Superconducting RF control issues at CESR

RF controls of the superconducting cavities have to deal with an extremely heavy beam loading in CESR. A feature of the CESR RF system operation is that superconducting cavities are under-coupled at high beam currents. This means that the RF system operates very close to Robinson stability limit. Analysis of the steady-state stability of the CESR RF system and the results of measurements with beam are presented. Two more SRF cavities will be installed in CESR for short bunch operation. This will tighten tolerances to RF signal regulation errors. New control electronics is under development to meet the challenge.