RA2. Accelerator System Status
ORIC Operations and Development (B. A. Tatum)
ORIC provided a 52-MeV proton beam for the neutron-rich RIB campaign during most of July and August. The machine ran quite well with only a few minor power supply instabilities. ORIC was shut down for the remainder of the year during the tandem tank opening, stable beam runs, and the Beryllium RIB campaign with the batch-mode ion source.
There were a few key maintenance and upgrade activities that took place during the shutdown. First, a new ion source service platform was installed that makes source maintenance much easier. This platform is considerably larger than its predecessor, has better access, and is designed to reduce the spread of possible radiological contamination. Second, the ORIC control system was converted from
Vistato the EPICS platform. This conversion was the final step in unifying all of the HRIBF control systems under EPICS and is expected to result in more efficient and reliable operation. Third, preparations were made for installation of the new ORIC beamline that will deliver beam to the High Power Target Laboratory. Installation of the beamline will begin in February 2005.
Tandem Operations and Development (M. J. Meigs)
The Tandem Accelerator was operational, to provide beam, for approximately 1769 hours since the last report. The machine ran at terminal potentials of 3.47 to 24.15 MV and the stable beams 1H, 7Li, 10B, 12C, 14N, 18O, 19F, 24Mg, 58Ni, 124Sn, and 130Te were provided. Radioactive beams of 7Be, 132,134Sn, and 132Te accounted for 571 hours. Ten tank openings were necessary during this period with the first being a scheduled maintenance period. During this scheduled opening, the new power supply for the terminal bending magnet and an additional ion pump were installed. The additional ion pump shares the gas load of the stripper with ion pump T-2 and allows better accelerator tube vacuum while allowing stripping at a higher gas pressure. Seven of the openings were for failures of the new supply after sparks. A separate article in this newsletter gives details on the status of this power supply. The other openings were for communication failures after sparks; once to D4 and once to the terminal. About 85 hours were spent on conditioning.
During this period an experiment was done with 100-MeV 7Be. This beam must be injected as the molecule 7Be16O and must be fully stripped in the terminal to achieve the desired energy. This was accomplished by breaking up the molecule with the gas stripper and fully stripping the 7Be with the foil stripper. Before the new gas stripper installation and relocation of the foil stripper above the gas stripper, this would not have been possible since the coulomb explosion from deep stripping with the foil stripper would have caused extremely low transmission down the high energy tube. This was in fact, experimentally confirmed by the operators who could get no transmission of beam with either stripper alone but had good transmission when using both strippers.
RIB Injector Operations and Development (P.E. Mueller)
During this reporting period, we delivered beams of
- 60 kpps 14+/26+ terminal foil / high energy foil stripped 530 MeV pure 132Sn to Beam Line 23,
- 64 kpps 14+/26+ terminal foil / high energy foil stripped 545 MeV pure 132Sn to Beam Line 23,
- 51 kpps 14+/27+ terminal foil / high energy foil stripped 560 MeV pure 132Sn to Beam Line 23,
- 29 kpps 15+/28+ terminal foil / high energy foil stripped 590 MeV pure 132Sn to Beam Line 23,
- 20 kpps 16+/29+ terminal foil / high energy foil stripped 620 MeV pure 132Sn to Beam Line 23,
- 450 pps 14+/25+ terminal foil / high energy foil stripped 500 MeV 40% 134Sn to Beam Line 23,
- 600 pps 14+/26+ terminal foil / high energy foil stripped 530 MeV 40% 134Sn to Beam Line 23,
- 200 kpps 1+/ 4+ terminal gas / post foil stripped 12 MeV pure 7Be to the Daresbury Recoil Separator, and
- 3.7 Mpps 4+ terminal gas / terminal foil stripped 100 MeV pure 7Be to the astrophysics endstation in Beam Line 21.
The tin beams were produced via proton-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 7.5-8 uA of 54-MeV 1H 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.
The neutron-rich campaign ended when the second stage mass separator (SIGMA PHI) second dipole upper coil developed a short in the middle winding and a water leak. During subsequent testing, the second dipole lower coil developed a short in the upper and lower windings. This ten-year-old magnet system has always been run well within specifications for current and cooling water flow. The second dipole upper and lower coils will be replaced in Spring 2005.
Fortunately, the first dipole and the remaining windings in the second dipole allow us to bend 200-keV 1- 17F, 18F, and 7BeO beams.
The 7Be beams were produced with a cesium sputter negative ion source with 19.6 mCi 7BeO in Ag powder in a Cu holder. Permanent magnets were installed around the beam line upstream of the first quadrupole multiplet to sweep away electrons. The recirculating cesium jet charge exchange cell was removed to maximize transmission.
The 100-MeV 4+ 7Be beam was produced by gas stripping followed by foil stripping in the terminal. This has only been possible since the new recirculating gas stripper was installed in front of the foil stripper a little over a year ago. Gas or foil stripping alone only allowed the transmission of a 3+ beam. Presumably, the combination of the two allowed lower charge state 7Be from less violent breakup of 7BeO in the gas to be fully stripped to the 4+ charge state in the foil.