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