Low-power test results and analysis of the modular cavity D. Bowring 1 with A. Haase 2 , T. Luo 3 , and J. van Pelt 2 1 Fermilab, 2 SLAC, and 3 LBNL May 11-15, 2014 D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 1 / 18
1. Introduction D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 2 / 18
Work done between May 11 and May 15, 2014 What was done? Repair N-to-975 adapter piece 1 With dead-soft OFHC Cu gaskets 2 and no vacuum seal, measure RF properties as a function of By whom? clamping bolt torque. Andy Haase (SLAC) Open cavity, replace gaskets, seal 3 cavity again. Tianhuan Luo (LBNL) Repeat item # 2. 4 John van Pelt (SLAC) Profilometry on gaskets to assess 5 Daniel Bowring (FNAL) “knife edge” indentation on gasket. Check for variation with angular position. (This work is in progress.) Discuss/plan for final proposal & 6 discussion at MAP meeting. D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 3 / 18
Summary of results We observed critical coupling using both sets of gaskets. Tightening clamp bolts improved RF properties monotonically and asymptotically. We observed no significant change between 70 inch-pounds of torque and 90 in-lbs in either case. Measurements were repeatable on loosening/re-tightening clamp bolts. The details of this repeatability have interesting implications for repair options, to be discussed later in this talk. D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 4 / 18
2. May 11, 2014 D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 5 / 18
Tianhuan assisted with measurements on May 11, 2014 1 Prior to her visit, the vacuum gaskets were removed from the cavity. The dead-soft, OFHC Cu RF gaskets were left in. 2 During shipping, the N-to-975 adapter piece was damaged. This damage was repaired. We observed some minor loss in the system during measurement (see below) that may be explained by this damage/repair process. 3 Bolts tightened with a torque wrench in 10 inch-pounnd increments. Frequency, Q measured at each increment. 4 Asymptotic behavior observed at and above 80 inch-pounds. D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 6 / 18
Tianhuan assisted with measurements on May 11, 2014 90 in-lb torque f0 f1 f2 f3 f4 804.615 804.633 804.598 804.648 804.581 6 6 9 9 3 Ql 11903 beta 0.948 Q0 23188 Qe 24408 D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 7 / 18 Ql measured by s21 -3dB points is 11893.
3. Photos from gasket swap D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 8 / 18
Gasket swap on May 15, 2014 D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 9 / 18
Gasket swap on May 15, 2014 D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 10 / 18
Gasket swap on May 15, 2014 D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 11 / 18
Gasket swap on May 15, 2014 D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 12 / 18
Gasket swap on May 15, 2014 D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 13 / 18
Gasket swap on May 15, 2014 D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 14 / 18
Gasket swap on May 15, 2014 D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 15 / 18
4. RF measurements on May 15, 2014 D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 16 / 18
RF measurements on May 15, 2014 β ≈ 1, f = 804 . 65 MHz. D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 17 / 18
Coupling is repeatable under repeated bolt tightening/loosening. After measurement at 100 inch-pounds, loosen upstream bolts to finger-tight. Tightening/loosening bolts moves repeatably between outer/inner circle. ∼ 10 o tightening on two bolts is sufficient to make this transition! D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 18 / 18
Interpretation of easily repeatable coupling transition End plate, gasket deform during clamping to make RF seal. Good news: This is demonstrably easy in this case. Bad news: We don’t control the deformation! This gives further support to SLAC’s proposed clamp ring re-design. c.f. “push bolts”. D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 19 / 18
What now? 1 SLAC will make their complete proposal at the MAP meeting. 2 On Tuesday they’ll circulate a written report so we can all be on the same page, prepared for the MAP meeting. 3 They’re currently evaluating a design that uses Mo-alloyed “super bolts”. These would eliminate the need to drill/tap new holes in the cavity. 4 I have a lot of photos to upload to the MTA site. D. Bowring (FNAL) Modular Cavity Status May 11-15, 2014 20 / 18
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