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FCC-ee optics tuning WG

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6/2-004 (CERN)

6/2-004

CERN

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FCC-ee optics tuning WG meeting
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65516078996
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Rogelio Tomas Garcia
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Joichi Sato, Introduction to JPARC

The JPARC facility, RCS + main ring, is described showing steady performance increase in beam power since the start in 2010.

Beta-beating below 2% achieved in ~2023 using Orbit response matrix methods. The 2% was needed to reduce beam losses, as observed.

 

Takashi Asami, Recent optics measurements and corrections in the JPARC Main ring

Correction of betatron resonances is crucial for JPARC performance. Quad errors in the main ring are up to 1%. 

Orbit Response Matrix (ORM) is used.

EM simulations of dynamic errors (eddy currents) agree with beam-based quadrupole error esitmates.

Latest resuts reach an rm beta-beat of 1.5% and are routinely used in operation.

Efforts are being made to determine sextupolar errors with this technique.

Turn-by-turn method was inefficient as it is destructive so ORM is better here.

No coupling measurement presented here or needed so far.

 

Y. Saito, BBA in JPARC

BPM diameter 130mm and resolution is 30um (closed orbit during 1ms). In single pass resolution is 100 um. Beam intensity is 1e13-14 protons per pulse.

Accuracy was observed to be 20-450 um in X and 20-90 um in Y.

Fast BBA is investigated as to speed-up BBA measurements by a factor 4. 

200um shift was observed in one BPM  BBA after several years (representative for all BPMs). For this case 20um BBA resolution is claimed.

Further developments to improve accuracy (including DAQ system) and extending to sextupoles are foreseen.

 

Marco Morrone et al., Configurations for FCC BPMs

For the BPM the concept is to have it integrated in the beam copper chamber. The final design is not available but an approach with a support attached to the quad is considered. 28.5 cm of free space would be needed for access. The BPM body is ~3cm. 

There are 4 options:

A: BPM on the quadrupole side. BPM-to-quad(fullquadlength) distance is 8.5cm.

B: Sextupole side. Same BPM-to-sext distance, however the coild dimension is 0.05m instead of 0.125m (for quad), so there is some ~7cm gain of putting the BPM at the sextupole. 

C: BPM in between quad and sextupole. Distance between quad and sext has to be increased to 28.5cm (from 5cm).

C*: more compact than C, assuming special tools, etc. Problem is that access to repair is not possible. ~1% BPM failure should be assumed?

The 2 dipole configuration, versus 3, will be studied.

BPM-to-quad alignment was given in the feasibility report as 100 um at the level of knowledge and measurement. The actual centers can be off by e.g. 1mm.

1 BPM measurement takes 1 day of one technician. Going to 300 um could relax this effort, to be studied.

A cooling channel will mitigate heating from SR, but mechanical stress is still to be studied. Quadrupole and sextupole positions are assumed to evolve freely over time. 

BBA simulations on these options will be performed during the summer to see how much BBA would degrade if BPM is attached to sextupole.

 

Vacuum has slight preference for A (quad). C and C* are too demanding.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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