B. Norman | Searcharxiv

arXiv2022

A Starry Byte -- proton beam measurements of single event upsets and other radiation effects in ABCStar ASIC Versions 0 and 1 for the ITk strip tracker

Single Event Effects (SEEs) - predominately bit-flips in electronics caused by particle interactions - are a major concern for ASICs operated in high radiation environments such as ABCStar ASICs, which are designed to be used in the future ATLAS ITk strip tracker. The chip design is therefore optimised to protect it from SEEs by implementing triplication techniques such as Triple Modular Redundancy (TMR). In order to verify the radiation protection mechanisms of the chip design, the cross-section for Single Event Upsets (SEUs), a particular class of SEEs, is measured by exposing the chip to high-intensity particle beams while monitoring it for observed SEUs. This study presents the setup, the performed measurements, and the results from SEU tests performed using the latest version of the ABCStar ASIC (ABCStar V1) using a 480 MeV proton beam.

physics.ins-det↗

arXiv2019

Finite-size Kosterlitz-Thouless transition in 2DXY Fe/W(001) ultrathin films

Magnetic susceptibility measurements of 3-4 ML Fe/W(001) ferromagnetic films demonstrate that this is a 2DXY system in which a finite-size Kosterlitz-Thouless (KT) transition occurs. The films are grown in ultrahigh vacuum and their magnetic response is measured using the magneto-optic Kerr effect (MOKE). The analysis of many independently grown films shows that the paramagnetic tail of the susceptibility is described by $χ(T) \sim \exp \bigr{(}B/(T/T_{KT}-1)^a\bigl{)}$, where $a=0.50\pm0.03$ and $B=3.48\pm0.16$, in quantitative agreement with KT theory. Below the finite-size transition temperature $T_C(L)$, the behavior is complicated by dissipation (likely related to the re-emergence of fourfold anisotropy and magnetic domains). A subset of measurements with very small dissipation most closely represents the idealized system treated by theory. In these, the temperature interval between the fitted Kosterlitz-Thouless transition temperature and the finite-size transition temperature is $T_C(L)/T_{KT} -1=0.065\pm0.016$. This yeids an estimate of the finite size $L$ affecting the film of order micrometers. This gives experimental support to the idea that even a mesoscopic limitation of the vortex-antivortex gas results in a substantial finite-size effect at the KT transition. In contrast, fitting the paramagnetic tail to a power law, appropriate to a second order critical transition, does not give reasonable results. The effective critical exponent $γ_{eff} \approx 3.7 \pm 0.7$ does not correspond to a known universality class, and the fitted transition temperature is much further below the peak in the susceptibility than is reasonable.

cond-mat.mtrl-sci↗