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Busbars WP3 WP6a
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Europe/Zurich
Present: Amalia Ballarino, Luca Bottura, Arnaud Devred, Attilio Milanese, Vittorio Parma, Hervé Prin, David Richter, Christian Scheuerlein, Ezio Todesco
Arnaud started the meeting, recalling that all the stakeholders are together, to discuss the “something” (in terms of cabling) that goes from the magnet leads to the sc. link.
Ezio presented a summary of the current baseline for the busbars Q1 to D1 (presentation done in MCF in January 2019).
- This covers the 1.9 K part of the circuit, without looking at the local powering of the high order correctors.
- Flat busbars go through the quadrupoles for their series powering: they will be provided by the US, and CERN will provide the Nb-Ti cable (same geometry as the leads of the magnets).
- The round cable for the N lines was chosen for its advantages in terms of handling and curvature radius. Two such 18 kA class cables have been produced by VKINP; a certain length was shipped to CERN and it’s available in LMF, though its actual cross section doesn’t seem to match the geometry shown by ET (slide 5). No engagement with VKINP is taken for producing more round cable.
- There is a proposal for the 2 kA cable, based on the 6 kA of the LHC, although bundles of 4 (plane dipole corrector) instead of 3 are needed.
- The geometry for the 13 kA cable for the D1 is also being discussed.
- Matthias Mentink performed simulations covering the various circuits to estimate the hot spot temperatures; reports are available on EDMS.
- In Ezio’s slides, we go through the plug with flat cable, for all circuits.
- In case of quench, the maximum temperature reached by the cables was initially 100 K, now 150 K. Amalia asked the reason why the temperature was increased – tbd discussed in one of the next meetings.
- A verification that the same cables are properly designed also for 4.5 K operation (that is, past the plug) is pending.
- A possibility could be to keep the same 18 kA flat geometry to bring through the plug also the 2 x 13 kA cables.
- There is no estimate for AC losses (at the wire and cable level) for the circuits, in particular the 18 kA.
- The Magnet Circuit Forum is looking into Vtaps scheme for quench detection; the guideline is to monitor every splice.
- The insulation layers need to be clarified.
Amalia showed material taken from the Internal Review of DFX, see indico 821876.
- This covers the 4.5 K part up to the sc link. The cables protruding in plug are within WP3 and were not presented.The geometry of those cable was presented by V. Parma and corresponds to the proposal of WP3 (see presentation of E. Todesco).
- The requirements in terms of temperature margin and hotspot temperatures are different than from the 1.9 K, namely 2 K instead of 5 K for temperature margin (some difference here is likely unavoidable, as we are getting close to critical temperature), and 100 K instead of 150 K for hotspot (so WP6arequirement here is more conservative). The assumed field level might also be different. Then, the acceptance criteria for Nb-Ti splices is slightly different, < 0.5 nOhm for WP6 while WP3 had 1 nOhm (WP6a is more conservative).
- The electrical insulation requirements for WP6a were also presented (they were discussed and agreed with the MCF). H. Prin asked how the electrical insulation of a circuit is done, and Amalia answered that when one circuit is tested, all other are grounde
- Some initial round cables were made by SCD to test the curvature radii and the volume inside the DFX.
- Would these satisfy the Cu and sc requirements for the 1.9 K part, and possibly be used for the N lines? Hervé will get from Julien Hurte some samples.
- The tension applied on the polyimide tapes around plays a role in the overall stiffness of the cables. Its definition of the insulation is part of the development.
Vittorio showed slides about the development in the lambda plate, including in particular the feedthroughs.
- The design philosophy is to reuse when possible LHC experience.
- So far, two families of cables are taken to go through the plug:
o the same Rutherford cable for the 18 kA / 13 kA / quadrupole trim circuits: there is a preference not to use a round cable, to avoid launching an R&D program on high current feedthrough with a different geometry;
o a round geometry for the dipole correctors.
- Demonstrators have been made and so far the outcome is satisfactory from the point of view of leak tightness.
- Vittorio explained the procedure for making the leak tightness of the round cable. The cable if opened, and then the resin is injected, so that there is resin around the Nb-Ti wires and copper core. Amalia commented that with such a procedure there is resin between the Nb-Ti wires and the copper core, with the risk of not having sharing of current with the superconductor and the stabilizer. To be discussed in the next meeting.
- A question on a possible impact of the quench propagation for the 2 kA cables through the plug was raised, as there they lose their adjacent contact with the stabilizer, although in a rather short section.
Christian did not present material on splices (and their characterization) yet: this will be for a future meeting. Christian in fact will for the moment cover the splices for the 1.9 K side, while somebody from SCD will cover the ones in the DFX.
A follow-up meeting will be organized by Ezio in two weeks.
Minutes by A. MIlanese
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