Masayuki Shimamoto

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.

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.

Vacuum System for Tristan Electron-Positron Collider

最 も大 きな 問題 はDIPの カ ソー ド材 料 で あ った. 1986年12月 に先行 して8台(約1000 mmLの 単位電極 を 6連 結 した ものを1台 と呼び この1台 は偏 向マグネ ッ ト 1台 に対応 す る)のAl-DIPの カ ソー ドをTiに 交 換 し た.1月 の運転 でTi-DIPの 排 気特 性 を検 討 した 結果 (Ti-DIPの 特性 については本連合講 演会で発表),す べ てのDIP264台 に つい て交換 したほ うが よい と決断 し 1987年 春の シャッ トダウンに作業 を行 った.次 の問題 は DCセ パ レータの電極構造 であ った.16台 のDCセ パ レ ータは ビームのない場合 は平行平板 電極 に±約90kVを 安定に印加保持する ことができる.と ころが ビームがあ る状態 では2台 が最悪 の場合,±20kVで も異常放 電を 起 こし,DCセ パ レータ として機能 しなか った.こ れは ビームに伴 う高周波壁電流の影響 で,高 電圧導入部 と並