 . When the photo-desorption coefficient is 10 −6 , a pressure of 10 −7 Pa will be realized. All chambers are baked before installation. By adopting “dryhood” technique, in situ bake out will be omitted. The pumping slots are backed up by mesh to prevent the penetration of a beam induced field which causes pump elements to heat up. The gap between flanges is filled using a Helicoflex vacuum seal. Contact force of a RF finger in a bellows is assured by a spring finger.

Surface study of Type 6063 aluminium alloys for vacuum chamber materials

Abstract The surface characterization of Type 6063 aluminum alloy was performed with the use of various surface analysis techniques, such as Auger electron spectroscopy, scanning electron microscopy, optical microscopy, surface roughness factor and thermal desorption spectroscopy. The samples prepared by two different surface treatments were chosen for utilization as a uhv chamber material; namely, the surfaces prepared by extrusion (Sample A) and finished with diamond lathe (Sample B). The surface roughness factor of Sample A measured by xenon adsorption was 12.6 which was 2.6 times larger than that of Sample B. Carbon was the main impurity on the surface of Sample A, and oxygen on Sample B. Magnesium was found to segregate almost entirely on the surface of Sample B, while it segregated partially on Sample A after heating at 300°C. H2O and CO were the main outgassing components below the practical baking temperature (150°C) for the aluminum alloys. The amount of gas released from Sample A was much larger than Sample B. This could be interpreted by the differences in the surface roughness factor and the thickness of the oxide layer.

Non-destructive emittance measurement of a beam transport line

Abstract In order to measure the transverse beam emittance non-destructively, we have developed a new method using profile monitors. The usual assumption of Gaussian distribution is not necessary for it to measure the percent emittance. So, even if the profile is far from Gaussian, the percent emittance can be measured accurately. This method was applied to the 20 MeV KEK beam transport line and resulted in horizontal and vertical emittances of ϵh = 85 mm mrad and ϵv = 25 mm mrad containing 85% of the particles.

Beam Profile Measurements for KEK 12 GeV Proton Synchrotron

Various beam profile monitor systems provide an invaluable tool for studying beam behavior throughout the acceleration cycle in the main ring and booster. Non-destructive slow profile monitors are used for injection, magnet, rf, internal target and fast extraction studies. The time resolution of the slow profile monitor is 30 ..mu..sec. A multiwire secondary emission profile monitor which is sensitive enough to work with single bunch is used for injection tuning. Single wire secondary emission scanners are used for the circulating beam. These profile monitors are cross-checked in precision. As an application of non-destructive profile monitoring, a position monitor is installed in main ring and booster.

Influence of synchrotron radiation on corrosion at the boundary of cooling water and metals-II. A6063, A2219, SiO2 film on aluminum and stainless steel 316L

Abstract Radiation damage due to synchrotron radiation has been studied at the boundary of cooling metals; aluminum alloys, A2219 and A6063; stainless steel 316L and SO 2 film about 10 micro thick on the inside of an aluminum alloy pipe. The damage was evaluated utilizing dissolved ion density of the irradiated sample water from the pure water circulating system. At 1000 h operating time (∼ a time integrated beam current of 6 Ah, ∼ 3.5 × 10 22 photons) for Al and Si, and at 1700 h (10 Ah, 4.8 × 10 22 photons) for stainless steel), the dissolved ion densities are: Ni of the order of 1 mg l −1 ; Fe of the order of 0.1 mg l −1 and Cr of the order of 0.01 mg l −1 from the stainless steel: Si from SiO 2 film and Alfrom aluminum alloys of the order of 0.1 mg l −1 . The data showed that these materials are suitable for vacuum chambers and components exposed to synchrotron radiation and cooling water. The order of magnitude of the dissolved ion density approximately coincides with that of the free energy of the formation of the oxides. SiO 2 coating film functions as a protecting film from the dissolving Al ions. The oxides or hydroxides on the aluminum alloys and stainless steel also function as protecting films from the dissolving ions of the base materials. The stability of the oxide film is higher than that of hydroxide. Therefore oxide film coating, not hydroxide film, is necessary to obtain the stability of the base material against irradiation.

Influence of synchrotron radiation on corrosion at the boundary of cooling water and a metal—I. Mo alloy

Abstract Corrosion characteristics at the boundary of cooling water and a Mo alloy under synchrotron radiation with an energy range of 30—300 keV, were investigated in the TRISTAN e+e- colliding ring analyzing the dissolving Mo ion density into pure water. The dissolving ion density under irradiation is two orders of magnitude higher than that of the non-irradiated. The ion density for irradiated and non-irradiated Mo increased linearly with the operating time and was 200 mg I−1 after 1800 h and 10 mg I−1 after 800 h, respectively. The resultant reduction of the irradiated Mo surface is 0.17 mm in thickness with 0.8 mm in FWHM of the synchrotron radiation beam.

Al alloy-ceramic ultrahigh vacuum and cryogenic feedthrough useful from dc to 6.5 GHz

A bakeable (150°C), coolable (<2.17°K) SMA coaxial vacuum feedthrough is described. The VSWR is less than 1.5 from dc to 6.5 GHz. An aluminium alloy outer shield and ceramic insulator are brazed with aluminium alloy solder in a vacuum furnace. The feedthrough can be welded directly to an aluminium alloy flange with an electron beam.

Analysis of micro-particles in TRISTAN vacuum chambers

Abstract Micro-particles in the beam chamber of a TRISTAN vacuum system were investigated from the point of view of suppressing micro-particles trapped in the accumulation ring. Micro-particles coming from ion pumps (IP) and distributed ion pumps (DIP), aluminum alloy particles produced during treatment of aluminum alloy chambers for welding, micro-particles from the environment, i.e. soil (granite rocks or amphiboles), particles of concrete and painting materials were identified. A molten iron particle found in a chamber suggests interaction between the particle and bunched electron beam. Most of the particles coming from outside the chambers can be avoided by using high class clean rooms. The particles from the ion pumps can be reduced using different pumps which do not emit particles. The particles produced during assembly of, for example, DIP must be suppressed by accepting different assembling methods from the traditional ones.

Beam Size Measurement of 12 GeV Accelerator by Fast Rotary Scraper

A new type of beam size measurement by a fast rotary scraper for the 12 GeV proton synchrotron has been developed. The profile of the acceleyating beam was measured by a non-destructive monitor. But we have a problem with the expansion of the profile by the space charge effect of a high intensity beam. A quantitative interpretation of the space charge effect, precise size measurement, and the scraped beam for accelerator studies are desirable.3J

Proposal of very low cost 5–6GeV synchrotron radiation ring for medical use using permanent magnets and aluminum beam pipe without flanges and bellows

We are designing a synchrotron radiation ring of medical application such an angiography for practical uses. Iodine is clinically used as a contrast agent, which has K-edge at an energy of about 33 keV.