K. Kanazawa

The vacuum system of KEKB

Abstract For the KEK B-factory, two rings with a circumference of 3016 m , mainly made of copper, were constructed. A gap between the flanges is filled using Helicoflex as a vacuum seal. The contact force of an RF finger in a bellows is assured by using a spring finger. Pumping slots are backed by crossing bars to prevent the penetration of beam-induced fields. To obtain a pressure of 10 −9 Torr with the beam when the photo-desorption coefficient reaches 10 −6 , the design of pump layout is aimed to realize 100 l s −1 m −1 . NEG strips are used as the main pump. Chemical polishing is applied to clean the extruded surface of a copper chamber. Almost all chambers were baked before installation. Only ion pumps were baked in situ. The photo-desorption coefficient at the start of commissioning was slightly higher than expected, but a decrease of the coefficient is as expected on the whole. At high currents, some bellows were found to be warmed by the TE mode of beam induced fields. The effect of the electron cloud became evident, especially in the LER. Direct damage by the beam is seen at the surface of the movable mask.

Present status of the KEK B-factory vacuum system

The KEK B-Factory (KEKB) is a two-ring electron-positron collider with asymmetric energies to quest the CP violation. The design beam currents are 1.1 A and 2.6 A for 8.0 GeV electron and 3.5 GeV positron ring, respectively. Most of beam chambers are made of oxygen free copper for its ability to withstand the intense heat load and to shield effectively the radiation from the high beam currents. The pumping scheme is a combination of the nonevaporable getter pumps and auxiliary sputter ion pumps. Special care is taken of the inside of beam chambers to avoid excitation of higher-order modes (HOM). The commissioning of KEKB started in December 1998. The vacuum system has been operating almost satisfactorily. The average pressure of about 3×10−7 Pa is achieved now for both rings at the beam current of about 1 A. The coefficient of photon-stimulated gas desorption has been decreasing steadily to less than 1×10−6 molecules photon−1 at the integrated linear photon density of about 7×1025 photons m−1. The presenc...

Design and construction of the SuperKEKB vacuum system

A two-ring electron-positron collider with asymmetric energies—called the SuperKEKB—has been designed by the High Energy Accelerator Research Organization (KEK) as an upgrade of the KEKB B-factory (KEKB), which completed 12 years of operation in 2010. It is anticipated that the SuperKEKB will reach a luminosity of 8 × 1035 cm−2 s−1, which is approximately 40 times larger than that of the original KEKB. The upgrade of the vacuum system is a key factor that will allow the SuperKEKB to achieve unprecedented high performance. Most of the beam pipes, especially in the positron ring, are newly manufactured to manage the electron cloud effect, and to reduce beam impedance, which is essential to keep the low-emittance beam stable. Our design of the vacuum system implements recent technologies and draws on various experiences and studies during the operation of the original KEKB. The basic design is near completion, and manufacturing of beam pipes and the major vacuum components, such as bellows chambers, gate valves and supports, are in progress. The installation of these components will start in 2013 with the aim of commissioning the SuperKEKB in 2014.A two-ring electron-positron collider with asymmetric energies—called the SuperKEKB—has been designed by the High Energy Accelerator Research Organization (KEK) as an upgrade of the KEKB B-factory (KEKB), which completed 12 years of operation in 2010. It is anticipated that the SuperKEKB will reach a luminosity of 8 × 1035 cm−2 s−1, which is approximately 40 times larger than that of the original KEKB. The upgrade of the vacuum system is a key factor that will allow the SuperKEKB to achieve unprecedented high performance. Most of the beam pipes, especially in the positron ring, are newly manufactured to manage the electron cloud effect, and to reduce beam impedance, which is essential to keep the low-emittance beam stable. Our design of the vacuum system implements recent technologies and draws on various experiences and studies during the operation of the original KEKB. The basic design is near completion, and manufacturing of beam pipes and the major vacuum components, such as bellows chambers, gate val...

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.

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...

Results and problems in the construction phase of the SuperKEKB vacuum system

The SuperKEKB, the upgrade of the KEKB, is an electron–positron collider with asymmetric energies, that is, 7.0 GeV electrons and 4.0 GeV positrons, designed for a luminosity of 8 × 1035 cm−2 s−1. As a key item of the upgrade project, a new vacuum system for the SuperKEKB has been in construction since 2010. Over 1000 beam pipes, vacuum pumps, bellows chambers, and other various vacuum components had almost been fabricated in 2014. All the new beam pipes were baked as a general rule before being installed in the KEKB tunnel. A thin TiN film with a low secondary-electron yield was coated on the inside of the beam pipes for the positron ring as a countermeasure against the electron cloud effect. The performance of the new built-in nonevaporable getter (NEG) pumps and the step-less connection flanges met the expectation. Although several problems such as damage to the bellows chambers due to a large earthquake, cracking of the welding lines of the aluminum beam pipes, and a relatively high air-leak rate at the connection flanges occurred during the construction work, approximately 99% of the beam pipes were successfully installed by the end of October 2015. The activation of the NEG pumps in the tunnel started at the beginning of 2015 and has also been completed in approximately 97% of the ring. The installed beam pipes and the bellows chambers in the tunnel were aligned to their specified positions as the final step of the installation work. The vacuum system was ready in 2015 with the aim of starting the first commissioning in 2016. The various experiences during the construction phase reported here will be a useful reference for the design and construction of other accelerators in the future.

Development of bellows and gate valves with a comb-type rf shield for high-current accelerators: four-year beam test at KEK B-Factory.

Since a comb-type rf shield was proposed in 2003 as a rf shield for future high-intensity accelerators, various types of bellow chambers and gate valves with this rf shield have been installed in the KEK B-Factory rings in series and tested with beams. Through beam tests to check the performance, a structural simplification has been tried in parallel. The temperatures of the bellow corrugations decreased by a factor of 3-6 compared to those with a conventional finger-type rf shield in most cases. The temperatures of the body of the gate valves also decreased by a factor of 2-5. These results demonstrated the availability of the comb-type rf shield. Although a discharge was observed in one simplified model, the latest model has shown no problem up to a stored beam current of 1.8 A (1.3 mA/bunch, 6 mm bunch length). Experiences with the comb-type rf shield in these four-year beam tests are reviewed here.

Control of KEKB vacuum system

In a vacuum system of the KEKB accelerator that is a two ring electron-positron collider, there are nearly 10,000 control points. A large number of vacuum related components should be controlled and/or monitored at the rings and the beam transport line from the linac. Those component hardwares are connected to their sub-interfaces such as ADC interfaced by devices of CAMAC, RS-232C, GP-IB, and programmable logic controller (PLC) via GP-IB. The all device interfaces are controlled with newly developed softwares based on EPICS (experimental physics industrial control system) and single board equipment control computers through a high speed network using a UNIX-based workstation with X-terminals or emulators as operator consoles. The control points of the hardware for the vacuum system have been successfully implemented for monitor, control and data acquisition after the commissioning for 8 months utilizing EPICS software.