Higher-energy damping ring for the FCCee injector #1

Monday 13 May 2024, 13:00 → 14:00 Europe/Zurich

13:00 → 14:00 Discussion

Speakers: Alexej Grudiev (CERN), Antonio De Santis, Catia Milardi (INFN e Laboratori Nazionali di Frascati (IT)), Hannes Bartosik (CERN), Ozgur Etisken (Ankara University (TR)), Paolo Craievich, Yannis Papaphilippou (CERN)

Partecipants: Alexej Grudiev, Antonio De Santis, Catia Milardi, Ozgur Etisken, Paolo Craievich, Yannis Papaphilippou, Frank Zimmeramann

Yannis presented the slides with initial considerations on using the pre-DR of CLIC as a damping ring for FCCee at 2.86 GeV. A first difference concerns the charge per single bunch, CLIC provides 0.6 nC while FCCee requires 5.4 nC. The DR involves the use of a TME arc cell because this choice was part of a PhD work that involved optimising parameters for a small emittance keeping a good dynamic aperture. In general it is a relaxed design and one could push it to reduce costs. The DR does not foresee the use of wigglers whereas for FCCee one could foresee SC wigglers with the aim of reducing the circumference by 100 m. Considering 400 MHz and a circumference of 290 m we could fill the entire ring with about 40 bunches separated by 25 ns. This seems compatible with the filling pattern of the booster.

Catia: operation and investement cost should be considered for the SC wigglers. 

Yannis: SC wigglers don't need a cryoplant but only cryocoolers, as in the SC wigglers at ANKA (?)

Question: Could SC technology be a showstopper?

Without SC wigglers it will be difficult to have a normalised emittance of 10 urads. The booster specification is 20 urad (H) x 2 urad (V) without taking into account the emittance growth in the high-energy linac.

Ozgur presented a summary table with the comparison between his proposal and the CLIC pre-DR one (https://indico.cern.ch/event/1402911/):

Frank's email:

Dear Hannes, Yannis, Catia and, Ozgur,

Michael asked me to (re-)send you the full requirements and input parameters*

Many thanks & best regards,

Frank

Input: 

Positron injection,

100 Hz injection with 4 bunches per pulse,

Normalized total beam emittance (x&y):  12 mm,

Rms momentum spread ~1.6%,

Rms bunch length 3.1 mm,

Bunch spacing of either 25 ns or 50 ns

 Questions: 

How many bunches can we store in total in either case ?

Do we need to fill the entire ring ?

What are the final emittances, bunch length, momentum spread, at extraction ?

We could aim for < 10x1 micron rms normalized emittance in x/y.

Do we need less or more damping (wigglers)?

Can we reduce the number of bunches (or could we use a smaller ring)?

An estimate of the power consumption could be based on the CLIC design, taking int account the different beam current.

Many thanks & best regards,

Frank

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* I. Chaikovska et al., Update on the FCC-ee positron source design studies, Proc. IPAC’23, Venice, Italy, paper MOPL095 https://doi.org/10.18429/JACoW-IPAC2023-MOPL095