RTNS-II: Experience at 14 MeV source strengths between 1x1013 and 4x1013 n/s

The RTNS-II Facility was built at LLNL from 1976 to 1978 to provide two 14-MeV sources dedicated to irradiation of materials and components for the Magnetic Fusion Program of the United States Department of Energy. Initial experiments began in early 1979 with a single source operating at a strength of 1x1013 n/s. In 1982, a five-year agreement was signed between the US DOE and the Ministry of Science, Education and Culture of the government of Japan to operate the facility jointly for fusion irradiation experiments. Under this agreement, both neutron sources became operational with source strengths rising to near the original design goal of 4x1013 n/s. Nominal source design parameters are 150 mA of D+ focused to a 1-cm diameter spot on a 5000 rpm titanium tritide target, producing a maximum useful flux of 1.3x1013 n/cm2s. In the past eight years, approximately one hundred 23-cm targets and seventy-five 50-cm targets have been produced and used. Target output decays with a half-life varying from 75 to 200 hours at currents near 125 mA. Average initial yield on a new target is 2.1x1011 n/s-mA; average total yield of a target before replacement is 1.1x1019 neutrons. Lifetimes of ion source components range from 200 hours for cathode assemblies to as much as 1200 hours for extraction electrodes. Power supplies, acceleration columns, most beam transport components and radiological systems have imposed no significant operational limitations. Maximum fluence delivered in irradiations to date has been 1x1019 n/cm2. Operation of the facility is currently scheduled to cease at the expiration of the joint agreement in February of 1987. The operational experience gained with accelerator, target and radiological systems will be reviewed, as well as design options and changes appropriate for inclusion in solid target 14-MeV generators designed to operate at higher source strengths. The prospects for upgrading a source of this type to 4x1014 n/s will be discussed. (author)