31 July 2016 to 5 August 2016
Gaylord Hotel and Conference Center
US/Eastern timezone

Low Density Plasma Channels Created by Hydrodynamic Expansion of OFI-heated Plasma Columns

2 Aug 2016, 13:30
20m
Woodrow Wilson CD (Gaylord Hotel)

Woodrow Wilson CD

Gaylord Hotel

Oral Working Group 1 WG1

Speaker

Prof. Simon Hooker (University of Oxford)

Abstract

We investigate the generation of low-density plasma channels by hydrodynamic expansion of a plasma column formed by optical field ionization in elliptically-polarized laser fields. We demonstrate numerically that this novel approach can generate channels with axial electron densities below $1 \times 10^{18} \mathrm{cm}^{-3}$ and matched spot sizes of tens of microns.

Summary

The development of plasma channels with axial plasma densities below $1 \times 10^{18} \mathrm{cm}^{-3}$ is of significant interest to plasma accelerators driven by particle bunches or laser pulses. For the latter it is also important to maintain a low matched spot size $W_\mathrm{M}$. For several potential applications of plasma accelerators, such as driving light sources, it would also be desirable to operate at high, i.e. multi-kilohertz, pulse repetition rates. These requirements are challenging for existing guiding methods owing to difficulties in maintaining small $W_\mathrm{M}$ at low densities, or avoiding optical or thermal damage at high repetition rates.

In this work we investigate a new twist to an old idea: the generation of a plasma channel by hydrodynamic expansion of a laser-heated column of plasma. In this prior work a plasma column is formed, then heated, by one or more laser pulses. Rapid radial expansion of the plasma column drives a radial shock wave into the surrounding gas to form a plasma channel.
In almost all previous work the plasma column was collisionally heated and ionized. However, for the heating to be sufficiently fast the initial plasma density must be high, limiting the axial density of the plasma channels to high values.

Here we explore an alternative approach in which the initial plasma column is formed and heated by optical field ionization (OFI) with elliptically-polarized laser pulses. This ionization mechanism generates electrons with energies in the range 10 - 1000 eV, and the mean electron energy can be controlled by adjusting the ellipticity of the laser field. Since OFI operates at the atomic level, the electron heating is independent of the initial density, and hence low-density plasma channels can be generated. Further, operation at high pulse repetition rate is in principle straightforward since the channel is not contained within a physical structure.

We will present numerical simulations which show that this new approach could generate plasma channels with axial electron densities below $1 \times 10^{18} \mathrm{cm}^{-3}$ and matched spot sizes of tens of microns.

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Primary author

Prof. Simon Hooker (University of Oxford)

Co-authors

Mr. Christopher Arran (University of Oxford) Dr. Jimmy Holloway (University of Oxford) Dr. Laura Corner (John Adams Institute, Oxford University) Mr. Robert Shalloo (University of Oxford) Prof. Roman Walczak (University of Oxford)

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