arXiv subjects

S. Palaniyappan

Publications and source records attributed to S. Palaniyappan.

6 recordsLinked to original sources

arXiv2021

Vacuum laser acceleration of super-ponderomotive electrons using relativistic transparency injection

Intense lasers can accelerate electrons to very high energy over a short distance. Such compact accelerators have several potential applications including fast ignition, high energy physics, and radiography. Among the various schemes of laser-based electron acceleration, vacuum laser acceleration has the merits of super-high acceleration gradient and great simplicity. Yet its realization has been difficult because injecting free electrons into the fast-oscillating laser field is not trivial. Here we demonstrate free-electron injection and subsequent vacuum laser acceleration of electrons up to 20 MeV using the relativistic transparency effect. When a high-contrast intense laser drives a thin solid foil, electrons from the dense opaque plasma are first accelerated to near-light speed by the standing laser wave in front of the solid foil and subsequently injected into the transmitted laser field as the opaque plasma becomes relativistically transparent. It is possible to further optimize the electron injection/acceleration by manipulating the laser polarization, incident angle, and temporal pulse shaping. Our result also sheds new light on the fundamental relativistic transparency process, crucial for producing secondary particle and light sources.

physics.plasm-ph↗

arXiv2021

High-yield and high-angular-flux neutron generation from deuterons accelerated by laser-driven collisionless shock

A bright collimated neutron source is an essential tool for global security missions and fundamental scientific research. In this paper, we study a compact high-yield and high-angular-flux neutron source utilizing the break-up reaction of laser-driven deuterons in a $^9\text{Be}$ converter. The neutron generation scaling from such a reaction is used to guide the choice and optimization of the acceleration process for the bulk ions in a low density $\text{CD}_2$ foam. In particular, the collisionless shock acceleration mechanism is exploited with proper choice in the laser and target parameter space to accelerate these ions towards energies above the temperature of the distribution. Particle-In-Cell and Monte Carlo simulations are coupled to investigate this concept and possible adverse effects, as well as the contribution from the surface ions accelerated and the optimal converter design. The simulation results indicated that our design can be a practical approach to increase both the neutron yield and forward flux of laser-driven neutron sources, reaching peak angular neutron flux $>10^{11}$ neutron/sr and yield $>10^{11}$ neutron/pulse with present-day kJ-class high-power lasers. Such developments will advance fundamental neutron science, high precision radiography and other global security applications with the laser-driven sources.

physics.plasm-ph↗

arXiv2021

Particle resonances and trapping of direct laser acceleration in a laser-plasma channel

As one of the leading acceleration mechanisms in laser-driven underdense plasmas, direct laser acceleration (DLA) is capable of producing high-energy-density electron beams in a plasma channel for many applications. However, the mechanism relies on highly nonlinear particle-laser resonances, rendering its modeling and control to be very challenging. Here, we report on novel physics of the particle resonances and, based on that, define a potential path toward more controlled DLA. Key findings are acquired by treating the electron propagation angle independently within a comprehensive model. This approach uncovers the complete particle resonances over broad propagation angles, the physical regimes under which paraxial/non-paraxial dynamics dominates, a unified picture for different harmonics, and crucially, the physical accessibility to these particle resonances. These new insights can have important implications where we address the basic issue of particle trapping as an example. We show how the uncovered trapping parameter space can lead to better acceleration control. More implications for the development of this basic type of acceleration are discussed.

physics.plasm-ph↗

arXiv2019

Measurement of BAS-TR imaging plate response to energetic aluminum ions

We measured the response of BAS-TR imaging plate (IP) to energetic aluminum ions in the 0 to 222 MeV energy range, and compared it with predictions from a Monte Carlo simulation code using two different IP models. Energetic aluminum ions were produced with an intense laser pulse, and the response was evaluated from cross-calibration between CR-39 track detector and IP energy spectrometer. For the first time, we obtained the response function of the BAS-TR IP for aluminum ions in the energy range from 0 to 222 MeV. Notably the IP sensitivity in the exponential model is nearly constant from 36 MeV to 160 MeV.

physics.ins-det↗

arXiv2014

Scaling of laser-driven ion energies in the relativistic transparent regime

Laser-driven ions have compelling properties and their potential use for medical applications has attracted a huge global interest. One of the major challenges of these applications is generating beams of the required energies. To date, there has been no systematic study of the effect of laser intensity on the generation of laser-driven ions from ultrathin foils during relativistic transparency. Here we present a scaling for ion energies with respect to the on-target laser intensity and in considering target thickness we find an optimum thickness closely related to the experimentally observed relativistic transparency. A steep linear scaling with the normalized laser amplitude a0 has been measured and verified with PIC simulations. In contrast to TNSA, this scaling is much steeper and has been measured for ions with Z > 1. Following our results, ion energies exceeding 100MeV/amu are already accessible with currently available laser systems enabling realization of numerous advanced applications

physics.plasm-ph↗

arXiv2013

160 MeV laser-accelerated protons from CH2 nano-targets for proton cancer therapy

Proton (and ion) cancer therapy has proven to be an extremely effective even supe-rior method of treatment for some tumors 1-4. A major problem, however, lies in the cost of the particle accelerator facilities; high procurement costs severely limit the availability of ion radiation therapy, with only ~26 centers worldwide. Moreover, high operating costs often prevent economic operation without state subsidies and have led to a shutdown of existing facilities 5,6. Laser-accelerated proton and ion beams have long been thought of as a way out of this dilemma, with the potential to provide the required ion beams at lower cost and smaller facility footprint 7-14. The biggest challenge has been the achievement of sufficient particle energy for therapy, in the 150-250 MeV range for protons 15,16. For the last decade, the maximum exper-imentally observed energy of laser-accelerated protons has remained at ~60 MeV 17. Here we the experimental demonstration of laser-accelerated protons to energies exceeding 150 MeV, reaching the therapy window. This was achieved through a dif-ferent acceleration regime rather than a larger laser, specifically a 150 TW laser with CH2 nano-targets in the relativistically transparent regime 18,19. We also demonstrate a clear scaling law with laser intensity based on analytical theory, computer simulations and experimental validation that will enable design of a pro-totype system spanning the full range of therapeutically desirable energies.

physics.plasm-ph↗