Jefferson Lab in the News
Jefferson Lab fabricated and tests a single cell accelerating cavity
NEWPORT NEWS, VA, UNITED STATES (UPI) - Jefferson Lab's Institute for Superconducting
Radiofrequency Science & Technology has, for the first time, successfully fabricated and tested a
single cell accelerating cavity made from a single crystal of niobium.
Preliminary tests reveal this new fabrication process could simplify manufacturing and reduce cost
and assembly time of future accelerator cavities, while delivering a product with high quality
performance.
Many particle accelerators require accelerating cavities made of niobium operating at temperatures
between -271 and -269 degrees centigrade, when niobium becomes superconducting with close to zero
electrical resistance.
Jefferson Lab's accelerator uses superconducting niobium cavities to accelerate electrons to energies
approaching six billion electron-volts for nuclear physics experiments in its three experimental
halls.
These cavities were fabricated from sheets of fine-grain niobium that were forged and rolled from a
niobium ingot. In addition to the benefits, this fabrication process poses some disadvantages.
\"Intermediate annealing steps are necessary to remove stresses in the material and re-crystallize
it. There manufacturing steps have the inherent risk of introducing unwanted impurities in the
material,\" says Peter Kneisel, senior staff scientist on the project.
But these steps are required to yield a high-quality cavity from fine-grain niobium metal.
Recently, a Jefferson Lab team, led by senior scientists Peter Kneisel and Ganapati Myneni, procured
regular ingots of large-grain and single crystal niobium through an industrial partnership with
Tadeu Carneiro, spokesperson and manager o Reference Metals.
The team fabricated four niobium single cell cavities from the ingots. Like salt crystals, niobium
crystals, or grains, can be grown in either larger or smaller sizes, so large-grain niobium consists
of larger niobium crystals.
Large-grain niobium sheets were obtained by simply slicing them off an ingot.
\"It's just like slicing up a sausage,\" Kneisel says. The team used some of these slices to
manufacture a single cell cavity in the same shape as the low-loss design proposed as an improvement
to the baseline for the International Linear Collider (ILC).
The cavity, though a scaled-down version of what the ILC would require, was made out of a single
crystal of niobium.
\"So the only difference between what we are doing now and typically what everyone else does, is
that we have a difference kind of material - not fine-grain material, but large-grain or single
crystal material,\" Kneisel explains.
In preliminary test conducted at -271 degrees centigrade, the cavity's accelerating gradient
(its ability to transfer energy into particles per unit of cavity length) exceeded the ILC
specification of 28 MV/m and eventual goal of 35 MV/m.
After a brief, low-temperature bake, the cavity achieved an accelerating gradient of 45 MV/m, equal
to Cornell's current world record of 46 MV/m, when measurement uncertainty is taken into account.
This new fabrication process, which eliminates the rolling procedure and related steps, could
simplify the manufacturing process while reducing cost and assembly time.
For instance, it's estimated that the new procedure could cut the cost of producing cavities by as
much as 35%.
The new fabrication process also provides cavities with smoother interior surfaces after only
chemical surface treatment, better mechanical performance and less time-consuming quality assurance
procedures.
The Jefferson Lab team fabricated two of the single cell cavities in Jefferson Lab's own 12 GeV
Upgrade design from large-grain niobium.
Two more single cell cavities were built from single niobium crystals, one in the ILC design and
the other in the 12 GeV design.
Kneisel says all the cavities performed well in early tests. Kneisel presented these results in a
poster session of the 2005 Particle Accelerator Conference in Knoxville, Tenn., on May 17.
The team who built the cavities and conducted the tests included: Peter Kneisel, Ganapati Myneni,
Gianluigi Ciovati, Jacek Sekutowicz (DESY), Larry Turlington, Robert Manus, Gary Slack, Steve
Manning and Pete Kushnick.
This work was performed under the auspices of the Institute of Superconducting Radio Frequency
Science and Technology, headed by Warren Funk, in Jefferson Lab's Accelerator Division under
Associate Director Swapan Chattopadhyay.