The pi-mode
resonant frequency of the 1.6-cell SLAC/BNL/UCLA style RF photoinjector
electron gun is conventionally tuned using cylindrical copper tuning
pieces that extend into the full cell cavity through holes in the side
of the gun. This design begins to fail in many versions of this popular
gun design at higher voltage levels, when the cavity undergoes electric
breakdown in the vicinity of the tuners. In order to remove the tuners
from the region of high electric field, mitigating this problem, one
must change the full cell geometry significantly. We have investigated
a method for accomplishing this, in which we stretch the gun structure
to tune the full cell frequency up by over 2 MHz. We constructed a device
to perform this stretching and tested the modified photoinjector in
an RF test bed. We succeed in putting approximately 8.4 MW of RF power
into the gun, an improvement over the 4 MW routinely achieved with a
similar gun using conventional tuning methods installed at the UCLA
Neptune laboratory. Recent results in testing this gun with a magnesium
cathode insert are reported as well.