May 24, 2016
A little less than a year ago, I wrote a Montage article entitled Spring Challenges. I could almost have used the same title for this article and, indeed, there have been a number of developments over the past few months that could merit comment. Nevertheless, at a laboratory like ours, there has to be a focus on running the accelerator for physics, and so that becomes the lens through which life is viewed.
After the mid-winter break, accelerator operations were started, but soon difficulties with the Central Helium Liquefier imposed a pause. After the cryogenic recovery, the accelerator recovery also had some difficulties of its own. It became clear that the path to good performance demanded an incisive move. The operations group systematically reset the machine so that the parameters matched the pre-holidays sweet spot. From that point on, the accelerator performance was impeccable. The experiments in Hall A to measure Deep Virtual Compton Scattering and the proton form factor began to accumulate useful amounts of data and were able to meet some of the experiments’ goals with the full 11 GeV beam. In Hall D also, high data volumes were accumulated using the 12 GeV electrons and helped by the good performance of the data acquisition system. Still calling it a commissioning run, different thicknesses of diamond radiator were tried. The solenoid magnet operated for several months at 1200 amps, and then in the final week, operation with 1345 amps was also demonstrated to be reliable. Expectations for eventual publications from these data are high.
In Hall B, the primary activity has continued to be the installation of the CLAS12 detector, in particular the new Torus magnet. This magnet has been featured in earlier Montage articles. Its coils were fabricated at Fermilab, encased in cryostats in the Test Lab, and assembled into a magnet in Hall B itself. After long work-days, and double shifts, the magnet, as of today, is pumping down nicely after a few weeks of intensive leak finding.
So, no physics in Hall B. Not exactly! The Heavy Photon Search experiment was installed downstream of CLAS 12, and planned to take data on weekends. Now there is a challenge! Changing a machine configuration on a Friday afternoon is usually taboo. But we decided to try, and HPS was able to take about 70-80% of the data desired with 2.2 GeV beam. That is a major success. The main part of the run ended in the last week of April, but, after a reconfiguration of the Central Helium Liquefiers to enable the summer maintenance program, we are operating the accelerator for Hall B only operation with 2 pass beam for PRad, an experiment which aims to clarify the controversy about the proton radius. Of course, as is now traditional (tongue in cheek), the experiment will mainly run on weekends and perhaps in the overnight periods, depending on Torus progress.
Spring Running is a title that can refer also to our Annual Run-A-Round, which took place on May 4. The weather was fine, something not guaranteed this year, and some of the usual suspects did well again. There were jokes at the start about how, given it was a new course, “perhaps Alexandre Deur, the anticipated leader, will get lost as had happened once before”. So Dave Abbott rode his bike out front and all went well. This year’s T-shirt winner, an entry from the Diversity and Inclusion Council, is turning out to be very popular.
There was, of course, excitement elsewhere, for example, with superconducting magnet fabrication proceeding in Brittany and in Pennsylvania, and the first LCLS-II cavity string coming out of the clean room. But the event that “took the cake”, broke the records”, “won the awards” was this year’s Open House. I recall estimates in the past of 6-7,000 visitors, or on one occasion 8,000, for our Open House. This year, 12,000!!!! Before 9 a.m., we had lines to get through the security check and they just kept coming. Allison Lung and I were accosted outside CEBAF Center by two women seeking the 3-D printers, and then the 3-D printed cars. They were hot to trot having heard how body parts might be fabricated by such techniques. They told us they were each in their upper eighties and admitted to high excitement. Allison saw them later, and all their desires had been fulfilled; and they sent us hand written cards to that effect. It was a famous day, for them, for 11,998 others, and for the lab. Thank you to all who made it happen!!
Spring Running in 2016 appears to have been a multiple success.