RHIC electron cloud and vacuum pressure rise characteristics

P.He, H.C.Hseuh, W.Fischer, U.Iriso, D.Gassner, J.Gullotta, R.Lee, L.Smart, D.Trbojevic, L.F.Wang and S.Y.Zhang

The 13th ICFA Beam Dynamics Mini-WorkshopBeam Induced Pressure Rise in Rings

Outline

Part I: Residual gas composition during RHIC pressure rise

Part II: Solenoid field effect on RHIC e-cloud

Accelerator Complex

G10G12

G8

G6G4

G2

Two type of pressure rises observed at RHIC 2003 run

*the beam transition pressure rise for ions

*the electron cloud induced pressure rise at the injection

The residual gas composition during multipacting and its evolution along the pressure rise is very helpful toward our

understanding in this critical issue

Gas Composition and its Evolution along the Pressure Rise(G2)-Beam

Transition Pressure Rise

H2

COH2O

1 min

More Concern about Gas Composition and its Evolution

along the Electron Cloud induced pressure rise at the injection

We will focus on that!

Gas Composition and its Evolution along the Pressure Rise(G2)

S.Y.Zhang

5 mins

Gas Composition and its Evolution along the Pressure Rise(G12)

H2 CO

H2O

Beam Intensity

CCG: 1e-10 to 1e-7 torr

10 mins

Gas Composition and its Evolution along the Pressure Rise(G4)

H2

CO

H2O

Beam Intensity

CCG: 1e-9 to 3e-7 torr

10 mins

Gas Composition and its Evolution along the Pressure Rise(G8)

H2

CO

H2O

Beam Intensity

CCG: 3e-11 to 1e-8 torr

10 mins

Residual Gas Spectrum, during multipacting

(CERN)

Different scale respect to the above figure, where peak 2(H2) and 28 have been omitted, to show the

behaviour of the peak 18(H2O)

H2

CO

H2O

CO230 mins

Extensive studies at CERN have shown that water vapour plays an important role in the contribution of the SEY. It is possible that the presence of water molecules increases the sticking probability for other gases.

In-Situ SEY Measurement

(CERN)

N.Hilleret

RHIC Installed 11 x 5.2m x 12cmΦ TiZrV coated pipes this summer

coated by SAES Getters with license from CERN

at Q3-Q4 with high P during d-Au runs

yo1, bo2, yi2(2), bi9(2), yi10(4), ip12

TiZrV NEG coating pipes

IR2

IR12

Solenoid, ~2 m

Cold cathode gauge - fast response

Ion pump/TSP/cold cathode gauge

yo1

bi1

bo2

yi2

yo12

bi12

1 3

4

5 6 7 8 9 10

2

4

1

3

6

5

pw3.

3

pw3.

2

pw3.

1

pw1

pwx

pwx

pw1

pw3.

1

pw3.

2

pw3.

3

bo11

yi11

RHIC Electron Detector Solenoid & NEG Pipe Locations19 September 2003L. Smart x2425

Numbers designate power supply

yi10bi9

Pin Diode

NEG Pipe

ED

New Components for 2004 Run

A. Rossi

NEG still pumping

H2

CO

CH4

Evidence of NEG saturation

A. Rossi

H2

CO

CH4

CO

H2

G12-PWXG12-PW1

G11-PW1G11-PWX

Run 2004: one NEG pipe at G11

RGA

CC Gauge

Comparison with Run 2003: no NEG pipe at G11

G12-PWXG12-PW1

G11-PWXG11-PW1

Beam Intensity

Run 2004: four NEG pipes at YI10

H2

CO

Enlarge this area

Beam IntensityCCG

RGA

RGA

CCG

Run 2004: two NEG pipes at YI2

RGA

CCG

Beam Intensity

Part I: Residual gas composition during RHIC pressure rise

Part II: Solenoid field effect on RHIC e-cloud

Noiselevel

Electron Energy Spectrum

Ubaldo

Solenoid Field Effect(1)-May 30L.Smart

CCG

Beam Intensity

CCG

Beam Intensity

Solenoid

ED

Solenoid Field Effect(2)-May 09

Cyclotron Resonance at RHIC?Cyclotron frequency does not match bunch spacing

-further study needed

Cyclotron Resonance

Condition

SLAC-PUB-9813

M.Pivi

B - Sweep during fill #3812. (N=1.5 •1010 p-pb).

Even at the maximum value of B, VED is only reduced by a factor of ~3 (not enough to fully suppress the cloud).~in RHIC we have ~7% solenoids covering,Maybe more solenoid needed in the future.

Solenoid Field Effect(3)

B can help to fully suppress the e-cloud during fill #3530. (N=1.1 •1010 p-pb).

PSR:

EC was reduced by a factor ~50 by ~20G solenoid field. However, there was no measurable effect on the instability threshold when weak solenoids covering ~10% of the ring circumference were excited.

R.Macek

Y. Suetsugu

KEK PF:

Non-uniform Solenoid Field (Opposite Polarity)

Uniform Solenoid Field(Equal Polarity)

0

0.2

0.4

0.6

0.8

1

0 20 40 60 80 100

Uniform Field

Non-uniform Field

Y. Suetsugu

Solenoid Field Effect(4)

From the simulation, we can see no electron in the center of the beam pipe if we use equal polarity solenoid field

Run 2004, RHIC solenoid in equal polarity

Solenoid at RHIC tunnel & Solenoid PS

Conclusions and Future Works

• Evidence that solenoid will help to reduce the electron cloud build up• Residual gas spectrum show electron stimulated desorption due to multipacting

• Improve electron detector design • Verify experimentally the effectiveness TiZrV NEG coating to reduce the electron cloud build up after activated at 250°C(max ~ 1.1) and also after saturation (max <1.2~1.3)

• More solenoid(~30%), more NEG pipes(~300m), in-situ SEY measurement