arXiv subjects

C. E. Clayton

Publications and source records attributed to C. E. Clayton.

4 recordsLinked to original sources

arXiv2020

Conservation of angular momentum in second harmonic generation from under-dense plasmas

Spin and orbital angular momentum of an optical beam are two independent parameters that exhibit distinct effects on mechanical objects. However, when laser beams with angular momentum interact with plasmas, one can observe the interplay between the spin and the orbital angular momentum. Here, by measuring the helical phase of the second harmonic 2ω radiation generated in an underdense plasma using a known spin and orbital angular momentum pump beam, we verify that the total angular momentum of photons is conserved and observe the conversion of spin to orbital angular momentum. We further determine the source of the 2ω photons by analyzing near field intensity distributions of the 2ω light. The 2ω images are consistent with these photons being generated near the largest intensity gradients of the pump beam in the plasma as predicted by the combined effect of spin and orbital angular momentum when Laguerre-Gaussian beams are used.

physics.plasm-ph↗

arXiv2019

Initializing anisotropic and unstable electron velocity distributions needed for investigating plasma kinetic instabilities

Plasmas with anisotropic electron velocity distribution functions are needed for the controlled study of kinetic plasma instabilities in the laboratory. We demonstrate that such plasma can be produced using ultrashort laser pulses via optical-field ionization (OFI). We experimentally show this control by using Thomson scattering as a diagnostic to probe the characteristic electron velocity distributions using linearly and circularly polarized laser pulses to ionize helium. Furthermore the He plasma produced by a circularly polarized light pulse exhibits the onset of the electron streaming instability within 300 fs of ionization, demonstrating applicability of OFI generated plasmas for studying the kinetic theory regime of plasma physics.

physics.plasm-ph↗

arXiv2018

Measurement of transverse wakefields induced by a misaligned positron bunch in a hollow channel plasma accelerator

Hollow channel plasma wakefield acceleration is a proposed method to provide high acceleration gradients for electrons and positrons alike: a key to future lepton colliders. However, beams which are misaligned from the channel axis induce strong transverse wakefields, deflecting beams and reducing the collider luminosity. This undesirable consequence sets a tight constraint on the alignment accuracy of the beam propagating through the channel. Direct measurements of beam misalignment-induced transverse wakefields are therefore essential for designing mitigation strategies. We present the first quantitative measurements of transverse wakefields in a hollow plasma channel, induced by an off-axis 20 GeV positron bunch, and measured with another 20 GeV lower charge trailing positron probe bunch. The measurements are largely consistent with theory.

physics.acc-ph↗

arXiv2015

Evidence for high-energy and low-emittance electron beams using ionization injection of charge in a plasma wakefield accelerator

Ionization injection in a plasma wakefield accelerator was investigated experimentally using two lithium plasma sources of different lengths. The ionization of the helium gas, used to confine the lithium, injects electrons in the wake. After acceleration, these injected electrons were observed as a distinct group from the drive beam on the energy spectrometer. They typically have a charge of tens of pC, an energy spread of a few GeV, and a maximum energy of up to 30 GeV. The emittance of this group of electrons can be many times smaller than the initial emittance of the drive beam. The energy scaling for the trapped charge from one plasma length to the other is consistent with the blowout theory of the plasma wakefield.

physics.acc-ph↗