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A study of the physics of separating and reattaching flows around bodies with sharp edges is reported. Data from direct numerical simulations of the flow around a rectangular cylinder with aspect ratio 5 at different Reynolds numbers are used. The flow is decomposed into multiple interacting flow phenomena such as the laminar boundary layer in the front face, the separated shear layer, the flow impingement at reattachment, the reverse boundary layer within the recirculating bubble and the near- and far-wake flow. A detailed analysis of the physics of these phenomena is provided, including the slow modulation induced by large-scale instabilities related with vortex shedding. The entrainment phenomena acting along the separated shear layer and their unbalance between its inner and outer sides are recognised as fundamental mechanisms determining the tendency of the flow to reattach and the overall fluxes of momentum and heat. The behaviour of entrainment is found to be strictly related with the shear-layer velocity difference that in turn is determined by the behaviour of the reverse boundary layer and by its strength in counteract adverse pressure gradients. The physical understanding of the compound role played by these and all the other mechanisms composing the flow, poses the basis for the formulation of theoretical frameworks able to unify all these interacting phenomena. Finally, the present work provides access to high-fidelity flow statistics of relevance for benchmark activities on bluff bodies with sharp edges.

Very High Energy Electron (VHEE) beams are a promising alternative to conventional radiotherapy due to their highly penetrating nature and their applicability as a modality for FLASH (ultra-high dose-rate) radiotherapy. The dose distributions due to VHEE need to be optimised; one option is through the use of quadrupole magnets to focus the beam, reducing the dose to healthy tissue and allowing for targeted dose delivery at conventional or FLASH dose-rates. This paper presents an in depth exploration of the focusing achievable at the current CLEAR (CERN Linear Electron Accelerator for Research) facility, for beam energies >200 MeV. A shorter, more optimal quadrupole setup was also investigated using the TOPAS code in Monte Carlo simulations, with dimensions and beam parameters more appropriate to a clinical situation. This work provides insight into how a focused VHEE radiotherapy beam delivery system might be achieved.

This paper presents the first plasmid DNA irradiations carried out with Very High Energy Electrons (VHEE) over 100–200 MeV at the CLEAR user facility at CERN to determine the Relative Biological Effectiveness (RBE) of VHEE. DNA damage yields were measured in dry and aqueous environments to determine that ~ 99% of total DNA breaks were caused by indirect effects, consistent with other published measurements for protons and photons. Double-Strand Break (DSB) yield was used as the biological endpoint for RBE calculation, with values found to be consistent with established radiotherapy modalities. Similarities in physical damage between VHEE and conventional modalities gives confidence that biological effects of VHEE will also be similar—key for clinical implementation. Damage yields were used as a baseline for track structure simulations of VHEE plasmid irradiation using GEANT4-DNA. Current models for DSB yield have shown reasonable agreement with experimental values. The growing interest in FLASH radiotherapy motivated a study into DSB yield variation with dose rate following VHEE irradiation. No significant variations were observed between conventional and FLASH dose rate irradiations, indicating that no FLASH effect is seen under these conditions.

Turbulence is investigated in the lee of an open-cell metal foam layer. In contrast to canonical grids, metal foams are locally irregular but statistically isotropic. The solid matrix is characterised by two lengths, the ligament thickness $d_f$ and the pore diameter $d_p$. A direct numerical simulation is conducted on a realistic metal foam geometry for which $d_f/d_p = 0.14$ and the porous layer thickness is five times the pore diameter. The Reynolds number based on the pore size is ${\\textit {Re}}_{d_p} = 4000$, corresponding to a Taylor-scale Reynolds number ${\\textit {Re}}_\\lambda \\approx 80$. Closer to the foam than two pore diameters, the pressure and turbulent transports of turbulent kinetic energy are non-negligible. In the same region, ${\\textit {Re}}_\\lambda$ undergoes a steep decrease whereas the dissipation coefficient $C_{\\epsilon }$ increases like ${\\textit {Re}}_\\lambda ^{-1}$. At larger distances from the porous layer, the classical grid turbulence situation is recovered, where the mean advection of turbulent kinetic energy equals dissipation. This entails a power-law decay of turbulent quantities and characteristic lengths. The decaying exponents of integral, Taylor and Kolmogorov scales are close to one-half, indicating that the turbulence simulated here differs from Saffman turbulence. Analysis of the scaling exponents of structure functions and the decorrelation length of dissipation reveals that small-scale fluctuations are weakly intermittent.

Systems based on wind energy harvesting can successfully meet part of the increasing green energy demand worldwide. However, wind turbines operation might be undermined by varying atmospheric conditions, which could result in an increase of angle of attack and consequent onset of flow separation phenomena, especially at low Reynolds numbers. Such conditions are strongly influenced by blades geometry, and they negatively affect structural integrity and power output of wind turbines. For this reason, it is crucial to define a tool capable of swiftly allowing numerical investigations on different geometrical configurations to delay and mitigate flow separation occurrence. The present work aims at modelling laminar-turbulent transition and turbulent flow separation over a wind turbine blade section operating at angle of attack = 15°, Re = 66000 and Pr = 0.71 by means of a steady RANS approach. Turbulence is treated by means of the Transition SST k-ω and the Transition k-kL-ω models. The main aerodynamic and thermal coefficients are evaluated and compared against a high-order accurate DNS database for validation. The results highlight, for the present test case, a better capability of the Transition SST k-ω of perceiving the main thermo-fluid dynamic features of the separated flow over the blade section.

