Collisionless shock acceleration of quasi-monoenergetic ions in ultra-relativistic regime

Collisionless shock acceleration of carbon ions (C$^{6+}$) is investigated in the ultra-relativistic regime of laser-plasma interaction by accounting for the radiation reaction force and the pair production in particle-in-cell simulations. Both radiation reaction force and pair plasma formation tend to slow down the shock velocity, reducing the energy of the accelerated ions, albeit extending the time scales of the acceleration process. Slab plasma target achieves lower energy spread while target with a tailored density profile yields higher ion acceleration energies.Comment: 10 pages,12 figure

Laboratory astrophysics and ion acceleration using intense lasers

Collisionless shocks are of great interest in astrophysical scenarios as they are believed to be responsible for high energy cosmic rays and non-thermal particles. The field of laboratory astrophysics attempts to study astrophysical phenomena in a laboratory with the help of intense lasers. In view of laboratory-astrophysics experiments and laser-driven ion acceleration, collisionless shocks are studied semi-analytically and with numerical simulations. In particular, how the particle collisions in plasma can affect the laser-driven shock formation and subsequent ion acceleration is investigated. It is shown in this thesis, how resistive reorganisation of electromagnetic fields in a plasma target leads to significant improvement in the shock-accelerated ion-beam-profile without any additional need of target-tailoring (i.e. a known technique currently used to achieve a monoenergetic profile of the shock-accelerated ion-beam). This result is beneficial especially for medical science that requires therapeutic proton beams, particularly for the treatment of cancer. At ultra-high laser ntensities, the effect of radiative losses on particle's trajectory become important. These losses due to radiation emission have been shown to modify the shock's field structure. It is also demonstrated that exclusion of radiative losses can lead to overestimation of maximum ion-energy in a thin-target regime

Effects of Progressive Muscle Relaxation Technique on Mental Skills of Volleyball Players

The present study was conducted to examine the effects of progressive muscle relaxation technique on mental skills of volleyball players. To obtain data for this study, the investigators had selected 20 male subjects were selected randomly from L.N.U.P.E volleyball match practice group in which 10 subjects were in experimental group and 10 subjects acted as control group. The purposive sampling technique was used to obtain the required data. To measure the level of mental skills of the subjects, the mental skills questionnaire constructed by Hardy and Nelson was administered. Analysis of covariance was used to determine significant differences for dependent variables within the two groups. When a significant difference among the group was observed, a pair wise comparison of the groups was done by using post-hoc test to indentify direction and significant differences between the groups. The level of significance was set at 0.05 in order to test the differences to be considered significant. The results revealed that progressive muscular relaxation technique was effective in improving the imagery ability, mental preparation and concentration ability and mental skill of subjects. Though the pre-test and post-test mean difference between control groups has shown marginal improvement as mean difference was found respectively

Instability of the heliopause driven by charge exchange interactions

The stability of the heliopause that separates the tenuous hot magnetized heliosheath plasma from the dense cool local interstellar magnetized plasma is examined using a fully general model that includes all the essential physical processes. Charge exchange coupling between plasma protons and primary interstellar neutral atoms provides an effective gravity that drives Rayleigh-Taylor (RT)-like instabilities. The velocity difference or shear between the heliosheath and interstellar flows, when coupled to energetic neutral atoms (ENAs), drives a Kelvin-Helmholtz (KH)-like instability on the heliopause. The shoulder region of the heliopause is unstable to a new instability that has characteristics of a mixed RT-KH-like mode. The instabilities are not stabilized by typical values of the magnetic fields in the inner and outer heliosheath (OHS). ENAs play an essential role in driving the KH-like instability, which is fully stabilized in their absence by magnetic fields. The nonlinear phase of these instabilities is briefly discussed. We also discuss the possibility that RT-like or mixed KH-RT-like instabilities drag outer heliosheath/very local interstellar medium (OHS/VLISM) magnetic field lines into the inner heliosheath (IHS) with the VLISM flow, and the possibility that IHS and VLISM magnetic field lines experience reconnection. Such reconnection may (1) greatly enhance the mixing of plasmas across the heliopause and (2) provide open magnetic field lines that allow easy ingress of galactic cosmic rays into the heliosphere and corresponding easy loss of anomalous cosmic rays from the heliosphere

Unforeseen advantage of looser focusing in vacuum laser acceleration

Acceleration of electrons in vacuum directly by intense laser fields, often termed vacuum laser acceleration (VLA), holds great promise for the creation of compact sources of high-charge, ultrashort, relativistic electron bunches. However, while the energy gain is expected to be higher with tighter focusing (i.e. stronger electric field), this does not account for the reduced acceleration range, which is limited by diffraction. Here, we present the results of an experimental investigation of VLA, using tungsten nanotips driven by relativistic-intensity few-cycle laser pulses. We demonstrate the acceleration of relativistic electron beams with typical charge of 100s pC to 15 MeV energies. Two different focusing geometries (tight and loose, with f-numbers one and three respectively) produced comparable results, despite a factor of ten difference in the peak intensities, which is evidence for the importance of post-injection acceleration mechanisms around the focus. Our results are in good agreement with the results of full-scale, three-dimensional particle-in-cell simulations

Towards ML-Based Diagnostics of Laser–Plasma Interactions

The power of machine learning (ML) in feature identification can be harnessed for determining quantities in experiments that are difficult to measure directly. However, if an ML model is trained on simulated data, rather than experimental results, the differences between the two can pose an obstacle to reliable data extraction. Here we report on the development of ML-based diagnostics for experiments on high-intensity laser–matter interactions. With the intention to accentuate robust, physics-governed features, the presence of which is tolerant to such differences, we test the application of principal component analysis, data augmentation and training with data that has superimposed noise of gradually increasing amplitude. Using synthetic data of simulated experiments, we identify that the approach based on the noise of increasing amplitude yields the most accurate ML models and thus is likely to be useful in similar projects on ML-based diagnostics