ILC GDE - ILCDR08 Cornell 8-11 July 2008 Electron Cloud Mitigation R&D at SLAC M. Pivi, D. Arnett, G. Collet, T. Markiewicz, D. Kharakh, R. Kirby, J. Seeman, L. Wang, T. Raubenheimer (SLAC) ILC Damping Ring - ILCDR08 Cornell University 8 to 11 July 2008

ILC GDE - ILCDR08 Cornell 8-11 July 2008 Simulations indicate that a secondary electron yield of ~1.2 results in a cloud density close to the instability threshold. The aim of experimental studies is to obtain a surface secondary electron yield of 1.1. Simulations indicate that techniques as grooves in the chamber walls or clearing electrodes, besides coating, will be effective at suppressing the development of an electron cloud. Work done for the ILC Reference Design Report RDR

ILC GDE - ILCDR08 Cornell 8-11 July 2008 R&D Goals: –Reduce the SEY below instability threshold. SEY ≤ 1.1. Surface Approach: –Coatings –Conditioning –Grooved surfaces –Clearing electrodes (KEK) Experiments in PEP-II: –Conditioning –Grooved chambers –Conditioning and grooved chambers in magnetic field regions Electron Cloud and SEY R&D Program

ILC GDE - ILCDR08 Cornell 8-11 July 2008 R&D work at SLAC on mitigation techniques Installed 6 chambers in PEP-II straight: –“ECLOUD1”: to monitor the reduction in-situ of the SEY due to conditioning –“ECLOUD2”: to test Groove chambers –ECLOUD3”: new Chicane to test in magnetic field chambers: Aluminum TiN coating Groove chamber (not installed) Non-evaporable getter NEG coating chamber (not installed) stopped due to FY08 budget

ILC GDE - ILCDR08 Cornell 8-11 July 2008 ECLOUD1: SEY station 1.5% of the ring Electron cloud chambers installed in PEP-II ILC tests - SLAC ECLOUD2: grooves tests ECLOUD3: Al uncoated and TiN-coated chamber in chicane

ILC GDE - ILCDR08 Cornell 8-11 July 2008 “ECLOUD1” SEY test station in PEP-II Transfer system at 0 o PEP-II LER e+  Transfer system at 45 o 2 samples facing beam pipe are irradiated by SR Isolation valves ILC tests, M. Pivi et al. – SLAC

ILC GDE - ILCDR08 Cornell 8-11 July 2008 Results of Conditioning in PEP-II LER beam line Tin samples measured before and after 2-months conditioning in the beam line. Samples inserted respectively in the plane of the synchrotron radiation fan (0 o position) and out (45 o ). ILC tests, M. Pivi et al. – SLAC Before installation in beam line After conditioning e- dose > 40mC/mm**2 Similar SEY measured in situ at KEKB by S. Kato et al.

ILC GDE - ILCDR08 Cornell 8-11 July 2008 sample surface exposed to SR PEP-II LER side SEY TESTS 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 to CERN and KEK studies 20 mm

ILC GDE - ILCDR08 Cornell 8-11 July 2008 LER#1 XPS Before installationXPS After exposure in PEP-II LER for 2 months (e dose 40mC/mm^2) Carbon (and oxygen) contents are strongly reduced after exposition to PEP-II radiation and electron environment. Contrary to electron (only) conditioning performed at many laboratories which shows carbon increase on surface. Surface analysis: Carbon content decrease X-ray Photon Spectroscopy. ILC tests, M. Pivi et al. – SLAC

ILC GDE - ILCDR08 Cornell 8-11 July 2008 Effect of recontamination in vacuum: SEY < 1 (!) for TiN sample in stand-by in vacuum after the conditioning period in PEP-II LER. In vacuum pressure typical of an accelerator environment: 1.0e-9 torr, 10:1 H2:CO. SEY recontamination after long term exposure in vacuum environment

ILC GDE - ILCDR08 Cornell 8-11 July 2008 Activated-NEG conditioning in PEP-II beam line R. Kirby, M. Pivi, ILC tests – SLAC NEG as received After beam conditioning March 2008 After NEG heating Caution: although we took best precautions, the vacuum ~1e-7 Torr environment during sample transferring for measurements, may not have been perfectly free from CO CO2 contaminantion. TiZrV Non-Evaporable Getter NEG coating. Activation = 2h at 200degC.

ILC GDE - ILCDR08 Cornell 8-11 July 2008 ECLOUD1: Uncoated aluminum in PEP-II … Daphne and CesrTA have most of chambers in aluminum M. Pivi, R. Kirby – SLAC SEY remain > 2 after conditioning in beam line.

