Summary Notes of Upgrade Meeting on 02/04/2007
Present: OB, UD, RdM, SF, MG, WH, MM, RT, FZ
Kick-off meeting for LHC upgrade studies: general perspective -> FZ (pdf file)
FZ described the various topics falling under the heading :HC upgrade, including IR upgrade, beam-parameter upgrade, beam-beam and beam-beam compensation studies, heat deposition issues, and injector upgrade. He listed the 9 members of LCU contributing to this activity for the LHC. The injector upgrade is treated in Gianluigi's section. Three NbTi low-gradient optics were developed by RdM and OB. In addition two nearly identical Nb3Sn optics exist for an advanced upgrade. In AT JPK pursues development of an early-separation optics with very small beta*. SF started looking at optimized IR schemes. A new initiative by Lyn Evans is a phase-I upgrade based on NbTi which should be implemented by 2012 and for which a design choice will be made in summer 2012. The phase-I upgrade should therefore be pushed with priority, using the three existing NbTi optics. As input to Lyn, LCU should provide a comparison of dynamic aperture, beam-beam performance, and heat deposition for the three alternatives. Possible help is expected from US-LARP. OB asks for input prior to the US-LARP meeting 14-18 April, which he will attend.
Kick-off meeting for the LCU LHC upgrade studies: introduction and scope -> MG (pdf file)
MG recalled that the LHC upgrade now forms part of the LCU mandate. Prior to MARS work packages were defined by FZ. MG described the task distribution in LCU, and a few recent changes necessitated from the new phase-I upgrade. OB commented that the phase-II should not be called the "real" upgrade, but rather "ambitious" upgrade. The third NbTi optics solution is called the "low-beta_max" one. MG stressed that the focus of the near-term work is to finalize the three NbTi optics, carry out performance assessments, and document the results.
LHC Phase 1 upgrade -> RdM (pdf file)
RDM recalled that a paper describing the three optics solutions is presently under approval as LHC report. He described the design guidelines invoked, including limits on the chromaticity, peak field, beta_max. The absolute maximum chromaticity that can be accepted corresponds to 22-23 km peak beta function, but would require particular choices of inter-IP phase advances. There was some discussion on the aperture budget. The 1 mm dispersion contribution in the draft report was erroneous and will be changed to 5 mm. An important limit arises from the maximum beta function as a function of gradient, calculated for zero-gap thick lens triplet, quadruplet, quintuplet etc. configurations. Superimposing the different constraints in the beta_max-gradient plane, the conditions can only be met in a limited range of (moderate) gradients. The three proposed optics solutions all lie in this range. They differ in aperture margin, chromatic properties, and modularity.
RDM pointed out that a quadruplet optics achieves 10-15% lower peak beta values compared with a triplet at the expense of larger chromaticity and enhanced length. OB stressed that the solution presented by Ezio was based on a thin-lens calculation, for a symmetric triplet, and does not correspond to any matched MAD optics. He also emphasized that in the modular solutions (2 + 3) there are 1-m free spaces between modules, allowing for large number of absorbers and/or correctors. Future studies should optimize the absorber elements. SF commented that the limit on beta_max for a high-gradient optics is 9.6 km. The low-gradient optics presented here may reach values below 10 km, without margin.
RDM described the various files and scripts available for studies. Apertures are not yet fully checked. For the full squeeze there is a quadrupole strength problem in IR4 and IR6. The arc quadrupoles are changed to compensate for a tune change at IR5. SF estimated that the beta beating should be of order 1% and he was surprised that this cannot be corrected by the beta matching sections.
It was discussed that RT and MM will help finalizing the three optics. SF recalled a rule of thumb that 6.6 T peak field at the coil entrance should be OK for NbTi. Extrapolating from this, he recommended to lower the 12 T value for Nb3Sn.
OB summarized the situation by saying that under very conservative assumptions we have arrived at three solutions, which shows that we are in business. SF suggested that in the modular optics, individual blocks could be transversely displaced to maximize the aperture. Flat beams and other variants can be considered. Already without playing any of these tricks, there is already more aperture margin than for the nominal LHC. Some open questions include the following: are the chromatic aberrations dominant? which aperture margin is needed for off-momentum beta beating etc.?
OB recalled the underlying design philosophy, that starting from the expected poor magnet lifetime, a modular approach was chosen which simplifies the spare magnet policy.
IR optics web repository -> RT
RT presented the HHH IR optics web repository. The page can be found here. The present web site contains a wide mixture of solutions for the nominal LHC, dipole first, quadrupole first, ones with and without optics files etc. Some felt that a single web site should contain all available optics. FZ recommended leaving the existing web site and creating two news ones for phase I and phase II, respectively, where only optics are posted and maintained that we are pursuing for the two phases of upgrade.
Last update: 2-Apr-07
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