We demonstrate a new highly tunable technique for generating meter-scale low density plasma waveguides. Such guides can enable electron acceleration to tens of GeV in a single stage. Plasma waveguides are imprinted in hydrogen gas by optical field ionization induced by two timeseparated Bessel beam pulses: The first pulse, a 𝐽 beam, generates the core of the waveguide, while the delayed second pulse, here a 𝐽 or 𝐽 beam, generates the waveguide cladding. We demonstrate guiding of intense laser pulses over hundreds of Rayleigh lengths with on axis plasma densities as low as 𝑁 ~5 × 10 cm .

Measuring the equations of state in a relaxed magnetohydrodynamic plasma." Physical Review 97.1, 011202(R).

We have explored the thermodynamics of compressed magnetized plasmas in laboratory experiments and we call these studies 'magnetothermodynamics'. The experiments are carried out in the Swarthmore Spheromak eXperiment device. In this device, a magnetized plasma source is located at one end and at the other end, a closed conducting can is installed. We generate parcels of magnetized plasma and observe their compression against the end wall of the conducting cylinder. The plasma parameters such as plasma density, temperature and magnetic field are measured during compression using HeNe laser interferometry, ion Doppler spectroscopy and a linearḂ probe array, respectively. To identify the instances of ion heating during compression, a PV diagram is constructed using measured density, temperature and a proxy for the volume of the magnetized plasma. Different equations of state are analysed to evaluate the adiabatic nature of the compressed plasma. A three-dimensional resistive magnetohydrodynamic code (NIMROD) is employed to simulate the twisted Taylor states and shows stagnation against the end wall of the closed conducting can. The simulation results are consistent to what we observe in our experiments.

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We demonstrate that an ultrashort high intensity laser pulse can propagate for hundreds of Rayleigh ranges in a prepared neutral hydrogen channel by generating its own plasma waveguide as it propagates; the front of the pulse generates a waveguide that confines the rest of the pulse. A wide range of suitable initial index structures will support this "self-waveguiding" process; the necessary feature is that the gas density on axis is a minimum. Here, we demonstrate self-waveguiding of pulses of at least 1.5 × 10 17 W/cm 2 (normalized vector potential 𝑎 0 ~0.3) over 10 cm, or ~100 Rayleigh ranges, limited only by our laser energy and length of our gas jet. We predict and observe characteristic oscillations corresponding to mode-beating during selfwaveguiding. The self-waveguiding pulse leaves in its wake a fully ionized low density plasma waveguide which can guide another pulse injected immediately following; we demonstrate optical guiding of such a follow-on probe pulse.

Bessel beams generated with non-ideal axicons are affected by aberrations. We introduce a method to retrieve the complex amplitude of a Bessel beam from intensity measurements alone, and then use this information to correct the wavefront and intensity profile using a deformable mirror.

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