First Pass

First Pass
February 25, 2014

The 12 GeV Upgrade Project at Jefferson Lab has many facets, and it is designed in such a way that some parts are completed and working while others are still in preparation. Recently, we have achieved a notable milestone. The accelerator commissioning was able to demonstrate 2.2 GeV of acceleration in a single pass around the upgraded accelerator.

We have seen the completion of the bulk of civil construction work with the Central Helium Liquefier (CHL) Building extension, accelerator utilities, the Hall D tagger area, and Hall D itself. There were moments, when the Hall D pit filled with rainwater, for example, when the sub-project was challenged. Since quite a while however, except for air conditioning work in the accelerator tunnel, it is complete.

In the CHL extension, we have been amassing large-scale equipment. Especially impressive have been the cold boxes, but the compressors and interconnections are also substantial. Substantial, yes, but also complex. While we are used to the idea that small devices, watches for example, can execute exquisite and complex movements, we give less thought to the possibility that large pieces also need to operate in concert to cool our equipment down to liquid helium temperatures. But they do, and so they need to be commissioned so that the nuances of operation can be learned and the refrigeration molded to its task. Towards the beginning of December 2013, this commissioning started to converge.

During that phase of CHL preparation, it had been possible to support several months of commissioning for the new C100 cryomodules built as part of the upgrade project and, over that same period, the re-commissioning of the C20 and C50 modules that had accelerated beam previously in the 6 GeV era of CEBAF.

During the 16 months of shutdown, many parts of the accelerator were changed or moved. All the arcs had seen their magnets removed, refurbished and replaced. Many valves were opened, closed, replaced. The accelerator team had planned for the restart. They had devised procedures that allowed them to check and double check the presence as appropriate, the polarity as appropriate, and the currents as appropriate to be sure that all the requisite devices were in place for safe operations.

Making the description straightforward, we were in a position in early January with both the North and South Linacs cooling down to start the commissioning of CEBAF as a whole. First the North Linac was brought up and beam run through it, then round the east arc. It is not easy to know by dead reckoning the accelerator energy. The usual approach is to measure the energy after acceleration in a spectrometer. The team used the complete east arc as its spectrometer. They cross calibrated all the individual cavities in this manner. Energy close to 1100 MeV was achieved. One linac done, one to go!

So on to the South Linac, which was by now also at 2 Kelvin. A few days of work and good progress, but then we received the news that the Secretary of Energy would soon visit. “Should we push?” asked Arne Freyberger, Accelerator Operations manager. He had been emphasizing care and attention to safety and detail; it was clearly the correct choice to continue in that vein. The team was close to its goal when the secretary visited, and he was suitably impressed.  But by the middle of the following week, just before the start of a month-long pause in operations, we were at 2.2 GeV in a single pass round to the “2R dumplet”.  For how long, a microsecond? No, several hours! What was the trip rate? Acceptable for test purposes! OK, Mike Epps, the Federal Project Director of the 12 GeV CEBAF Upgrade, agreed that we had made the goal. A very important Key Performance Parameter for the project.

Achieving this goal is not the end of the story; in many ways, it is only the beginning. Nevertheless, a large fraction of the lab staff had something to do with this important achievement and we celebrated with an MCC meeting in the auditorium with breakfast afterwards.

Within a few weeks, we will be trying to move on to multiple passes and to extraction of the beam into Hall A. To do that, we have subjected the new pieces of the accelerator and the Experimental Readiness Review process in Hall A to rigorous scrutiny. The checks looked good; we are in good shape. The spectrometer magnets are cooling. The schedule also calls for us to do 5.5 pass beam for Hall D in this Spring 2014 running. The excitement is palpable.

In the fall, we will be getting beam into Hall D and commissioning the experimental apparatus in an integrated manner. Detectors are being installed in Hall B. In Hall C, the massive structure that is the Super High Momentum Spectrometer (SHMS) carriage is almost complete. Some of the detectors are ready and waiting, including those from our partner institutions across the US and the world.  At Michigan State U. and in England, a dipole and quadrupole for Hall C are making steady progress towards completion, while in France, winding of the first coil of the SHMS main dipole started last week. At Jefferson Lab, we are cooling down the practice coil of the Hall B Torus magnet, and at Fermilab, the first production coil has been successfully wound.

I think that you can tell that this author is very excited by the prospects for pulling this project through to a successful conclusion and to physics for our user community over the next couple of years.

First pass, 2.2 GeV in CEBAF!!!!!