COLLISIONALLY EXCITED X-RAY LASER SCHEMES - PROGRESS AT RUTHERFORD-APPLETON-LABORATORY - LEWIS,CLS; ONEILL,DM; NEELY,D; UHOMOIBHI,JO; BURGE,R; SLARK,G; BROWN,M; MICHETTE,A; JAEGLE,P; KLISNICK,A; CARILLON,A; DHEZ,P; et al. (SPIE - INT SOC OPTICAL ENGINEERING, 1992)