We present the observation and the detailed investigation of coherent Cherenkov diffraction radiation (CChDR) in terms of spectral-angular characteristics. Electromagnetic simulations have been performed to optimize the design of a prismatic dielectric radiator and the performance of a detection system with the aim of providing longitudinal beam diagnostics. Successful experimental validations have been organized on the CLEAR and the CLARA facilities based at CERN and Daresbury laboratory respectively. With ps to sub-ps long electron bunches, the emitted radiation spectra extend up to the THz frequency range. Bunch length measurements based on CChDR have been compared to longitudinal bunch profiles obtained using a radio frequency deflecting cavity or coherent transition radiation (CTR). The retrieval of the temporal profile of both Gaussian and non-Gaussian bunches has also been demonstrated. The proposed detection scheme paves the way to a new kind of beam instrumentation, simple and compact for monitoring short bunches of charged particles, particularly well-adapted to novel accelerator technologies, such as dielectric and plasma accelerators. Finally, CChDR could be used for generating intense THz radiation pulses at the MW level in existing radiation facilities, providing broader opportunities for the user community.

Active plasma lenses are compact devices developed as a promising beam-focusing alternative for charged particle beams, capable of short focal lengths for high-energy beams. We have previously shown that linear magnetic fields with gradients of around 0.3 kT/m can be achieved in argon-filled plasma lenses that preserve beam emittance [C.A. Lindstrøm et al., Phys. Rev. Lett. 121, 194801 (2018)]. Here we show that with argon in a500μmdiameter capillary, the fields are still linear with a focusing gradient of 3.6 kT/m, which is an order of magnitude higher than the gradients of quadrupole magnets. The current pulses that generate the magnetic field are provided by compact Marx banks, and are highly repeatable. The demonstrated operation with simultaneously high-gradient, linear fields and good repeatability establish active plasma lenses as an ideal device for pulsed particle beam applications requiring very high focusing gradients that are uniform throughout the lens aperture.

Background The real burden of human cystic echinococcosis (CE) remains elusive, due to the peculiar characteristics of the disease and the heterogeneous and incomplete data recording of clinical cases. Furthermore, official notification systems do not collect pivotal clinical information, which would allow the comparison of different treatment outcomes, and thus circumvent the difficulty of implementing clinical trials for CE. The Italian Register of CE (RIEC) was launched in 2012 and expanded in 2014 into the European Register of CE (ERCE). The primary aim of the ERCE was to highlight the magnitude of CE underreporting, through the recording of cases that were not captured by official records. We present an overview of data collated in the ERCE and discuss its future, five years after its inception. Methods The ERCE database was explored on March 31st 2019; data concerning participating centres and registered cases were descriptively analysed. Results Forty-four centres from 15 countries (7 non-European) were affiliated to the ERCE. Thirty-four centres (77%) registered at least one patient; of these, 18 (53%) recorded at least one visit within the past 18 months. A total of 2097 patients were registered, 19.9% of whom were immigrants. Cyst characteristics were reported for at least one cyst at least in one visit in 1643 (78.3%) patients, and cyst staging was used by 27 centres. In total, 3386 cysts were recorded at first registration; mostly located in the liver (75.5%). Data concerning clinical management could be analysed for 920 “cyst stage-location-management” observations, showing great heterogeneity in the implementation of the stage-specific management approach recommended by the WHO. Conclusions The ERCE achieved its goal in showing that CE is a relevant but neglected public health problem in Europe and beyond, since a proportion of patients reaching medical attention are not captured by official notification systems. The ERCE may provide a valuable starting platform to complement hospital-derived data, to obtain a better picture of the epidemiology of clinical CE, and to collect clinical data for the issue of evidence-based recommendations. The ERCE will be expanded into the International Register of CE (IRCE) and restructured aiming to overcome its current criticalities and fulfil these aims.

The operation of an extended power budget long reach access network is experimentally demonstrated using commercially available small form pluggable directly modulated transmitters and a simplified coherent receiver free from digital signal processing and phase-locked loops. An ad-hoc choice of photodiode bandwidth allows no penalty compared with external modulation based transmitters.

We report on the radiation studies performed at the CLEAR facility of CERN in the sub-THz range, exploiting picosecond ultrarelativistic electron bunches for the production of coherent radiation. The coherent radiation, produced by different mechanisms (in particular coherent transition radiation), has been fully characterized using different techniques and detectors. The main aim has been that to setup a new beam-based source of radiation in the mm-waves for external users, individuating the performances and the limitations. Moreover the coherent radiation has been used for longitudinal diagnostics, providing reliable bunch length values consistent with other diagnostics. Transverse shaping of the radiation source has been also demonstrated via control of the size and divergence of the electron bunch at the source plane. The mechanism yielding the highest peak-power has been the Cherenkov-Diffraction Radiation, providing∼0.1MW. The current performances of the CLEAR THz source seem to be more suitable for high-average-power than high-peak-power applications. Future plans and strategies will look toward the realization of a high-peak-power source, providing∼10–100MWTHzpulses.