Plasma Wavelength Λp Research Articles

Indirect self-modulation instability measurement concept for the AWAKE proton beam

AWAKE, the Advanced Proton-Driven Plasma Wakefield Acceleration Experiment, is a proof-of-principle R&D experiment at CERN using a 400GeV/c proton beam from the CERN SPS (longitudinal beam size σz=12cm) which will be sent into a 10m long plasma section with a nominal density of ≈7×1014atoms/cm3 (plasma wavelength λp=1.2mm). In this paper we show that by measuring the time integrated transverse profile of the proton bunch at two locations downstream of the AWAKE plasma, information about the occurrence of the self-modulation instability (SMI) can be inferred. In particular we show that measuring defocused protons with an angle of 1mrad corresponds to having electric fields in the order of GV/m and fully developed self-modulation of the proton bunch. Additionally, by measuring the defocused beam edge of the self-modulated bunch, information about the growth rate of the instability can be extracted. If hosing instability occurs, it could be detected by measuring a non-uniform defocused beam shape with changing radius. Using a 1mm thick Chromox scintillation screen for imaging of the self-modulated proton bunch, an edge resolution of 0.6mm and hence an SMI saturation point resolution of 1.2m can be achieved.

Near-infrared reflection from Al-doped ZnO films prepared by multi-target reactive sputtering

Thin films of aluminium-doped zinc oxide (ZnO:Al) as heat reflective coatings were prepared by multi-target reactive sputtering using metallic Zn and Al targets. An optimization of Al content and a reduction in oxygen partial pressure were crucial in increasing the carrier concentration Ne and the Hall mobility μ. The ZnO:Al film with the highest Ne achieved the shortest plasma wavelength λp of 1375 nm, which shifted the near-infrared reflectance spectrum closer to the visible region. The high μ reduced the optical absorption and enhanced the reflectance. Moreover, the multi-target system enabled intermittent doping of Al, which was applied to stack multilayers consisting of non-doped and Al-doped ZnO layers. A drop in the refractive indices n above λp for the ZnO:Al layers formed the periodic distribution of n in the thickness direction, which provided a high reflectance zone from 1000 to 1400 nm in wavelength.

Transition from Casimir to van der Waals force between macroscopic bodies

The transition of van der Waals to Casimir forces between macroscopic gold surfaces is investigated by atomic force microscopy in the plane-sphere geometry. It was found that the transition appears to take place at separations ∼10% the plasma wavelength λp for evaporated gold surfaces, which compares to theoretical predictions by incorporation of experimental optical data and roughness corrections. Moreover, the force data allow estimation of the Hamaker constant AH in the van der Waals regime, which is in good agreement with the Lifshitz theory predictions (even if roughness corrections are taken into account) and former surface force apparatus measurements.

A method for determining the static conductivity of semiconductor transparent heat mirrors

A simple method for determining the static conductivity of semiconductor transparent heat mirrors is developed that is based on the relationships of Drude theory and high-frequency optical measurements. The method consists of two steps. In the first step, the dielectric permittivity of the lattice eL and the plasma wavelength λp of the semiconductor film (a part of the heat mirror) are determined graphically using the reflectance measured at extreme points of interference fringes that are observed in the transparency regions of the reflectance spectra. The second step consists in the numerical computation of relaxation times and the static conductivity using the derived values of eL and λp and an experimental value of total emittance. The method was tested with transparent heat mirrors based on films of tin-doped indium oxide.