Abstract
Active plasma lenses have attracted interest in novel accelerator applications due to their ability to provide large-field-gradient (short focal length), tunable, and radially symmetric focusing for charged particle beams. However, if the discharge current is not flowing uniformly as a function of radius, one can expect a radially varying field gradient as well as potential emittance degradation. We have investigated this experimentally for a 1-mm-diameter active plasma lens. The measured near-axis field gradient is approximately 35% larger than expected for a uniform current distribution, and at overfocusing currents ring-shaped electron beams are observed. These observations are explained by simulations.
Highlights
Laser plasma accelerators (LPAs) [1] have produced MeV to multi-GeV electron beams in mm-cm scale plasma structures [2,3,4,5,6,7,8,9]
Active plasma lenses have attracted interest in novel accelerator applications due to their ability to provide large-field-gradient, tunable, and radially symmetric focusing for charged particle beams
When considering traditional transport elements for cm-scale focusing, challenges will be encountered: (i) Due to the 1=γ2 scaling of the focusing strength, with γ the electron relativistic Lorentz factor, solenoids have weak focusing for relativistic electrons and have only been applied to energies of a few MeV or less [21]. (ii) The strong field gradients of miniature quadrupoles are promising, as is the more favorable 1=γ scaling of the focusing strength, but the effective focal length is strongly increased when one considers that three lenses of varying and opposite strengths need to be combined to achieve equal focusing in both planes [23]
Summary
Laser plasma accelerators (LPAs) [1] have produced MeV to multi-GeV electron beams in mm-cm scale plasma structures [2,3,4,5,6,7,8,9]. The LPA community is pursuing applications such as ultrafast electron beam pump-probe studies [10], compact light sources including coherent x rays [11,12,13,14] and incoherent MeV photons [15,16,17,18], and high energy particle colliders driven by multiple LPA stages [19,20]. For these applications, collimation and focusing of electron beams over short, cm-scale distances is important.
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