First 4 GeV Three-Beam Split at Jefferson Lab's CEBAF
On 20 August 1997, a five-pass, 4.045 GeV cw electron beam was split for delivery to the three experimental halls of Jefferson Lab's Continuous Electron Beam Accelerator Facility (CEBAF). With Hall A having joined Hall C in full operation for nuclear physics, and with Hall B in advanced stages of commissioning, this was the first demonstration of CEBAF's capability to provide beams for three simultaneous experiments at the accelerator's full design energy.
The achievement also represents further progress toward significantly exceeding the design energy. After initial use of all three RF separators together, the three-way split was sustained by two separators running at slightly higher power -- a substantial indication of a three-separator capability for the three-way splitting of 6 GeV beams.
CEBAF at Jefferson Lab Operated at Maximum Design Current
The CEBAF accelerator at Jefferson Lab has been operated at its design energy and maximum current. The accelerator first reached full 4 GeV energy in May 1995, and has been supporting the planned experimental program -- first in Hall C alone, and later in Hall A as well. More recently, with Hall B nearly fully commissioned and about to come on-line, full-energy beam was first split three ways, as reported last month. Then the machine's design current was reached as well in a special test unrelated to the experiments, none of which yet requires high current. On 16 September, sustained, stable, physics-quality full-energy beam was run at 200 microamperes.
From Scott:
These increased demands from the accelerator will place increasingly high demands on the RadCon staff. Our group put in quite a bit of overtime last year and was asked to reduce such overtime in this fiscal year as a result of shrinking Federal funds. As a result, we have been having to "calibrate" the rest of the laboratory, especially the Users, on proper scheduling for RadCon support.
The Free Electron Laser (FEL) facility at Jefferson Lab has also provided some challenges. Since it is a new building, and installation of machine components has been proceeding, they have found out that it is necessary to retrofit some of the building structure to install certain parts. Since the building itself serves as the bulk of the radiation shielding, we have had to keep a close eye and assist in making this work. We are ever mindful that we are here as operations support, helping to add to the project as a whole, with appropriate controls, but not serving solely as an impediment. I might ask the question for you in each of your facilities... are you acting as an impediment, or serving to contribute to the success of your organization?
An interesting situation that we have: since Title 10, Code of Federal Regulations Part 835 (10CFR835) requires posting based on actual radiation levels rather than potential levels, we have some "conditional postings" in place here. Specifically, we have conditional Airborne Radiation Areas, conditional Radiation Areas, etc.; each of these is conditional on some sort of visual signal - a rotating beacon or the like. For instance, we have air samplers constantly sampling our experimental halls, so that if the airborne radioactivity exceeds 10% of the Derived Air Concentration (DAC), a beacon lights. Below this beacon is a sign that indicates that if the beacon is lit, the area is an Airborne Radiation Area. Appropriate cautions are also made on the sign.
We think that this type of setup keeps us in strict compliance with 10CFR835, and yet does not require us to post and depost an area every few minutes. I spoke with a colleague of mine in another accelerator facility who posts much more conservatively - by the highest expected levels. One might argue that they are conservative and therefore justified, but another might argue that they are not in compliance with the law (posting an area which has conditions that does not match the posting) and are desensitizing the workers.
This may be food for thought for your next contribution to the Newsletter.
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