Minutes, FHI meeting, 1st July 2014, 09:00, 6-2-004
Present: M Meddahi, D Schulte, W Bartmann, W Herr, B Goddard, B Holzer, G Rumolo, J Osborne
Slides: https://indico.cern.ch/event/326057/
Action follow-up:
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Minimum beta at TDI: Info from A. Perillo Marcone that presently there is no material which
can withstand safely HL emittances with the existing optics; TDI needs to be moved together
with the MKIs (90 deg); should take the optics flexibility to increase the beta function to
compensate for smaller emittances wrt design values.
Impact of shorter ramps on long. Plane – next meeting
IP8 optics without triplets, with crossing (Werner):
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Optics outside of Q4 left and right untouched; at Q4s antisymmetric
Dx wihtout crossing peaking at 20 cm through full IR8, with crossing at 40 cm; crossing in
middle of the quad, single aperture
Werner suggests as alternative: crossing at the IP with a ‘low’ beta insertion with betas 15-25
m, no constraint on L*
o Keep D1 and D2; single aperture magnets and crossing in drift
o Larger beta* allows smaller aperture
o Doublet or triplet to be checked
o This version is more stable wrt imperfections; smaller angle and dispersion required;
10% fewer long range interactions
o Shift “back” Q5l-Q5r by 11.2 m to symmetrisize IP8; shift goes in direction P7; should
be OK for injection
A copy of the IP4 crossing would be difficult due to the injection optics constraints
List of potential TL magnets (Attilio):
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3 bending magnet options
o TI 2/TI 8 dipoles, NC: 1.8 T
o JPARC combined function, SC: 2.56 T
o Tevatron, SC: 3.9 T
Any new design possible
Required injection straight length of FCC (Wolfgang)
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Parametrisation of the required injection straight length as a funciton of the vertical height
difference between LHC and FCC at P1 and the magnet technology
No horizontal bending taken into account
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For 20 – 200 m height difference and reasonable magnet technologies get about 0.5 to 1.5
km injection straight length per beam
Assumed filling factor 0.75
o depending on magnet technology (check factor for combined fct) and protection
elements
have to add constant of 100 – 500 m for injection protection downstream; should not limit
this to fully exploit the injection capacity in terms of transferred bunches and thus collider
luminosity
depending on FCC design, injection can be in one long straight or into shorter straights
separated by arcs
Optimum depth of FCC due to geology/CE (John):
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Defined study area with 6 ring options: 1 circular and 2 racetracks for ~80 and ~100 km
Data collected from Swiss and French geological, topographical, geothermic, hydrological and
man hazards maps
High risk areas identified: e.g. Le Vuache (Fort Ecluse)
Depth: Molasse (best), Moraine (risky, difficult to estimate risk now), Immersion (not likely,
to look at all possibilities
Results in LHC – FCC distances at P1:
Presently no straight section foreseen in the racetrack arcs; probably need one little straight
in the middle for the beam crossing; Upright racetrack would need 4 short injection straigths
Reasonable options:
o 83 km circular and racetrack seem to fit well and their position/angle can be
optimized wrt the transfer line length
o 100 km circle and lower racetrack cross LHC with almost 90 deg; these options would
lead to long transfer lines (10-20 km) and possibly require different extraction points
than the presently foreseen P1
o 100 km upright racetrack would require an extension of the study area in direction
Grand Lac; extraction from P4, shift RF to P5
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Tool to study CE with all variables (vert./hor position, inclination, size,…) available after
summer; TL can’t be included; need draughtsman to iterate various options; resources to be
clarified
Severeness of geology limits to be defined on the the outer corners like Fort Ecluse, Jura,
Lake, Aravis, Chablais
Actions:
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Severeness of geological study area borders
Longitudinal plane for faster ramp rates
Filling factor for different magnet technologies
Shifted IP8 injection
Minimum beta function for TDI – check if beta can be matched to higher values to
compensate for ratio of design/BCMS emittance
Check dispersion in IP8 with crossing
Global aperture check
Inventory of magnets and circuits, current and ramp rates
Start write up of LSS modifications: optics design, insertion changes, performance in ramp
speed, circuit list
o Add on: FT physics
Establish expected filling time
List of transfer line magnets/bending radii
Minimum FCC injection straight length
Write up arguments why certain approaches were ruled out (eg. running at 4K)
Next meetings:
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15th July
o Impact on longitudinal parameters due to faster ramp (Elena)
o Magnet inventory (Attilio)
o Iteration on circuit list, magnet removal (Werner will send the list)
th
29 July
o Severeness of geology limits (John)