Outgassing Measurement of PEPII ByPass Beampipe Presented to LCLSII Acc Phy Mtg 4/6/2016 Dale K. Gill

Issue PEP II ByPass Line operated with pressures in the E-6 Torr range. – LI 16 VG_7630 ~2E-7 Torr (Jan Dec 2007) 1.8E-11 Torr-L/sec-cm2 – PEP-II Measure from M. Ramos analysis 4/3/13 Pressure 5E-6 Torr (5000 nTorr) 2.5E-11 Torr-L/sec-cm2 – Simulation of PEP-II by M. Ferreira, 3/5/2014, 5E-5 Torr average over 2105 m, dominated by long pump spacing between 150 m and 400 m. 1.0E-10 Torr-L/sec-cm2.

LI 16 Pressure History Gauge located 22 m from pump, pump spacing 100 m.

Bypass Vacuum LCLS-II Requirement 4 LCLS-II Requirement Current: Proposed: 100m 200m 300m 100m 200m PEP-II Measured 3.5E-6 Torr Average

5 Simulation by M. Ferreira, 3/5/2014 using PRESSUR5 Program

Long Tube Formula Fit Measurements Engineering Note LCLSII- Test Method – Ion Gauge at end of long tube. – Ion Pump at other end. – Fit gauge reading to Long Tube Pressure formula using Excel spreadsheet OneD by Scott DeBarger. Adjust assumed outgassing rate to match gauge reading.

Tube on Bake Station

Gauge Readings after 80 hours 120 C dehydration bake. Fitted outgassing rates Long Tube 1.3E-10 Torr-L/sec-cm2 Short Tube 1.8E-10 Torr-L/sec-cm2

Outgassing Rate after bake at 250 C 24 hours baking – Long Tube 2.45E-10 Torr-L/sec-cm2 – Short Tube 4.53E-10 Torr-L/sec-cm2. – Issues with result Insufficient cool down time, tubes not at 20 C. 86 hours baking – Long Tube 1.23E-10 Torr-L/sec-cm2 – Short Tube 1.85E-10 Torr-L/sec-cm2

Issues with Measurement Bake Station Base Pressure was too high – Station had been heavily contaminated by previous hardware. – Clean up of station resulted in acceptable RGA spectrum. – Base pressure was only low E-8 Torr. Not flagged prior to test. Ion Gauge Controller – Taken from storage and calibration not evaluated. – Post measurement comparison with Bake Station Controllers showed major mis-calibration. Test Gauge Controller/Manifold Gauge Controller = 8.7 Test Gauge Controller /IP Gauge Controller = 5.0

Scaled Outgassing Rates Scaled DateLongShortHours at 250 CHours cooldown 9/29/ E E /2/ E E /6/ E E /16/ E E Measurements on 10/16/2015 were on second bake station with acceptable base pressure.

Orifice Outgassing Measurement Sample tube removed from PEPII LE bypass (SIT line) at beginning of sector 30, between ion pump at 2997 m and beam stopper at 3002 m. Sample tube stored pinched off.

Test Method Throughput method. Calculated Conductance orifice. Two gauge pressure drop measurement

Photo of Assembly

Ion Gauge Controllers

Gauge Errors Evaluated

Long Tube Sample on Bake Oven

RGA spectrum of Dehydration Bake

RGA Trend during Outgassing Test

Delta P across Orifice Average pressure drop 5.23E-9 Torr, sample standard deviation 1.49E-9 Torr, nitrogen equivalent pressure.

Calculated Outgassing Rate Convert to hydrogen pressure – Ionization factor 0.46 hydrogen/nitrogen. – Hydrogen pressure drop 1.14E-8 Torr Orifice Conductance – 1.83 L/sec hydrogen. Sample Tube surface area – 6197 cm2 Outgassing rate – 3.36+/-0.96E-12 Torr-L/sec-cm2

Summary of Outgassing Data SourceDateReported RateCorrected to Hydrogen OneD modeled average pressure, Hydrogen conductance M. Ramos assumption 4/3/ E-11no1.76E-7 M. Ferreira Pressur5 fit to PEPII archived data 3/5/20141E-10unknown7.02E-7 Long Tube Fit10/20/ to 6.75 E-12yes2.95 to 4.74E-8 Fit to LI 16 PEPII archived data 3/31/ E-11yes1.26E-7 Orifice Measurement 4/4/ E-12yes2.36E-8