Introduction SixMonth FollowUp on Action Items of Feb

Introduction Six-Month Follow-Up on Action Items of Feb 2016 CEBAF Field Emitter Workshop Rongli Geng September 12, 2016

Workshop Feb 29, 2016 NL 12 Meeting May 25, 2016 CEBAF Stay. Treat June 28 -30, 2016 Feb Mar Apr May Jun Jul Today Six-month follow-up Sep 12, 2016 Aug Sep Oct C 50 -12 commissioning @ NL 12 C 50 -12 CM assembly CMTF testing C 50 -12 pairs VTA testing NL 12 Girder C 50 -12 Installation NL 12 Girder Removal

Workshop Action Items # Actions 1 Determine the source of field emission degradation during the string SRF assembly and tunnel installation 2 Determine the next generation beamline vacuum systems. Try to get SRF/VAC/OPS a new system in time for the C 50 -12 installation this summer. 3 Halt all ion-pump hi-potting on CEBAF and LERF systems. Develop a VAC/ENG/OPS path forward, which might include replacing the pumps that need hi -potting. Develop a particulate transport model for CEBAF. SRF/CASA/OPS 4 5 6 7 Owner Develop an improved temporary clean room environment for tunnel VAC/SRF work. Determine the particulate generation characteristics of ion pumps, SRF/VAC gate vales*. Develop a beam line venting procedure for low particulate SRF/VAC movement.

The Workshop • Mini-workshop on beam-line field-emitter particulates in CEBAF SRF linacs – February 29, 2016 – https: //www. jlab. org/indico/event/139/ • JLAB-TN-16 -008 – https: //jlabdoc/docushare/dsweb/Get/Document 117729/16 -008. pdf

Goal Evaluate field-emission impact to operation of CEBAF SRF linacs. Identify the root cause(s) of particulate field-emitters in operational SRF cavities, with a focus on the particulates originating from the UHV beam-line components. Develop solutions for “particulate-free” beamline components for future SRF linacs as well as mitigations against accumulated field emitter particulates for operational SRF linacs.

Topics • Observations and experiences with beam-line particulates and correlation with field-emission. • Sources of particulates in UHV beam-line components. • Roles of condensed residual gases. • Mechanisms of particulate transportation in UHV beam-lines. • UHV beam-line component design for lowest particulate generation. • UHV beam-line component cleaning, handling, assembly and operation procedure for lowest particulate generation. • Mitigation against field-emitter particulate in operational SRF linacs. • Techniques for removal of accumulated field emission particulates. • UHV beam line-particulate detection technique. • Fast detectors for in operando monitoring of field-emission turn on.

Sources of C 100 FE Onset Degradation 90% FE onset degradation originated from field emitters introduced into cavities before they were placed in tunnel

Time Evolution of FE Onset of C 100 Modules 18 16 Module Avg FE Onset [MV/m] 14 12 10 8 6 4 2 0 2 L 24 2 L 25 2 L 23 2 L 22 1 L 24 1 L 23 Module (in order of tunnel placement) 1 L 25 1 l 26 2 l 26

NL 12 Meeting - May 25, 2016

NL 12 Meeting – May 25, 2016

white board photos attached. 1 NL 12 removal and associated warm girders ===================== : SRF: OPS: <2016 -05 -25 Wed 09: 00> 1. 1 Attendees ~~~~~~~ Akers, Suhring, Drury, Reilly, Krafft, Reece, Geng, Dipette, Coopers, Wright, Benesch (briefly)

1. 2 Workscope ~~~~~~~ * 1. 2. 1 Present Workscope + Remove NL 12 and install C 50 -12 + Requires warm up on NL 11, NL 12 and NL 13 - NL 11 already warm

* 1. 2. 2 Proposed Additional Workscope + 1. 2. 2. 1 Warm Girders + Remove upstream and downstream warm girders + Take vacuum surface particulate swipes in tunnel as soon as accessible, prior to removal from tunnel. + Move warm girders to SRF workspace + Disassemble warm girder so that vacuum pipes can be processed by SRF - requires quadrupole to be disassembled - Special care with BPM + process (clean) vacuum surfaces of warm girder + assemble warm girder + leak check + move to tunnel + install on beam line + 1. 2. 2. 2 Valve Change out + internal manual valves on NL 11 and NL 13 to be replaced with new or rebuilt valves. + valves on the warm girders to be replaced with new or rebuilt valves. + 1. 2. 2. 3 Ion Pumps + Preferred option: new particulate free ion pumps to be installed on NL 12 and NL 13. (so call B pumps) + Next preferred option: new ion pumps to be installed on NL 12 and NL 13. + This applies to the ion pump on the cryomodule and the ion pump on the warm girder.

1. 3 Schedule Highlights ~~~~~~~~~~~~ * 1. 3. 1 Present Schedule + [2016 -06 -22 Wed] Beam Terminates + [2016 -06 -27 Mon] NL 12 Removal + [2016 -06 -08 Wed] C 50 -12 Installation * 1. 3. 2 Proposed Schedule + Warm up on NL 12, NL 13 starts when beam terminates [2016 -06 -22 Wed] + Installation group to work 5 th pass separator, 6 T YR removal in parallel with module warm up: [2016 -06 -22 Wed]--[2016 -06 -27 Mon] + When NL 11, NL 12, NL 13 are warm start the warm girder removal, nominal date of [2016 -06 -27 Mon]. + plan to have the warm girders returned to the tunnel by last week in July [2016 -07 -25 Mon]. + Advance the NL 12 removal if convenient

1. 4 White Board Action Items ~~~~~~~~~~~~~~ + Beamline valves, it is ok to use rebuilt beam line valves on the warm girders? + rebuilt manual valves are already used inside the cryomodules. + *ACTION* provide guidance on the use of rebuilt beamline valves in the warm region. Who: Reilly/Drury When: [2016 -06 -15 Wed] + Ion pump replacement, are the ion pumps sufficiently particulate free? Is there a better choice out there? + Rongli recommends Agilent as a better ion pump than the present CEBAF choice. + *ACTION* compare the present ion-pump choice with comparable models (pump speed) and make a decision on ion-pumps for the cryomodules and warm-regions. If desired, purchase some pumps for testing. Once decision is made, communicate the make/model number of Pam Kjeldsen so that the controls group can start programming the controls interface. Who: Reilly/Geng When: [2016 -06 -08 Wed] + SRF staff has a detailed assembly procedure for LCLS-II that CEBAF might benefit from. + *ACTION* Reilly and Dipette will coordinate Installation Staff cross training on SRF procedure. Who: Reilly/Dipette When: TBD + Is the present ownership paradigm correct? SRF own the module, Installation/Vac group owns the warm region vacuum. + *ACTION* Reilly/Dipette to discuss possible changes and/or develop a more integrated approach that has the two groups working to the same specification. Who: Reilly/Dipette When: TBD

The Follow-up • It has been about six months since the February 29 miniworkshop on field emitter particulates in CEBAF beamlines. • Progresses have been made or are being made in several fronts related to the action items, all aligned with the goal of understanding and reduce field emission in CEBAF. • A six-month follow-up is deemed conducive to the final goal of reversing the "lost gradient" in CEBAF. Toward that end, a special PIT meting is to be conducted on September 12, 2016 to allow capturing and measuring the initial results of all efforts related to the action items.