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FCC-BI Specs for FCC-ee
FCC-Beam Instrumentation SPECIFICATIONS FCC-ee
26/09/2016
Present:
Jean-Jacques Gras (sec.), Bernard Holzer, Rhodri Jones, Hermann Schmickler (chair), Jorg Wenninger.
Excused:
Mauro Migliorati (no Vidyo in the room), Markus Zerlauth
INDICO Link:
https://indico.cern.ch/event/565880/
Comments:
On JORG/BERNARD’S slides:
Direct competition with ILC
45GeV to 175GeV per beam
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45.5GeV Z
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80GeV W pair
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120GeV H (ZH production)
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175GeV t
Maximum SR of 50MW per beam
Fixed energy rings (2 rings one for e+ one for e-) with booster for top-up injection
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No design for booster at the moment but its instrumentation will have to be specified too.
Beam current scales with 1/E^4 based on top SR power
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~90,000 bunches at 45GeV
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~100 bunches at 175GeV
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Bunch population 1e10 - 2e11 (min of 1e9)
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400MHz RF nearly entirely filled for 45GeV
Vertical emittance ~2pm - similar to light sources & CLIC DR
Beta* of 1mm
One optics for all energies considered at the moment
Beamstrahlung - effect of one beam on the other
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EM field of one beam causes other to emit photons
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Leads to bunch lengthening & loss of particles
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70mm circular aperture with anti-chamber
Bunch by bunch & turn by turn capability for all instruments
BPMs
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~4000 BPMs per beam with most probably no directional BPMs
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Alignment to < 50um
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If possible without beam based alignment!
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CLIC input
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Need BPM to quadrupole to be ~20um (including electronic offsets)
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Closed orbit
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Resolution of 100nm short term (minutes)
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Micron resolution over hours
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10um reproducibility over weeks
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Probably implies temperature stabilized machine
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- < >
10-100um per bunch
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Some BPMs with bunch by bunch (do not need all)
Tune
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PLL tune tracking
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1Hz feedback (Non-ramping machine so can keep bandwidth very small)
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1e-5 for PLL & 1e-4 for FFT
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Coupling feedback may also be required
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Synchro-betatron resonances an issue
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Standard chromaticity measurement
Beam Current
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DC: 1.5A to 6mA
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Loss rates on bunch by bunch basis
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Resolution to allow 1% change to be seen (can average)
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2.5ns resolution for bunch by bunch
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Transverse emittance
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Synch light
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Vertical emittance <1pm
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Size: 22um for beta=500m
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Horizontal ~1pm
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Calibration with WS to be discussed?
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The measurement of all bunches of the beam must be available on a ‘time scale of minutes’. This BtB vertical emittance monitoring could probably a good diagnostic tool.
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Would it be a good option to measure divergence instead of beam size (BEXE in LEP)?
Bunch Length
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Bunch length important to monitor strength of Beamstrahlung at IP and for energy calibration (energy spread). It may also be used to monitor collective effects (head-tail instabilities).
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The measurement must be available bunch by bunch. A full beam measurement should be available on the time scale of ‘minutes’.
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The required precision is completely dominated by the requirements of energy calibration (for energy spread determination).
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3ps bunch length with 6fs accuracy!
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Relative accuracy of 0.1% - i.e. at same level as above
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BLM
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Standard e-beam BLM system that can distinguish particle loss from X-rays
Luminosity & Beamstrahlung
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Coarse machine luminometers
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No absolute normalisation required - just good rate monitors
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Photon detector to measure beamstrahlung on both beam lines
X-ray BPM
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Interlock on light fan position?
NEXT:
Next meeting/discussion will be in 3 months. In the meantime, BI will trig internal discussions to evaluate possible answers to open points, i.e. transverse profile, longitudinal profile measurements and monitoring of the vertical alignment along the machine.
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