arXiv subjects

B. Mercier

Publications and source records attributed to B. Mercier.

8 recordsLinked to original sources

arXiv2026

Study of Nb Surface Under Ultra High Vacuum After Heat Treatments For SRF Cavities

Specific heat treatments applied to superconducting radiofrequency (SRF) cavities, such as nitrogen infusion or Mid T baking, aim to improve the quality factor (Q0) at medium accelerating fields (10 to 20 MV/m). These treatments reduce the BCS surface resistance by tuning the mean free path of niobium over a few hundred nanometers, either by diffusing oxygen from the native oxide layer or by diffusing nitrogen after the dissolution of the oxide layer. However, these treatments preclude the usual chemical polishing, as it would reverse the beneficial effects of the heat treatments, making the cavities highly sensitive to surface contamination. In particular, the formation of niobium carbides, which can mask the expected benefits, strongly depends on the annealing conditions, surface preparation, and the materials history. Several hypotheses are considered regard-ing the origin of carbon: vacuum contamination, surface pollution, or internal migration from the niobium itself, potentially enriched with carbon during previous chemi-cal treatments (BCP, EP). This work aims to identify the primary source of carbon responsible for niobium carbide growth, using techniques such as X Ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and secondary ion mass spectrometry (SIMS). The study will also help pinpoint the key influencing parameters, thereby contributing to a better understanding of and potential mitigation strategies for their impact on SRF cavity performance.

physics.acc-ph↗

arXiv2026

Insitu X Ray Photoemission Study of Nb Surface Under Plasma Cleaning During MID T BAKING For SRF Cavities

Specific heat treatments applied to superconducting radiofrequency (SRF) cavities, such as nitrogen infusion or Mid T baking, aim to improve the quality factor (Qo) at medium accelerating fields (10 to 20 MV/m). These treatments reduce the BCS surface resistance by tuning the mean free path of niobium over a few hundred na-nometers, either by diffusing oxygen from the native oxide layer or by diffusing nitrogen after the dissolution of the oxide layer. However, these treatments preclude the usual chemical polishing, as it would reverse the beneficial effects of the heat treatments, making the cavities highly sensitive to surface contamination. In particular, the formation of niobium carbides, which can mask the expected benefits, strongly depends on the annealing conditions, surface preparation, and the materials history. To better understand these phenomena, niobium samples was annealed under ultrahigh vacuum (Mid T baking) with Ar/O2 plasma treatment to investi-gate surface contamination with insitu heat treatment at 500 C and XPS analysis.

physics.acc-ph↗

arXiv2026

Improvement of Heat-Treated Niobium Surface by In-situ Plasma Treatment Applied to Superconducting RF Resonator

A specific heat treatment at 300 C, named medium-temperature baking (Mid-T baking) is applied to superconducting radio-frequency (SRF) accelerating cavities to improve the quality factor (Qo) at medium accelerating fields (10 to 20 MV/m). This treatment is very successful when done properly as it can reduce by almost a factor of two the power dissipations in this field range. However, surface contamination can lead to the degradation of Qo instead. Plasma-based surface treatment provides an effective approach to eliminate contaminants from the Niobium surface. In this study an insitu plasma cleaning process with argon containing 10 % O2 was performed to remove hydrocarbons from Niobium surface. The treatment was applied before and after a heat treatment at 500 C under ultra-high vacuum conditions (Mid-T baking). Changes in chemical speciation and oxide layer alteration induced by plasma processing were analyzed using insitu X-ray photoelectron spectroscopy (XPS) and exsitu scanning electron microscopy (SEM). The results show that plasma treatment modifies the composition of Niobium oxides, converting a Nb2O5 layer into NbO2. Furthermore, a plasma treatment before Mid-T baking helps reduce unstable oxides such as NbxO and significantly increases the proportion of metallic Niobium at the surface. The Niobium sample treated by plasma prior to Mid-T baking showed a 53 % reduction in carbide formation. Moreover, the C1s component attributed to NbC bonds shifts toward lower binding energy, indicating the formation of a more metallic NbC phase. Whereas without plasma treatment, the higher binding energy component observed after Mid T baking is consistent with Nb2C.

