arXiv subjects

Kamel Dougdag

Publications and source records attributed to Kamel Dougdag.

3 recordsLinked to original sources

arXiv2025

Effects of the vibrations and electromagnetic pollution induced by a closed-cycle pulse-tube cryostat on high-accuracy electrical measurements

A paradigm shift in achieving (sub-)Kelvin environments is currently underway with the democratization of cryogen-free cryocoolers. This transition is driven by their user-friendly, continuous operation and the elimination of liquid helium, which is becoming increasingly scarce and expensive. Thanks to their large sample space and high cooling power, these systems can host superconducting magnets, making them an ideal platform for quantum technologies, materials science, low-temperature detectors, and even medical applications.The drawback is that this type of systems is inherently based on gas compression that induces a certain level of vibrations and electromagnetic perturbations, which can potentially prevent the determination of low amplitude signals or spoil their stability. In this paper we demonstrate that pulse-tube based cryocoolers can be used for electrical precision measurements under high magnetic field, using a commercial cryomagnetic system combined with a customized coaxial cryoprobe. Parts-per-billion level of measurement uncertainties in resistance determination, based on the quantum Hall resistance standard, is achievable, matching the state-of-the-art involving conventional cryostats based on liquid helium. We performed an extensive characterization of the cryomagnetic system to determine the level of vibrations and electromagnetic perturbations, revealing the drastic effect of the magnetic field on the electromagnetic noise level. If interferences can happen in some measurements, others appear immune to the perturbations, meaning that the cryogen-free system is not inherently a source of disturbance. The set of characterization measurements presented here is easily implementable in laboratories, which can help to determine the vibrations and electromagnetic pollution generated by any cryocooler.

cond-mat.other↗

arXiv2024

Finite Element Analysis of the Uncertainty Contribution from Mechanical Imperfections in the LNE's Thompson-Lampard Calculable Capacitor

Thompson-Lampard type calculable capacitors (TLCC) serve as electrical capacitance standards, enabling the realization of the farad in the International System of Units (SI) with a combined uncertainty on the order of one part in $10^8$. This paper presents an electrostatic finite element (FEM) simulation study focusing on the mechanical imperfections inherent in the developed second generation TLCC at LNE and their influence on the combined uncertainty of the practical realization of the farad. In particular, this study establishes the acceptable tolerances for deviations from perfect geometrical arrangements of the TLCC electrodes required to achieve the target relative uncertainty of one part in $10^8$. The simulation predictions are compared with corresponding experimental observations which were conducted with the help of the sub-micron level control of the standard's electrode geometry. In the second generation of the LNE's TLCC, the uncertainty contribution from mechanical imperfections was reduced by at least a factor of 4, as demonstrated by the present FEM analysis. Combined with other improvements, the standard's overall uncertainty meets the target level.

physics.ins-det↗

arXiv2024

Measuring Non-linearity in AH 2700A Capacitance Bridges with sub-ppm level uncertainty

The stability and non-linearity of a commercial AH 2700A capacitance bridge were studied beyond its specified capabilities using the Thompson-Lampard Calculable Capacitor (TLCC) at LNE. The TLCC allows for continuous variation of measured capacitance between 0.4 pF and 1.2 pF with a resolution of 2 parts in $10^{7}$ and stability better than 1 part in $10^{9}$ over 2 days. The study aimed to determine root cause of the saw-tooth non-linearity pattern observed in the AH 2700A capacitance bridge. This pattern becomes apparent when the internal calibration is no longer valid, indicating deviations in the bridge circuit. Additionally, the dependence of capacitance non-linearity on various factors such as frequency and capacitance value are described. This work enables automatic calibration of the commercial bridge with an uncertainty of sub-ppm level and allows for quick evaluation of TLCC's non-linearity and monitoring of any changes over time through in-situ measurements.

physics.ins-det↗