Dissertation / PhD Thesis

PUBDB-2025-01873

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Towards Spin-Polarized Electron Beams from a Laser-Plasma Accelerator

Stehr, F. P. G. (Corresponding author)DESY* ; List, J. (Thesis advisor)DESY* ; Moortgat-Pick, G. (Thesis advisor)DESY*

2025
Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky Hamburg

This record in other databases:

Please use a persistent id in citations: urn:nbn:de:gbv:18-ediss-128363  doi:10.3204/PUBDB-2025-01873

Abstract: The LEAP (Laser Electron Acceleration with Polarization) project at DESY is a proof-of-principle experiment aiming to demonstrate the generation -- thus also the transport -- of spin-polarized electron beams from a laser-plasma accelerator (LPA). This is expected to be achieved using a pre-polarized plasma source, generated via the photodissociation of HCl molecules with an ultraviolet (UV) dissociation laser. Compton transmission polarimetry is envisioned for polarization measurements, inferring electron polarization from the transmission asymmetry of bremsstrahlung photons through magnetized iron. This thesis explores three key aspects of LEAP, focusing on development an experimental realization. First, a feasibility study was conducted to generate the UV dissociation laser via cascaded second-harmonic generation in two beta-barium borate crystals directly from the LPA driver laser. A measured conversion efficiency of $\eta_{\omega \rightarrow 4\omega}\approx0.8\,\%$ into the UV demonstrates the feasibility of this approach. Second, a homogeneous Cherenkov lead-glass calorimeter was built as an integral part of the LEAP Compton transmission polarimeter. Furthermore, it was tested and calibrated with single electrons at the DESYII Test Beam Facility. The derived calorimeter energy resolution of $\frac{\sigma_{E}}{\langle E \rangle} < 2\,\%$ at TeV-scale total energies meets the requirement for its application within the LEAP polarimeter. GEANT4 simulations indicate a nonlinear calorimeter response to low-energy particles ($<10\,$MeV). The uncertainty of this response introduces a relative uncertainty of $\sim1.5\,\%$ on the simulated analyzing power of the polarimeter.Finally, the full polarimeter setup, consisting of a solenoid magnet and the Cherenkov calorimeter, was commissioned at the FLARE facility using an unpolarized LPA electron beam. Initial system tests, beam charge and energy characterization, and operational polarization measurements were conducted. Simulations determined the analyzing power of the system to be $A=11.74\pm0.18\,\%$ ($\frac{\Delta A}{A} = 1.6\,\%$) with the dominant uncertainty arising from the calorimeter response. The actual measurement was found to be primarily influenced by beam stability and control. In particular, observed asymmetries -- unrelated to beam polarization -- can be explained by potential energy drifts. Extrapolation to realistic polarization measurements indicates that shot-to-shot charge and energy stability must be provided at the $\leq 1\,\%$ level to enable reliable polarization measurements.

Note: Dissertation, University of Hamburg, 2025

---

Contributing Institute(s):

1. Technol. zukünft. Teilchenph. Experim. (FTX)
2. Plasma Accelerators (MPA)

Research Program(s):

1. PHGS, VH-GS-500 - PIER Helmholtz Graduate School (2015_IFV-VH-GS-500) (2015_IFV-VH-GS-500)
2. 622 - Detector Technologies and Systems (POF4-622) (POF4-622)

Experiment(s):

1. Plasma Accelerators
2. DESY: TestBeamline 24 (DESY II)

Appears in the scientific report 2025

---

Database coverage:
;

---