JLab, Newport News, Virginia, USA
RadiaSoft LLC, Boulder, Colorado, USA
BNL, Upton, New York, USA
DESY, Hamburg, Germany
Cornell University, Ithaca, New York, USA
Tech-X, Boulder, Colorado, USA
SLAC, Menlo Park, California, USA
ANL, Lemont, Illinois, USA
ODU, Norfolk, Virginia, USA
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Douglas Consulting, York, Virginia, USA
Muons, Inc, Illinois, USA
Northern Illinois University, DeKalb, Illinois, USA
Stanford University, Stanford, California, USA
Texas A&M University, College Station, USA
Fermilab, Batavia, Illinois, USA
FRIB, East Lansing, Michigan, USA
CalPoly, San Luis Obispo, California, USA
MIT, Cambridge, Massachusetts, USA
LBNL, Berkeley, California, USA
Dimtel, Redwood City, California, USA
NSCL, East Lansing, Michigan, USA
ANL, Lemont, Illinois, USA
Dimtel, Redwood City, California, USA
The Advanced Photon Source Upgrade will suffer longitudinal multi-bunch instability because of the presence of several monopole higher-order mode (HOMs) of the 12 352-MHz rf cavities. Even with a feedback system, it would be good to mitigate any driving terms with conventional means such as tuning HOM frequencies with temperature. However the latter is problematic because there will be 90 or so HOMs that are potentially harmful. A scheme is developed, utilizing the measured spectrum of HOMs, to find the best temperature setting for each cavity. We present measurements of 30 or so HOMs, and a thermal model of HOM frequencies using cavity wall power and cooling water temperature as inputs to maintain the optimum tuning condition with sufficient accuracy. The newly acquired Dimtel iGp12 processor box is central to the HOM frequency measurements.