Speaker
Description
Laser Wakefield accelerators (LWFAs) are compact, affordable sources of 50-250 MeV electrons, known clinically as "very-high-energy electrons" (VHEE). Such electrons are used in VHEE radiotherapy of deep tumors because of their long (~ several cm) penetration depths [1]. In a separate contribution to the AAC workshop, we show that when VHEE beams from an LWFA heat targets immersed in water, rapid thermal expansion of the heated region launches megahertz ultrasound waves into the water than external transducers readily detect. These signals can potentially provide in-situ dosimetry, in-situ images of the irradiated target, and in-situ information on sound speed or density distribution within the target during VHEE therapy. However, such applications rely on a clear theoretical understanding of the spectrum, amplitude, and angular distribution of the ultrasound signal and their relationship to the shape and material composition of the target.
In this work, we present an analytical study of LWFA-driven ultrasound in cylindrical and elliptical targets. Closed-form and eigenmode-based solutions are derived for the generated acoustic pressure fields using cylindrical-coordinate Bessel expansions and elliptical-coordinate Mathieu function formulations. The analysis investigates the influence of target geometry, boundary conditions, relativistic beam energy deposition profiles, and transducer detector position on acoustic mode spectral response from pressure evolution. Analytical frequency-domain results are validated through comparison with frequency spectra obtained from Fourier-transformed time-domain K-Wave simulations. Emphasis is placed on the differences between cylindrical and elliptical geometries, including symmetry breaking and directional acoustic behavior relevant to tomographic reconstruction. The long-term objective of this work is to develop a framework for reconstructing either unknown sound-speed or density distributions within a target from measured acoustic signals, assuming known target geometry and initial instantaneous heating pressure distributions. These results provide a theoretical foundation for improving future compact high-resolution acoustic tomography systems enabled by advanced accelerator technologies.
[1] K Svendsen, D Guénot, JB Svensson, K Petersson, A Persson, O Lundh, "A focused very high energy electron beam for fractionated radiotherapy," Scientific Reports 11, 5844 (2021).
| Working group | WG6 |
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