arXiv subjects

R. Steiner

Publications and source records attributed to R. Steiner.

5 recordsLinked to original sources

arXiv2014

Pico- and nanosecond laser ablation of mixed tungsten / aluminium films

In order to extend the investigation of laser-assisted cleaning of ITER-relevant first mirror materials to the picosecond regime, a commercial laser system delivering 10 picosecond pulses at 355 nm at a frequency of up to 1 MHz has been used to investigate the ablation of mixed aluminium (oxide) / tungsten (oxide) layers deposited on poly- and nanocrystalline molybdenum as well as nanocrystalline rhodium mirrors. Characterization before and after cleaning using scanning electron microscopy (SEM) and spectrophotometry shows heavy dust formation, resulting in a degradation of the reflectivity. Cleaning using a 5 nanosecond pulses at 350 and 532 nm, on the other hand, proved very promising. The structure of the film remnants suggests that in this case buckling was the underlying removal mechanism rather than ablation. Repeated coating and cleaning using nanosecond pulses is demonstrated.

cond-mat.mtrl-sci↗

arXiv2014

Confining Boundary conditions from dynamical Coupling Constants

It is shown that it is possible to consistently and gauge invariantly formulate models where the coupling constant is a non trivial function of a scalar field . In the $U(1)$ case the coupling to the gauge field contains a term of the form $g(ϕ)j_μ(A^μ +\partial^μB)$ where $B$ is an auxiliary field and $j_μ$ is the Dirac current. The scalar field $ϕ$ determines the local value of the coupling of the gauge field to the Dirac particle. The consistency of the equations determine the condition $\partial^μϕj_μ= 0$ which implies that the Dirac current cannot have a component in the direction of the gradient of the scalar field. As a consequence, if $ϕ$ has a soliton behaviour, like defining a bubble that connects two vacuua, we obtain that the Dirac current cannot have a flux through the wall of the bubble, defining a confinement mechanism where the fermions are kept inside those bags. Consistent models with time dependent fine structure constant can be also constructed

hep-th↗

arXiv2012

Laser damage thresholds of ITER mirror materials and first results on in situ laser cleaning of stainless steel mirrors

A laser ablation system has been constructed and used to determine the damage threshold of stainless steel, rhodium and single-, poly- and nanocrystalline molybdenum in vacuum, at a number of wavelengths between 220 and 1064 nm using 5 ns pulses. All materials show an increase of the damage threshold with decreasing wavelength below 400 nm. Tests in a nitrogen atmosphere showed a decrease of the damage threshold by a factor of two to three. Cleaning tests have been performed in vacuum on stainless steel samples after applying mixed Al/W/C/D coatings using magnetron sputtering. In situ XPS analysis during the cleaning process as well ex situ reflectivity measurements demonstrate near complete removal of the coating and a substantial recovery of the reflectivity. The first results also show that the reflectivity obtained through cleaning at 532 nm may be further increased by additional exposure to UV light, in this case 230 nm, an effect which is attributed to the removal of tungsten dust from the surface.

physics.ins-det↗

arXiv2011

Electromagnetic Mach principle

We will introduce a gauge model which an electromagnetic coupling constant and local mass are related to all the charge in the universe. we will use the standard Dirac action, but where the mass and the electromagnetic coupling constant are a function of the sum of all the charge in the universe, which represent Mach principle for electromagnetic coupling constant. The formalisation is not manifestly Lorentz invariant, however Lorentz invariance can be restored by performing a phase transformation of the Dirac field.

hep-th↗

arXiv1999

Nuclear Structure Functions in the Large x Large Q^2 Kinematic Region in Neutrino Deep Inelastic Scattering

Data from the CCFR E770 Neutrino Deep Inelastic Scattering (DIS) experiment at Fermilab contain events with large Bjorken x (x>0.7) and high momentum transfer (Q^2>50 (GeV/c)^2). A comparison of the data with a model based on no nuclear effects at large x, shows a significant excess of events in the data. Addition of Fermi gas motion of the nucleons in the nucleus to the model does not explain the excess. Adding a higher momentum tail due to the formation of ``quasi-deuterons'' makes some improvement. An exponentially falling F_2 \propto e^-s(x-x_0) at large x, predicted by ``multi-quark clusters'' and ``few-nucleon correlations'', can describe the data. A value of s=8.3 \pm 0.7(stat.)\pm 0.7(sys.) yields the best agreement with the data.

hep-ex↗