  Mid-T heat treatments in the range from 250 to 400 C on superconducting
radio-frequency (SRF) cavities have been shown to provide high quality factors
that rise with applied rf field strength in high frequency, electro-polished
(EP), elliptical cavities operating at 2K, similar to nitrogen doped cavities.
The rise in quality factor is attributed to a decrease in the temperature
dependent part of the surface resistance $R_{BCS}$. Until now, no results have
been reported for these new treatments on quarter-wave resonators (QWR) and
half-wave resonators (HWR). The TRIUMF multi-mode coaxial cavities are
dedicated test cavities that allow frequency and temperature resolved
performance characterization of treatments without changing environments,
therefore providing an excellent test vehicle to test these new treatments with
rf frequencies ranging from 200 to 1200 MHz. In this paper, performance
measurements from both QWR and HWR cavities are reported and their performance
compared with four different treatments: baseline, a conventional 120C low
temperature bake for 48 hours, and two mid-T bakes at 300 and 400C for 3 hours.
In addition, sample analysis using SEM, EDX and SIMS of witness samples is also
shown. It is found that the mid-T bakes are not directly transferable to low
frequency cavities. In the fundamental modes of the two test cavities, no
performance gain over the baseline treatment nor a decreasing temperature
dependent component with rising rf amplitude was observed. At frequencies above
1GHz and low temperatures, the mid-T bakes show a reduced field dependence of
$R_{BCS}$ compared to both the baseline and 120C treatments.

Accelerator Physics