9-12 april 2007 international linear collider dr electron cloud r&d effort: clearing electrode...
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9-12 April 2007
International Linear Collider DR electron cloud R&D effort:Clearing electrode and triangular fin
M. Pivi
T. Raubenheimer, J. Seeman, T. Markiewicz, R. Kirby, F. King, B. McKee, M. Munro, D. Hoffman, G. Collet, L. Wang, A. Krasnykh, D. Arnett, (SLAC) M. Venturini, M. Furman, D. Plate (LBNL), D. Alesini (LNF Frascati), R. Macek (LANL)
ECLOUD 07
Daegu, S. Korea
2
Milestones to the ILC Engineering Design Report (EDR)
1. Characterize electron-cloud build-up. (Very High Priority)
2. Develop electron-cloud suppression techniques. (Very High Priority)
Priority: characterize coating techniques and testing of conditioning and recontamination in situ.
Clearing electrodes concepts by installation of chambers in accelerators. Characterization of impedance, HOM and power load deposited to the electrodes.
Groove, slots and other concepts. Characterization of impedance, and HOM.
3. Develop modeling tools for electron-cloud instabilities. (Very High Priority)
4. Determine electron-cloud instability thresholds. (Very High Priority)
Characterization the electron cloud instability: various codes in use PETHS, HEAD-TAIL, WARP/POSINST, CMAD
• R&D Goals:– Estimate e-cloud build-up and single-bunch instability thresholds– Reduce surface secondary electron yield (SEY) below electron cloud
threshold for ILC DR: SEY ≤ 1.2
• Surface approaches– Thin film coatings– Electron and photon surface conditioning– Clearing electrodes– Grooved surfaces
• Projects:– ONGOING: conditioning TiN and NEG coatings in PEP-II straights– ONGOING: rectangular groove chambers in PEP-II straights– PLANNED: clearing electrode chamber in magnets– PLANNED: triangular groove chamber in magnets
E-cloud and SEY R&D Program SLAC
ONGOING TESTS AT SLAC:
Projects
CLEARING ELECTRODES
BEND … end 2007 Design
FINS TRIANG. BEND … end 2007 Design
TEST in LOCATION Ready for INSTALLATION
Status
SEY TESTS STRAIGHT PEP-II LER PR12 November 2006 Ready
FINS RECTANG. STRAIGHT PEP-II LER PR12 November 2006Coating of
extruded Al chambers
ONGOING PROJECTS:
Clearing Electrode Concept of a clearing electrode
Model: Wire (Rod) type
L.Wang et al., EPAC2006
Beam duct
Rod (Electrode)
Ceramics Support
Feed-through
Ceramics Supportwith thin metal coating
Beam
2007/03/1-2 Y. Suetsugu KEK - ECL2 CERN 28
Clearing of electron cloud in ILC Clearing of electron cloud in ILC dipole magnetdipole magnet
-20 -10 0 10 20
-20
-15
-10
-5
0
5
10
15
20
X (mm)
Y
(mm
)
Clearing field (left) and effect (right) of a traditional stripline type of electrode. The red color in (left) shows the electrode. The blue and black dots in right plot show the electrons with different size of electrode.
The width of low electron density region increases with the size of the electrode.
Clearing field 0 Voltage 100 Voltage
L. Wang, SLAC June 2006
Simulation unsing POSINST code of electron cloud build-up and suppression with clearing electrodes. ILC DR positron 6 km ring.
Curved clearing electrodes: Curved clearing electrodes: simulationssimulationsCurved clearing electrodes: Curved clearing electrodes: simulationssimulations
BEND chamber with curved clearing electrodes
M. Pivi – P. Raimondi, L. Wang, T. Raubenheimer SLAC, Mar 2006
Curved clearing electrodes Curved clearing electrodes effecteffectCurved clearing electrodes Curved clearing electrodes effecteffect
ns 3~ in wall theback to electron
])[2.0]/[2000(
V/m .2000
V 100
TvmVexm
E
V
CE
CE
+ 100 V
Assume electron at rest near wall before bunch pass.
Electron is first accelerated by the beam to the center chamber and then attracted back by the biased +100V electrode. Electron back to the wall after 3 ns, much before the next bunch passage.
Electron cloud build-up is strongly suppressed !
