Tandem Operations

This reporting period covers October 1995 through October 1996 for the James R. Macdonald Laboratory at Kansas State University. The EN tandem Van de Graaff accelerator at Kansas State University has operated very well this reporting period. Tandem openings have been routine with no real unexpected problems.

One major modification was done to the tandem in November of 1995, this being the installation of a Balzers TMU 260 turbo pump in the terminal of the tandem. Problems have existed with the turbo pump controller throughout this reporting period, but while in operation the turbo has given us great capabilities that we have not had before in our laboratory. Measurements made on fluorine beams injected into the tandem show that the recirculating gas stripper gives a factor of 2.5 increase over optimal gas stripping without the recirculator. Further, the vacuums at both the low and high ends of the tandem were improved a factor of 2 or more when the recirculator was operational. We observed that we had to run very little stripping gas to achieve maximum beam as measured on the high energy cup or on the cup following the 90 degree analyzing magnet. We have, however, had problems with tank sparks. We are using a Balzers drag turbo as the recirculator pump, running it in standby mode and driving it with a Balzers 121 turbo controller. The tank sparks destroy the output driver board in the controller. The new Balzers turbos are 4-phase systems and thus are not compatible with running off of 3-phase power as may be available from a 3-phase alternator or a "Georator". We are studying the problem and will soon try to protect the controller from the EMF generated in the turbo motor windings by the sparks with a combination of spark gaps and/or other energy absorbing units such as neon bulbs, ferrites, etc.

Through this reporting period the tandem has logged 2807.0 hours of actual beam time operation. Down time during this period has totaled 672.0 hours of which 360 hours were used for the installation of the terminal turbo pump. The remaining 312 hours were used for routine maintenance.

Ion Sources

The EN tandem Van de Graaff accelerator at Kansas State University is injected with two different ion sources. First, the Middelton high intensity sputter source which has operated 90% of the time has been the main work horse for the laboratory throughout this reporting period. Beams produced out of the Middelton source have been carbon, oxygen, fluorine, silicon, copper, boron, chlorine, and iodine. An HVEC diode source is used the remaining 10% of the time, producing beams of hydrogen, carbon and fluorine.

Linac

Several upgrades of the Linac and its supporting LHe plant were made during the last year. These projects were performed using in-house staff with support from ATLAS personnel from Argonne National Laboratory where that was appropriate. The upgrades were:

1. The large Sullair compressor for the LHe refrigerator was moved from its original location on the laboratory roof to a new prefab building adjacent to the laboratory. This was done to reduce noise and vibration levels within the lab. A new prefab building was erected by an outside contractor and the compressor was relocated to that building. New control systems were installed to allow for remote compressor control and monitoring, new piping runs were installed, and modifications were made to the cold box and oil management system. The project took three months to complete.
2. The new RF control modules (one per resonator) were completed in the lab electronics shop and installed on the Linac. These modules are based on the designs provided by ATLAS personnel. The new modules allow conditioning of the individual resonators using the standard running electronics and thus greatly speed up what had previously been a very time consuming and tedious process.
3. New PIN diode pulsers were designed in-house. These units are air cooled instead of being water cooled. The problems associated with water cooling thus have been eliminated.
4. New Balzers TPU 330 and 550 turbopumps were installed on the Linac cryostats for reasons of field serviceability and reliability.

Acknowledgment

This work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research, U.S. Department of Energy.