High-efficiency directed positron generation through binary photon collisions in laser-driven plasmas
Abstract
Creation of matter from light alone is a basic prediction of quantum electrodynamics, but it is yet to be observed in the laboratory because achieving relevant conditions is extremely challenging and, until recently, was deemed impossible. The ongoing development of high-power high-intensity lasers promises to provide the experimental tools needed to overcome the difficulties. Most of the attention has been focused on the approach where highly energetic gamma-rays collide with an ultra-high- intensity laser, producing electron-positron pairs via a multi-photon process. The process involves one gamma-ray and multiple optical photons representing the laser field. The strong dependence of the pair yield on the laser intensity means that the intensities required for an appreciable yield are out of reach in the foreseeable future. The goal of this project is to experimentally implement a promising alternative approach involving binary or photon-photon collisions that has been recently discovered by us using simulations. The approach takes advantage of the fact that a high intensity laser pulse propagating through a dense plasma can generate a dense population of energetic gamma-rays. Even though it is known that the laser in this setup can generate a forward-directed gamma-ray beam, the possibility of efficient backward gamma-ray emission has been overlooked. The two populations form a self-organized gamma-ray collider that moves forward with the laser pulse. The laser pressure at the leading edge of the pulse also creates a strong forward-directed electric field that serves as an adjoining accelerator for the produced positrons, generating an ultra-relativistic positron beam. There are several important advantages of our regime. It requires a simple setup, because it relies on the collective phenomena involving relativistic electromagnetic waves in plasmas. Only one laser pulse is needed for its implementation and the currently available laser intensities are sufficient to achieve an appreciable positron yield. All these advantages translate into being able to implement this regime at existing laser facilities. The project is a collaborative effort that leverages simulation-theory expertise directly relevant to the project at the University of California San Diego, Lawrence Livermore National Laboratory (LLNL), General Atomics (GA), and the University of York, UK. Computational and theoretical research will guide the experiments by identifying ways to optimize the positron yield and improve positron acceleration through laser and target parameters. Moreover, UCSD and the University of York will implement an algorithm for the photon-photon pair production into the open-access open- source kinetic particle-in-cell code EPOCH that has a wide user base in the laser-plasma community. LLNL and GA will lead the development of a new positron detector for our experiments. The bulk of the research will be performed by graduate students. The training for graduate students in the area of high-power, high-intensity lasers will contribute to preparing a highly-qualified workforce. An important element of this project is efficient generation of a directed gamma-ray beam using a high-intensity laser pulse. Various applications can benefit from a compact source of gamma-rays, including active interrogation and material testing. However, a compact source that converts at least several percent of laser energy into gamma-rays is yet to be experimentally demonstrated. As a part of our project, we will demonstrate efficient gamma-ray emission, which can potentially unlock multiple applications and stimulate work on their further development.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 05, 2025
- Source ID
- FA95502410053
Entities
People
- Alexey V Arefiev
Organizations
- Air Force Office of Scientific Research
- United States Air Force
- University of California, San Diego