Minutes of the LRFF Task Force
15th meeting on Tuesday 16/10/2012 (09:00-11:00 max, 6-R-018)
LRFF members: Alessandro Bertarelli (AlessandroB), Alexej Grudiev (AG), Benoit Salvant (BS), Elias Metral (EM), Fritz Caspers (FC), Giuseppe Bregliozzi (GB), Hugo Alistair Day (HD), Jose Miguel Jimenez (JMJ), Marco Garlasche (MG), Mike Barnes (MB), Olav Ejner Berrig (OB), Oleksiy Kononenko (OK), Oliver Aberle (OA), Ralph Assmann (RA), Raymond Veness (RV), Rhodri Jones (RJ), Roberto Losito (RL), Sergio Calatroni (SC), Stefano Redaelli (SR), Vincent Baglin (VB), Vittorio Parma (VP), Wim Weterings (WW).
Present/Excused: AlessandroB, AG, BS, EM, FC, GB, HD, JMJ, MG, MB, OB, OK, OA, RA, RV, RJ, RL, SC, SR, VB, VP, WW, Christine Vollinger, Oliver Aberle, Carlo Rossi.
1) Comments on the last minutes + Actions
- REMINDER: UNLESS EXPLICITELY MENTIONNED THE LRFF MEETINGS START AT 09:00 (sharp... as some people have other meetings at 10:00 or 10:30).
- All the actions (18) of the last meeting were reviewed to agree again on what remains to be done.
- For Action 4 "Take into account the temperature dependence of the mu' and mu" of the ferrite for the future power loss estimates", as it was mentioned, it is a coupled problem with the thermal analysis (i.e. between Impedance team and AlessandroB's team) => Coupled simulations needed in principle but the idea is to see by how much it could change the power loss estimate.
- The actions 7 and 8 will be discussed today.
- For Action 9 "How can we cool the ferrite if it becomes too hot? FC is in contact with some people to try and improve the conduction from ferrite as most of the time only radiation is used (given the general brittleness of the ferrite we cannot apply big contact). What are the future possible solutions?", FC will report in the future about his current studies (in particular with plasma spray etc. and collaboration with some university).
2) Measured TT2-111R ferrite's properties - EM-wise (ChristineV): pptx + additional slide (after the meeting)
- 1st slide shows a material measurement provided by the manufacturer (TT = Trans-Tech). Note that the maximum of mu" is at ~ 10 MHz. We have a rough idea of how they measured it, using the torus method. It is a good standard method but the only pb is that we have to cut material for this and cutting ferrite is always delicate as ferrite is very brittle.
- Comment/suggestion from FC: why cutting the material (as it is brittle etc.)? It is much simpler to machine metal than ceramics with adequate precision. In this case (with ferrite) he thinks that one should build the measurement device around the ferrite => This is what they did and what they report about, using readily available ferrite tiles of 6 cm * 6 cm * 5 mm thickness, and a transmission measurement method.
- Nice pictures of the measurement device and SH (Sample Holder), which we could even touch and look at during the meeting.
- Mode conversion (above some frequencies a mode split into several ones): in practice it is not an issue according to FC.
- FC and ChristineV did the reverse calculation about what TT did to see how the S21 should look like. They used they exact analytical computations (which should appear in the note they are currently writing and should publish soon). Their measurements are then compared to the ones from TT, which are similar but different => Difficult to say which numbers are more correct... As mentioned by AG the TT method was made many years ago and it might depend on the sample and/or technicians who made the measurements at that time => Maybe more precise to consider the new measurements. But, for practical applications the difference between the 2 results are not relevant. See also the additional slide sent after the meeting which reveals a good agreement with measurements by W. Barry et. al., (1993, LBL-33734 , p. 14).
- Reminder: The penetration as a function of frequency is the important parameter in the end => See more discussions about this foreseen for the 17th meeting (on 30/10/12). ~ 1 cm is the ferrite penetration depth they deduced at ~ 1 GHz from their measurements.
- Comment: We should measure up to ~ 2 GHz as it is important for the LHC. AG reminded us that for CLIC we should go up to 40 GHz.
- Reminder from FC: up to ~ 3-4 GHz, there is no electric loss but then it starts => One should be able to have measurements until ~ 3-4 GHz.
- Question from AlessandroB: what is the practical recommendation for the ferrite thickness? FC mentioned that it does not make sense to make the ferrite thickness larger than ~ the ferrite penetration depth => Will be discussed in more detail during the 17th meeting on 30/10/12 (see Action 1 below).
- Slide 7: With the short (closer to TT method) they can reproduce the bump.
- They don't want to go below 100 dB and this is why they want to reduce the length of the sample to go to higher frequencies. They don't think they have significant air gaps in their measurements.
- The method can also be used for SiC => AG discussed this with FC and ChristineV after the meeting.
- Would be interesting also in the future to benchmark also with CarloZ et al's measurements.
3) Measured TT2-111R ferrite's properties - vacuum-wise (VB): pptx
- VB presented the ferrite outgassing results for future LHC collimators (TCTP).
