Collimated GeV proton beam generated by the interaction of ultra-intense laser with a uniform near-critical underdense plasmaY. J. Gu, Z. Zhu, Y. Y. Li, X. F. Li, C. Y. Chen, Q. Kong and S. KawataEPL, 95 3 (2011) 35001DOI: https://doi.org/10.1209/0295-5075/95/35001