Teflon Target Research Articles

Particle energization in colliding subcritical collisionless shocks investigated in the laboratory

Context. Colliding collisionless shocks appear across a broad variety of astrophysical phenomena and are thought to be possible sources of particle acceleration in the Universe. Aims. The main goal of our experimental and computational work is to understand the effect of the interpenetration between two subcritical collisionless shocks on particle energization. Methods. To investigate the detailed dynamics of this phenomenon, we performed a dedicated laboratory experiment. We generated two counter-streaming subcritical collisionless magnetized shocks by irradiating two Teflon (C2F4) targets with 100 J, 1 ns laser beams on the LULI2000 laser facility. The interaction region between the plasma flows was pre-filled with a low-density background hydrogen plasma and initialized with an externally applied homogeneous magnetic field perpendicular to the shocks. We also modeled the macroscopic evolution of the system via hydrodynamic simulations and the microphysics at play during the interaction via particle-in-cell (PIC) simulations. Results. Here, we report our measurements of the plasma density and temperature during the formation of the supercritical shocks, their transition to subcritical, and their final interpenetration. We find that in the presence of two shocks, the ambient ions reach energies around 1.5 times of those obtained with single shocks. Both the presence of the downstream zone of the second shock and of the downstream zone common for the two shocks play a role in the different energization: the characteristics of the perpendicular electric fields in the two areas indeed allow for certain particles to continue being accelerated or, at least, to avoid being decelerated. Conclusions. The findings of our laboratory investigation are relevant for our understanding of the energy distribution of high-energy particles that populate the interplanetary space in our solar system and the very local interstellar medium around the heliopause, where observations have indicated evidence of subcritical collisionless shocks that may eventually go on to collide with one another.

Laboratory modelling of equatorial ‘tongue’ accretion channels in young stellar objects caused by the Rayleigh-Taylor instability

Context. The equatorial accretion scenario, caused by the development of the Rayleigh-Taylor (RT) instability at the disk edge, was suggested by accurate three-dimensional magnetohydrodynamic (MHD) modelling, but no observational or experimental confirmation of such phenomena has been evidenced yet. Aims. We studied the propagation of a laterally extended laser-generated plasma stream across a magnetic field and investigated if this kind of structure can be scaled to the case of equatorial ‘tongue’ accretion channels in young stellar objects (YSOs); if so, this would support the possibility of equatorial accretion in young accreting stars. Methods. We conducted a scaled laboratory experiment at the PEARL laser facility. The experiment consists in an optical laser pulse that is focused onto the surface of a Teflon target. The irradiation of the target leads to the expansion of a hot plasma stream into the vacuum, perpendicularly to an externally applied magnetic field. We used a Mach-Zehnder interferometer to diagnose the plasma stream propagation along two axes, to obtain the three-dimensional distribution of the plasma stream. Results. The laboratory experiment shows the propagation of a laterally extended laser-generated plasma stream across a magnetic field. We demonstrate that: (i) such a stream is subject to the development of the RT instability, and (ii) the stream, decomposed into tongues, is able to efficiently propagate perpendicular to the magnetic field. Based on numerical simulations, we show that the origin of the development of the instability in the laboratory is similar to that observed in MHD models of equatorial tongue accretion in YSOs. Conclusions. As we verify that the laboratory plasma scales favourably to accretion inflows of YSOs, our laboratory results support the argument in favour of the possibility of the RT-instability-caused equatorial tongue accretion scenario in the astrophysical case.

Observation of quasi-monochromatic resonant Cherenkov diffraction radiation

The first observation and investigation of a new mechanism of resonant Cherenkov diffraction radiation appearing when relativistic 6 MeV electrons move alongside a periodically shaped Teflon target have been presented and analysed. Numerical simulations performed using computer code KARAT are in good agreement with the experimental results. This new mechanism is a promising technique for generation and monochromatisation of THz and sub-THz radiation beams that could be integrated into any short bunch linear accelerator facility including 4th generation light sources providing new opportunities for user community.

Fabrication of transition metal (TM = Fe, Co) difluorides–carbon nanocomposite films by magnetron co-sputtered deposition of Fe/Co and Teflon targets

We present a general synthesis of transition metal difluorides (TMF2)–carbon nanocomposite films by magnetron co-sputtering the Fe/Co and polytetrafluoroethylene (Teflon) targets. The composites consist of binary TMF2 (TM = Fe, Co) nanoparticles with a crystallite size of ∼8 nm immersed in a carbon matrix. The antiferromagnetic nature of TMF2 nanoparticles with the Néel temperature T N of 40 K (TM = Co) and 78 K (TM = Fe) is confirmed. The ability to create the sputter-deposited TMF2–carbon nanocomposites may not only allow for possible energy applications but also provide a platform for investigating the particulate disordered antiferromagnets.

