Motivation ILC Positron Damping Ring 6.6km will suffer Electron Cloud in magnets R&D Goals:

• Motivation– ILC Positron Damping Ring 6.6km will suffer Electron Cloud in magnets

• R&D Goals:– Reduce surface Secondary Electron Yield (SEY) below electron cloud

threshold for ILC DR: SEY ≤ 1.2

• Surface approaches– Thin film coatings TiN or NEG– Electron and photon conditioning in beam line– Clearing electrodes– Grooved surfaces

• Projects:– ONGOING: conditioning TiN and NEG coatings in PEP-II straights– ONGOING: rectangular groove chambers in PEP-II straights– PLAN: TiN coated chambers in PEP-II new magnets, FY07-FY08– PLAN: clearing electrode and groove chambers in magnets KEKB, FY08

ILC electron cloud R&D program: SLAC

M. Pivi, SLAC Jul 26, 2007

SEY GROOVE 1 GROOVE 2FLAT 1 FLAT 2

COLLECTORSENERGY ANALYZER

THERMOCOUPLES

GROOVE CHAMBERS EXPERIMENTSEY TEST STATION

SLAC test chambers installationSLAC test chambers installationSLAC test chambers installationSLAC test chambers installation

SEY station can be used to expose samples to PEP-II beam environment and then measure the Secondary Electron Yield in lab setup (transport in Ultra-High Vacuum load-lock)

Grooved and Flat chambers installed to measure performance inPEP-II beam environment

PEP-II LER sideRF seal location

SEY test station: TiN and NEGSEY test station: TiN and NEGSEY test station: TiN and NEGSEY test station: TiN and NEG

Expose samples to PEP-II LER synchrotron radiation and electron conditioning. Then, measure Secondary Electron Yield (SEY) in laboratory. Samples transferred under vacuum.

Complementary at SPS and KEK studies

20mm

Exposed to beam line

26 July, 2007 PEP-II meeting, Jul 26, 2007

SEY test station in PEP-II LER (SLAC)SEY test station in PEP-II LER (SLAC)SEY test station in PEP-II LER (SLAC)SEY test station in PEP-II LER (SLAC)

Manipulator at 0o

PEP-II LER e+

Manipulator at 45o

2 Sample locations inside beam line

Isolation valves

ILC tests, M. Pivi et al. – SLAC


Electron energy spectrum analyzer


Transferring system connected to lab set-up (SLAC)Transferring system connected to lab set-up (SLAC)Transferring system connected to lab set-up (SLAC)Transferring system connected to lab set-up (SLAC)

Transferring system with sample (UHV)

SEY analysis chamber Connected for UHV

sample transferring

Isolation valve Manipulator valve

ILC tests, R. Kirby et al. SLAC


Results of Conditioning in PEP-II LER beam line

SEY of Tin-samples measured before and after 2-months conditioning in the beam line. 2 samples inserted respectively in the synchrotron radiation fan plane (0o position) and out of this plane (45o).


Before installation in beam line

After conditioning

e- dose > 40mC/mm**2

Similar low SEY recently measured in situ in KEKB beam line S. Kato, Y. Suetsugu et al.

PEP-II meeting, Jul 26, 2007

LER#1

XPS Before installation XPS After exposure in PEP-II LER for 2 months (e dose 40mC/mm^2)

Carbon content is strongly reduced after exposition to PEP-II LER synchrotron radiation + electron + ion conditioning. This is a different result if compared to electron (only) conditioning in laboratory set-up where carbon crystals growth has been observed by many laboratories.

Surface analysis: Carbon content decrease

X-ray Photon Spectroscopy.



Carbon content is strongly reduced after exposition to PEP-II LER synchrotron radiation + electron + ion conditioning. This is a different result if compared to electron (only) conditioning in laboratory set-up where carbon crystals growth has been observed by many laboratories.

Surface analysis: Carbon content decrease

X-ray Photon Spectroscopy.


Groove chambers tests

p.12

Design - Fin Extrusions - SLACDesign - Fin Extrusions - SLAC

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

Goal: build Rectangular Groove (Fin) chambers by Al extrusion, TiN coat and install in Straight Section PEP-II LER for tests

p.13

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

p.14

Design- Port DetailDesign- Port Detail

4” port shown here, 500 holes, 25 x 20, holes 1.6 mm

1.5” port hole pattern is 50 holes, 10x5, holes 1.6 mm

Electron collector inserted in portElectron collector inserted in portElectron collector inserted in portElectron collector inserted in port

Test samples inserted during TiN-chamber Test samples inserted during TiN-chamber coating: measured before installation in PEP-II coating: measured before installation in PEP-II Test samples inserted during TiN-chamber Test samples inserted during TiN-chamber coating: measured before installation in PEP-II coating: measured before installation in PEP-II

Installation in PEP-II LER: Fin chambersInstallation in PEP-II LER: Fin chambersInstallation in PEP-II LER: Fin chambersInstallation in PEP-II LER: Fin chambers

Fin chamber

Flat chamber

Electron detectors

Connecting Flange

PEP-II LER straight section

e+

Bend magnet upstream


Groove testsGroove testsGroove testsGroove tests

• Installed TiN/Al extruded chambers with Rectangular Grooves in Straight Section PEP-II LER just downstream of arcs. Last arc bend at ~18 meters.

Initial Results:

• Electron signal in Flat & Fin chambers is much lower than Stainless Steel chamber.

