Measuring Magnetic Fields Using Protons for Characterizing Laser-Driven Collisionless Shocks*

We present progress in the use of proton deflectometry and radiography to study collisionless shocks in experiments at the OMEGA {\&} OMEGA EP laser facilities. Collisionless shocks are important for astrophysical phenomena such as supernova remnants and ultra high-energy cosmic ray acceleration. The shocks will be created by two laser-ablated counter-streaming supersonic CH$_{2}$ plasmas with v = 1000 km/s and n$_{i}$ = 10$^{17}$ -- 10$^{18}$ cm$^{-3}$, sufficient that the ion-ion collisional mean free path is larger than the mm-scale system. Hydrodynamic simulations predict possible regular grad(n) x grad(T) magnetic fields; particle-in-cell simulations predict filaments and turbulent magnetic fields B$_{t}$ that change direction with a correlation length L. Turbulent fields blur the proton beam; for example, 5 MeV protons blur $\approx $ 2 mrad for B$_{t}$ = 20 kG and L = 100 $\mu $m. The particle-in-cell code LSP has been used to generate synthetic proton images and explore the sensitivity of proton diagnostics to the signatures of collisionless shock development. *Prepared by LLNL under Contract DE-AC52-07NA27344.