Triple Langmuir probe measurements in a low-energy tongue-flared configuration plasma thruster

The pulsed plasma thruster is a type of electric propulsion, which has attracted a lot of interest due to its application in microsatellite. In this study, a side-fed, tongue-flared configuration PPT is operated at 2 J and a triple Langmuir probe is used to measure the plasma characteristics, namely electron temperature, Te and electron density, ne. These measurements were carried out in both perpendicular and parallel planes to the thruster electrode. The radial profiles of plasma expulsion in both planes were also measured and compared. The mean ion velocity was calculated from the plasma transit times from the teflon target where surface discharge was first initiated to the probe positions. These plasma characteristics were compared to other systems operated over a wide range of energy.

Flat-field VLS spectrometer for a wavelength range of 50 – 275 Å

A flat-field VLS spectrograph for a wavelength range ∼50 – 275 Å with an average linear dispersion of 0.18 mm Å−1, which makes use of a grazing-incidence varied line-space (VLS) grating, was calculated and implemented (a spectrograph of Harada class). To fabricate the VLS grating by interference lithography technique, an algorithm was developed for calculating the writing configuration with an auxiliary aberrating mirror (the solution of the inverse problem of interference lithography). The spectrograph was put to a test and line spectra were recorded from the laser-produced plasma of lithium fluoride and teflon targets, which were excited by a focused laser beam (0.5 J, 8 ns, 1.06 μm). A resolving power λ/d l = 800 was demonstrated in a wavelength region of 135 Å.

Measurement of proton inelastic scattering cross sections on fluorine

Differential cross-sections for proton inelastic scattering on fluorine, 19F(p,p’)19F, from the first five excited levels of 19F at 110, 197, 1346, 1459 and 1554keV were measured for beam energies from 3 to 7MeV at a scattering angle of 150° using a LiF thin target (50μg/cm2) evaporated on a self-supporting C thin film (30μg/cm2). Absolute differential cross-sections were calculated with a method not dependent on the absolute values of collected beam charge and detector solid angle. The validity of the measured inelastic scattering cross sections was then tested by successfully reproducing EBS spectra collected from a thick Teflon (CF2) target. As a practical application of these measured inelastic scattering cross sections in elastic backscattering spectroscopy (EBS), the feasibility of quantitative light element (C, N and O) analysis in aerosol particulate matter samples collected on Teflon by EBS measurements and spectra simulation is demonstrated.

Polarization Radiation in a Teflon Target

Contribution of Cherenkov radiation and Diffraction radiation when electrons are moving close to a dielectric prism for different angles of the prism face in respect to the electron beam direction was experimentally investigated. The comparison of experimental results with calculations using the known theoretical model shows the significant discrepancy in angular dependence for different orientation angles. The experimental analysis of the causes of discrepancy was performed. The experiment was performed on the relativistic electron beam with energy 6.2 MeV in Tomsk Polytechnic University.

Position-resolved Positron Annihilation Lifetime Spectroscopy

A new method which allows for position-resolved positron lifetime spectroscopy studies in extended volume samples is presented. In addition to the existing technique of in-situ production of positrons inside large (cm3) bulk samples using high-energy photons up to 16 MeV from bremsstrahlung production, granular position-sensitive photon detectors have been employed. A beam of intense bremsstrahlung is provided by the superconducting electron linear accelerator ELBE (Electron Linear Accelerator with high Brilliance and low Emittance) which delivers electron bunches of less than 10 ps temporal width and an adjustable bunch separation of multiples of 38 ns, average beam currents of 1 mA, and energies up to 40 MeV. Since the generation of bremsstrahlung and the transport to the sample preserves the sharp timing of the electron beam, positrons generated inside the entire sample volume by pair production feature a sharp start time stamp for positron annihilation lifetime studies with high timing resolutions and high signal to background ratios due to the coincident detection of two annihilation photons. Two commercially available detectors from a high-resolution medial positron-emission tomography system are being employed with 169 individual Lu2SiO5:Ce scintillation crystals, each. In first experiments, a positron-lifetime gated image of a planar Si/SiO2 (pieces of 12.5 mm × 25 mm size) sample and a 3-D structured metal in Teflon target could be obtained proving the feasibility of a three dimensional lifetime-gated tomographic system.

Experimental Research of the Diffraction and Vavilov-Cherenkov Radiation Generation in a Teflon Target

Geometry of Vavilov-Cherenkov (VChR) radiation when an electron moves close to a dielectric target is in analogy to diffraction radiation (DR) geometry. In this case we may expect DR generation from the upstream face of the target besides that VChR. The joint observation of these booth types of radiation is very interesting from the pseudo-photon viewpoint, which is applicable for relativistic electrons. Unexpected results obtained in our experiment insist on reflection about nature both DR and VChR. The experiment was performed on the relativistic electron beam of the microtron of Tomsk Polytechnic University.

