Yusuke Suetsugu

APPLICATION OF THE MONTE CARLO METHOD TO PRESSURE CALCULATION

The Monte Carlo method, which has been used for simulation of steady‐state molecular flow and estimation of static pressure in relation to vacuum science, is applied to a calculation of the time dependent pressure distribution in a vacuum system. The calculation follows the usual simulation process, but the locations of the test particles are recorded at various values of time. In this way the pressure distribution in a vacuum system can be obtained at any time from the beginning of gas desorption. The pressure propagation along a beam line and the steady‐state pressure distribution in a vacuum system with an orifice and a pump are presented as two examples.

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...

Temporal Behaviour of ECR Plasmas Produced by a Lisitano Coil

In order to clarify the mechanism of production of a plasma produced by electron cyclotron resonance heating (ECRH) using a Lisitano coil, the temporal behaviour of the plasma was measured in detail by a sampling method. It was found that the plasma is produced not only around the Lisitano coil but also near the center. The plasma density was also confirmed to attain a value above the cutoff density by measuring the field intensities of the microwaves.

RF Field Distributions in a Slotted-Type Lisitano Coil

The field distributions in a slotted-type Lisitano coil are analyzed using a simple antenna model, and the microwave power is theoretically found to be supplied near the center of the coil. Field intensities in the Lisitano coil measured with a calibrated loop antenna are compared with the theoretical values, and results supporting the analysis are obtained. The field distributions in a vacuum chamber were also measured.

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.

Application of a Matsumoto-Ohtsuka-type vacuum flange to beam ducts for future accelerators

The Matsumoto-Ohtsuka (MO)-type vacuum flange, which can provide a gapless connection and a highly reliable electric contact between flanges, was studied experimentally for a possible application to beam ducts for high-current accelerators, where the apertures have a complicated structure, such as the combination of a beam channel and one or two flat rectangular antechambers. In spite of the complex aperture, test flanges showed a good vacuum-sealing property. Vacuum sealing was successfully achieved with a reasonable fastening torque (15–20Nm), and remained sealed after baking at 250°C for 24h. A twist between flanges of up to about 5mrad was also manageable. A pseudoelastic structural analysis well reproduced the observed deformation of the flange. This analysis should be available for optimizing the flange structure. The MO-type vacuum flange was found to be promising for connecting flanges of the beam duct with a complicated aperture in future accelerators. The flange will also be available as a compa...

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 copper-alloy Matsumoto–Ohtsuka-type vacuum flanges and its application to accelerator beam pipes

The possibility of employing copper-alloy Matsumoto–Ohtsuka-type flanges in a vacuum beam pipes with complicated apertures for a particle accelerator is experimentally studied. Copper-alloy flanges can mitigate the heating problems arising as a result of high-intensity beams more efficiently than stainless-steel flanges. Baking of beam pipes up to a temperature of 200 °C was acceptable with copper-alloy flanges. Moreover, direct electron-beam welding to a copper beam pipe became available, which made the manufacturing easy. In this study, several beam pipes with copper-alloy flanges were installed in the KEKB B-factory positron ring, and the performance was investigated using the high-intensity beams.

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.