Laser-plasma accelerators (LPAs) can have high acceleration gradients on the order of 100 GeV/m. The high acceleration gradients of LPAs offer the possibility of powering future colliders at the TeV range and reducing the size of particle accelerators at present energy levels. LPAs need tightly focused, high intensity laser pulses and require guiding structures to maintain the laser focus over the optimum acceleration length. It is necessary to match the parameters of the guiding structure and the laser pulse to couple the maximum laser energy into the guiding structure. Optically field ionized (OFI) plasma channels are a guiding structure capable of matching the parameters of the petawatt (PW) laser facility at the Berkeley Lab Laser Accelerator (BELLA) Center [1, 2]. We will present results on the optimization of laser coupling into OFI plasma channels on BELLA PW. We will also discuss how optimization of laser coupling relates to upcoming staging experiments on BELLA PW.

Laser-plasma accelerators (LPAs) have potential to enable compact light sources and high-energy linear colliders. At the BErkeley Lab Laser Accelerator (BELLA) PW facility, electron bunches with energy up to 8 GeV have been generated using laser pulses with peak power of 0.85 PW (energy 31 J) and an acceleration length of 20  cm. In order to accelerate over this distance of 15 diffraction lengths, a preformed plasma waveguide based on inverse bremsstrahlung (IB) heating inside a capillary discharge was used [1]. Simulations show the energy gain can be increased to beyond 10 GeV, but with lower density than is feasible with IB heating. The recent addition of a second beamline to BELLA PW has allowed for the use of plasma channels formed by optically field ionization [2-4], which enables optimized density. We will present guiding and acceleration results using this new capability.

Due to their compactness, laser-plasma accelerators are a promising approach to future energy frontier electron accelerators. To reach multi-GeV energies in a single accelerator stage, the high-intensity drive laser pulse must be kept focused over several tens of centimeters through a sufficiently low density plasma. Without an external guiding mechanism, the laser will diffract reducing the laser intensity, which in turn limits acceleration to ~1 cm. Optically generated plasma channels have recently gained attention as a promising method to keep high-intensity laser pulses tightly focused over the meter scale [1,2]. Understanding how the laser pulse evolves in the spatial and temporal domain during propagation is critical for high energy gain, and maintaining high bunch quality. We present experimental results investigating drive laser propagation in optically formed plasma channels at the BELLA PW laser. We demonstrate conditions under which the channel can be tailored to match the drive laser focus at plasma densities suitable for multi-GeV accelerators.

Laser-plasma accelerators (LPAs) can have high acceleration gradients on the order of 100 GeV/m. The high acceleration gradients of LPAs offer the possibility of powering future colliders at the TeV range and reducing the size of particle accelerators at present energy levels. LPAs need tightly focused, high intensity laser pulses and require guiding structures to maintain the laser focus over the optimum acceleration length. It is necessary to match the parameters of the guiding structure and the laser pulse to couple the maximum laser energy into the guiding structure. Optically field ionized (OFI) plasma channels are a guiding structure capable of matching the parameters of the petawatt (PW) laser facility at the Berkeley Lab Laser Accelerator (BELLA) Center [1, 2]. We will present results on the optimization of laser coupling into OFI plasma channels on BELLA PW. We will also discuss how optimization of laser coupling relates to upcoming staging experiments on BELLA PW.