Application of clutter reduction techniques for detection of metallic and low dielectric target behind the brick wall by stepped frequency continuous wave radar in ultra-wideband range

A study of clutter reduction techniques for detection of metallic and non-metallic (low dielectric constant) targets behind a brick wall with the help of ultra-wideband (UWB) through wall imaging system is presented. It is known that sometimes the clutter level is comparable to the level of target reflection that makes it difficult to detect the target correctly. Detection of low dielectric constant materials becomes more difficult due to low reflection from such targets. Therefore there is a need to analyse various clutter removal techniques and check the performance of these techniques for enhancement of target signal-to-clutter ratio. For this purpose, an UWB stepped frequency wave radar is indigenously assembled with the use of vector network analyser, which works in the frequency range of 3.95–5.85 GHz. An experiment is carried out for detection of metal as well as Teflon (low dielectric constant) targets with the application of clutter reduction techniques. The authors have considered statistical-based techniques like singular value decomposition, principle component analysis, factor analysis and independent component analysis (ICA) for clutter removal. It is observed that the signal-to-clutter ratio for metal target detection is quite enhanced by all the four techniques, whereas only ICA is able to enhance the signal-to-clutter ratio for a low dielectric constant target like Teflon.

Nontarget Deposition and Losses of Chlorothalonil in Irrigation Runoff Water from a Commercial Foliage Plant Nursery

Commercial foliage plant production requires the use of pesticides for controlling pests and pathogens that can reduce aesthetic qualities of crops, rendering them unwanted by consumers. Chlorothalonil is a common, broad-spectrum, foliar fungicide used for protecting plants from a variety of fungal diseases. This fungicide may also be acutely toxic to nontarget aquatic organisms due to its mode of action. This study evaluated the amount of chlorothalonil deposited on nontarget ground surfaces during normal sprayer applications at a commercial nursery using Teflon targets. One day following application, irrigation runoff events were initiated and runoff water samples were collected and analyzed for chlorothalonil. Discharge volumes were also measured to allow estimation of the total mass of chlorothalonil discharged during each event. Results indicated that 9.8 to 53.6% of the active ingredient applied landed on nontarget ground surfaces depending on plant size, spacing, and row lengths (short rows sprayed from one side vs. longer rows sprayed from both ends). On an entire production-area scale, 29.2% of the active ingredient applied was deposited on ground surfaces. Of the total nontarget deposition, 0.25 to 0.53% was detected in runoff water discharged from the production area. Concentrations ranged from 1.2 to 500 microg/L during the first runoff events following application.

Noble-gas liquid detectors: measurement of light diffusion and reflectivity on commonly adopted inner surface materials

Noble-gas liquids, such as xenon and argon, have been recently proposed as Vacuum Ultra Violet (VUV) light scintillators in some experiments dedicated to neutrino physics and dark matter research. Fundamental parameters for the photon detection are the diffusion coefficient and the reflectivity of the materials that surround the active volume of the apparatus. We carried out a investigation on the most commonly used materials at the scintillation wavelength λ ∼ 172 nm (close to the liquid xenon wavelength). The measurement has been performed at various incident angles by means of a collimated VUV source. The experimental set-up and the results obtained at room temperature with stainless steel, aluminum, peek and teflon targets are presented.

X-ray spectroscopy observation of fast ions generation in plasma produced by short low-contrast laser pulse irradiation of solid targets

X-ray spectra of plasma produced by the interaction of Ti:Sa laser pulses (duration from 60 fs to 1 ps, and energy from 15 mJ to 128 mJ) with foil and solid Teflon and AL targets are investigated. It is shown experimentally and theoretically that the use of low contrast (10−2 – 10−4) short laser pulses, essentially promotes the conditions for generation of fast multi-charged ions. This effect is caused by self-focusing of the main laser pulse in a preplasma produced by intense laser prepulses. Modeling of the observed spectral line shape gives evidence of a considerable (about 3%) amount of multi-charged He-like F ions with energy E ∼ 1 MeV at rather low values of laser intensity IL ≈ 6 × 1016 W cm−2.

Generation of fast ions in femto-and picosecond laser plasmas at low intensities of the heating radiation

X-ray spectra from Teflon targets irradiated by laser pulses with a duration of 60 fs to 1 ps have been investigated experimentally. It is shown that, when the contrast of the laser pulse is sufficiently low, the effect of self-focusing of the main laser pulse in the plasma produced by the prepulse can significantly enhance the generation efficiency of fast particles. In this case, ions with energies as high as ∼1 MeV are observed at relatively low laser intensities, qlas ≈ (4–6) × 1016 W/cm2.

