Minutes of the 10th LHC Insertions Upgrade Working Group held on 21st February 2008
Present: F. Cerutti, S. Chemli, S. Fartoukh, P. Fessia, N. Kos, J.-P. Koutchouk, K.H. Meß, Y. Muttoni, D. Nisbet, R. Ostojic, V. Parma, L. Tavian, E. Todesco, D. Tommasini, R. Van Weelderen, E. Wildner
Excused:
Invited: J. Bruer, F. Butin, M. Mauri, A. Mereghetti, R. Tomas
1. News and approval of the minutes of the last meeting
The minutes of the last meeting are approved without any comments.
2. Alternatives for the D1 separation dipoles (D. Tommasini, ppt file)
Davide first summarized the various requirements on D1, in particular in terms of aperture (e.g. 120 mm gap for a warm D1) and integrated strength (see also minutes of the LIUWG#6). Based on these requirements, Davide then discussed three possible options for D1, all with some draw-backs and advantages in terms of cost, running cost, cryogenic consumption and possibility of reusing some already existing hardware.
- a normal conducting D1, based on the design already proposed by M. Karppinen at the LIUWG#6, which would be compatible with the powering scheme and the cooling stations of the actual D1. The overall cost of this new D1 is estimated to be around 7.5 MCHF (for 2*2*6 modules and two spares), with a high running cost of about 0.5 MCHF/year (assuming a flat top running of 5000 hours per year).
- a super-ferric D1, a bit more compact than the previous version, working at an operational temperature of 4.2 K, therefore with a moderate additional load onto the cryogenic system, but requiring new PC's of 8.5 KA. The overall cost is estimated to about 6 MCHF for this option (2*2*6 modules and two spares, not including the new PC's).
- a single-layer super-conducting D1, based on the present well characterized Nb-Ti technology (LHC dipole type cables). This option is very attractive in terms of magnet compactness (one single 6-7 m long D1 magnet per IP side, fitting into the actual vacuum vessel of the LHC main dipoles and equipped with two 80 mm diameter heat exchangers). However, as for the previous version, this option would require new power supplies of 10.5 kA. The overall cost is estimated to be less than 5MCHF in this case (for 4 magnets, plus one spare, not including the new PC's). This superconducting D1 would operate with a comfortable margin, more precisely with a peak field of 4.5 T at 1.9K. However, depending on the heat deposition generated by the debris coming from the IP (50 W per D1 as roughly estimated by Davide but possibly a factor of 2 optimistic for the target luminosity of phase I), the cryogenic consumption of this new D1 would be far from being negligible compared to the 400W @ 1.9 K capacity reserved for the inner triplet.
Davide's presentation triggered several comments and questions.
RVW asked whether the operating temperature of the proposed super-conducting D1 could not be increased to 4.5 K in order to avoid increasing the load onto the 1.9K cryogenic loop. This question raised some going forth and back but the final conclusion was that D1 could a priori operate with the same field at 4.5K as its short sample margin would pass from 55% @ 1.9 K to about 80% at 4.5 K. The length of the magnet would therefore not need to be changed (but, of course, the final length would be confirmed after a full design).
SF commented that the 120 mm aperture requirement for D1 refers in fact to the gap height of a warm D1. In case D1 is cold, its aperture should be similar, if not identical, to that of the inner triplet quadrupoles (e.g. 130 mm). Davide took note while arguing that this new D1 could be easily reoptimized for an aperture of 130 mm, and even possibly 140 mm.
ET insisted on the fact that a super-conducting D1 would be a low cost magnet, using a well-characterized technology.
JPK commented that the new D1 should be ideally compatible with the phase II requirement, that is in particular an aperture of about 160 mm. He then asked what is the variation of the cost with aperture for the different options envisaged. Davide replied that a 160 mm gap height is a priori excluded for a normal-conducting D1 (cost increase of about 1 MCHF/10 mm, see Mikko's presentation at the LIUWG#6). Such an aperture would be at the limit for a cold D1, but a priori still accessible for a two-layer super-conducting D1, provided a sizeable increase of its length. Then, Davide concluded that a super-ferric D1 could be a priori the most promising option to go towards very large aperture.
SF informed the audience that R. Tomas already set up a local crab-cavity scheme, located in between D1 and D2. This would require an inter-beam distance of about 27 cm and an integrated strength as high as 70 T.m for D1, therefore excluding a warm or super-ferric D1 for phase II.
RO concluded that the final decision for the choice of technology to be used for D1 will mainly depend on the level of energy deposition which is expected in this magnet (debris coming from the IP). The study will start in March and first results should be available in the next few weeks for a report to the working group beginning of April.
3. Topics for the next meetings (R. Ostojic, ppt file)
Ranko presented briefly a list of topics which will be discussed in the next meetings. The goal is to obtain a first consistent proposal for the triplet layout and the optics by end of May.
4. A.O.B.
Next meeting scheduled for 6 March 2008: Triplet-experiment interface, estimate of the volume of the powering equipments and of the available tunnel space.
S. Fartoukh and R. Ostojic