AIP Digital Archive
Electrical Engineering, Measurement and Control Technology
The thermally induced change of the birefringence of a high-birefringence fused-silica optical fiber, when exposed to a proton beam (2 MeV, 0.5–44 nA, 5-mm spot diameter), was measured with a fiber-optic polarimetric sensor. A short length (5 cm) of 125-μ-diam, single-mode, polarization-maintaining optical fiber was put orthogonally to the beam in vacuo and the linear polarization of a HeNe laser beam launched into the fiber was analyzed by a polarizer and recorded by a photodetector. The response of the sensor both to a continuous and to a modulated proton beam was studied. The photodetector output, which varies with the cosine of the induced relative phase retardance between the fiber eigenmodes, provides a dc or an ac (10 Hz test modulation frequency) measurement of the beam current. This device acts as a proton beam intensity monitor, with minimum beam perturbation and a sensitivity of 0.1 nA. Its possible use also as a beam position monitor or as a wire-scanner beam profiler is suggested.
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