- Vacuum requirements for the LHC collimators (M. Jimenez, EDMS 428155):
- UHV cleaned according to CERN specification,
- Thermal treatment / vacuum firing of material (ex ferrite, CFC, tungsten),
- Material to follow bake out at 250C for 24h00 (48h00 for collimator),
- Specific material outgassing flow rate ≈ 10E-12 mbar.l / (s.cm^2),
- Maximum outgassed flow of one collimator 10E-7 mbar.l / s.
- Vacuum validation test of the ferrite (TT2-111R from Skyworks supplier):
- Thermally treated under: Air furnace at 400C for 24h00 + vacuum furnace at 400C for 24h00 (which is a recipe from past experience).
- Vacuum test cycle carried out: 250C under vacuum for 24h00 + RGA (Residual Gas Analyzer) analysis + Ultimate pressure record for total N2 equivalent outgassed flow measure by conductance method.
- Extended thermal study: Measure of outgassing flow by accumulation (accumulation means you insert a device inside a vacuum box and we let the sample outgas for some time, then we open the valve and we measure the gas going outside.), from R.T. to 250C.
- The noticeable TCTP collimator's features are
- Total (huge) surface of ferrite per collimator, equal to 1600 cm^2.
- Tungsten is the constitutive material of the jaws (with a total surface of 2300 cm^2) => OK with the LHC vacuum specification.
- Ferrite's outgassing results:
- The results were not very good compared to other ferrites (at RT it is 1 order of magnitude above the SS...),
- A factor 10 can be gained in outgassing rate for 100C temperature increase,
- Scaled to the TCTP collimator, it would mean an outgassing per TCTP collimator of 9E-8 mbar.l / s, i.e. very close to the LHC specification limit of 10E-7 mbar.l / s => No margin left!
- RGA => No contamination visible up to mass 100.
- Conclusions:
- The estimated outgassing flow of 1 TCTP collimator is 9 10E-8 mbar.l / s, which is is already very close to specified limit of 10E-7 mbar.l / s => No margin!
- If the temperature will increase from RT to 50C => Outgassed flow will double.
- If the temperature will increase from 50C to 100C => Outgassed flow will increase by a factor 10.
- RGA analysis shows no contamination
=> The present solution does not present any safety margin in order to remain within the LHC vacuum specification should the ferrite temperature increase.
=> VSC proposal: Vacuum test of ferrite with increased thermal treatment temperature (see Action 2 below).
- OliverA mentioned that the dimensions of the ferrite used for the vacuum tests (provided by OliverA) are smaller than the ones used by ChristineV and FC for their EM measurements => They might want also to measure this ferrite to see the effect of a smaller length (see Action 3 below).
- Reminder: We are always limited by the conducatnce of the tube => 10 l / s is a good order or magnitude.
- Reminder: the higher the temperature the higher the outgassing and therefore the shorter time we have to wait => Typically we need ~ 2 weeks.
- Reminder on the outgassin plots: on the right we have RT (Room Temperaturea) and then each point corresponds to 50C.
- Note that the MKI ferrites (behaving better) have been burned at 1000C.
- Reminder: TT2-111R was developed for the AA and therefore is was expected to be very good for vacuum.
- We know that 8C11 is also a very good ferrite (which we put in the VMTSA) for outgassing (but the Curie temperature is much lower than the one for TT2-111R... this was the point).
- Question from VB (see Action 3 below): what is the beam behaviour with some pressure bumps? => VB et al. will redo the outgassing tests and then they will present the vacuum profiles and we will see what we can do with them.
- Reminder: One can gain a factor 10 in outgassing with NEG as the NEG coating can absorb only 1 monolayer of gas, whereas with a cryo pump you can pump for ever.
- In CLIC they use SiC and there is a standard treatment (1000 deg?).
- Reminder: With the RGA, we see the residual gas composition vs. mass and we can in particular identify the presence of hydrocarbons, particularly critical as they have large cross sections.
4) Actions
- Old actions.
- New actions:
- Action 1 (EM and impedance team): Practical recommendation for the ferrite's thickness to be used.
- Action 2 (VB): Update of the estimated outgassing flow of 1 TCTP collimator after new vacuum test of the TT2-111R ferrite with increased thermal treatment temperature.
- Action 3 (ChristineV and FC): OliverA mentioned that the dimensions of the ferrite used for the vacuum tests are smaller than the ones used by ChristineV and FC for their EM measurements => Might be good also to measure this ferrite to see the effect of a smaller length.
- Action 4 (EM): Question from VB: what is the beam behaviour with some pressure bumps? => VB et al. will redo the outgassing tests and then they will present the vacuum profiles.
5) Miscellaneous
- The next (16th) meeting will take place on 23/10/2012 between 09:00 and 11:00 (max.) in room 6-R-018 => Agenda:
1) Follow-up of the previous actions (everybody) => Starts to become URGENT!
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 25/10/2012.