66506-2604
The EN tandem Van de Graaff accelerator at Kansas State University has operated through this reporting period extremely well. Again, the usual and unexpected problems have occurred with the tandem and associated equipment which has required some down time.
One of our major concerns this reporting period has been with the electrolysis that has been occurring with all of our major magnet power supplies. This was noticed a few years ago when maintenance was performed on these power supplies. The electrolysis just seemed to be getting worse, so in June of this year water tests were performed on our closed loop chiller system and we found that our water resistivity was extremely low, in the order of 1200 micromhos (833 ohms). Since August of l997 we have improved our water resistivity in our closed loop chiller system to approximately 20 micromhos (50K ohms). We hope to maintain a value in the order of 100 micromhos (10k ohms).
Through this reporting period the tandem has logged 3418.0 hours of actual beam time operation. Down time during this period has totaled 144.0 hours of which the tandem was only opened once for routine maintenance in November of 1996.
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 operates 90% of the time has been again the main work horse for the laboratory throughout this reporting period. Beams produced out of the Middelton source have been carbon, oxygen, fluorine, copper, boron, chlorine and iodine. The Diode ion source is used the other 10%, producing beams of hydrogen.
During the last year the Linac has been used for experimental work on a very limited basis. Primarily we have provided time bunched beams with time widths of less than 150 ps for time of flight measurements. We have made modifications to the two low beta cryostats to improve the LN2 cooling system . We installed closed LN2 dewars on the heat shields, rewired the cryostats to minimize the number of insulated penetrations from the LN2 space and the cryostat vacuum space, and rerouted the thermometry wiring in order to reduce the number of connections passing through the LN2 space. The primary motivation for these reworking of these two cryostats was to improve the system reliability and reduce the number of failures leading to LN2 leaks into the cryostat vacuum space. We completed the upgrade of the rf control units for the individual resonators. The new control modules have sufficient gain that we can now condition through the low lying barriers in the resonators using the rf control module in lieu of having to condition each resonator individually with the high power test system which was a very time consuming and labor intensive process.
Cryogenics Systems
The He refrigerator has operated very reliably during the last year. We have had the continuing problem of oil leakage occurring at the shaft seal on the Sullair compressor. We have replaced that seal on several occasions with and without direct supervision from the seal manufacturer. We have yet to solve this problem.
Currently the last seal which was removed is undergoing inspection and tests at the manufacturer. This problem with the shaft seal is a bother , but does not really affect the system operation. We have ordered a spare cold engine from Cryo Technologies and it is to be shipped by this coming December. This will allow us to minimize the down time when one of the two cold engines is in need of maintenance that requires that we pull that engine off of the cold box. We can remove the particular engine and replace it immediately while the plant remains in operation at a reduced level , start the replacement engine and return to full operational status in the minimum time possible (usually an hour or so). Our cryogenics system has now been operational for 10 ½ years with only one major failure, that being the self destruction of the 400 hp drive motor on the compressor.
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.
