RA2. Accelerator System Status
ORIC Operations and Development (B. A. Tatum)
ORIC provided proton, deuteron, and alpha beams to the RIB injector through the end of September for the production of radioactive ion beams required by the experimental program. In late October and early December, ORIC was utilized for commissioning of the new High Power Target Laboratory. Details of the project and commissioning are presented in a separate article.
The latter part of the year was particularly challenging due to considerable problems with the ORIC rf system. Due to a chain reaction of problems, the system would not operate stably at the 19 MHz frequency required for proton acceleration. With some careful nurturing, we were successful in operating around 12 MHz which is required for both deuteron and alpha acceleration. The difficulties centered on the failure of major components in the rf tuning circuit. Four glass-envelope tunable vacuum capacitors are utilized in the plate circuit of the power amplifier tube. These fragile plate capacitors began to fail with age as some have in the past. Unfortunately, our spare units all showed signs of vacuum degradation due to deteriorated bellows seals. Most of these had never been used but deteriorated on the shelf after many years.
We have recently purchased and installed a set of modern tunable capacitors with ceramic envelopes. Testing of the system with these units has been quite successful, and the rf system appears to be running reliably again following an extended maintenance shutdown.
RIB Injector Operations and Development (P.E. Mueller)
During the period from 1 July 2005 to 1 October 2005, the 25 MV Tandem Electrostatic Accelerator delivered beams of
2.7 Mpps [18.7 MV 7+/9+ terminal foil/post foil stripped] 150 MeV pure 18F,
240 kpps [4.58 MV 2+ terminal gas stripped] 14.0 MeV 20:1 18F, and
100 kpps [5.57 MV 2+ terminal gas stripped] 17.0 MeV 23:1 18F to the astrophysics endstation in Beam Line 21, and
2 kpps [22.4 MV 14+/25+ terminal foil/high energy foil stripped] 500 MeV 0.36 134Sn,
20 kpps [22.14 MV 14+/25+ terminal foil/high energy foil stripped] 489 MeV 0.9 132Sn, and
17 kpps [21.90 MV 13+/24+ terminal foil/high energy foil stripped] 465 MeV 0.9 132Sn to the time-of-flight endstation in Beam Line 23.
The 18F beams were produced via the 16O(4He,pn) 18F reaction by bombarding a fibrous HfO2 target coupled to a Kinetic Ejection Negative Ion Source (KENIS) with 2-3 uA of 85-MeV 4He from the Oak Ridge Isochronous Cyclotron (ORIC).
The tin beams were produced via deuteron induced fission of 238U by bombarding a uranium carbide coating on a reticulated vitreous carbon fiber target coupled to an Electron Beam Plasma (positive) Ion Source (EBPIS) with 5-6 uA of 43 MeV 2H and passing the positive tin sulfide beam through the recirculating cesium jet charge exchange cell and selecting the negative tin beam resulting from molecular breakup.
Tandem Development (M. Meigs)
The Tandem Accelerator was operated for almost 3000 hours since the last report. The machine ran at terminal potentials of 1.52 to 24.34 MV and the stable beams 1H, 4He, 16O, 17O, 40Ca, 54Fe, 58Ni, 80Se, 88Sr, 90Zr, 124Sn, 124Te, 126Te, 130Te and 197Au were provided. This is the first time He has been accelerated at our facility. Radioactive beams of 18F, 132Sn, 134Sn, and 134Te accounted for 559 hours of beam on target. Only two tank openings were necessary during this period with one being a scheduled maintenance opening. The other tank opening was a quick one-day to replace a failed power supply on the column base quadrupole. The regular maintenance period allowed replacing bad bearings in the power shafts, replacement of foils in the terminal, refurbishing an ion pump in the terminal, and other minor maintenance and cleaning. About 195 hours were spent on conditioning with the goal of operation up to 24.5 MV for the neutron-rich program.