30GHz system improvements Jan Kovermann RF meeting

First of all: Many thanks to Alexandra Andersson and Mathias Gerbaux!!!

What we measure: Waveforms of Incident RF Transmitted RF Reflected RF Faraday Cup What is calculated: Timing of all signals Missing Energy FC Charge Breakdown rate … and all possible correlations It is very important to have a reliable missing energy measurement! All values from spectroscopy (light, electrons, ions and xray) have to be correlated to it!

structure Incident power Reflected power Transmitted power 31.5GHz 1.5GHz source 1.5GHz DCDC DCDC VAVA 30GHz Pin from PETS 31.5GHz Acquiris DAQ I Q I Q Demodulator I Q I Q 3GHz The 30GHz setup (very similar to 12GHZ TBTS) Down mixer box

But when looking at the obvious correlations….

Improvements and discoveries afterwards: Simple but effective: The reflected signal was disturbed by a 1.5GHz signal arriving at the Acquiris card: incident and transmitted channels were limited by the cards to 250MHz bandwidth reflected channel had a bandwidth of 1GHz leading to an aliasing effect Be careful: two different pulses!

250MHz low pass filter inserted in reflected signal channel  Reflected signal can now be measured with much less noise and is useful now!

We discovered a temperature dependency: The system is not protected against a direct flow of (cold) air from the air-conditioning: About 5% shift with air-conditioning on/off on all channels Covering of 30GHz equipment helps Seems to be a collective effect, we were unable to find a single source for this effect  Racks have been closed by doors from one side and from top to prevent direct air flow on the 30GHz components, effect is now invisible on hour timescale  There is certainly a temperature dependency on a longer timescale!  The air-conditioning-system has been refilled with new coolant last week…

The baseline problem: The baseline of the Acquiris cards has been subtracted from the measured waveforms using a fixed value from the initial calibration  These values are drifting within days! E.g. INC power signal baseline doubled in 4 weeks  Values are also dependent on the amplifier used in the cards Applied new calibration 4 weeks later Automatic baseline subtraction has been implemented for each pulse!

Further preparations done for a new run:  New LabView based DAQ system, independent of the conditioning software  Automatic calculation of the expected pulse from incident pulse and S-parameters  Storage of raw I and Q signals for all channels (we have the phase information now!) More reflection than expected…

The last run of 2008, now the picture is different… Ok, only three consecutive days… Before After

Phase measurements  Phase measurement is now possible with the separate DAQ-software

Correlation between INC phase and losses? Further investigations ongoing… unstable phase relation between I and Q?

Breakdowns influence power measurement: Directivity and isolation problems in directional couplers? Difficult to measure for -50dB coupler… better use -30dB plus attenuators?

Our proposal: Introduce automatic calibration system for all high-power RF measurements!  Directional coupler feed known pulse directly into the signal lines every hour between pulses  No need for a special trigger  No new hardware necessary (signal generator is remote controllable etc.)  Software changes will be necessary as long as we do not switch to raw data storage (what I strongly recommend!!!!!!) Synthesizer structure Mixing and DAQ DC Network

Conclusion and Outlook  We understand more and more of the RF measurement system  Reflected pulse resolution has been drastically improved  Baseline problem seems to be solved  I and Q signals are now stored using separate software (important for BD research)  Phase can be reconstructed for all events  Temperature dependency found and hopefully solved  Validity of calibration is less than a week (each weekend run would need a new one)  We need an automatic calibration system  Now you ask for an estimation of the error before and after the improvements… Uncorrected baseline shifts: +/- 30% …corrected now! Error on attenuation of the system: +/- 10% …replace DC? Temperature drift due to air-conditioning: +/- 2.5% …corrected now! Error due to dependency of phase and TRA signal: unknown! Remember: All measurements are relative to INC power which we cannot really check precisely…

There is still hope for good ME correlations: THANK YOU!