arXiv subjects

Laurence Wroe

Publications and source records attributed to Laurence Wroe.

4 recordsLinked to original sources

arXiv2026

Initial Characterisation of a Prototype TMR Assembly for an Electron-Driven CANS at CERN's CLEAR Facility

The Versatile ULtra-Compact Accelerator-based Neutron source (VULCAN) project is developing a compact accelerator-driven neutron source (CANS) optimised for neutron diffractometry in industrial and university settings. Central to VULCAN is a novel target-moderator-reflector (TMR) assembly optimised to convert a 35 MeV pulsed electron beam into short neutron pulses (FWHM < 20 μs) in the 1.5-3.5 Å wavelength range. To validate the simulation-driven design process, a prototype TMR was developed for testing at CERN's CLEAR facility, and this paper presents the design, installation, and results of the first experimental campaign. While moderated neutron pulses were successfully detected, significant discrepancies were observed between the experimental and simulated energy spectra. Potential causes are discussed and recommendations for follow-up measurements are provided.

physics.ins-det↗

arXiv2026

RadMaps: A Geospatial Framework for Simultaneously Modelling Capacity and Geographic Constraints on Radiotherapy Access

Background: Access to radiotherapy (RT) is constrained by two compounding factors: insufficient machine capacity to meet patient demand and geographic distance from treatment facilities. Existing analyses address these factors separately, constraining the insights available to planners and policymakers. This paper presents RadMaps, an open-source geospatial framework that simultaneously models capacity and geographic constraints on RT access at any spatial scale. Methods: RadMaps operates on Uber's H3 hexagonal grid and integrates population density data with national cancer incidence estimates and RT facility inventories. RT demand is estimated using cancer-site-specific RT utilisation rates, and geographic access is modelled via configurable decay functions using either distance, driving time, or public transport time. A greedy nearest-first allocation algorithm assigns demand to facilities subject to both capacity and geographic constraints, producing a localised access metric for every H3 hexagon. Results: Applied globally with a 200 km step-function access threshold, RadMaps computes a capacity-only access of 70 %, a geography-only access of 91 %, and a combined RT access of 60 %, illustrating the compounding effect of capacity and geographic constraints to significantly reduce effective access. High-resolution analyses of six countries demonstrate the tool's ability to localise access deficits at sub-national scale and reveal distinct access profiles: capacity-limited, geographically-limited, and doubly-constrained. Conclusions: RadMaps provides a flexible, open-access framework for visualising and identifying RT access gaps at regional to global scales, with applications in infrastructure planning and policy prioritisation. RadMaps' modular framework is also readily extensible to other spatial access modelling applications.

physics.med-ph↗

arXiv2026

Controlling the Transverse Multipole Components in RF Cavity Modes using the Azimuthal Modulation Method

Recent work introduced a systematic method for designing so-called azimuthally modulated RF cavities that support transverse magnetic modes composed of user-desired multipoles, enabling precision control of the magnitude and orientation of multipolar components in RF cavity design. This paper extends this method to practical implementation by deriving the multipolar expansion of the longitudinal electric field in such RF cavities with beam pipes, as well as the momentum change of ultra-relativistic particles traversing these modes. The derived equations explicitly show the radial variation of the change in longitudinal and transverse momentum follows a polynomial rather than Bessel-function relationship. The expression for the longitudinal electric field is then compared to a field map obtained from the 3D electromagnetic simulation of an azimuthally modulated cavity designed to support a mode composed of monopole, dipole, and quadrupole components. Beam dynamics studies are presented to assess the derived expressions for the change in momentum, including the effects of relaxing the ultra-relativistic assumption. Finally, two example applications are presented: the first demonstrates the removal of unwanted transverse multipoles to create a multipole-free accelerating structure with a single-port coupler, whereas the second illustrates the synthesis of desired multipoles to create an RF cavity that transforms the transverse distribution of a beam from Gaussian to uniform.

physics.acc-ph↗

arXiv2026

When Are Two Networks the Same? Tensor Similarity for Mechanistic Interpretability

Mechanistic interpretability aims to break models into meaningful parts; verifying that two such parts implement the same computation is a prerequisite. Existing similarity measures evaluate either empirical behaviour, leaving them blind to out-of-distribution mechanisms, or basis-dependent parameters, meaning they disregard weight-space symmetries. To address these issues for the class of tensor-based models, we introduce a weight-based metric, tensor similarity, that is invariant to such symmetries. This metric captures global functional equivalence and accounts for cross-layer mechanisms using an efficient recursive algorithm. Empirically, tensor similarity tracks functional training dynamics, such as grokking and backdoor insertion, with higher fidelity than existing metrics. This reduces measuring similarity and verifying faithfulness into a solved algebraic problem rather than one of empirical approximation.

cs.LG↗