Produc duction o n of INFN NFN TTC Meeting, East Lansing, 21 – 24 February 2017 medium me um be beta cavi vities s for ESS SS From the design to the Vertical Test of the cavity prototype integrated in the tank Paolo Michelato on behalf of the LASA group Paolo Michelato
Cavity RF Parameters INFN Design TTC Meeting, East Lansing, 21 – 24 February 2017 Parameters INFN design ESS spec. ≥47 R iris (mm) 50 • Design philosophy: Geometrical beta 0.67 0.67 - Boundaries fully Frequency (MHz) 704.42 704.42 compatible to ESS Acc. length (m) 0.855 0.855 requirement. 1.55% ↗ (+26%) Cell to cell coupling k - We design the cells! π -5 π/ 6 mode sep.(MHz) 0.70 ↗ (+30%) >0.45 • Our goal: G (Ω) 198.8 Optimum beta, β opt 0.705 0.705 - To have large cell-to-cell Max R/Q at β opt (Ω) 374 ↘ (-6%) coupling factor, k>1.5% E acc at β opt (MV/m) 16.7 16.7 - Allowing for a slight 2.55 ↗ (+7%) E peak /E acc modest sacrifice on E peak E peak (MV/m) 42.6 < 45 and R/Q 4.95 ↗ (+3%) B peak /E acc (mT/MV/m) >5 × 10 9 >5 × 10 9 Q 0 at nominal gradient 7.8 × 10 5 5.9~8 × 10 5 Q ext Paolo Michelato
Cavity Mechanical Parameters INFN Design TTC Meeting, East Lansing, 21 – 24 February 2017 INFN Mechanical parameter Pressure test scenario: Design - Cavity fully constrained Cavity wall thickness (mm) 4.5 - Pressure in the tank Stiffening ring radius (mm) 70 Internal volume (l) 69 The maximum pressure difference allowable is Cavity internal surface (m 2 ) 1.8 - 2.60 bar for 50 MPa VM (worst scenario) Stiffness (kN/mm) 1.7 - 3.64 bar for 70 MPa VM (best scenario) Tuning sensitivity K T (kHz/mm) -210 Vacuum sensitivity K V for 31 K ext ~ 21 kN/mm (Hz/mbar) LFD coefficient K L for -1.7 K ext ~ 21 kN/mm (Hz/(MV/m) 2 ) Scenario: - Cavity with one free end - Increasing displacement on free end The maximum displacement allowable is - 2.59 mm for 50 MPa VM (worst scenario) - 3.60 mm for 70 MPa VM (best scenario) Paolo Michelato
Frequency and length evolution TTC Meeting, East Lansing, 21 – 24 February 2017 • A key point in the cavity fabrication is the estimation of the cavity frequency just after production and before any treatment, because at this frequency we need to produce the DB. ∆ f Effect Cavity Frequency [MHz] [MHz] Cavity @ 2K in vacuum - 704.42 Tuner pre-load -0.2 704.22 Cavity @ 300K in vacuum -1.03 703.19 Cavity @ 300K in air -0.23 702.96 Cavity @ 300K in air before BCP +0.58 703.53 (180 µ m) Paolo Michelato
DB fabrication TTC Meeting, East Lansing, 21 – 24 February 2017 • The DBs have been trimmed to proper length («frequency») taking into account also the step- and-recess needed for cavity assembly. Paolo Michelato
Cavity Composition TTC Meeting, East Lansing, 21 – 24 February 2017 • Mechanical after welding • Based on relaxed tolerances from CEA, the cavity length foreseen is 1259.4 ± 3 mm. • The MB001 length after welding was 1256.88 mm • Frequency • The expected frequency, as reported before, was 703.53 MHz. • The MB001 frequency after welding was 703.52 MHz • Field Flatness • After fabrication, FF ≈ 70 % Paolo Michelato
Surface treatments fully done at the industry (EZ) TTC Meeting, East Lansing, 21 – 24 February 2017 • Bulk & final BCP: 1:1:2 • BCP1: 60 min, subdivided in 2 steps (20 min + 40 min). • BCP2: 90 min, cavity is turned upside down. • Heat treatment at 600 °C, 12 h • Final BCP (15 min) Cavity weight monitoring for each treatment For each BCP treatment, barrel and output acid temperature are acquired, together with acid throughput 6 thermocouple sensors (t1,…,t6) are placed on cavity surface, continuously acquiring temperature during chemical etching IR camera with standard emissivity dots monitoring during BCP A Nb sample is placed inside cavity (through MC) for monitor etching rate and RRR variation Cavity thickness measurement with ultrasound gauge before and after etching Paolo Michelato
BCP treatment TTC Meeting, East Lansing, 21 – 24 February 2017 BULK BCP1 A BCP1 B BCP2 Final BCP STEP BCP 20 min 40 min 90 min 15 min total Cavity weight change (g) 434 795 1685 2914 22 Cavity removed thick. ( µ m) 28 51 109 188 (expected) Cavity etching rate ( µ m/min) 1.4 1.3 1.2 Sample weight change (g) 1.53 3.08 4.15 1.20 Sample removed thick. ( µ m) 40 81 110 32 Sample etch. rate ( µ m/min) 2.0 2.0 1.2 2.10 Acid throughput: 20 l/min Nb sample Paolo Michelato
