ILC Damping Ring update on collective effect electron cloud R&D Mauro Pivi SLAC ILCDR06 Cornell Workshop September 26-28, 2006.

ILC Damping Ring update on collective effect

electron cloud R&D

Mauro Pivi

SLAC

ILCDR06 Cornell Workshop

September 26-28, 2006

p.2

OutlineOutline

Overview of the effect for different DR options

Status of experimental R&D

Mitigation techniques R&D plan

Simulations plan: what is left to do

Analysis

Conclusions

Secondary electron yield SEY

Compare options: Compare options: simulations recent historysimulations recent historyCompare options: Compare options: simulations recent historysimulations recent history

Cloud density near (r=1mm) beam (m-3) before bunch passage, values are taken at a cloud equilibrium density. Solenoids decrease the cloud density in DRIFT regions, where they are only effective. Compare options LowQ and LowQ+train gaps. All cases wiggler aperture 46mm.

An electron cloud generates if the metal surface secondary electron yield (SEY) is high enough for electron multiplication. In the ILC Damping Ring an electron cloud develop mostly in BENDS and WIGGLERS. Typically SEY <1.2 is required.

• R&D Goals– Reduce and stabilize the surface SEY below electron cloud threshold

in the ILC damping ring. Challenge: SEY ≤ 1.2.

• Approaches– Electron and photon conditioning– Metal surfaces with fins (grooves) profile– Clearing electrodes

• Plan:– Measure the SEY of samples directly exposed to PEP-II LER

synchrotron radiation and electron conditioning.– Test new structure concepts with very low effective SEY < 1: – grooved surfaces in PEP-II LER– clearing electrodes in PEP-II LER

Electron Cloud and SEY R&D Program

Sep 26, 2006

Ongoing chamber projects at SLAC:

Projects

CLEARING ELECTRODES

BEND PEP-II LER PR12 2007 Design

FINS TRIANG. BEND PEP-II LER PR12 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

Next chamber projects:

M. Pivi, SLAC

Some past experience

Laboratory measurements:

conditioning: SEY~1. In vacuum de-conditioning brings up SEY ~ 1.3

KEKB tests:

conditioning in situ. [Cross-benchmarking with simulations gives low SEY~1]

SPS-CERN:

conditioning in situ in the SPS. Minimum measured conditioned surface

SEY~1.5. De-conditioning effect. Electron cloud effects decreased in time

PSR-LANL:

conditioning slow in time and de-conditioning. Still an issue. Measuring

electron cloud since 1989!

Dane:

Luminosity reach is limited. (Aluminum SEY ~2.0 after conditioning)

Bfactories:

KEKB: smaller bunch spacing is limited by electron cloud. Still after years

PEP-II: no problem up to 2.7A.

Surface Conditioning (scrubbing)

Ongoing tests

KEKB, CESRc, Dafne, PEP-II

Next

LHC will soon give answers.

Note: LHC issues are heat load and single-bunch instability (p+ 450 GeV inj. energy). ILC DR issues are single-bunch instability and very small emittance preservation.

Conditioning (scrubbing)

Coated sample exposed to SR in contact to chamber through RF seal

PEP-II LER sideRF seal location

RF seal provide both RF sealing and thermal contact (Synch radiation load = 1W/cm at 4.7A)

SEY TESTS TiN and NEGSEY TESTS TiN and NEGSEY TESTS TiN and NEGSEY TESTS TiN and NEG

Expose samples to PEP-II LER synchrotron radiation and electron conditioning. Then, measure SEY in laboratory. Sample transferring under vacuum.

Sep 26, 2006

Sample position

Stripe of SR

Port with holes for electron cloud collector

p.17

Design- Fin ExtrusionsDesign- Fin Extrusions

FIN TIPS= I.D. OF CHAMFAN HITS HERE FIRST

LIGHT PASSES THRU SLOTS BETW FINSBECAUSE FAN IS “THICKER” THAN FIN

FAN EVENTUALLY HITS “BOTTOM” OF SLOT FOR FULL SR STRIKE

VIEW IS ROTATED 90 CCW FROM ACTUAL FAN ORIENTATION

p.18

Design- Fin ChamberDesign- Fin Chamber

Chambers are constructed of Al extrusions machined to length with end preps for masks & flanges.

Al extrusions were chosen for their economy and ease of manufacture

Bonus - cooling is integral to the cross section, not welded to the outside

Flanges are bi-metal Atlas flanges that are welded directly to chamber

Insufficient space between the chamber and the flange knife edge for a bi-metal transition

Bottom sides of chambers are perforated at the ports Inside surfaces are TiN coated

Reduce thermal outgassing & PSD Reduce secondary electron yield?

Fin chamber weight ~ 32 lbs

EXTRUSIONS

Fin and flat chambers with cooling tubes, extrusion completed

Sep 26, 2006

Ongoing chamber projects at SLAC:

Projects

CLEARING ELECTRODES

BEND PEP-II LER PR12 2007 Design

FINS TRIANG. BEND PEP-II LER PR12 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:

M. Pivi, SLAC

Remedies simulation summary (see also L. Wang/M. Pivi talk

Vancouver)

-20 -10 0 10 20

-20

-15

-10

-5

0

5

10

15

20

X (mm)

Y

(mm

)

L. Wang CLOUD_LAND code

P. Raimondi, M. Pivi POSINST code

0 Voltage 100 Voltage

Bunch spacing = 6ns ! Bunch spacing = 1.5ns !!

