Magnetic field generation during intense laser channelling in underdense plasma by Smyth, A, Sarri, G, Vranic, M, Amano, Y, Doria, D, Guillaume, E, Habara, H, Heathcote, R, Hicks, G, Najmudin, Z, Nakamura, H, Norreys, P, Kar, S, Silva, L, Tanaka, K, Vieira, J, Borghesi, M