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

• 45.5GeV Z

• 80GeV W pair

• 120GeV H (ZH production)

• 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

• 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

• ~90,000 bunches at 45GeV

• ~100 bunches at 175GeV

• Bunch population 1e10 - 2e11 (min of 1e9)

• 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

• EM field of one beam causes other to emit photons

  • Leads to bunch lengthening & loss of particles

70mm circular aperture with anti-chamber

Bunch by bunch & turn by turn capability for all instruments

BPMs

• ~4000 BPMs per beam with most probably no directional BPMs

• Alignment to < 50um

  • If possible without beam based alignment!

  • CLIC input

  • Need BPM to quadrupole to be ~20um (including electronic offsets)

• Closed orbit

  • Resolution of 100nm short term (minutes)

  • Micron resolution over hours

  • 10um reproducibility over weeks

    • Probably implies temperature stabilized machine

• < >

  10-100um per bunch

• Some BPMs with bunch by bunch (do not need all)

Tune

• PLL tune tracking

  • 1Hz feedback (Non-ramping machine so can keep bandwidth very small)

  • 1e-5 for PLL & 1e-4 for FFT

• Coupling feedback may also be required

  • Synchro-betatron resonances an issue

• Standard chromaticity measurement

Beam Current

• DC: 1.5A to 6mA

• Loss rates on bunch by bunch basis

  • Resolution to allow 1% change to be seen (can average)

  • 2.5ns resolution for bunch by bunch

Transverse emittance

• Synch light

  • Vertical emittance <1pm

    • Size: 22um for beta=500m

  • Horizontal ~1pm

• Calibration with WS to be discussed?

• 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.

• Would it be a good option to measure divergence instead of beam size (BEXE in LEP)?

Bunch Length

• 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).

• The measurement must be available bunch by bunch. A full beam measurement should be available on the time scale of ‘minutes’.

• The required precision is completely dominated by the requirements of energy calibration (for energy spread determination).

• 3ps bunch length with 6fs accuracy!

  • Relative accuracy of 0.1% - i.e. at same level as above

BLM

• Standard e-beam BLM system that can distinguish particle loss from X-rays

Luminosity & Beamstrahlung

• Coarse machine luminometers

  • No absolute normalisation required - just good rate monitors

• Photon detector to measure beamstrahlung on both beam lines

X-ray BPM

• 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.