• Recently, we found that groove chambers were NOT properly aligned

• An Horizontal offset 5mm (!) results in a masking effect of some chambers from being hit by synchrotron radiation, leading to “Fuzzy results”.

• Now, we have aligned all the chambers straight and tested again.


Sketch of initial chamber misalignment

x=-5.2mm x=-4.2mm

2.27m1.86182m 2.27m

S=17m S=21mG1 F1 G2 F2S=22.9m

_photon=2.3mrad

1.86m

_photon=1.7mrad

View from Top

H. Imfeld - Alignment GroupSketch by L. Wang, SLAC


Chambers alignment

2007-JUL-09


After alignment: effect of groove chamber on electron signal

Electron signal in Groove TiN-chambers « Flat TiN-chambers and Stainless steel chamber

M. Pivi, SLAC Jul 26, 2007


Effect of external solenoid

External solenoid on/off (10A Bz~20 Gauss).


BrainstormingBrainstormingBrainstormingBrainstorming

Proposal: Installation of more TiN/Al groove chambers in PEP-II LER straights.

Potential for increase in peak Luminosity

Pro:

• Additional reduction of electron cloud by 1-2 order of magnitude

• TiN/Aluminum chambers lower impedance then stainless steel

• Grooves may be efficient to suppressing very HOM (A. Novokhatski, 2005)

• Chamber extrusion costs by ILC

Furthermore:

• No HOM reported from groove chambers installed in PEP-II

• Very safe from field emission in PEP-II (B. Levtchenko, Jun 2007)

Contro:

• Chambers conditioning time, larger surface area


SummarySummarySummarySummary

• Installed 5 chambers in PEP-II in January 2007.

• SEY station operation is clean

• Secondary Electron Yield ~0.9 for TiN samples after conditioning in beam lines at SLAC and KEK. This is good news for ILC DR.

– Full characterization of conditioning /coatings ongoing

• Built and installed rectangular Fin chambers. Measured a SEY < 1 for rectangular samples

– Measured an electron signal in Fin & Flat chambers which is much lower than stainless steel chamber.

– Found misalignment and masking of Flat chambers.

– Aligned chambers

– Groove chambers electron signal lower than flat (no-groove) chamber

• Proposal to install more groove chambers in PEP-II LER straights


Thanks! To contributors and collaborators: R. Kirby, L. Wang, T. Raubenheimer, J. Seeman, K. Ohmi, S. Kato, K. Oide, Y. Suetsugu,

D. Arnett, G. Collet, R. Kirby, N. Kurita, T. Markiewicz, B. Mckee, M. Morrison, G. Stupakov, N. Phinney, U. Wienands, M. Sullivan, A. Kulikov, F-J Decker (SLAC), M. Palmer, D. Rubin, D. Rice, L. Schachter, J. Codner, E. Tanke, J. Crittenden (Cornell), J. Gao (HIPEP), A. Markovic et al. (Rostock Univ.), M. Zisman, S. De Santis, C. Celata, M. Furman, J.L. Vay, S. De Santis (LBNL), S. Kato, K. Oide, K. Ohmi, Y. Suetsugu (KEK), F. Willeke, R. Wanzenberg (DESY), J.M. Laurent, A. Rossi, E. Benedetto, F. Zimmermann, G. Rumolo, J.M. Jimenez, J-P. Delahaye (CERN), A. Wolski (Cockroft Uniiv.), B. Macek (LANL), C. Vaccarezza, S. Guiducci, R. Cimino, P. Raimondi (Frascati), O. Malyshev et many other colleagues…

26 July, 2007


Additional slides below

Compare vacuum chamber e- currents

Measured e- current in grooved and TiN flat chambers << StSt chamber. PEP-II LER current still raising (2.7A 4A)

OLD DATA - BEFORE ALIGNMENT

p.29

Design – Ecloud LayoutDesign – Ecloud Layout

Each chamber SR strike is approx 275 watts Vertical fan height ~ 2 mm Fin height (thickness) ~ 0.5 mm

Full SR strike on fin occurs at last 28 inches of chamber Instrument ports located in this area for maximum SR

HORIZONTAL SECTION-VIEW LOOKING DOWNLER DIRECTION

p.30

Design – Existing Ring LayoutDesign – Existing Ring Layout

LER DIRECTION

ELEVATION VIEW

PLAN VIEW

BEND B1

AISLE SIDE

TIN/Al GROOVE/FLAT CHAMBERS HERESEY CHAMBER HERE

p.31

Design- MasksDesign- Masks

Each chamber has an aluminum mask section welded to its downbeam end which protects the flange pair and the gap ring

Diameter and length driven by Space constraints for bolt loading, wrench clearance & cooling hardware 1:10 taper, RF Thermal stresses are well within material limits Standardized length of mask Mask design protects downbeam flanges for up to 6 mrad missteer

p.32

Design- Masks (cont’d)Design- Masks (cont’d)

Summary of grazing angle power deposited on each mask Mask 1 (cham 1) : .391 mrad fan , 170 watts , 2.67 w/ mm

Mask 2 (cham 2) : .051 mrad fan , 22 watts , .34 w/ mm

Mask 3 (cham 3) : .204 mrad fan , 89 watts , 1.40 w/ mm

Mask 4 (cham 4) : .035 mrad fan , 15 watts , .24 w/ mm

Documents

Motivation ILC Positron Damping Ring 6.6km will suffer Electron Cloud in magnets R&D Goals: