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Home > Physics > Research > Particle Physics > John Adams Institute > Cavity beam position monitors (cBPM)
More in this section Boogert Stewart

Cavity beam position monitors (cBPM)

Beam position monitors are essential diagnostics devices to monitor the alignment of a charged beam with respect to magnetic elements such as quadrupoles. The overall performance of an accelerator can be limited by lack of knowledge of the beam position. Resonant cavity beam position monitors are devices that can detect the beam position to within a few nanometers. These devices are simple metallic cylindrical cavities placed around the beam that resonate with an electromagnetic standing wave when excited by a charged beam passing through. Depending on the geometry of a cavity the main standing wave to be excited in the cavity is the position dependent lowest order transverse magnetic mode. By carefully measuring the strength of the stored electromagnetic wave, a very precise determination of the beam position can be made. In collaboration with KEK, SLAC and other UK universities we verified these devices could routinely measure beam position differences of order 15 nanometers. These devices, although simple in concept, are difficult to use routinely and this research furthers the use of cavity BPMs as routine accelerator diagnostic tools. In addition when combined with a precise magnetic bending system, the BPM position can be used to determine the accelerated beam energy to high accuracy, 1 part in 104, which is required for the particle physics studies at a future linear collider


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