During the spacing between bunches: (ECE
= cl. electrode field near wall)
SuperB and ILC DR
Lattice SUPERB OCS
Circumference [m] 6114 6114
Energy [GeV] 5.066 5.066
Harmonic number 13256 13256
Bunch charge [1010] 2.0 2.0
Bunch Spacing [ns] 1.54 6.154
Mom. comp. [10-4] 1.62 1.62
Bunch length [mm] sigz 6.0 6.0
Sigx, sigy in BEND [m] 620, 8 620, 8
Energy spread [10-3] 1.29 1.29
Synchrotron Tune [10-2] 3.37 3.37
Compare electron cloud in SuperB and ILC
Difference in bunch spacing: SUPERB=1.5 ns and ILC=6.15 ns
Mar 2006
SUPERB bends clearing electrodesSUPERB bends clearing electrodesSUPERB bends clearing electrodesSUPERB bends clearing electrodes
POSINST code
Near beam electron cloud density.
M. Pivi – P. Raimondi, L. Wang, T. Raubenheimer SLAC, Mar 2006
E-cloud build-up and suppression with/without clearing electrodes in bends of SUPERB factory (bs=1.54ns)
Compare electron cloud in SuperB and ILC
Difference in bunch spacing: SUPERB=1.5 ns and ILC=6.15 ns
Compare electron cloud in SuperB and ILC
Difference in bunch spacing: SUPERB=1.5 ns and ILC=6.15 ns
EnamelEnamel
Vitreous material, generated Vitreous material, generated in melting process, contents in melting process, contents a number of anorganic and a number of anorganic and oxidic-silicatic fractionsoxidic-silicatic fractions
Melting on metal- or Melting on metal- or glassubstrate, chemical and glassubstrate, chemical and micromechanical connection micromechanical connection between the layer and metall between the layer and metall surfacesurface
Universal dissolver for Universal dissolver for anorganic, metallic oxidesanorganic, metallic oxides
Countless possibilities of Countless possibilities of variatyvariaty
Generally free from any Generally free from any organic material organic material
ECL2 Workshop CERN, March 2007
double enamel coating – the new e- cloud killer(F. Caspers, F.-J. Behler, P. Hellmold, J. Wendel)
ECL2 Workshop CERN, March 2007
59”~25”
tapered chamber 1
3.5”
1.73”
Grooved chamber(?!)
Clearing electrode chamber
spool chamber
Layout installation – in PEP-II
(D-BOX)
tapered chamber 2
BEND BEND
D-BOX=diagnostic box, electron detection centered on BEND and 13.5” long
Chamber cross section
22”
(D-BOX)
BEND BEND
reduction to ILC DRchamber diameter
4-bend chicane
Sketch clearing electrode chamber and diagnostic
Electron cloud diagnostic
R. Macek LANL
max: 5”
• Test chamber with clearing electrodes
• Test chamber in PEP-II in a special chicane with 4 identical magnets
• magnets: SLC Final Focus correctors
• Chamber aperture constraint from the magnet aperture: max 5 ”
M. Pivi SLAC -February 13, 2007
Test Chamber Assembly, 1.5M Long (59.00”)
Vacuum Tube,
4.00 OD x 3.50 ID
Vacuum Tube, 3.75 OD x 3.51 ID
3.375” CFF, Non-Rotatable
Feedthrough, Ceramtec #1084-01-WMounted to 1.33” CFF
3.375” CFF, Rotatable
Tube, 2.00” OD x 1.73” IDFlange to Flange Length = 59.00”
Collector Port Flange
1.33” CFF access port
Test Chamber with Electrode
Electrode, Copper 0.063” x ~1.0” x 50.0”(49.606” between feedthrough centers)
Clearance between Electrode and chamberVaries between .070” and .080”
Electrode Connection
Space between chamber and electrode = 0.08”
(2mm all around)
Electrode Connection
Collector Port, 20.00” x 1.00” Collector Port Flange, 21.50” x 2.50”
0.125” Dia. Holes
Rpipe
1
h3 t
LTOT
LTAP
h1
h2
First discontinuity
Dimensions:LTOT630 mmLTAP115mmRpipe=44 mm=60 degh1,h3,h3=5 mmt=2 mm
1st Geometry: 2 Ports 50 Ohm2nd Geometry: 1 Ports 50 Ohm
David Alesini, Frascati, Feb 2007
A. Krasnykh, SLAC, Mar 2007D.Alesini, LNF, Frascati
HFSS Results on Copper electrode stainless steel chamber
Longitudinal Impedance: power deposited to electrode ~10W with PEP-II beam, and ~2W for ILC DR beam.
