Tuning ILC cavities for tests
Mentor:  Bill Ashmanskas

The proposed International Linear Collider (ILC) will allow particle
physicists to study collisions between electrons and positrons at a
new energy frontier, addressing some of the most fundamental questions
about the nature of matter, energy, space, and time.  To build the
ILC, scientists will need to fabricate and to test many thousands of
niobium Superconducting Radio Frequency (SRF) cavities.  Scientists at
laboratories around the world, including Cornell, are now working to
develop the procedures for this fabrication and testing.

One step in preparing and testing each cavity is to measure the
magnitude of the electric field at the center of each of its nine
cells and to make small mechanical adjustments (called "tuning"), if
necessary, to keep the field uniform from cell to cell.  The system
that we now use for tuning ILC cavities at Cornell can be improved.
First, the data collection can be streamlined, so that less human
intervention is needed during measurements.  Second, the system of
motors and pulleys that moves a metal bead through the cavity to
determine the field profile needs to be replicated, so that it is
independent of the system used to tune non-ILC cavities.  Third, I'd
like to look into using an inexpensive ($500), commercially available
PC-based network analyzer, in place of the expensive ($20000)
dedicated network analyzer now in use, which is shared between several
test areas.  The PC/USB-based analyzer has limited bandwidth (100
MHz), so we'll need to use a ~ 1300 MHz frequency source and a pair of
mixers to shift between the ~ 1300 MHz resonant frequency of the
cavity and the ~ 50 MHz needed for the analyzer.

The student will gain programming and data-acquisition experience,
which is a generally useful skill for many fields of experimental
science.  He or she will gain comfort with some basic Radio Frequency
components: mixers, filters, oscillators, and network analyzers.  He
or she will work with an ILC cavity as an example of a system of 9
nearly identical oscillators with nearest-neighbor coupling --
textbook sophomore physics.  He or she will probably have a chance to
tune one or two ILC cavities: to move a little bead back and forth
under computer control, to collect data from the network analyzer, to
analyze the data, and then to use a vice-like contraption to deform
(gently!) a $100K niobium cavity into proper tune.  This should be
lots of fun for someone who likes to do hands-on work.