From the Acting Director of SSRL: Deliberate, Stepwise Progress to 500 mA
At the time I wrote my last article for SLAC Today, the Stanford Synchrotron Radiation Lightsource was just starting to come out of the summer shutdown having completed improvements that would enable the SPEAR3 storage ring to run with top-off injection at 500 mA. I am happy to report that in spite of rainstorms, the power outage and a water leak in a beamline mask, we have made excellent progress toward that goal over the past four months.
The process for reaching this goal must, by necessity, be deliberate, with safety and performance tests being performed at each step. For example, before we are able to routinely operate a beamline with shutters open during injection, careful tests are performed by the Radiation Protection Department to insure that there are no hazardous radiation levels present during injection. These tests are performed beamline by beamline every two weeks during the accelerator physics days and require an active collaboration between the Accelerator, Beamline and Radiation Protection groups. Remember that except for the two accelerator physics days every two weeks, we are running in production mode for users that come for periods as short as 8 hours. As of this week, only one beamline remains to be certified. We hope to complete this phase of the process during the next two-week accelerator physics cycle.
In parallel, we have also started to test the "trickle charge" approach in which frequent injections are utilized to maintain a high average current. For example, instead of injecting every 8 hours, which allows the beam to decay from 200 mA to 140 mA, an injection frequency of less than 10 minutes would maintain the 200 mA current to within 1 mA. In order to operate in this mode without overheating the SPEAR3 injector, a new running mode was developed to allow the injection system to be quickly turned on only for the short injection cycle, then turned off for the time between injections. Not only does this save wear and tear on the injector but it also reduces power consumption.
However, we must ask the question: can users take data during injection? Many experiments look for very small changes in the signal coming from their samples in which changes as small as 0.1 percent are significant and these experiments can operate continuously for many hours. Therefore, a rapid increase in current, as would happen during injection, could potentially compromise the quality of the data. The first comprehensive tests of this concept were performed two weeks ago and the results have been very promising. In these tests, beamline staff set up typical experiments on as many beamlines as possible and collected real data. A second round of tests is being scheduled for the next accelerator physics cycle with more challenging experiments. Assuming the results continue to be positive, we will be working with our users to introduce trickle charge injection mode during the next few months. Higher current running will be the next step. Again, we will extensively test each beamline to make sure that the safety requirements are met and that the users can continue to collect excellent data.
With all this activity, the next five months of the run will go by quickly and thanks to the hard work of all the staff from multiple directorates, we will be bringing SPEAR3 operations to the next level.