physics.acc-ph↗

arXiv2024

Technical Status Report on Plasma Components and Systems in the context of EuPRAXIA

The EuPRAXIA project aims to construct two state-of-the-art accelerator facilities based on plasma accelerator technology. Plasma-based accelerators offer the possibility of a significant reduction in facility size and cost savings over current radio frequency (RF) accelerators. The two facilities - one laser-driven one a beam-driven - are envisioned to provide electron beams with an energy in the range of 1-5 GeV and beam quality comparable to existing RF machines. This will enable a versatile portfolio of applications from compact free-electron laser (FEL) drivers to sources for medical and industrial imaging. At the heart of both facilities is the use of plasma-based accelerator components and systems which encompass not only the accelerating medium itself, but also a range of auxiliary systems such as plasma-based electron beam optics and plasma-based mirrors for high-intensity lasers. From a technical standpoint, a high-degree of control over these plasma devices will be essential for EuPRAXIA to achieve its target performance goals. The ability to diagnose and characterize these plasma devices and to simulate their operation will be further essential success factors. Additionally, compatibility with extended operation at high-repetition rates and integration into the accelerator beamline will also prove crucial. In this work, we aim to review the current status of plasma components and related systems for both laser-driven and beam-driven plasma accelerators and to assess challenges to be addressed regarding implementation at future EuPRAXIA facilities.

physics.plasm-ph↗

arXiv2023

Two-chamber gas target for laser-plasma accelerator electron source

Exploring new target schemes for laser wakefield accelerators is essential to meet the challenge of increasing repetition rates while ensuring stability and quality of the produced electron beams. The prototyping of a two-chamber gas cell integrated into the beam line and operating in continuous gas flow is introduced and discussed in the frame of ionisation injection. We report the numerical fluid modeling used to assist the density profile shaping. We describe the test bench used for cell prototype assessment, in particular the plasma electron density and longitudinal distribution of species relevant for ionisation injection. The lifetime of the target key part is measured for different materials. Perspectives to high power operation are outlined.

physics.acc-ph↗

arXiv2012

PHIL photoinjector test line

LAL is now equiped with its own platform for photoinjectors tests and Research and Developement, named PHIL (PHotoInjectors at LAL). This facility has two main purposes: push the limits of the photoinjectors performances working on both the design and the associated technology and provide a low energy (MeV) short pulses (ps) electron beam for the interested users. Another very important goal of this machine will be to provide an opportunity to form accelerator physics students, working in a high technology environment. To achieve this goal a test line was realised equipped with an RF source, magnets and beam diagnostics. In this article we will desrcibe the PHIL beamline and its characteristics together with the description of the first two photoinjector realised in LAL and tested: the ALPHAX and the PHIN RF Guns.

physics.acc-ph↗

arXiv2011

Non-planar four-mirror optical cavity for high intensity gamma ray flux production by pulsed laser beam Compton scattering off GeV-electrons

As part of the R&D toward the production of high flux of polarised Gamma-rays we have designed and built a non-planar four-mirror optical cavity with a high finesse and operated it at a particle accelerator. We report on the main challenges of such cavity, such as the design of a suitable laser based on fiber technology, the mechanical difficulties of having a high tunability and a high mechanical stability in an accelerator environment and the active stabilization of such cavity by implementing a double feedback loop in a FPGA.

physics.acc-ph↗

arXiv2001

Classical solutions in the Einstein-Born-Infeld-Abelian-Higgs model

We consider the classical equations of the Born-Infeld-Abelian-Higgs model (with and without coupling to gravity) in an axially symmetric ansatz. A numerical analysis of the equations reveals that the (gravitating) Nielsen-Olesen vortices are smoothly deformed by the Born-Infeld interaction, characterized by a coupling constant $β^2$, and that these solutions cease to exist at a critical value of $β^2$. When the critical value is approached, the length of the magnetic field on the symmetry axis becomes infinite.

hep-th↗