Counter-facing plasma guns for efficient extreme ultra-violet plasma light source Yusuke Kuroda, Akiko Yamamoto, Hajime Kuwabara, Mitsuo Nakajima, Tohru Kawamura and Kazuhiko Horioka EPJ Web of Conferences, 59 (2013) 18006 Published online: 15 November 2013 DOI: 10.1051/epjconf/20135918006