Combined electron and focused ion beam system for improvement of secondary ion yield in secondary ion mass spectrometry instrument

Using a combined electron and focused ion beam system to improve performance of secondary ion mass spectrometry instruments has been investigated experimentally. The secondary ion yield for an Al target has been enhanced to about one order of magnitude higher with the postionization induced by the low energy electrons in the combined beam. It can be further improved with the increase of electron beam current. When the combined beam is applied to insulating targets, sample charging is also eliminated. For Teflon targets, the secondary ion signal is increased by more than a factor of 20.

Dual ion-beam sputtering deposition of palladium-fluoropolymer nano-composites

The morphological (TEM) and chemical (XPS, ARXPS) characterizations of fluoropolymer films modified with palladium particles (CFx(Pd)) are reported in this article. The films, which have different levels of metal content, have been deposited by ion beam co-sputtering a Teflon target and a palladium one. Composite films with a thickness of a few nanometers have also been deposited and analyzed. For all degrees of thickness, the analyses show the fluoropolymer nature of the hosting material, the nanoscopic character of metal domains, and their uniform distribution in the polymer matrix. The likely application of this ion sputter-deposited material in the sensor field has also been preliminary tested.

Deposition and analytical characterization of fluoropolymer thin films modified by palladium nanoparticles

Palladium–fluoropolymer nanostructured composites (Pd–CF x ) are deposited by a separate and simultaneous sputtering of bulk Teflon and palladium targets in a vacuum chamber. Such nano-material can find application as active layer in sensing devices, as it swells when exposed to the vapors of organic solvents such as acetone, chloroform, 2-propanol. Ellipsometry shows that the swelling extent linearly depends on the solvent partial pressure in the measuring chamber. Moreover, Pd–CF x sensitivity and selectivity features are different to those of a parent gold–fluoropolymer (Au–CF x ) nanocomposite, investigated in previous studies. In particular, Pd–CF x layers are generally more sensitive than Au–CF x ones, particularly in the case of chlorinated solvents, which are scarcely detectable by Au–CF x nanocomposites. The material morphological and chemical structure has been investigated by means of atomic force and transmission electron microscopies along with X-ray photoelectron (XPS) and Fourier transform infra-red spectroscopies. The analytical characterization demonstrates that morphological similarities exist between Pd–CF x films and Au–CF x ones having the same metal volume fraction ϕ. XPS also reveals an almost identical surface structure for the dispersing polymer matrix of homologous Pd–CF x and Au–CF x films. Metal fluorides and oxides are identified as well and differences in the materials sensing performances are then ascribed to the presence of different amounts of these species that also have a different chemical reactivity and selectivity.

Investigation of dynamic and stability of laser-produced plasma in strong transverse magnetic field

The paper presents results of investigations of the process of the creation of a diamagnetic cavity by a laser-produced plasma in a strong transverse magnetic field of 10 T in induction. The plasma was produced from a flat, teflon target by an Nd laser of 5 J in energy and about 1 ns in pulse duration. The investigations were carried on by means of a three-frame interferometry and a non-contact magnetic probe, a so called remote magnetic probe (RMP). For the needs of this work, we developed a methodology for the measurement of the dimensions of the cavity during its expansion by means of the RMP, taking into account the plasma expansion geometry that is specific to flat targets. The dynamics of the process of creation of the diamagnetic cavity, its shape and dimensions have been determined. A very good consistency of dimensions of the diamagnetic cavity and plasma boundary in their quasisteady state, obtained with both diagnostics, allows us to apply the RMP method not only for the investigation of diamagnetic properties of various laser-produced plasmas, but also for the evaluation of their initial kinetic energy and its transformation in magnetic field.

Measurements of electron density in plasma disturbed by strong transverse magnetic field

We present results of studies of the behavior of a laser-produced plasma in a strong external transverse magnetic field of above 10 T in induction generated from a flat teflon target at the laser power densities of about 1014 W/cm2. In the measurements of plasma parameters, a two-channel automated interferometric system (Pisarczyk et al. 1994) was applied. The interferometric measurements have shown that the transverse magnetic field induces an asymmetry of the plasma distinctly apparent in the interferograms registered in two mutually perpendicular directions. Due to the lack of axial symmetry of the plasma, the Abel's transformation could not be applied in quantitative processing of the interferograms. To reconstruct a spatial distribution of electron density in a plasma stream of disturbed axial symmetry, a methodology prepared for this experiment was used. Analyzing the spatial and temporal distributions of electron concentration obtained in the transverse magnetic field, it has been proved that the factor responsible for the disturbance of the axial symmetry of the plasma is the Rayleigh–Taylor (R–T) instability corresponding to the ion unmagnetization state.