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IR design progress update
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Europe/Zurich
6/R-012 - conference room (CERN)
Roman Martin - News on DA and IR design
DA studies with lattice V4 were presented
Settings:
-MQX error tables as from hl-lhc.
-More fringe field effects might come with further triplet splitting
-b1,b2,a1,a2 are turned off
-no nonlinear correctors yet (in contrast to hl-lhc)
-head on collision
not yet comparable due missing arc errors and crossing angles
with crossing angle:
dispersion of orbit correctors not corrected , which is one reason for a minimum DA of 0 sigma at the moment
in few cases corrections did not work out.
comparisons at this stage difficult with hl -lhc
Average DA without crossing angle is not too discouraging
need for future a corrector package like for hl-lhc (or lhc)
B. Dalena asked if the used V4 lattice is this still baseline? R. Martin replied it was used to have an idea for different L* and V5 was not ready yet.
Dispersion correction should be studied also for V5.
Emilia Cruz Alaniz - IR orbit correction studies
Correction of IT alignment errors were presented.
used several orbit correctors
intalled bpms for orbit correction, close to quads, also correctors at q4, but not used yet.
introduced 0.5mm x/y misalignment errors (max value not gaussian distributed)
used correct function in madx
strength of correctors and max deviation of the orbit was calculated
a few seeds <10% above 0.5mm orbit deviations (which was a limit in LHC studies)
tried different schemes, with correctors at different locations
only ~25% met the 0.5mm orbit deviation limit
to do: explore further, optimise location of correctors + use additional correctors
R. Tomas asks for the computed kicks (which seem large) what does this mean for the magnet (its length, super conduction needed?, will it fit in lattice). Also, 0.5mm might be too ambitious, in 1st order guess we would expect maybe a factor 2 more compared to LHC.
R. Martin commented that at the moment between q2a and q2b there is just 1m space, we would need a number of how much (more) space would be needed.
Ilaria Besana - Status of studies for L*=45m
Studies were done with the 45m L* and increased triplet length. crossing angle is at 90µrad, gaps between the triplets were introduced.
energie depositon at TAS is lower compared to the 36m case
for neutral particles the triplet is in the shadow of the TAS.
more pions enter q1 due to larger TAS aperture, but this should not be a problem due to larger coil aperture and lower gradients.
improving of the situation could be done by splitting q1 and play with apertures.
R. Tomas comments the impact of a smaller TAS should be studied
TAS aperture should be agreed upon
showed difference between horizontal and vertical crossing. A larger peak at end of q1,
Split q2b can have positive impact for horizontal crossing.
Outlook:
Investigate the effect of detector and compensatory dipoles, peak dose values, angular position peaks.
Xavier Buffat - Minimum beta*
introduced the luminosity model which he used, using effects of limi burns, synchro damping, quantum excitation, IBS, geom. reduction factor, hour glass factor (decoupled), crossing angle change to keep const. long range beam-beam (bb).
With relaxed bb limit the average limi production rate increases significantly.
Realistic would be something in between both scenarios.
Change beta* to 0.1, shows only a slight increase, because one is limited by the geometric factor.
Introducing crab cavity -> further increase of luminosity production. Beam can be burned very fast, which compensates shrinking emittance.
D. Schulte wonders that the values for the luminosity are very large compared to the ultimate baseline scenario. X. Buffat found a bug offline and updated the values (conclusions remain the same)
beta* scan, no improvement below 5cm
reduce beta* to keep emittance/beta* const.
keep same aperture in triplet and keep the same beam stay clear, etc. but collimation needs to be adapted as well.
More challenging IR designs might have many benefits.
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