1. CesrTA Vacuum System Conversion and Operational Experiences Yulin Li for the CesrTA Team Cornell Laboratory for Accelerator-based ScienceS and Education (CLASSE) Cornell University, Ithaca, New York, USA Third Workshop on the Operation of LArge Vacuum systems, July 11-14, 2011 Oak Ridge, TN Supported by: DOE (contract # DE-FC02-08ER41538) and NSF (PHY-0734867 & PHY-0131508)

2. CESR as a Test Accelerator (CesrTA) for ILC DR Global R&D Efforts Electron Cloud (EC) build-up in International Linear Collider (ILC) Positron Damping Ring (DR) is one of the principle risk factors CesrTA provide unique opportunities for EC build-up and suppression studies

3. Reconfiguration of CESR Vacuum System for CesrTA Created 4 dedicated EC Experimental Regions  L0 Wiggler EC Region  L3 EC Region  Q15W/E Regions Many EC diagnostics deployed  Retarding field analyzers (RFAs)  RF shielded pickups (SPUs)  TE-wave A variety of EC suppression techniques evaluated  Coatings  Grooved surfaces  Clearing electrode

4. CESR-c Superconducting Wigglers (SCWs) are model design for ILC DR 6 SCWs were installed at the L0 Region for EC studies in wiggler field, after removal of CLEO HEP Center Detector L0 Wiggler EC Study Region 1.RFA-equipped SCWs 2.CESR-c SCWs

5. L3 EC Experimental Region EC studies in dipole chambers (4-dipole chicane) using RFAs (TiN coating) EC studied in quadrupole chambers with RFAs (aluminum, and TiN coated Alum.) EC studies in drifts (RFAs, SPUs). Grooved, TiN-, & NEG-coated beampipes In-situ SEY measurement systems (samples: Al, a-C, TiN, DLC coatings)

6. Q15W&E Short Experimental Sections Two very short section in CESR arcs maybe isolated with GVs. Many EC test chambers rotated through these sections. EC chambers instrumented with RFA and SPUs

7. Retarding Field Analyzers – Primary EC Instrument A)Flanged insertable RFA B)RFA port, with small holes allowing electrons drift into RFA port, while cut-off beam-RF C)Typical RFA structure  Metal fine meshes (2) nested in dielectric frames (1)  Segmented collector for spatial measurement RFAs were deployed in the drifts, as well as in dipole, quadrupole, and wiggler magnets

8. Thin-Style RFAs in Dipole Chamber Entire RFA fits in ~3.1mm Space

9. Thin-Style RFAs in Quadrupole Chamber

10. Implement RFAs in SCWs Thin-style RFAs implemented in a SCW at three locations in the wiggler field, by replacing SCW beampipe w/o disturbing wiggler magnet/cryo systems Each RFA has provide transverse EC distribution information RFA structure fits into 2.5-mm gap

11. Thin-Style RFAs in Four SCWs

12. Some Unique Components/Materials in Thin RFAs Copper meshes (Au-plated) with very high transparency (>90%) used extensively. The meshes (15-µm thick) were electro-formed onto customer SST frames. PEEK (Poly-ether-ether-ketone) found to be very good alternative to ceramic.  UHV-compatible;  T up to 275C;  Radiation-hard;  Easy to machine (down to 0.75-mm thin) Flexible printed circuits made of clad-Cu on Kapton film used extensively as electron collectors Kapton w/ Silicone adhesives – Si-contamination (?)

13. EC Test Chambers in Q15W/E RFA data SPU data RFA provide EC spatial information SPUs provide time-resolved EC data

14. SEY-reducing Coatings Performances

15. SEY-reducing Coatings Performances – RGA

16. EC Suppression Techniques Evaluated SEY-reduction coatings are most economical. Tested coatings include: TiN (drifts, quadrupole, dipole and wiggles), a-C & DL-C (drift), NEG (drift) Grooves (rectangular and triangular) are also effective, and passive. Evaluated in drift, dipole and wigglers Clearing electrode – very effective, but costly. (Keep low beam impedance a key consideration.) Solenoids in drifts

17. In-situ SEY Systems Load-locks allow sample replacement, sample exposure to SR. Two systems, one in direct SR fan, one out of SR fan Each measurement takes about 2-hour, easily fit within accelerator access

18. In-situ SEY Systems – Some Results 6061-T6 TiN/Aluma-C/Alum

19. Brief Conclusions CESR vacuum system was reconfigured for CesrTA, and successfully achieved the two main goals:  To create environments where both local and collaborators provided test chambers and equipment can be easily installed.  To ensure the continuing successful operations of Cornell High Energy Synchrotron Sources (CHESS) at CESR. Over 40 new vacuum chambers were constructed and installed as a part of the CesrTA conversion in the past three years. Many of the new chambers were instrumented with EC diagnostics, and implemented with EC suppression techniques CesrTA vacuum operational experiences provide important inputs to the ILC DR vacuum system design