Add Synchrotron radiation in PEP-II +40W power load 50W onto electrode
Summary clearing electrodes
• Clearing electrode/s suppress cloud build-up and perfectly eliminate the cloud at center beam.
• Concern: Removal of power load from clearing electrode!
• Stripe line kicker design tests first
• Clearing electrode on isolator substrate: “enamel” more studies needed.
ONGOING TESTS AT SLAC:
Projects
CLEARING ELECTRODES
BEND … end 2007 Design
FINS TRIANG. BEND … end 2007 Design
TEST in LOCATION Ready for INSTALLATION
Status
SEY TESTS STRAIGHT PEP-II LER PR12 November 2006 Ready
FINS RECTANG. STRAIGHT PEP-II LER PR12 November 2006Coating of
extruded Al chambers
ONGOING PROJECTS:
L. Wang, SLAC
Note: fin chambers needed in magnet regions covering ~12% of the ILC DR
27M. Venturini, M. Furman LBNL 20 Feb. 2007
Smoother tips spoil effectiveness of grooves (POSINST)
Spoiling effect of smooth groove-tips can be compensated by making the grooves deeper.
Generally, a finite groove-tip radius enhances dependence of groove effectiveness on groove height
Max of cloud density vs. groove-tip radiusfor two groove height hg
Max of cloud density vs. height hg for 3 choices of groove-tip radius
Summary triangular fins in magnetic field regions
• Triangular groove are very promising at reducing the electron cloud build-up in bends and wigglers.
• In magnets, reduced groove area needed only on top and bottom chamber. Photons leave the chamber more efficiently (<< lower accumulation of photoe- than with a uniform groove distribution around chamber perimeter)
• Sharpness of tips important to reduce SEY.
Triangular groove chamber
Self-consistent code CMAD
At SLAC, developing self-consistent code including simulation of cloud build-up and beam instabilities. Parallel computation allows tracking the beam in a MAD lattice, instability studies, threshold SEY, dynamic aperture study, frequency map analysis, tune shift computation..
MAD deck to track beam with an electron cloud in the ILC DR.
Bunch at injection
Self-consistent code developmentDynamics• MAD input lattice• Tracking 1 bunch in the ring lattice by 2nd order transport maps (R, T)
– Not symplectic (but 99% phase space conservation if ILC DR 500 turns)
• Tracking 6D beam phase space, 3D beam dynamics• 3D electron dynamics• Apply beam-cloud interaction at each element of MAD lattice• 2D forces beam-cloud, cloud-cloud computed at interaction point• Electron dynamics: cloud pinching and magnetic fields included
Approximations:• Assign same cloud distribution and density for each class of elements
(ex: 1E+12 em-3 in quadrupoles, 4E+12 em-3 in wigglers) • Evolution of cloud build-up updated at each beam turn (weak beam
changes turn by turn) – [NOTE: cloud build-up part is not included yet]• If beam sizes are identical at two elements, apply earlier computed cloud-
to-beam kick – [switched OFF]
CMAD status
First results: few synchrotron oscillation periods (9min * 320 CPUs / turn) CMAD tracking, ILC DR beam at extraction, with average cloud density 1e10 e/m3 (below threshold).
Electron cloud distribution in bends and straights (so far from POSINST)
Completed. Single-bunch instability part: studies ongoing.
Build-up electron cloud to be added, vacuum chamber, SEY, etc. Use POSINST now
Bottleneck => in ILC DR, beam aspect ratio reaches x/y=200, demanding Particle in Cell grid ratios num-gridx >> num-gridy, to correctly simulate Electric field.
s=0.067e- density 1e10 e/m3 macrop
Summary
• Latest results (SLAC/KEK) of direct measurements in B-factories beam line indicate very low SEY for thin film coatings.
• R&D effort for ILC DR on development of coating mitigation techniques + antechamber design
• In parallel, R&D studies should continue for other possible mitigation techniques (ILC DR upgrade, SuperB)
• Simulations: clearing electrodes are most efficient at eliminating rather than just reducing the electron cloud - actual concern: remove power on clearing electrodes