EMP mitigation and novel detection strategies for laser-plasma experiments

Student thesis: Doctoral Thesis

Abstract

Laser driven particle and radiation sources have the potential to become an alternative to conventional accelerators for a number of applications. Many laser-driven sources have been demonstrated, including x-rays, protons, electrons and positrons. The laser driven production of exotic particles such as muons has been theorised. Proposed applications for some of these novel particle and photon sources include a compact source of ions for cancer treatment, electrons for radar imaging, x-rays for probing high density objects, and muons to be deployed for the imaging of large dense structures including nuclear reactor cores and inspect large containers for forbidden fissile elements, to name a few. Ideally, to achieve these applications, laser-driven sources must be developed to have high conversion efficiency, high resolution and controlled directionality. Electromagnetic pulse (EMP) emission is prevalent in high power laser-plasma interactions and primarily arises due to the return current induced by the ejection of hot electrons from the target.It is important to study these emissions at high power laser facilities as it has been shown to interfere with experimental diagnostics. Many facilities currently under development will be able to produce higher intensity laser pulses at a high repetition rate and therefore EMP may become significantly disruptive to experiments. Due to this, EMP has recently attracted considerable interest and therefore the first two experimental chapters of this thesis focus on EMP energy correlations with proton and electron measurements, and EMP control and mitigation. The first investigation reports on experimental studies into the EMP scaling with sheath accelerated protons in laser-solid interactions in the intensity region of <1019W/cm2. The results demonstrate that EMP increases with the maximum proton energy, supported by additional escaping electron data. Producing higher energy protons may become a concern for more powerful high repetition rate systems and will require implementation of EMP mitigation techniques.This is studied in the second experimental chapter in a laser-solid interaction with an intensity of 1021 W/cm2. It was demonstrated that the generated EMP can be successfully reduced by introducing longer target mounting stalks, and by the use of insulating materials. The EMP production also displayed a considerable increase with target substrate size. For high repetition rates of the order of >10 Hz, there will be a need for improved diagnostics which can operate at such repetition rates, and are also resistant to EMP. The final study presents the development of an optical based technique coupled to a fast and sensitive photon detector, able to operate at high repetition rates and is largely unaffected by EMP. It can be used to detect any relativistic charged particles, and can measure relative beam charge providing an on-shot electron beam diagnostic in electron acceleration experiments.
Date of Award25 Nov 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council) & University of Strathclyde
SupervisorPaul McKenna (Supervisor) & Martin King (Supervisor)

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