This is a rough tuning procedure for a two cavity RF station under LLRF9 control. The procedure assumes that channel loss factors have already been established (based on power meter measurements, cavity parameters, possibly with beam-based calibration).

Start from resetting interlocks and turning on the station in an open-loop mode. Tuner loops should be open. Setpoint should be chosen as follows:

• High enough to generate forward power in each cavity above the tuner loop minimum power level
• Low enough not to generate a reflected power trip with fully detuned cavity

Typically, minimum forward power threshold is several orders of magnitude lower than reflected power trip level, a suitable setpoint is easy to find. Lower values are, in general, preferable.

Turn on the network analyzer excitation at relatively low level (-48 to -60 dB). Set sweep span to 600  kHz. For each cavity, do the following:

• Set network analyzer input to cavity 1 or 2 rotated
• Move tuner motor manually to tune the cavity on resonance

Displayed transfer function is more or less sufficient to perform this step, but Matlab tools can be used to speed up the process and to make more precise measurements. Use the following two commands to read out RTNA data and to fit the cavity response:

data = read_rtna('LLRF', 'BRD1');
data1 = direct_fit(data, [-300e3 300e3]);