  A second harmonic tunable RF cavity is being developed for the Fermilab
Booster. This device, which promises reduction of the particle beam loss at the
injection, transition, and extraction stages, employs perpendicularly biased
garnet material for frequency tuning. The required range of the tuning is
significantly wider than in previously built and tested tunable RF devices. As
a result, the magnetic field in the garnet comes fairly close to the
gyromagnetic resonance line at the lower end of the frequency range. The chosen
design concept of a tuner for the cavity cannot ensure uniform magnetic field
in the garnet material; thus, it is important to know the static magnetic
properties of the material to avoid significant increase in the local RF loss
power density. This report summarizes studies performed at Fermilab to
understand variations in the magnetic properties of the AL800 garnet material
used to build the tuner of the cavity.
