  A concept of a high-power magnetron transmitter for operation within a
wideband control feedback loop in phase and amplitude is presented. This
transmitter is proposed to drive Superconducting RF (SRF) cavities for
intensity-frontier GeV-scale proton/ion linacs. The transmitter performance at
the dynamic control was verified in experiments with CW, S-Band, 1 kW
magnetrons. The wideband control of magnetrons, required for the
superconducting linacs, was realized using the magnetrons, injection-locked by
the phase-modulated signals. The capabilities of the magnetrons
injection-locked by the phase-modulated signals and adequateness for feeding of
SRF cavities were verified by measurements of the transfer function magnitude
characteristics of single and 2-cascade magnetrons, by measurements the
magnetrons phase performance and by measurements of spectra of the carrier
frequency. At the ratio of power of locking signal to output power less than
-13 dB (in 2-cascade scheme per magnetron, respectively) we demonstrated a
phase modulation bandwidth of over 1.0 MHz. The carrier frequency spectrum
width about of 1 Hz at the level less than -60 dBc did not demonstrate
broadening at wide range of magnitude and frequency of the phase modulation of
the injection-locking signal. The wideband dynamic control of output power of
the transmitter model was first experimentally demonstrated using two
magnetrons, combined in power and injection-locked by the phase-modulated
signals. The experiments with the injection-locked magnetrons adequately
emulated the wideband dynamic control with a feedback control system, which
will allow suppressing all known parasitic modulation of the accelerating field
in the SRF cavities. The magnetron transmitter concept, tests of the setups and
injection-locking of magnetrons by phase-modulated signals are discussed in
this work.
