Non-Destructive Beam Monitoring via Secondary Radiation Detection with Ce-Doped Silica Fibers

TL;DR

This paper presents a non-invasive fiber-based monitor using Ce-doped silica fibers to detect secondary radiation, enabling precise beam diagnostics in medical cyclotrons without degrading beam quality.

Contribution

It introduces a novel external fiber monitor (EFM) leveraging Ce-doped silica fibers for non-destructive beam diagnostics in medical cyclotrons, demonstrating its effectiveness across multiple use cases.

Findings

EFM signal linearly correlates with beam current over three orders of magnitude.

Beam-loss proxy from EFM scales with electrical loss proxy across focusing settings.

Fiber signal ratios provide sensitive, decoupled measurements of beam displacements.

Abstract

Non-destructive beam diagnostics are essential for low-energy medical cyclotrons, where even thin interceptive devices can severely degrade beam quality. We investigate an external fiber monitor (EFM) based on Ce-doped silica scintillating fibers that detects secondary radiation generated at existing beamline components of the 18 MeV Bern Medical Cyclotron beam transfer line (BTL). Three use cases were studied: (i) beam intensity monitoring around an electrically isolated, water-cooled beam dump; (ii) beam-loss monitoring around a 10 mm collimator under varying the beam focusing; and (iii) by steering a 6.5 mm $\times$ 6.5 mm beam spot on a beam dump. For case (i), the summed EFM signal exhibits a linear dependence on the current on target over nearly three orders of magnitude. In case (ii), a normalized EFM-based beam-loss proxy scales monotonically with an electrical loss proxy across several focusing settings. Furthermore, opposing-fiber signal ratios provide decoupled, monotonic sensitivity to horizontal and vertical beam displacements.