PULSE SHAPING ISSUES FOR THE PETS TESTING PROGRAM AT SLAC A.Cappelletti SLAC, Oct 2008

I Q GHz HYBHYB HYBHYB Other experiment… Delay (2 round trips) + Mode conversion HYBHYB HYBHYB STRUCTURE AMPLITUDE – PHASE DETECTION SYSTEM LAPTOP (LABVIEW CODE) ATTENUATOR PH. SHIFTER ATTENUATOR - AFG MODULATIONPOWER SUPPLY PULSE COMPRESSION FEEDBACK SYSTEM OVERVIEW  s  

MODULATION Amplitude and phase data seem to fit, so we should use polar data instead of cartesian I-Q data, but practical concerns make I-Q data a better choice. Manipulating amplitude and phase of a carrier sine would be expensive, difficult and not as flexible as a circuit that uses I-Q waveforms. We control amplitude and phase of an RF carrier by operating the amplitudes of separate I and Q inputs.

ASTA (Accelerating Structure Test Area) hosts two 50 MW Klystrons, supplying up to ns (and almost ns); 90 MW if delay lines are not used. A relative phase shift of either 0 or 180 degrees allows to direct the power towards a specific hybrid output. POWER SUPPLY

SLED II uses low-loss resonant lines (yielding flat-topped output pulses), 26 ft long, and mode transducers. 1 RTT (Round Trip Time) = 132 ns; we use 2 RTT. One compressed-pulse-time from the end, the phase of the input is reversed, so that the field reflected from the coupling interface adds constructively to the field emitted from the charged cavity; then the stored energy is extracted. We worked with 8 sub-intervals, 132 ns each. PULSE COMPRESSION

FEEDBACK SYSTEM  MIXER GHz signal 10 MHz signal GHz FM GHz Amp. Detection Amp. - Phase Detection  A A (slow…) Low noise block downconverter ( LNB )

Non-idealities in the klystrons outputs, as well as in the pulse compressor, make the pulses not constant both in amplitude and in phase. As a result, the system produces pulses affected by ripple: this is deemed to be responsible of a 30 % loss in terms of efficiency (presently, efficiency level is 60%) Objective: developing an algorithm for point-by-point correction of the waveform which the system is initially fed. FEEDBACK CORRECTION

“Early” LabVIEW interface for coarse shaping… System setup (…hardware/system interfacing… )

… but an automatic correction code is required to be developed, in the framework of a longer-term cooperation with SLAC  Training program; o SO (safety) o EOSH (environmental safety and health) o GERT (radiological training) o Electrical Safety o RWT 1 (work in radiation areas) o ASTA Operator o …