The first two-foot long linear particle accelerator
by Diana Rogers)
By Tom Mead
A two-foot long linear particle accelerator section from
Fermilab recently arrived at SLAC. It is one of the first fruits of the
collaboration between these two high energy physics labs working to design
and build the Next Linear Collider (NLC). Moreover, it is a visible sign
of Fermilab’s increasing role in the NLC and evidence of closer
collaborative ties between Fermilab and SLAC.
This collaboration is focused on learning to build
accelerator sections in a manner consistent with efficient industrial
methods and practices. Since the NLC will need tens of thousands of these
structures, it will be necessary to contract them out to industrial
manufacturers for fabrication.
The Fermilab structure is a single section of the proposed
NLC accelerator. It, and the dozen that follow, will be integrated into
the Next Linear Collider Test Accelerator (NLCTA) as a test and
demonstration of the basic linac accelerator system unit.
SLAC physicist Marc Ross explained, "The goal for the NLC
is to attain record-high accelerating fields in these structures so we can
make the NLC more compact and try to understand the limits of this type of
technology, which was pioneered at Stanford many years ago."
While each accelerator structure is made to SLAC
specifications for the NLC design, some of the Fermilab assembly processes
differ from the methods used at SLAC. The big difference between the the
two processes is in the cleaning and brazing.
At SLAC, the copper components of the completed structure
are cleaned and brazed together by bathing them in hydrogen within an
800-degree Centigrade flame. The hydrogen and the heat attack the surface
of the copper and clean it.
At Fermilab, the structures are cleaned and brazed in a
vacuum furnace. The object is placed inside a vacuum furnace that is
heated to about 900 degrees Centigrade. The radiant heat drives the
contaminants out of the copper.
Last November, the Fermilab unit was wrapped in heater
tape, covered with aluminum foil and baked to 220 degrees Centigrade to
rid it of most residual contaminants introduced by post-production
handling in the air. The unit was recently powered up to see how it
functions as a high gradient accelerator. Its general behavior should be
known by January and feedback will be given to the Fermilab group that
In the next 18 months, different pieces from laboratories
all over the world will be collected in the NLCTA—enough for about a dozen
complete accelerator structures.
When assembled, the pieces provided by the international
collaborators will form a basic test module and will comprise about 1/10th
of 1 percent of the full NLC linac. Thus, the assembly and performance of
the completed accelerator unit can be seen as a test bed for the success
of the international NLC collaboration.
For more on the NLC, see: