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Electron Cloud Studies for Tevatron and Main Injector. Xiaolong Zhang AD/Tevatron. In This Report …. What’s Electron Cloud and it’s Effects; The impact on Main Injector Upgrades and the research activities at Accelerator Division; Simulation methods, programs and results; - PowerPoint PPT Presentation
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Electron Cloud Studies for Tevatron and Main Injector
Xiaolong Zhang AD/Tevatron
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
In This Report …
What’s Electron Cloud and it’s Effects;The impact on Main Injector Upgrades
and the research activities at Accelerator Division;
Simulation methods, programs and results;
Future study plans.
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Mechanism of Electron Cloud Buildup
Short bunch: Initial electron produced by photos, beam loss, ionization, etc. Density of the electron increased by generating secondary electrons. Exponential growth of electron density happens with appropriate
beam conditions. Electron cloud saturated by its space charge effect.
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Electrons Trapped in the Beam
Long bunch or coasting beam Initial electron generated Electrons are trapped by beam potential Trailing edge multipacting (long bunch case)
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Effects of Electron Cloud
Vacuum instabilities: Fast vacuum jumps of several order of magnitude
Beam instabilitiesBeam lossesHeat loadingNoise on beam instruments
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
History of Electron Cloud Studies
1967 Novosibirk proton rings with coasting beam: Two Stream Beam Instabilities; Cure: various beam intensity and clearing electrode
1970 CERN ISR coasting beam Cure: clearing electrode
1977 ISR bunched beam. Vacuum pressure jumps
End of 80s: KEK PF Beam instabilities when switched from electron to positron PSR Beam instabilities
1995 Two B-Factories: KEKB: Simulation code PEI; Beam studies KEK-BEPC; PEPII: Simulation code POSINST; LBNL-SLAC; TiN coating
1997 ECLOUD for LHC and SPS. CESR, APS, SNS, RHIC, etc. New simulation codes and methods keep appearing. Extensive SEY measurements; material and surface treatments.
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Electron Cloud for Various Accelerators
MI
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Effects of the Electron CloudBeam Instabilities
KEKBBEPC
PSR, 1988
Sideband Peak Height
Betatron Oscillation Sidebands
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Effects of the Electron CloudBeam Emittance Growth
0
1
2
3
4
5
0 200 400 600 800 1000 1200 1400 1600
Ver
tica
l b
eam
siz
e@IP
(m
icro
n)
LER beam current (mA)
1 train, 1153 bunches, 4 rf bucket spacing
2001 July : on
2001 Dec. : on
2002 Feb. : on
2001 July : off
KEKB SPS
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Effects of the Electron CloudVacuum Pressure Bump
0
2
4
6
8
10
12
14
0.E+00 1.E+10 2.E+10 3.E+10 4.E+10 5.E+10 6.E+10 7.E+10 8.E+10 9.E+10 1.E+11
Proton bunch intensity
P/P
Duty cycle ~ 45 %after 17h integratedtime of LHC beam
0
2
4
6
8
10
0.0E+00 2.0E+10 4.0E+10 6.0E+10 8.0E+10 1.0E+11Protons bunch intensity
P/P
Duty cycle ~ 45 %after 17h integratedtime of LHC beam
dipole field
no field
RHIC SPS
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Effects of the Electron CloudNoise on BPM Pickup
SPS
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Effects of the Electron CloudBeam Loss
SPS
RHIC
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Effects of the Electron CloudEstimation of the Heat Load for LHC (Frank Zimmermann)
high luminosity
arc heat load vs. intensity, 25 ns spacing, ‘best’ model
calculation for 1 train
R=0.5
max=1.7
max=1.5
max=1.3max=1.1
max=1.3-1.4 suffices
BS cooling capacityinjection
low luminosity
ECLOUDsimulation
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Mitigations (1)
Beam Scrubbing
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Mitigations (2)
Bunched Beam Injection Pattern Solenoid
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Mitigations (3)
Surface Coating with TiN or TiZrV (NEG)Surface Grooving
1 mm
Measured SEY reduction < 0.8. More reduction depending
geometry.
Measured SEY reduction < 0.8. More reduction depending
geometry.
Special surface profile design, Cu OFHC. EDM wire cutting. Groove: 0.8mm depth, 0.35mm step, 0.05mm thickness.
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Mitigations (4)
Clearing Electrode
E
Feedthrough
E
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Simulations
Small section of the beam pipe. Macro particles and discrete beam kick Space charge, electron and beam image
charge included. Gaussian bunches (longitudinal bunch profile
available for long bunches) Realistic secondary electron yield model. Electron longitudinal motion neglected Theoretical primary electron distributions
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Secondary Electron Yield
CERNSLAC
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Activities at Accelerator Division
Initial observation of pressure rise at Tevatron with high intensity uncoalesced beam in Dec. 2002.
Initiated by Weiren Chou and Francois Ostiguy for Proton Driver Study in April 2005.
More beam studies at Tevatron and some observations at Main Injector
Obtained simulation codes POSINST, ECLOUD, PEI, etc.
Collaborations with LBNL, CERN, APS, BNL, SLAC, etc.
Got 2 RFA electron detector as gifts from APS
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
RFA Testing Beam Pipe in Tevatron and MI
RFA ION GAUGEION PUMP
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Beam Studies at Tevatron (1)
Bunch intensity threshold around 4e10/bunch for 30 bunches, vacuum worsen @warm section A0, D0, C0, E0, not @B0 and F0
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Beam Studies at Tevatron (2)
Beam lifetime 24.4hrs Emittance growth 34.8/hr
Tevatron 150GeV, 116e10/30bunches
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Beam Studies at Tevatron (3)
Some beam Schottky power rise observed when the vacuum pressure rising
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Simulations for MI Upgrades
Basic beam parameters
Beam energy 8.9 GeV
Ring circumference 3319.419 m
Maximum bunch intensity 30e10/bunch
Bunch number 6 batch of 84 bunches
Bunch spacing 5.645 m
Maximum bunch length 0.75 m Gaussian
Beam size rms 5 mm round
Residual gas pressure 20 nTorr, room tempeture
Beam pipe 6.15 cm x 2.15 cm elliptical
Electrons/proton loss 1.27e-7 (e/p)/m
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Elliptical Beam Pipe
Gröbner multipacting parameterHorz 1.28 Vert: 8.04
@30e10/bunch Energy required for electrons to
traverse beam chamber in one RF period
Horz: 120 eV Vert: 19 eV Electron energy gain at the
extremities of the ellipse (impulse aproximation)
Horz: 2.3 eV Vert: 7.3 KeV Maximum beam kick (finite
bunch length) 772 eVLarmor radius: 0.47 mm @ 2 KGs
(From Miguel Furman)
2/ bebbm rrLNG
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Elliptical Beam Pipe
Electron Cloud in Bend
1.0E+00
1.0E+02
1.0E+04
1.0E+06
1.0E+08
0.2 0.4 0.6 0.8
Full Bunch length (m)
Ave
rag
e D
ensi
ty N
e (e
/cm
**3)
6e10, SEY 1.3
3e11, SEY 1.2
With normal MI elliptical vacuum chamber and within bend magnets, at proton bunch intensity of 6e10, the electron cloud threshold for the bunch length of 0.54m, which means electron cloud happens during ramping and transition crossing where bunch length becomes shorter
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Elliptical Beam PipeWith Clearing Electrode
Above electron cloud can be suppressed by the 500V clearing electrode in the beam pipe.
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
6” Beam Pipe
For the 6” beam pipe, the electron cloud happens even at bunch intensity of 10e10 proton/bunch at low SEY=1.3
The electron cloud can be suppressed by 50Gs solenoid or over 500V clearing electrode
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Future Plan
Continue the detailed simulation for various beam and surface conditions
Beam studies at Tevatron and MI: Electron density vs. beam intensity. Electron energy spectrum. Bunch by bunch tunes, loss, emittances. Vacuum changes.
● Comparing and benchmarking the simulation codes● Test of mitigation methods with the test beam pipe:
Solenoid, clearing electrodes, coating, grooving, etc.● Does it exists in Booster?
6/5/2006 Xiaolong Zhang-FNAL, AD/Tevatron
Summary
Electron cloud effect is a limiting factor to the high energy, high intensity accelerator performance.
It might have some impacts on magnet design. The simulations and initial observations show
the electron cloud will be a problem for SNuMi and future Fermi neutrino programs.
More studies and investments should be put into this researches.