Last week US facilities reached a milestone in testing superconducting cavities for the ILC.

Last week, after undergoing a buffered chemical polishing (BCP) treatment at Cornell University, the first US purchased, processed and tested International Linear Collider superconducting cavity achieved a milestone accelerating gradient of 26 MV/m (megavolts per meter). A joint effort of the SMTF (Superconducting Module Test Facility) collaboration, this accomplishment was a first test for the US facilities for ILC.

"This is a good achievement for the first step that we are going to take," said Hasan Padamsee of Cornell University. "ILC cavities have not been tested in the US yet, and none of our facilities have been checked out to that extent. We decided to do a standard treatment that has been done for some years now, and we got the best result that you can hope to get at this stage."

An etching process to essentially clean the cavity, the BCP treatment removes the damaged layer – typically 100 micrometers thick. Subsequently there is high pressure water rinsing to thoroughly scrub the surface clean. In addition to surpassing the desired gradient goal for this first BCP stage, which is 25 MV/m, the cavity showed no field emission. "Field emission is what you get when there is dirt on the cavity," Padamsee said. "We showed no field emission, which means that our process is very clean."

Purchased from the ACCEL Instruments in Germany (see ILC NewsLine, 20 October 2005), the cavity underwent mechanical measuring and testing at Fermilab before being sent to the SMTF collaboration partners Cornell and JLab. At Cornell, Curtis Crawford played a key role in all the preparation and testing operations.

Within the next few weeks, this cavity will be sent to JLab for electropolishing. After undergoing the electropolishing process, scientists expect that these cavities will achieve the desired gradient of 35 mv/m.

"We have a triangle of activity and cooperation between Fermilab, Cornell and JLab," said SMTF co-spokesperson Nigel Lockyer. "We are working together, and each laboratory is contributing a piece to the puzzle. It is a pretty impressive gradient to have achieved at this first stage, and that tells you that the Cornell facility is working extremely well."

Scientists expect to have more cavity results from Cornell and JLab this summer.

-- Elizabeth Clements