PULSE SHAPING ISSUES PULSE SHAPING ISSUES FOR THE PETS TESTING - - PowerPoint PPT Presentation

PULSE SHAPING ISSUES PULSE SHAPING ISSUES FOR THE PETS TESTING PROGRAM AT SLAC

• A. Cappelletti

SLAC, 13-30 Oct 2008

SYSTEM OVERVIEW

AMPLITUDE – PHASE LAPTOP

S

STRUCTURE

AMPLITUDE – PHASE DETECTION SYSTEM LAPTOP (LABVIEW CODE) AFG

PULSE COMPRESSION FEEDBACK H Y B FEEDBACK I

Delay (2 round trips) + Mode conversion ATTENUATOR CW @ 11.424 GHz

H Y B

Other experiment

• 50 MW @ 1.5 µs

Q

experiment…

• PH. SHIFTER

ATTENUATOR

π/2 MODULATION POWER SUPPLY

MODULATION

• Amplitude and phase data seem to fit, so we should use polar

data instead of cartesian I-Q data, but practical concerns make 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 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.

POWER SUPPLY

• ASTA (Accelerating Structure Test Area) hosts two 50 MW

Klystrons supplying up to 500 MW @ 64 ns (and almost 300 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

p g direct the power towards a specific hybrid output.

PULSE COMPRESSION

• 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. O d l i f h d h h f h i i d

• 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.

FEEDBACK SYSTEM

10.25 GHz 1.174 GHz

MIXER

10 MHz signal

FM

Amp. Detection

A Low noise block downconverter ( LNB )

11.424 GHz signal

• Amp. - Phase

Detection

φ A (slow…)

FEEDBACK CORRECTION

• Non-idealities in the klystrons outputs, as well as in the pulse compressor, make

the pulses not constant both in amplitude and in phase. A l h d l ff d b i l hi i d d b

• 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
• Objective: developing an algorithm for point-by-point correction of the waveform

which the system is initially fed.

System setup ( h d / (…hardware/system interfacing… ) “Early” LabVIEW interface for coarse shaping… f p g

• … but an automatic correction code is

required to be developed, in the framework of a longer-term cooperation with SLAC g p Training program;

• SO (safety)

( y)

• EOSH (environmental safety and health)

GERT (radiological training)

• GERT (radiological training)
• Electrical Safety
• RWT 1 (work in radiation areas)
• ASTA Operator

p

• …