RA2. Accelerator System Status
ORIC Operations and Development (B. A. Tatum)
Extensive upgrades to the ORIC rf system were reported in the last edition of this newsletter. This effort appears to have paid off. ORIC operated with proton beam on target for RIB production for more than 1500 hours over a six month period from June 1 though the end of November. Over 700 of those hours were recorded in October and November. A scheduled maintenance period began in December. Unfortunately, an HPTL development run scheduled for December was delayed due to bearing failure on the main field MG set. The bearing was repaired and the MG set is back in service. ORIC will run periodically until mid-March when tandem shutdown is complete
As for the rf system, we are now running routinely, and reliably, with two 500-watt AR Kalmus rf amplifiers and two Werlatone commercial combiner/divider units. The tunable, ceramic-envelope plate capacitors that were also installed last year have operated flawlessly. Thanks to the Facilities and Operations Directorate, our battery bank that is needed for emergency lighting and starting the main field MG set has been totally replaced. Twenty new 6 Vdc batteries and a seismic rack system have been installed. F&O also funded a new vacuum breaker for the 13.8kV switchgear that is required for starting the MG-set. It has been received and is slated for installation in January.
RIB Injector Operations and Development (P.E. Mueller)
During the period from 1 July 2006 to 31 December 2006, the 25 MV Tandem Electrostatic Accelerator delivered beams of
200 kpps [24.6 MV 16+/29+ terminal foil / high energy foil stripped] 630 MeV 99% 130Sn, 90 kpps [24.6 MV 16+/29+ terminal foil / high energy foil stripped] 630 MeV 95% 132Sn, and 330 kpps [24.1 MV 17+/30+ terminal foil / high energy foil stripped] 643 MeV 134Te to the astrophysics endstation in Beam Line 41, and 280 pps [17.5 MV 12+ terminal foil stripped] 228 MeV 76Cu, 30 pps [17.3 MV 12+ terminal foil stripped] 225 MeV 77Cu, 3 pps [17.1 MV 12+ terminal foil stripped] 221 MeV 78Cu, 0.13 pps [19.8 MV 11+ terminal foil stripped] 237 MeV 79Cu, 60 pps [16.0 MV 12+ terminal foil stripped] 209 MeV 83Ga, 2.7 pps [15.9 MV 12+ terminal foil stripped] 206 MeV 84Ga, and 0.1 pps [15.9 MV 12+ terminal foil stripped] 206 MeV 85Ga to the decay spectroscopy endstation in Beam Line 21.
These beams were produced via proton induced fission of 238U by bombarding a pressed powder uranium carbide target coupled to an Electron Beam Plasma (positive) Ion Source (EBPIS) with 8 - 12 uA of 54 MeV 1H. Additionally, the high purity tin beams were produced by passing a positive tin sulfide beam through the recirculating cesium jet charge exchange cell and selecting the negative tin beam resulting from molecular breakup.
Tandem Operations and Development (M. Meigs)
The Tandem Accelerator was operated for almost 3000 hours since the last report. The machine ran at terminal potentials of 9.97 to 24.6 MV and the stable beams 1H, 32S, 48Ti, 54,56Fe, 58Ni, 70,72,76Ge, 76,78,80,82Se, 98Mo, 107Ag, 118,124Sn, 122,124,125,126,130Te and 238U were provided, with Mo being accelerated in the Tandem for the first time. 238U was provided from the RIB injector uranium carbide source and proved easier to tune than previous tries with the stable injector. Radioactive beams of 76,77,78,79Cu, 83,84,85Ga, 132,134Sn, and 134Te accounted for more than 1000 hours of beam on target. Deconditioning after some sparks required about 50 hours of conditioning. The affected units were examined carefully when the tank was opened for maintenance on December 5, and a thorough leak check was done, but no cause was found. In any case, the deconditioning phenomenon was observed after only a small fraction of sparks. The Tandem Accelerator has run for almost a year without having to open for maintenance...a record!
The highlight of this reporting period was that the accelerator ran for weeks on end above 24 MV with relatively little trouble. This high voltage operation was helped by the new gas handling procedure which allowed the accelerator tank to be filled to a higher SF6 pressure. A shipment of SF6 should arrive in a month or so and we can try for even higher voltages.