title: OCTOPUS – A High Repetition Rate Detector for Laser-Accelerated Particles
Creators: name: Hesse, Markus
Publisher: name: UNSPECIFIED
Year: 2022

description: This thesis presents the development, construction and experimental validation of a detector for laseraccelerated particles. The dissertation was carried out in the Laser- &amp; Plasma Physics group of Prof. Dr. Markus Roth at the Institute of Nuclear Physics at the Technical University of Darmstadt. The continuous development of high-intensity lasers for particle acceleration is significantly increasing their repetition rate. Until now, the repetition rate of laser systems was limited to a few interactions per day. Modern lasers have the ability to perform acceleration processes with up to several Hertz. Current detection methods for laser accelerated particles are not able to keep up with these high repetition rates. They are often only suitable for single use, or require a significant amount of time to be redeployable. Therefore, the development of modern particle detectors with high repetition rates is necessary. The newly developed Online Compact Tracker Of Particles Using Scintillators (OCTOPUS) in this dissertation is a spatially and energetically resolved detector for deployment at high repetition rates. It has an active area of 44×40 mm² and can detect nine different energies between 5.8 MeV and 30.3 MeV with a spatial resolution of about 3.6×3.3 mm². The development of the OCTOPUS detector is based on the analysis of existing detector systems. Strengths and weaknesses of the different systems were investigated in order to define a list of requirements for the OCTOPUS detector. Among other things, this list contains energetic and spatial resolution of particles and the resistance to electromagnetic pulses as key criteria. In accordance with the list of requirements, a novel detection principle was developed and simulations were carried out to determine its performance. This detection principle is based on scintillators, which are embedded in a repeating pattern at different depths in a support structure. For the construction of the OCTOPUS, the scintillators themselves were manufactured. Like the entire detector, they are based on PMMA (Polymethyl methacrylate) and have been optimized in fabrication and light yield according to the detector requirements. Depending on the depth of the scintillators in the support structure, the particle beam must have a minimum energy to excite the scintillator. This defined structure of a scintillator array is also called a macro pixel and forms a detection pixel of the detector with an energy resolution corresponding to the number of scintillators present. The arrangement of many macro pixels allows to spatially resolve the energy spectrum of a particle beam. Each individual scintillator converts the deposited particle energy into photons and transmits them via optical fibers to a camera system. The camera system digitizes the image information. Subsequently, an evaluation of the particle spectrum can be performed. In an experiment at the Petawatt High Energy Laser for Heavy Ion Experiments (PHELIX) at the GSI Helmholtzzentrum für Schwerionenforschung, the OCTOPUS detector was put to a final experimental test. The novel developed detector was calibrated with the results of radiochromic films. It was demonstrated that the OCTOPUS detector can measure spatially and energetically resolved the absolute deposited energy of a particle beam. The OCTOPUS thus presents itself as a solution to spatially and spectrally resolved particle detection at a high repetition rate.