1. Experience for vacuum plants during XFEL cavity production at companies and at LASA Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay Paolo Michelato INFN – LASA TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 2014

2. General comments on vacuum plants used for XFEL cavity production Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay Unusual operational conditions: many pumping and venting operations, in some cases many tens/week. Consequences and actions a)Impact on system reliability, e.g. shorter lifetime of TMP and of scroll pumps with respect to usual operative conditions. Service must be done more frequently than foreseen, great attention to precursor of failures (noise, bad vacuum, etc) b)RGA SEM sensitivity large decrease (at least in one firm, using RGA with MCP electron multiplier). Sum of the values of pp doesn't give the total pressure, error could be orders of magnitude! Signal/noise ratio reduced! Frequent calibration operation or use of RGA as a “percent” meter or ion current meter and normalization is done later. Fixed (partially) using a valve on the RGA.

3. Janez Setina, Vacuum Symposium 2011 Well known problem! But not for order of magnitude in few months! Someone had similar experience?

4. General comments on vacuum plants used for cavity production (cont.) Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay Unusual operational conditions: many pumping and venting operations, some tens/week. Consequences and actions a)Accumulation of impurities: all times the system will pump a “new” chamber, the cavity with its amount of contaminants. If they are transferred to the vacuum system, for instance during 800 °C or 120 °C treatment, and they have a low vapor pressure, they could be accumulated on the vacuum system. Transfer mechanism of these compounds could be intricate, due to memory effects. Vacuum quality becomes worst. To avoid and / or control this effect, a bake out (120°C) could help a lot maintaining the vacuum systems more clean (done in one firm). ANY SIMILAR EXPERIENCE IN OTHER LABS? Rga No sulfur! Mass 64? Phtatales? Where? Everywhere! Correlations: no correlations. Venting EZ Ar 6.0, Bake out: periodically, typ 1time/week

5. SPSV system at the firms for XFEL cavities Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay Both firms use a similar architecture and technique Dry primary pump Hybrid TMP (High compression ratio for He) Large MFC to control gas throughput in the pumping line Small MFC for the venting High quality (6.0) filtered (40 nm) gas for venting, Ar or N 2 Diffuser on the venting line (3 nm) Optimized timing strategy for reducing pressure bumps (valves) RGA on the high vacuum side Dedicated commercial He mass spectrometer for leak detection connected on the TMP discharge line 10 -9 mbar range Cal leak (specs leak rate < 1x10 -10 mbarl/s) PLC controlled, all data are stored in a server.

6. EZ slow pumping slow venting system Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay Courtesy EZ

7. SPSV system at LASA for the 3.9 cavities Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay Reduced number of cavities: 10 x 3.9 GHz for the third harmonic system Different strategy used with respect to usual SPSV: forevacuum pump is stalled during first part of pumpdown by the flow coming through the venting line. After the equilibrium conditions are reached (few tens of seconds, i.e. the same throughput in the pump and in the venting line, no pressure change) the venting MFC start to reduce its opening and therefore pressure is going down. Advantages: reduced pressure bump, MFC are already operative when the pressure start to decrease.

8. SPSV system at LASA (cont) Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay Direct flow leak detector, MS sensor head installed in the high vacuum side (Inficon LDS1000), while its TMP is on the foreline line. Two TMPs in series, for higher compression ratio Differential MKS capacitive sensor (100 mbar) for check the end of the venting procedure, controlling that a small overpressure on the cavity (5 mbar) is present. Controlled by an industrial microcontroller (Saia Burges) Labview interface only for visualization

9. INFN - LASA slow pumping slow venting system Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay

10. RGA and vacuum quality: some comments Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay Hydrocarbon free vacuum, for the XFEL, is defined when the ratio between the total pressure, as the sum of partial pressures, and the highest contaminant partial pressure is over a factor 1000. Drawbacks using this definition: if total pressure is quite low, as after the 120 deg heat treatment, the partial pressure of contaminants is quite low as absolute value, but could be significant with respect to the total pressure (> 1/1000). Effects of contaminants are related to their partial pressure absolute values and not (directly) to their ratio with the total pressure. It would means that vacuum quality would be better if the partial pressure of water or mass 28 is higher, maintaining constant the partial pressure of contaminants! But there is the problem of SEM degradation…

11. RGA spectra interpretation and contaminants Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay In many spectra anomalous mass 32 high, wrt air leak (but no leak!) Mass 64: may be sulfur, but the relative isotopes abundance for mass 32 and 34 are not in good agreement with mass 64. Sulfur concentration in the ethanol is quite low. Some “unusual” compounds: around mass 50, mass 58, 79 and 91 Sources: in my opinion some low concentration contaminants that are accumulated in the vacuum system, that have a low vapor pressure and that are difficult to be removed. As for phthalates, long chain alkanes, etc. Investigation on UPW and ethanol are under way.

12. RGA spectra: some example Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay At the end of the 120 °C treatment, total pressure 3x10-8 mbar

13. RGA spectra: some example Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay At the end of the 120 °C treatment, the final treatment. Total pressure 3x10 -9 mbar. Contaminant level is in the 10 -12 mbar range. 55, 56 64 77, 78

14. RGA spectra: some example Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay Intermediate leak check, after the 800 °C annealing Total pressure: 5x10 -7 mbar 50 - 5864 77, 78 32! 91

15. Effects on cavities? Paolo Michelato TTC Topical Workshop on SRF Cryomodule Clean Room Assembly, November 12 – 14 2104, CEA Saclay Up to now, we are sure that trivial problems as vacuum system malfunctioning, human error, not correct venting, etc produces dramatic effects on the accelerating field. One cavity vented with not filtered air had shown an accelerating gradient of few MV/m while, after HPR, the cavity was completely restored. Up to now, from preliminary investigations, no correlation had been found between the partial pressure of contaminants and the cavity performances. Why differences between two cavities treated together? Or one just after the other? While differences in the accelerating gradient could be caused by human factor (FE) what is the reason for Q 0 differences also at low field? Good question…