Laboratory tests Copper Strips

Copper Foil Strips 1mil 5mil 20mil Used

Coated with Kapton 3M Tape #5413 2.7mil thickness

Brett Kuekan, Anatoly Krasnykh, M. Pivi SLAC Sep 2006

Preliminary reflection test HP 4 Channel

reflectometer

Brett Kuekan, Anatoly Krasnykh, M. Pivi SLAC Sep 2006

CVk / 10 5.4 9Measured loss factor

100

80

60

40

20

0

Lon

g.

Imp

ed

an

ce (

ž)

30002500200015001000500

Frequency (MHz)

Longitudinal impedance bench measurements LBNL

Experimental setup - coaxial wire method

Initial results: peaks spacing is ~379 MHz i.e. a wavelength equal to twice the length of the test electrode (/2 resonance). Our test pipe cutoff is around 3 GHz.

Z// 2Zc ln(S21DUT / S21

REF )

Walling log formula for distributed impedances

378.75 MHz

k 5 10 9 V /CLoss factor (back of the envelope estimate)

(Ohm

)

S. De Santis LBNL, M. Pivi SLAC Sep 2006

Expected power load onto electrode

kloss [V/C] Bs [s] I [A] P [W]

PEP-II 3.4e9 4.2e-9

3.0 125

ILCDR 1.6e10 6.2e-9

0.5 24

Beam impedance related to impedance of transmission line

tchamb

cgap

rk

14/1

4

120

2IkP b

Beam impedance

Power onto electrode

Where longitudinal gap between wall and electrode gap=0.003 and PEP-II t=40ps, rchamb=0.045m. ILC DR t=20ps, rchamb=0.022m.

Brett Kuekan, Anatoly Krasnykh, M. Pivi SLAC Sep 2006

Option 1: four magnets chicaneOption 1: four magnets chicaneOption 1: four magnets chicaneOption 1: four magnets chicane

Layout PEP-II installation, PR12 LER

e+

INSERTION BENDS 2kG

Chamber layout PEP-II

1200mm

Terminations load

Triangular grooved surface in wiggler

Effective SEY of an isosceles triangular surface with rounded tip. max=1.74, max=330eV, B0=0.2Tesla, Rtip=0.2mm, W=4.52mm.

)

W

0 100 200 300 400 500 600 7000

0.2

0.4

0.6

0.8

1

1.2

1.4

Energy (eV)

SE

Y

=65o, =50o

=70o, =40o

=75o, =30o

=80o, =20o

Effective SEY from an isosceles triangular surface in a dipole magnetic field. max=1.74, max=330eV, B0=1.6Tesla and W=1.89mm

0 100 200 300 400 500 600 700

0.2

0.4

0.6

0.8

1

1.2

Energy (eV)S

EY

=70o

=75o

=80o

To reduce the impedance

The effective SEY of triangular grooved surface has very weak dependence on the size W and magnetic field.

(slac-pub-12001)Experiment in PEPII Dipole & CESR Wiggler

L. Wang, SLAC

PROPOSED LABORATORY MEASUREMENTS: SEY OF GROOVE IN BEND

e- beam

triangular groove

SLC FF 0.2 T

“Milestones” Date Project 1. Fabrication of the prototype rectangular chambers…............. Done

Installation in PEP-II LER ……………………………………… Nov 2006Project 2. Fabrication of SEY test chamber………………………………. Done

Installation in PEP-II LER……………….…………………..…. Nov 2006Project 3: Fabrication of clearing electrode chamber……………………. Mar 2007 Complementary to Project 3: End Station A (SLAC) tests…... Mar 2007 Installation in PEP-II LER ……………………………………..... Summer 2007Project 4: Fabrication of triangular grooved chamber………………….… May 2007

Installation in PEP-II LER……………………..……………....… Summer 2007 Complementary to Project 4: meas. SEY in dipole….……….. May 2007

LANL: measure electron trapping in quadrupole field PSR …………...... OngoingFrascati: installation of electron cloud diagnostic in Dafne ring……....… Summer 06Cornell: measurements of electron cloud in wigglers………………...….. 2008

Experimental R&D

Collective effects: Electron cloud simulation plans for FY07

Simulations on build-up for ILC DR, quadrupole and wigglers in progress

Simulations on possible remedies to optimize design: clearing electr., RF, grooves in progress

Maintain simulations codes POSINST, CLOUDLAND, and benchmarking ILC DR simulations with other codes ECLOUD, PEI, in progress

Benchmarking simulations with ongoing experiments in PSR quadrupole in progress

Simulations on fill pattern to reduce the electron cloud build-up in ILC DR Jan 2007

Benchmarking simulations with experiments in PEP-II Jan 2007

Benchmarking simulations with experiments in LHC Nov 2007

Developing “CMAD” self-consistent simulation code including e-cloud build-up and beam instabilities. Allow: tracking the beam in a MAD real lattice, interaction with cloud at each element of the ring, single- and coupled-bunch instability studies, threshold for SEY, dynamic aperture studies and frequency map analysis, tune shift. Status 85% done Feb 2007

Self-consistent simulation code: simulations for ILC and LHC (LARP collabor.) Mar 2007

Self-consistent simulation code: benchmarking with other single-bunch instability codes (HEAD-TAIL/PEHTS,ORBIT/QUICKPIC/WARP..) Apr 2007

Self-consistent simulation code: benchmarking with existing machines and LHC Nov 2007

----- M. Pivi, SLAC 26 Sep 2006 -----