Beam position monitor

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A beam position monitor or beam position sensor ( English Beam Position Monitor , BPM for short) is a sensor assembly that is mainly used in particle accelerators and optical systems to measure the spatial intensity distribution of radiation . The term radiation here includes any type of electromagnetic radiation , such as visible light , infrared or gamma radiation , and particle radiation such as electron beams or proton beams .

Measurement methods

The intensity distribution can be measured with different degrees of accuracy using different criteria. The distribution of the intensity is determined by measuring one or a combination of measured values, such as

  • Intensity at a specific location (or integral on a section surface defined in terms of location and extent)
  • Location of the highest intensity on a defined cutting surface
  • Location of the center of gravity of the intensity distribution on a cut surface
  • Location profile of the intensity on a cut surface
Beam Profile Monitor for measuring the intensity distribution of laser radiation

In the latter case, the sensor is usually assigned to a separate group of measuring elements under the name Beam Profile Monitor (also abbreviation BPM ). Compared to the beam position sensor, these can provide far more differentiated statements about the beam than simple beam position sensors allow.

Since the properties of different types of electromagnetic radiation and particle radiation differ greatly, there are a large number of different modes of operation. On the one hand, this refers to the physical operating principles for converting the radiation acting on a surface element into a measurement signal. On the other hand, there are also the principles at which points of the cross-sectional area of ​​a beam are measured (e.g. segmentation , aperture area, passage area through a diaphragm, etc.) and whether this is done integrally or as a profile over a surface or a line.

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