Speaker
Description
Currently, conventional particle accelerators, such as cyclotrons or linear accelerators, can accelerate charged particles to extremely high energies, and are therefore fundamental in applications including hadron therapy, and radioisotope production for medical diagnostics. However, the acceleration gradients in these systems are typically limited to values on the order of tens of MV/m, requiring the construction of large-scale facilities to achieve the energy levels needed for these applications. Laser-based accelerators can reach electric fields of up to $10^{12}$ V/m, orders of magnitude above conventional accelerators, reducing the acceleration distance to the μm scale, which enables the development of more compact and cost-effective alternatives.
Proton acceleration is typically achieved via the Target Normal Sheath Acceleration (TNSA) mechanism, based on the irradiation of a solid target by an ultra-intense laser pulse. Hot electrons generated in this interaction propagate through the target and escape from its rear surface, establishing an intense electrostatic sheath field that accelerates ions from the target's surface impurities. However, the generated ion beams exhibit significant limitations, such as high divergence and broad energy spread. In this work, the use of metallic helical structures coupled to thin solid targets is studied as an alternative to improve the quality of proton beams. The transient electromagnetic pulse guided by the coil enables the focusing, collimation, post-acceleration, and energy selection of protons synchronized with the pulse. The performed analysis demonstrates an effective reduction of the angular divergence of 3-5 MeV protons below 1º and post-acceleration gradients up to 1.5 GeV/m at higher energies. Furthermore, a Monte Carlo particle-tracing code was developed to reproduce the experimental results, yielding beam profiles and energy distributions consistent with the experimental measurements. The simulations are also used to predict the behavior of the helical targets fabricated for our laboratory (Laser Laboratory of Acceleration and Applications, L2A2), showing efficient collimation, energy gains of 2 to 3 MeV, and the formation of narrow, quasi-monoenergetic spectral peaks controllable through the coil pitch.