Microbubble implosions in finite hollow spheres

TL;DR

This work extends microbubble implosion (MBI) to finite hollow spheres, where freely redistributing electrons alter charge separation and implosion dynamics. It develops a polytropic electron-distribution model with $\gamma=5/3$ and solves Poisson's equation to obtain $n_e(\phi)$, validated against MD simulations and the Peano charge-separation fit, then demonstrates finite-sphere MBI using a 1D hybrid, shell-based code. Results show robust density compressions around $n/n_0 \sim 10^{4}$ in finite targets, with cavity filling and ion-flashing highly sensitive to the aspect ratio $\xi_{ar}$ and the optimal Debye parameter $\Lambda_{opt}$. The findings indicate finite hollow targets are viable for proof-of-principle experiments and offer design guidelines to balance core compression against detectability of ion flashing for applications such as high-field QED and particle acceleration.

Abstract

Microbubble implosion (MBI) is a recently proposed novel mechanism with many interesting and exciting potential applications. MBI predicts that the inner layers of a spherical target with a hollow cavity can be compressed into a core with a density 105 times that of the solid density. Furthermore, this ultra-compressed core mostly consists of ions. This leads to the generation of ultra-high electric fields, which may be applicable to gamma-ray lensing or pair creation. However, MBI has yet to be studied for finite hollow spheres whose electrons are free to redistribute themselves after being given an initial temperature. This paper studies MBI under finite sphere conditions. Using an electron distribution model, the electron distribution after receiving an initial temperature is studied. Then, the optimal parameters required to fill a hollow cavity with electrons are calculated. The dynamics of MBI is simulated using a hybrid one-dimensional code. The simulation demonstrates that MBI occurs even for finite spheres, and high-density compression is still achievable with this setup. It also shows the optimal target structure, which maximizes ion flashing.

Figures (8)

• Figure 1: Calculated normalized electron density profile for the model and MD simulations for different values of $\Lambda$.
• Figure 2: Calculated charge separation from the numerically solved Poisson's equation and the model derived by Peano et al. Peano2007
• Figure 3: Electron density profile of a hollow target for various values of $\Lambda$. Dotted line denotes the ion density profile.
• Figure 4: Numerically calculated $\Lambda_{opt}$ as a function of $\xi_{ar}$ along with the power-law fit and the normalized number of electrons within the cavity.
• Figure 5: Trajectory of a hollow sphere with 1-µm cavity undergoing MBI for different aspect ratios: (a) $\xi_{ar} = 2$, (b) $\xi_{ar}=3$, and (c) $\xi_{ar}=4$.