BCP treatment TTC Meeting, East Lansing, 21 – 24 February 2017 BCP1 A: 20 min 35 60 t1 t2 30 50 t3 throughput (L/min) Temperature (°C) 25 40 20 30 15 20 10 t4 10 t5 5 T tank t6 0 0 16:32:10 16:37:55 16:43:41 16:49:26 16:55:12 t1 t2 t3 T out t4 t5 t6 Nb sample T tank throughput T out Acid flow Paolo Michelato
Annealing and dehydrogenation TTC Meeting, East Lansing, 21 – 24 February 2017 700 1.E-04 600 Temperature 500 Pressure 1.E-05 P (mbar) 400 T (°C) 300 1.E-06 200 100 0 1.E-07 0 500 1000 1500 2000 2500 3000 3500 4000 1.0E-5 H2 H2O N2 O2 CO2 TPressure 1.0E-6 H 2 1.0E-7 Pressure (Torr) 1.0E-8 1.0E-9 1.0E-10 1.0E-11 0 500 1000 1500 2000 2500 3000 3500 4000 Paolo Michelato Minutes
Annealing and dehydrogenation TTC Meeting, East Lansing, 21 – 24 February 2017 700 1.E-04 600 Temperature 500 Pressure 1.E-05 P (mbar) 400 T (°C) 300 1.E-06 200 100 0 1.E-07 0 500 1000 1500 2000 2500 3000 3500 4000 1.0E-5 H2 H2O N2 O2 CO2 TPressure 1.0E-6 H 2 1.0E-7 Pressure (Torr) 1.0E-8 1.0E-9 1.0E-10 1.0E-11 0 500 1000 1500 2000 2500 3000 3500 4000 Paolo Michelato Minutes
Treatments: Iris Equator ratio TTC Meeting, East Lansing, 21 – 24 February 2017 • A simple model as well as a code are used to analyze the Iris/equator removal ratio in each BCP. A cross-check of calculated weight for the estimated ratio and the measured weight shows good consistency. • Calculation shows the iris/equator removal ratio ranges from 1.1 to 1.5. dF π BCP Weight Ave.remov Fsens Ir/Eq dR eq dR ir Weight dW/ meas (g) (kHz) (um) (kHz/um) (um) (um) estm (g) W 1A 434 28 -2.2 1.5 22 34 409 - 6% -62 1B 795 51 -3.0 1.1 49 54 776 - 3% -155 2 1685 109 -2.8 1.2 99 119 1651 - 2% -306 Paolo Michelato
RF Parameters after final tuning TTC Meeting, East Lansing, 21 – 24 February 2017 • Frequency at 300 K: 702.9 MHz • Field Flatness: > 97 % • HOM measurement Measurement Fsim = 1740 MHz Simulation About 2.5 MHz lower than the one at 2K. Paolo Michelato
LASA Installation of the naked cavity for cold test TTC Meeting, East Lansing, 21 – 24 February 2017 Paolo Michelato
Cavity properties TTC Meeting, East Lansing, 21 – 24 February 2017 • Frequency @ 2K 704.213 MHz (as expected) • Length @ room temperature • 1257.6 mm Paolo Michelato
Power Rise @ 2K TTC Meeting, East Lansing, 21 – 24 February 2017 100 W CW cryo power, i.e. 16,7 MV/m @ Q 0 5e9 Paolo Michelato
MP and SEY TTC Meeting, East Lansing, 21 – 24 February 2017 • MP simulations with “FishPact” and “MultiPac” codes consistently show that stable trajectories of 1 st order two-point MP appear in a very small region near equator center, with E acc in range from 7 to 14 MV/m and a maximum impact energy (Ef) around 30 eV at E acc = 11 MV/m. • We do expect soft barriers if the initial SEY is higher. 35 SEY for Nb Inner cell 30 End cell 25 Ef(eV) 20 15 10 5 6 7 8 9 10 11 12 13 14 15 Eacc (MV/m) End Cell Inner Cell Paolo Michelato
Radiation TTC Meeting, East Lansing, 21 – 24 February 2017 Radiation due to multipacting is seen in the first cold test, but it was conditioned. In fact, it disappered during the second test done just after some minutes. The data are consistent with the simulation. Paolo Michelato
Radiation TTC Meeting, East Lansing, 21 – 24 February 2017 100000 10000 X ray spectrum @21.5MV/m 1000 counts 100 10 1 0 500 1000 1500 2000 2500 3000 3500 Energy (keV) 2.5E+2 20-22 MV/m (quench field) 2.0E+2 uSv/h 1.5E+2 Conditioning 1.0E+2 ∼ 10 MV/m attempt 5.0E+1 0.0E+0 19:40:48 20:09:36 20:38:24 21:07:12 21:36:00 22:04:48 22:33:36 time Paolo Michelato
HOM TTC Meeting, East Lansing, 21 – 24 February 2017 • The monopole mode close to 5th machine line - Directly measured at 2K, F = 1741.8 MHz (>19 MHz from machine line at 1761.05 MHz) - Close to expected value, <1 MHz to simulation at 1742.4 MHz. Paolo Michelato
Tolerances Q ext sensitivity to fabrication errors TTC Meeting, East Lansing, 21 – 24 February 2017 • Selected values in the following table are based on practical mechanical tolerances in cavity fabrication process. Mechanical Q ext variation Dimention Etching effect in 68 + 0.15 mm 7.8E5 - 0.12E5 beam pipe (A) A EndCell distance to C 35 ± 0.1 mm 7.8E5 ± 0.05E5 coupler port (B) B Antenna tip to 60.26 ± 0.1 mm 7.8E5 ± 0.06E5 D cavity axis (C) Coulper port E blended edge 7 ± 1 mm 7.8E5 ∓ 0.07E5 radius (D) Inner conductor of antenna distance 85 ± 0.1 mm 7.8E5 ± 0.03E5 to EndCell iris (E) Paolo Michelato
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