ILC GDE - ILCDR08 Cornell 8-11 July 2008 ECLOUD1: Summary Goal: monitor the reduction in-situ of the SEY due to conditioning Results: –TiN coating: SEY reduced to 1000 h) recontamination exposure to H and CO under vacuum. –Uncoated aluminum: SEY > 2 with/without conditioning.

ILC GDE - ILCDR08 Cornell 8-11 July 2008 ECLOUD1: Summary –Other findings: Activated NEG coating: SEY ~ 1.1 Copper: SEY reduced to < 1.2 Stainless steel: SEY reduced to < 1.2, but increased to 1.5 after recontamination exposure in vacuum References: –M. Pivi et al. MOPP064 EPAC 2008; –paper being prepared for submission to Physical Review ST AB –F. Le Pimpec et al. Nucl. Inst. and Meth., A564 (2006) 44; –F. Le Pimpec et al. Nucl. Inst. and Meth., A551 (2005) 187;

ILC GDE - ILCDR08 Cornell 8-11 July 2008 SEY before installation SEY after conditioning TiN/Al TiZrV Al StSt Cu Summary ECLOUD1 experiment Summary of samples conditioned in the accelerator beam line

ILC GDE - ILCDR08 Cornell 8-11 July 2008 Rectangular Grooves to Reduce SEY Schematic of rectangular grooves Without B field Rectangular grooves can reduce the SEY without generating geometric wakefields. The resistive wall impedance is roughly increased by the ratio to tip to floor. Schematic of rectangular grooves With B field

ILC GDE - ILCDR08 Cornell 8-11 July 2008 Special surface profile design, Cu OFHC. EDM wire cutting. Groove: 0.8mm depth, 0.35mm step, 0.05mm thickness. 1 mm Rectangular (!) groove Laboratory measurements SLAC M.P. and G. Stupakov, SLAC Artificially increasing surface roughness. Measured SEY reduction < 0.8. More reduction depending geometry. Measured SEY reduction < 0.8. More reduction depending geometry. 5mm depth (PEP-II) Same SEY results 5mm depth (PEP-II) Same SEY results Ref: A. Krasnov LHC-Proj-Rep-617

ILC GDE - ILCDR08 Cornell 8-11 July 2008 ECLOUD2: Design - Fin Extrusions - SLAC FIN TIPS= I.D. OF CHAM FAN HITS HERE FIRST LIGHT PASSES THRU SLOTS BETW FINS BECAUSE 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

ECLOUD2 – Grooved Chambers in PEP-II Standard (flat) chambers also installed as reference. All aluminum with TiN coating installed in straight sections. Rectangular groove (or “fin”) chambers fabricated by extrusion. e+ Grooved chamber Flat chamber Electron detectors

ECLOUD2 – Grooved Chambers Performance M. Pivi et al, SLAC Electron cloud signal in two smooth (flat) TiN-chambers and two grooved TiN-chambers installed in PEP-II. Electron cloud signal in stainless steel chamber.

ECLOUD2 – Summary *Goal: Measure performance of electron cloud suppression using grooved chambers *Electron cloud signal is ~ factor of 20 smaller in grooved TiN chambers compared to flat TiN chambers *Confirmed reduced electron cloud build-up in TiN coated chambers compared with uncoated stainless steel chambers. *References: –M. Pivi et al. MOPP064 EPAC 2008 –paper being prepared for submission to Phys. Rev. Lett.

Additional Plans: Grooved chamber for Cesr-TA *Grooved chamber for dipole: Chamber fabricated, needs assembly and TiN coating (originally built for ELCOUD3, but was not installed due to budget cuts.) Morrison, Pivi, Wang, SLAC

2mm Aluminum+coating triangular grooves (pictures above), manufactured by SLAC. Extrusion manufacturing limited by the groove sharpness requirements. 1mm depth stainlees steel grooved insertion under development: CERN/SLAC Lanfa Wang, SLAC Tip Valley Aluminum triangular groove, SLAC. Depth 1.9mm, Opening angle 20 o, radius top 95um, radius valley 144um Mauro Pivi - SLAC April 2008 Tip Additional Plans: Grooved chamber for CERN SPS

Additional Plans *KEK-B: –Provide groove insertions for experiment at KEK-B –Compare grooved and flat TiN coated surfaces, and clearing electrodes  see Suetsugu-san next presentation. *CesrTA: –Redeploy all experiments ECLOUD1,2,3 (plus grooved chamber in dipole). *Project-X: –Re-deploy ECLOUD1 (SEY Station) to Fermilab (after CesrTA)

Summary *A successful R&D program on electron cloud has been carried out at SLAC. *TiN coating has been demonstrated to have an SEY reliably below the instability threshold. Work continues to address a few remaining issues. *Requirements at future colliders - 2 picometer emittance in the ILC DR - are challenging. *Key collaboration with other labs to develop complementary mitigation techniques.