The thickness of the outer ice shell plays an important role in several geodynamical processes at ocean worlds. Here, we show that observations of tidally driven diurnal surface displacements can constrain the mean ice shell thickness, d∼ice ${\tilde{d}}_{\mathit{ice}}$. Such estimates are sensitive to any significant structural features that break spherical symmetry such as faults and lateral variation in ice shell thickness and structure. We develop a finite‐element model of Enceladus to calculate diurnal tidal displacements for a range of d∼ice ${\tilde{d}}_{\mathit{ice}}$ values in the presence of such structural heterogeneities. Consistent with results from prior studies, we find that the presence of variations in ice shell thickness can significantly amplify deformation in thinned regions. If major faults are also activated by tidal forcing—such as Tiger Stripes on Enceladus—their characteristic surface displacement patterns could easily be measured using modern geodetic methods. Within the family of Enceladus models explored, estimates of d∼ice ${\tilde{d}}_{\mathit{ice}}$ that assume spherical symmetry a priori can deviate from the true value by as much as ∼41% when structural heterogeneities are present. Additionally, we show that crustal heterogeneities near the South Pole produce differences of up to 35% between Love numbers evaluated at different spherical harmonic orders. A ∼41% range in estimates of d∼ice ${\tilde{d}}_{\mathit{ice}}$ from Love numbers is smaller than that found with approaches relying on static gravity and topography (∼250%) or analyzing diurnal libration amplitudes (∼85%) to infer d∼ice ${\tilde{d}}_{\mathit{ice}}$ at Enceladus. As such, we find that analysis of diurnal tidal deformation is a relatively robust approach to inferring mean crustal thickness.

The thickness of the outer ice shell plays an important role in several geodynamical processes at ocean worlds. Here we show that observations of tidally-driven diurnal surface displacements can constrain the mean effective elastic thickness, ˜del, of the ice shell. Such estimates are sensitive to any significant structural features that break spherical symmetry such as faults and lateral variation in ice shell thickness and structure. We develop a finite-element model of Enceladus to calculate diurnal tidal displacements for a range of ˜del values in the presence of such structural heterogeneities. We find that the presence of variations in ice shell thickness can significantly amplify deformation in thinned regions. If major faults are also activated by tidal forcing—such as Tiger Stripes on Enceladus—their characteristic surface displacement patterns could easily be measured using modern geodetic methods. Within the family of Enceladus models explored, estimates of ˜del that assume spherical symmetry a priori can deviate from the true value by as much as ~ 20% when structural heterogeneities are present. Such uncertainty is smaller than that found with approaches that rely on static gravity and topography (~ 250%) or analyzing diurnal libration amplitudes (~ 25%) to infer ˜del at Enceladus. As such, despite the impact of structural heterogeneities, we find that analysis of diurnal tidal deformation is a relatively robust approach to inferring ˜del.

When relativistic electrons are used to irradiate tissues, such as during FLASH pre-clinical irradiations, the electron beam energy is one of the critical parameters that determine the dose distribution. Moreover, during such irradiations, linear accelerators (linacs) usually operate with significant beam loading, where a small change in the accelerator output current can lead to beam energy reduction. Optimisation of the tuning of the accelerator’s radio frequency system is often required. We describe here a robust, easy-to-use device for non-interceptive monitoring of potential variations in the electron beam energy during every linac macro-pulse of an irradiation run. Our approach monitors the accelerated electron fringe beam using two unbiased aluminium annular charge collection plates, positioned in the beam path and with apertures (5 cm in diameter) for the central beam. These plates are complemented by two thin annular screening plates to eliminate crosstalk and equalise the capacitances of the charge collection plates. The ratio of the charge picked up on the downstream collection plate to the sum of charges picked up on the both plates is sensitive to the beam energy and to changes in the energy spectrum shape. The energy sensitivity range is optimised to the investigated beam by the choice of thickness of the first plate. We present simulation and measurement data using electrons generated by a nominal 6 MeV energy linac as well as information on the design, the practical implementation and the use of this monitor.

Constraining the spatial variability of the thickness of the ice shell of Enceladus (i.e., the crust) is central to our understanding of its thermodynamics and habitability. In this study, we develop a new methodology to infer regional variations in crustal thickness using measurements of tidally-driven elastic strain. As proof of concept, we recover thickness variations from synthetic finite-element models of the crust subjected to diurnal eccentricity tides. We demonstrate recovery of crustal thickness to within ~2 km of true values with < 0.2 km error over spherical harmonic degrees l ≤ 12 (corresponding to half-wavelengths ≥ 60 km). Our computed uncertainty is significantly smaller than the inherent ~10 km ambiguity associated with inferring variations in crustal thickness solely from gravity and topography measurements. We therefore conclude that measuring elastic strain provides a relatively robust approach for probing crustal structure at Enceladus.