Proton acceleration by a relativistic laser frequency-chirp driven plasma snowplow

TL;DR

This paper introduces the ChITA scheme, where a relativistic laser with a controlled frequency chirp drives a plasma snowplow to accelerate protons, with analytical modeling and simulations showing tunable proton energies.

Contribution

The paper presents a novel analytical model and simulation validation for the ChITA scheme, enabling controlled proton acceleration via a chirped relativistic laser.

Findings

ChITA snowplow velocity depends on laser chirp rate and plasma gradient.

Simulations confirm snowplow formation and propagation matching analytical predictions.

Protons reflect off the snowplow and achieve mono-energetic acceleration.

Abstract

We analyze the use of a relativistic laser pulse with a controlled frequency chirp incident on a rising plasma density gradient to drive an acceleration structure for proton and light-ion acceleration. The Chirp Induced Transparency Acceleration (ChITA) scheme is described with an analytical model of the velocity of the snowplow at critical density on a pre-formed rising plasma density gradient that is driven by a positive-chirp in the frequency of a relativistic laser pulse. The velocity of the ChITA-snowplow is shown to depend upon rate of rise of the frequency of the relativistic laser pulse represented by $\frac{\epsilon_0}{\theta}$ where, $\epsilon_0 = \frac{\Delta\omega_0}{\omega_0}$ and chirping spatial scale-length, $\theta$, the normalized magnetic vector potential of the laser pulse $a_0$ and the plasma density gradient scale-length, $\alpha$. We observe using 1-D OSIRIS simulations the formation and forward propagation of ChITA-snowplow, being continuously pushed by the chirping laser at a velocity in accordance with the analytical results. The trace protons reflect off of this propagating snowplow structure and accelerate mono-energetically. The control over ChITA-snowplow velocity allows the tuning of accelerated proton energies.