Vacuum Pressures at IR Contents Y.Suetsugu KEKB Vac. Group 1.Outline of Vacuum System at IR 2.Behavior of Pressures 3.Remedies for Heating of Vacuum Components

Vacuum System at IR Here IR (Interaction region) means the straight section in ±~100 m from IP (Interaction Point), especially upstream side of each ring. Material of beam duct: OFC (Oxygen Free Copper) for most part (both rings). Aluminum alloy for complicated chamber just near to IP. [OFC] [Aluminum Alloy]

Vacuum System at IR Vacuum pump: Main pump = NEG (st707) : almost every 1 m (0.2 m 3 /s), Auxiliary pump = Ion pumps : almost every 10 m (0.2 m 3 /s). In average, about 0.7 m 3 /s/m just after an activation of NEG. NEG module (just near to IP) NEG cartridge (arc section)

Vacuum System at IR Vacuum gauge = CCG (Cold Cathode Gauge) just above ion pumps (every ~10 m). A small dipole magnet (permanent magnet) is attached at the neck of gauge port to eliminate photoelectron effect. CCG ~100 G Without Manget

Vacuum System at IR Location of Gauges and Pumps near to IP IP LER HER (D02_H24) D02_H23A D01_H01A D01_H02A D02_H23 D01_H02 [Inside of BELLE Solenoid] Integrated NEG 0 5 m 10 m

Vacuum System at IR HER Upstream Side (straight section, ~100 m) Straight : No bending magnet Gauges: every ~10 m IP D01_H01A D01_H02A D01_H03 D01_H8 D01_H04 D01_H09 D01_H05 D01_H10 D01_H06 D01_H7 D01_H11 HER GV BS

Vacuum System at IR LER Upstream Side (straight section, ~100 m) Local correction region: 13 bending magnets Gauges: every ~10 m LER D02_H23A D02_L24 D02_L23 D02_L22 D02_L21 D02_L20 D02_L19 D02_L18 D02_L17 D02_L16 IP GV BS GV

Behavior of Pressure HER_1 IP D01_H8 D01_H06 D01_H7 2x10 -7 Pa A Heat Source = Gate Valve Three days including several beam Injections. P IbIb Big BG Source D01_H01AD01_H02AD01_H03D01_H04

Behavior of Pressure HER_2 Three days including several beam injections. D01_H8 D01_H09 D01_H10 D01_H06 D01_H7 D01_H11 Heat Source = HOM Absorber, Taper Heat Source = Stopper (~ Gate Valve) Gate Valve

Behavior of Pressure LER_1 Three days including several beam aborts. D02_H23A D02_L24 D02_L23 D02_L22 D02_L21 D02_L20 D02_L19 D02_L18 IP Heat Source = Gate Valve ? (NEG?) Heating +NEG? Multipactoring? 3x10 -7 Pa A P IbIb

Behavior of Pressure LER_2 Three days including several beam aborts. D02_L20 D02_L19 D02_L18 D02_L17 D02_L16 D02_L15 Heat Source = Stopper Heat Source = Taper ? (NEG?) Gate Valve

Present Status The pressures near to IP is <1x10 -7 Pa for HER and ~2x10 -7 Pa for LER at the maximum operation current. The pressures at upstream side of IP (IR) is almost less than 1x10 -7 Pa, but affected by the heating of components, such as gate valves, stoppers, HOM absorbers and NEG(?). The same harmful effect by heating can be seen widely in arc sections too.  A major problem for further improvement of pressure.

Remedies to heating Main reason of the heating is HOM. Tentative measure = Cooling from outside [Bellows] [Gate Valve] Heating of Gate Valves, Stoppers and Bellows –Finger-type RF shield is not enough for high current –TE mode can easily coupled to modes outside symptomatic therapy

Remedies to heating Future (more essential) measure –Proposal of a New RF-shield structure –Comb-type RF-shield –6 circular-type and 1 race-track-type has been installed in LER, and showed good results. –Application to gate valves are now planed and a test model will be installed in the ring this winter.

Remedies to heating Heating of NEG –Gas desorption from heated NEG had been observed near collimators. –HOM (TE-mode) intruded through a grid into pump port. Tentative measure = use a special gasket HOM absorber were installed finally.  = 6 mm t = 2 mm Cu Lead to heating of other components

Remedies to heating Heating by other HOM sources, such as collimators or tapers. Slot Beam Chamber SiC Wing SiC Install HOM absorber chamber –Example installed near collimators –HOM absorber = SiC Require Space ! How about IR?

Summary The pressures at upstream side of IP is almost less than 1x10 -7 Pa, but also affected by the heating of components, such as gate valves, stoppers, tapers, NEG and HOM absorbers. The problem had been solved accordingly so far. But, essential (drastic) remedies, such as employing new RF- shield or installing HOM absorbers, will be required for future high current operation. Improvement of pumping speeds and cooling capacity are of course important.

References

Present Status Typical Run(11/09/2004) Ave. Pressure  Pa Beam Current 1.2A x 1.6 A Lifetime 230, 180 min Luminosity ~1.1x10 34 cm -2 /s Beam currents are usually limited by any problems in vacuum components

Present Status Vacuum Aging (arc section, -2004/10/31) –  P/  I :  1x10 -7 Pa/A – Photo-desorption coefficient,  :  3x10 -7 mole./photon – Effect of photoelectrons were eliminated by magnets. – HER seems to be effected by heating of components. (If S = 0.3 m 3 /s/m) [PM]:Set permanent magnets to every gauge port  P/  I Max. I  P/  I PM [Pa/mA] [mA] [LER] [HER] (Corrected)

Present Status Vacuum pressures in HER (~300 gauges) Just near to GV! (ARES) (SCC)