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Resonant Cavities (BCMs) |
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Two resonnant cavities are positionned in the beam line behind and in front
of the Unser monitor;
they are respectively called "Upstream" and "Downstream" cavities. These cavities are two cylindrical wave guides made out of 304 stainless steel. Their dimensions are 15.48cm in diameter and 15.24cm in length. The resonnant frequency is adjusted to the 1497MHz frequency of the Cebaf beam by a stub tuner mounted on a micrometer that can be moved in and out of the cavity. Inside the body a magnetic field probe, a loop antenna, is located on the circumference, where the electrical field is minimum and the magnetic field is maximum. The probe is coupled to one of the resonnant modes of the cavity and used to couple the beam signal out of the cavity. |
![]() Electrical & Magnetic fields inside the cavity body |
Q=W.f/Pdor if we assume that the dissipation of the energy occurs only on the walls of the cavity: Q=Volume/AreaQ=3000 for these cavities. |