High-charge 10 GeV electron acceleration in a 10 cm nanoparticle-assisted hybrid wakefield accelerator

In an electron wakefield accelerator, an intense laser pulse or charged particle beam excites plasma waves. Under proper conditions, electrons from the background plasma are trapped in the plasma wave and accelerated to ultra-relativistic velocities. We present recent results from a proof-of-principle wakefield acceleration experiment that reveal a unique synergy between a laser-driven and particle-driven accelerator: a high-charge laser-wakefield accelerated electron bunch can drive its own wakefield while simultaneously drawing energy from the laser pulse via direct laser acceleration. This process continues to accelerate electrons beyond the usual decelerating phase of the wakefield, thus reaching much higher energies. We find that the 10-centimeter-long nanoparticle-assisted wakefield accelerator can generate 340 pC, 10.4+-0.6 GeV electron bunches with 3.4 GeV RMS convolved energy spread and 0.9 mrad RMS divergence. It can also produce bunches with lower energy, a few percent energy spread, and a higher charge. This synergistic mechanism and the simplicity of the experimental setup represent a step closer to compact tabletop particle accelerators suitable for applications requiring high charge at high energies, such as free electron lasers or radiation sources producing muon beams

Generation, measurement and application of x-rays from laser-plasma electron accelerators

This dissertation presents a comprehensive study of the generation mechanisms, diagnostic techniques and possible applications of few keV to 100 MeV x-rays generated by laser wakefield electron accelerators. Chapters 1-3 review the principles of x-ray science and laser wakefield acceleration, and 3 mechanisms by which laser wakefield accelerators produce x-rays: 1) betatron oscillations of the electrons while still accelerating; 2) inverse Compton scatter (ICS) x-rays involving electron oscillations induced when electrons collide with a counter-propagating laser pulse after exiting the accelerator; 3) bremsstrahlung from the impact of accelerated electrons with a solid target. Chapters 4-6 then present original, recently published work, starting in chapter 4 with experiments that characterized secondary x-rays from a laser wakefield accelerator at Helmholtz-Zentrum Dresden Rossendorf. In this work, a laser wakefield accelerator was driven by the 150 TW DRACO laser system and produced electrons tunable in energy from 250 to 350 MeV. I co-designed and built a compact calorimeter consisting of a stack of x-ray absorbers alternating with imaging plates. This single device enabled me to unfold spectra of all three major types of x-rays, both individually and in mixtures: 1) few-keV betatron x-rays, 2) ICS x-rays that were spectrally peaked at ~1 MeV photon energy, and 3) broadband bremsstrahlung with an average energy of ~30 MeV and a high energy tail extending beyond 100 MeV photon energy. Chapter 5 presents results obtained at The University of Texas in which I extended the work in chapter 4 and used a redesigned compact calorimeter to characterize secondary x-rays generated from a GeV-class accelerator. In this work, the accelerator was driven by the 1 PW Texas Petawatt Laser (TPW) which accelerated electrons to energies ranging from 500 MeV to 2 GeV. The compact calorimeter was redesigned for improved sensitivity to photons from 1 MeV to >100 MeV and enabled me to unfold ICS x-rays that were peaked at ~10 MeV photon energy, and broadband bremsstrahlung with average energies ~80 MeV. Chapter 6 then presents additional results obtained on the DRACO laser system in which I characterized the capabilities of a LPA and plasma mirror to generate ICS x-rays in both a linear and nonlinear regime. I used a CsI(Tl) scintillator to characterize the strength and divergence of ICS x-rays generated by retro-reflecting the accelerator’s spent drive laser pulse back onto the accelerated electrons using a plasma mirror. These measurements showed that the laser-electron interaction ranged from sub-relativistic to relativistic, depending on the plasma mirror distance from the accelerator exit. Finally, chapter 7 presents unpublished results from the TPW and presents unfolded spectra from a bremsstrahlung target scan in which a series of targets ranging from 25 μm-thick Kapton to 7.6 mm-thick Pb were used to produce Bremsstrahlung with average energies ranging from 60 MeV to >100 MeV. Chapter 7 also presents preliminary results from the application of bremsstrahlung x-rays to nuclear activation of copper. This dissertation concludes with a summary of the presented results and a discussion of future directions for laser plasma produced x-ray science.Physic

The acceleration of a high-charge electron bunch to 10 GeV in a 10-cm nanoparticle-assisted wakefield accelerator

An intense laser pulse focused onto a plasma can excite nonlinear plasma waves. Under appropriate conditions, electrons from the background plasma are trapped in the plasma wave and accelerated to ultra-relativistic velocities. This scheme is called a laser wakefield accelerator. In this work, we present results from a laser wakefield acceleration experiment using a petawatt-class laser to excite the wakefields as well as nanoparticles to assist the injection of electrons into the accelerating phase of the wakefields. We find that a 10-cm-long, nanoparticle-assisted laser wakefield accelerator can generate 340 pC, 10 ± 1.86 GeV electron bunches with a 3.4 GeV rms convolved energy spread and a 0.9 mrad rms divergence. It can also produce bunches with lower energies in the 4–6 GeV range

The acceleration of a high-charge electron bunch to 10 GeV in a 10-cm nanoparticle-assisted wakefield accelerator

An intense laser pulse focused onto a plasma can excite nonlinear plasma waves. Under appropriate conditions, electrons from the background plasma are trapped in the plasma wave and accelerated to ultra-relativistic velocities. This scheme is called a laser wakefield accelerator. In this work, we present results from a laser wakefield acceleration experiment using a petawatt-class laser to excite the wakefields as well as nanoparticles to assist the injection of electrons into the accelerating phase of the wakefields. We find that a 10-cm-long, nanoparticle-assisted laser wakefield accelerator can generate 340 pC, 10 ± 1.86 GeV electron bunches with a 3.4 GeV rms convolved energy spread and a 0.9 mrad rms divergence. It can also produce bunches with lower energies in the 4–6 GeV range