RA2. Accelerator System Status
ORIC Operations and Development (B. A. Tatum)
ORIC was shut down during the first part of the reporting period for the development, installation, and testing of a new driver amplifier system for the rf system. This system previously consisted of four ENI A300, 300-watt, amplifiers which were coupled to the RCA 4648A power amplifier (PA) tube grid by means of an in-house-constructed combiner/divider unit. The ENI amplifiers served us well for many years, but they are no longer manufactured and most parts are unobtainable.
Consequently, four 500-watt replacement units were purchased from AR Kalmus. During the installation and testing period, problems were encountered with the combiner/divider because of high third-harmonic content in the output of the new amplifiers. Therefore, a new commercially-available combiner/divider unit with higher bandwidth was also purchased from Werlatone, Inc. It was also discovered that the output circuitry of the new amplifiers was vulnerable to rf system transients, but our staff worked with the manufacturer to add transformer coupling to the output stage to make them more robust. Unfortunately, the amplifiers had to be returned to the manufacturer on more than one occasion. After further development and design improvements, we have now been able to operate with two new amplifiers, a 2-1 commercial combiner, and a 1-4 commercial divider. This configuration allows us to have two spare AR amplifiers, as well as two old ENI amplifiers that will drive the system if necessary. Combined with the installation of new ceramic plate capacitors last December we look forward to more reliable rf system operation.
Progress has been made in upgrading portions of the utilities infrastructure. Facilities and Operations Directorate funds have been used to purchase a new vacuum breaker for the 13.8kV switchgear that is required for starting the main field MG-set. The old breaker has recently experienced several component failures. A new battery bank related to the MG-set and emergency lighting system has also been ordered. During the latter portion of the period, ORIC operation resumed with the delivery of 10-15 uA of 54 Mev protons for the production of neutron-rich RIBs.
RIB Injector Operations and Development (P.E. Mueller)
During the week of 4 June 2006, the 25 MV Tandem Electrostatic Accelerator delivered a beam of
- 14.6 pps [17.5 MV 12+ terminal foil stripped] 228 MeV 76Cu to general purpose Beam Line 21.
This beam was 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 8 μA of 42 MeV 1H. Over one hundred times as much 76Ga was additionally in the beam.
Tandem Development (M. Meigs)
The Tandem Accelerator was operated for about 2580 hours since the last report. The machine ran at terminal potentials of 1.27 to 23.6 MV and the stable beams 1H, 12C, 14N, 16O, 17O, 18O, 48Ti, 54Fe, 58Ni, 76Ge, 76Se, 82Sr, 79Br, 124Sn, 126Te, 130Te and 197Au were provided. Radioactive beams of 76Cu, and 83Ga accounted for 348 hours of beam on target. About 245 hours were spent on conditioning with the goal of operation up to 24.5 MV for the neutron-rich program. The tank was still open for a few days for scheduled maintenance at the beginning of the period. An obstruction over a light-link port caused another tank opening immediately after the tank was closed. A wooden platform had been inadvertently placed over the port during tank closing. Only one other tank opening was done in this period and that only to allow National Geographic to film inside the tank; no maintenance was done during this opening. The Tandem has run for about six months with no maintenance!
In February, nanotube carbon foils were tested in the tandem terminal. This is the first time that nanotube foils have ever been used for stripping beam in an accelerator. These first tests showed that the nanotube foils do not last as long or have as good transmission as the laser-ablated carbon foils, but they are very easy to work with. Very thin foils, 2-3 µg/cm2, can be handled like 50 µg/cm2 conventional foils. If the homogeneity of the nanotube foils can be improved, they may begin to approach the laser-ablated foils lifetime and transmission.