PULSE SHAPING ISSUESFOR THE PETS TESTING PROGRAM

AT SLAC

A. CappellettiSLAC, 13-30 Oct 2008

I

Q

CW @ 11.424 GHz

KLY.

KLY.

TWT

H Y B Other

experiment…

Delay (2 round trips) + Mode conversion

H Y B

STRUCTUREAMPLITUDE – PHASE DETECTION SYSTEM

LAPTOP (LABVIEW CODE)

ATTENUATOR

PH. SHIFTERATTENUATOR

-

AFG

MODULATION POWER SUPPLY

PULSE COMPRESSION

FEEDBACK

SYSTEM OVERVIEW

50 MW @ 1.5 ms /p2

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 500 MW @ 64 ns (and almost 300 MW @ 260 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

AMP.

11.424 GHz signal

10 MHz signal

10.25 GHz

FM

1.174 GHz

Amp. Detection

Amp. - Phase Detection

f

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 Safetyo RWT 1 (work in radiation areas)o ASTA Operatoro …