We present the characteristics of track formation on the front and rear surfaces of CR-39 produced by laser-driven protons and carbon ions. A methodological approach, based on bulk etch length, is proposed to uniquely characterize the particle tracks in CR-39, enabling comparative description of the track characteristics in different experiments. The response of CR-39 to ions is studied based on the energy dependent growth rate of the track diameter to understand the intrinsic particle stopping process within the material. A large non-uniformity in the track diameter is observed for CR-39 with thickness matching with the stopping range of particles. Simulation and experimental results show the imprint of longitudinal range straggling for energetic protons. Moreover, by exploiting the energy dependence of the track diameter, the energy resolution (δE/E) of CR-39 for few MeV protons and Carbon ion is found to be about 3%.
The absolute calibration of a microchannel plate (MCP) assembly using a Thomson spectrometer for laser-driven ion beams is described. In order to obtain the response of the whole detection system to the particles’ impact, a slotted solid state nuclear track detector (CR-39) was installed in front of the MCP to record the ions simultaneously on both detectors. The response of the MCP (counts/particles) was measured for 5–58 MeV carbon ions and for protons in the energy range 2–17.3 MeV. The response of the MCP detector is non-trivial when the stopping range of particles becomes larger than the thickness of the detector. Protons with energies E ≳ 10 MeV are energetic enough that they can pass through the MCP detector. Quantitative analysis of the pits formed in CR-39 and the signal generated in the MCP allowed to determine the MCP response to particles in this energy range. Moreover, a theoretical model allows to predict the response of MCP at even higher proton energies. This suggests that in this regime the MCP response is a slowly decreasing function of energy, consistently with the decrease of the deposited energy. These calibration data will enable particle spectra to be obtained in absolute terms over a broad energy range.
We investigated the effect of plasma treatment on single-walled carbon nanotube (SWCNT) field emitters, which were fabricated by printing a photoimageable SWCNT paste, to improve emission lifetime. The treatment was performed by applying a dc pulsed voltage between two electrodes, where the cathode was the SWCNT emitter to be treated and the anode was a bare indium-doped tin oxide glass, under inert gas (Xe∕Ne) atmosphere. With increasing applied voltage and treatment time, the stability of the emission current at a constant electric field is improved, while the field to reach a required emission current becomes high. We attribute the improved emission stability to the removal of a small portion of protruding emitters, which dominate initial emission characteristics. The elimination of small number of prominent emitters allows a greater number of emitters to be active on emission with a compensation for higher electric-field application. We expect that the plasma treatment introduced in this letter will provide a quick and easy way to improve emission lifetime, which is essential for the commercialization of field emission display.
Electron emission current degradation is often observed from printed single wall carbon nanotube emitters during field emission process. After a highly imposed emission, structural deformation of emitters from thin crystalline nanotube bundle to thick amorphous-type carbon fiber was observed. This deformation seems to relate to the current degradation, deteriorating the efficiency of field emission either by increasing the resistance of emitters or by decreasing the field enhancement factor of emitter tips. Two possible mechanisms of structural deformation are internal structural transformation by Joule heating under excessively imposed emission current and continuous adsorption of carbon particles on actively working emitters.
Electroluminescence ͑EL͒ was observed on conventional cathodoluminescent ͑CL͒ phosphor with the incorporation of carbon nanotube ͑CNT͒ at ambient air. The role of CNT can be understood as enhancing the local electrical field, which allows electron injection to the active center of phosphor at relatively low operating voltages. In this EL device, the brightness of CL phosphor was significantly improved from no light emission in the case of no addition of CNT to 35 cd/ m 2 with 1 wt % CNT at 10 kHz of ac 300 V.
Ion acceleration resulting from the interaction of ultra-high intensity and ultra-high contrast (∼10−10) laser pulses with thin Al foil targets at 30° angle of laser incidence is studied. Proton maximum energies of 30 and 18 MeV are measured along the target normal rear and front sides, respectively, showing intensity scaling as Ib. For the target front bfront= 0.5–0.6 and for the target rear brear= 0.7–0.8 is observed in the intensity range 1020–1021 W/cm2. The fast scaling from the target rear ∼I0.75 can be attributed enhancement of laser energy absorption as already observed at relatively low intensities. The backward acceleration of the front side protons with intensity scaling as ∼I0.5 can be attributed to the to the formation of a positively charged cavity at the target front via ponderomotive displacement of the target electrons at the interaction of relativistic intense laser pulses with a solid target. The experimental results are in a good agreement with theoretical predictions.
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