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Neutrino Factory/Muon Collider Document 13-v1

Heat Distribution in a Beryllium Foil Used in a High Gradient RF Cavity

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MuCool Note
Submitted by:
John Urish
Updated by:
John Urish
Document Created:
28 Dec 1998, 12:00
Contents Revised:
28 Dec 1998, 12:00
Metadata Revised:
28 Dec 1998, 12:00
Actually Revised:
14 Sep 2006, 13:35
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Heat Distribution in a Beryllium Foil Used in a High Gradient RF

In any scheme for a muon collider the preparation of the muons has to be done as soon as
possible due to the finite lifetime of the muon. Therefore the production, the capture, the
cooling and the acceleration requires high gradient rf structures (generally well above 20-
30 MV/m) in a frequency range of 0.03 to 1.0 GHz. In the cooling channel low energy
muons (??2, ??0.85) travel through absorbing material and loose transverse and
longitudinal momentum. In the accelerating rf structures only longitudinal momentum is
replaced which results in a reduction in transverse phase space (transverse cooling). High
gradient 805 MHz rf-structures are foreseen which operate at a gradient well above 30
MV/m and at a duty cycle mainly given by the filling time of the structure and the pulse
repetition rate.. One of the specialties of the structure is a 125 ?m beryllium window,
build into each iris, to increase the electric field strength on axis (Epeak = Eacc). Apart from
the difficulty to incorporate the beryllium window in the manufacturing process, the
Beryllium and Copper do have significantly different material properties, which makes rf
operation difficult as well. The power dissipation in the beryllium foil and the subsequent
heating is investigated in this paper.

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Norbert Holtkamp
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