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

Workshop Feb 29, 2016 NL12 Meeting May 25, 2016 Today Six-month follow-up Sep 12, 2016 CEBAF StayTreat June 28-30, 2016 Feb Mar Apr May Jun Jul Aug Sep Oct C50-12 commissioning @ NL12 NL12 Girder C50-12 Installation C50-12 CM assembly CMTF testing NL12 Girder Removal C50-12 pairs VTA testing

Workshop Action Items # Actions Owner 1 Determine the source of field emission degradation during the string assembly and tunnel installation SRF 2 Determine the next generation beamline vacuum systems. Try to get a new system in time for the C50-12 installation this summer. SRF/VAC/OPS 3 Halt all ion-pump hi-potting on CEBAF and LERF systems. Develop a path forward, which might include replacing the pumps that need hi-potting. VAC/ENG/OPS 4 Develop a particulate transport model for CEBAF. SRF/CASA/OPS 5 Develop an improved temporary clean room environment for tunnel work. VAC/SRF 6 Determine the particulate generation characteristics of ion pumps, gate vales*. SRF/VAC 7 Develop a beam line venting procedure for low particulate 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” beam-line 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 C100 FE Onset Degradation 90% FE onset degradation originated from field emitters introduced into cavities before they were placed in tunnel

NL12 Meeting - May 25, 2016

NL12 Meeting – May 25, 2016

white board photos attached. 1 NL12 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 NL12 and install and install C50-12 + Requires warm up on NL11, NL12 and NL13 - NL11 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 NL11 and NL13 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 NL12 and NL13. (so call B pumps) + Next preferred option: new ion pumps to be installed on NL12 and NL13. + 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] NL12 Removal + [2016-06-08 Wed] C50-12 Installation * 1.3.2 Proposed Schedule + Warm up on NL12, NL13 starts when beam terminates [2016-06-22 Wed] + Installation group to work 5th pass separator, 6T YR removal in parallel with module warm up: [2016-06-22 Wed]--[2016-06-27 Mon] + When NL11, NL12, NL13 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 NL12 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.

The Follow-up It has been about six months since the February 29 mini-workshop 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.