5-10 May 2019
MedILS
Europe/Berlin timezone

Optical measurements of nanosecond-scale plasma channel evolution excited by beam-driven plasma wakes at FACET

6 May 2019, 18:00
15m
Main Hall (MedILS)

Main Hall

MedILS

Oral Contribution Diagnostics

Speaker

Rafal Zgadzaj (University of Texas at Austin)

Description

The energy density deposited in a highly nonlinear “blowout” regime wake reaches that of the rest energy density of plasma electrons [1]. This energy relaxes through a complex redistribution between e.g. accelerated electrons, undirected hot electrons, ion-channel formation, ionization and excitation of surrounding gas and radiation over ns or longer time scales. These relaxation dynamics ultimately govern the repetition rate of plasma accelerators. Although simulations have predicted that strongly nonlinear electron wakes can spawn “ion wakes” of unique structure and dynamics [1-3], experiments have not yet explored this long-term evolution. Here, we present ps-time-resolved optical shadowgraphic measurements of cylindrically symmetric ion channels that emerge from broken plasma wakes generated in singly self-ionized lithium (Li) plasma (ne=8 1016 cm-3) of meter length, by SLAC’s 20 GeV, 2 nC electron bunches (σxy=30 μm, σz=50 μm). Results show that the plasma column remains peaked on axis and grows continuously in radius from <10 μm at time delay Δt<10 ps after passage of the drive bunch to several hundred μm at Δt=1.5ns. Measurements at longer Δt show that a strongly refracting plasma column persists at microsecond delays. Simulations using the fully relativistic particle-in-cell code OSIRIS [4] and the quasi-static LCODE [5] model the evolving plasma column out to Δt∼1.4 ns, and yield an evolving density profile consistent with measurements.
[1] K. V. Lotov et al., Phys. Rev. Lett. 112, 194801 (2014).
[2] A. Sahai and T. Katsouleas, ArXiv.1504.03735 (2015).
[3] J. Vieira et al., Phys. Rev. Lett. 109, 145005 (2012).
[4] R.A. Fonseca et al., Plasma Phys. Controlled Fusion 55, 124011 (2013).
[5] A.P. Sosedkin, K.V. Lotov, Nuclear Instr. Methods A829, 350 (2016).

Working group Diagnostics

Primary authors

Rafal Zgadzaj (University of Texas at Austin) Prof. Michael Downer (University of Texas at Austin) Mark Hogan Mr Vadim Khudyakov (Budker INP) Konstantin Lotov (Budker INP) Thales Silva (Instituto Superior Técnico) Alexander Sosedkin (Budker INP) Jorge Vieira (Instituto Superior Técnico) Dr Vitaly Yakimenko (SLAC)

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