Speaker
Description
Gaseous detectors with scintillation light readout allow for low material budget beam monitoring while exploiting the high readout granularity provided by state-of-the-art imaging sensors. The pixellated readout approach of optically read out MicroPattern Gaseous Detectors (MPGDs) enables 2D images of particle and photon beam profiles.
We report on the development and characterisation of a beam monitoring detector prototype based on Gaseous Electron Multipliers (GEMs) under low-energy X-ray irradiation and in particle beams including proton, muon and pion beams. The detector was configured with a variable number of GEMs from a single foil to a stack of 5 GEMs to cope with different beam intensities. In addition to the amplification stage, an ionisation chamber was added for accurate intensity monitoring. A gas mixture of Ar/CF4 was used for visible scintillation light emission matching the QE of scientific CCD and CMOS cameras. A high-resolution, high-sensitivity camera was used for recording integrated beam profiles while a high-frame-rate CMOS camera enabled the acquisition of individual particle tracks.
To minimise material budget, the camera was located outside of the beam path and light was coupled from the amplification stage to the imaging sensors with a mirror and a lens. Together with the use of thin foil windows and electrodes, this resulted in a water equivalent thickness of <700 µm for the configuration with a single GEM foil. Linearity of response under X-ray irradiation and imaging capabilities with wide field X-ray irradiation were verified in lab measurements.
Intensity distributions reflecting particle beam profiles were recorded and match the information provided by reference detectors both for integrated imaging as well as for event-by-event particle counting modes. The 2D pixellated intensity maps enable accurate visualisation of non-uniformities in the beam profiles that may not be apparent on projected 1D profiles.
Real-time image processing can enable the use of optically read out beam monitoring detectors for providing fast feedback on key beam parameters including position, profiles and intensity. An algorithm detecting events from a low-energy X-ray source in real-time was developed and shown to achieve good energy resolution and accurate determination of interaction locations.
The optical beam monitoring approach can be compatible with a wide range of beam parameters and may be employed for dose monitoring in medical applications as well as for secondary particle beams in high-energy physics.
| Position | Staff |
|---|---|
| Affiliation | CERN |
| Country | Switzerland |