Vacuum Pressures at IR

Contents

Y.SuetsuguKEKB Vac. Group

1. Outline of Vacuum System at IR2. 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 m3/s), Auxiliary pump = Ion pumps : almost every 10 m (0.2 m3/s). In average, about 0.7 m3/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_H23AD01_H01AD01_H02A

D02_H23D01_H02

[Inside of BELLE Solenoid]

Integrated NEG

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_H01AD01_H02AD01_H03

D01_H8

D01_H04

D01_H09

D01_H05

D01_H10

D01_H06D01_H7

D01_H11

HER

GV

GV

GVBS

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

GV

Behavior of Pressure• HER_1

IP

D01_H8 D01_H06D01_H7

2x10-7 Pa

00 1.4 A

Heat Source = Gate Valve

Three daysincluding several beam Injections.

P

Ib

Big BG Source

D01_H01AD01_H02AD01_H03D01_H04

Behavior of Pressure• HER_2

Three daysincluding several beam injections.

D01_H8

D01_H09D01_H10

D01_H06

D01_H7

D01_H11Heat Source = HOM Absorber, Taper

Heat Source = Stopper (~ Gate Valve)

Gate Valve

Gate Valve

Behavior of Pressure• LER_1

Three daysincluding several beam aborts.

D02_H23A D02_L24 D02_L23 D02_L22D02_L21

D02_L20 D02_L19 D02_L18

IP

Heat Source = Gate Valve

? (NEG?)

Heating +NEG? Multipactoring?

3x10-7 Pa

00 2.0 A

P

Ib

Behavior of Pressure• LER_2

Three daysincluding several beam aborts.

D02_L20 D02_L19 D02_L18

D02_L17 D02_L16 D02_L15Heat Source = Stopper

Heat Source = Taper

? (NEG?)

Gate Valve

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 mmt = 2 mmCu

Lead to heating of other components

Remedies to heating• Heating by other HOM sources, such as

collimators or tapers.

Slot

Beam Chamber

SiC

WingSiC

• 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 10-7 Pa

Beam Current 1.2A x 1.6 A

Lifetime 230, 180

min

Luminosity~1.1x1034cm-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 m3/s/m)

[PM]:Set permanent magnets to every gauge port

P/IMax. I Max. IP/I

PM

PM

[Pa

/mA

]

[Pa

/mA

]

[mA

]

[mA

]

[LER] [HER]

(Corrected)

Present Status• Vacuum pressures in HER (~300 gauges)

Just near to GV!

(ARES)(ARES)

(SCC) (SCC)