| | The design of a 150 MHz lambda/4, 3- and 4- gap
structures with two and three loading elements, for the
velocity range beta = 0.015 - 0.12 has been accomplished.
Rotary and displacement tuners are developed for
multi-stub superconducting RF resonators. The
effectiveness of these tuners is made possible because
the resonators have low currents between their outer
conductors and tuner elements. Computer simulations
and experimental data show that the devices provide a
tuning range up to 100 kHz with a frequency resolution
of about 1 Hz. The manufacturing of the 150 MHz 2-
QWR with rotary tuner has been completed. A credible
design of 2-QWR and its rotary tuner have been
developed and tested at room temperature. The PbSn
plating, exercised on the existing split loop resonators,
will be extended to the 2-QWR as a straightforward
step to quickly explore the superconducting
performance of the new geometry. The commissioning
of the plating equipment has been started. In the longer
term, the Nb sputter coating will be researched because,
in principle, it can produce films competitive to the
much more expensive solid niobium option and
performs at higher fields than plated lead. The twelve
split loop resonators have been electroplated with
96%Pb4%Sn film to the final thickness of 1.5 micron
using methyl sulfonic acid chemistry achieving average
acceleration field of 3.5 MV/m off-line. Measurement
of the non-linear surface impedance and
intermodulation distortion (IMD) has been conducted
on the full-scale split-loop resonators (SLR). IMD
measurements allow more sensitive detection of nonlinearity
as compared to surface impedance
measurements. The source of the non-linearity in the
resonator structure, such as magnetic flux penetration
can be located by its contribution to the non-linear
IMD response above a critical RF power level. | |