FONT Hardware Processing electronics and current beam tests Stephen Molloy Queen Mary, University of...

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Transcript of FONT Hardware Processing electronics and current beam tests Stephen Molloy Queen Mary, University of...

  • FONT Hardware

    Processing electronics and current beam testsStephen MolloyQueen Mary, University of London

  • FONTFast feedback scheme to maintain luminosity at GLC/NLC.FONT 1NLCTA, September 2002./ of pickoff signals mixed to baseband.FONT 2NLCTA, January 2004.Log ratio of pickoff signals mixed to baseband.FONT 3Currently conducting beam tests at ATF.

  • FONT 1BPM with resonant pickoffs.Used splitters and phase shifters to create and .1/ calculated digitally so this was from an earlier pulse.First order correction to account for this.

  • FONT 1 Processing circuit

  • FONT 2 First stage processingSame BPM hardware as FONT 1, but new processing electronics.First stage of processing.Attenuate X-band signal to suitable level.Mix to 400MHz.Amplify to suitable level for second stage.

  • FONT 2 Second stageSynchronous demodulator mixes 400MHz to baseband.Use log amplifiers to give:Log(top pickoff)Log(bottom pickoff)The difference of these is the normalised position.

  • Processor installed in tunnel

  • Monitor electronics outside tunnel

  • ResolutionResolution =~ 14m

  • ATF beam testsTwo purposes of present beam tests:Analysis of extraction line jitter.Tests of processing electronics for a future feedback experiment at ATF.Jitter measurement:Jitter between trains.Jitter within a train.Processing electronics:Two variations of a / scheme.

  • Jitter monitor

  • Jitter monitor - componentsIrregular coupler:Striplines with coupling:F(z)=0.5 [1+cos(2(z/L))]Delta function produces ~500MHz sine out.Matches to 50 impedance at a broad range of frequencies.Diode switch between outputs:Provides possibility of shorting outputs.Allows measurement of common mode rejection of hybrid.

  • Jitter monitor - componentsPIN diode controller:Forward bias diode with 12V to close switch.Reverse bias with -12V to open switch and insure low coupling between channels.12V is supplied to the diode via coupler output lines.180 Hybrid:Gives and of coupler output.Final amplifier to increase resolution.

  • Coupler output first bunch

  • Coupler output - multibunch

  • Processing electronicsPosition output is mixed down .Difference lies in LO source:Mix with 714MHz reference.Requires stable reference phase.Mix with .Requires flat charge profile over train.

  • 714MHz reference stability

  • Next weekFurther jitter measurementsCalibration using upstream correctors.Full multi-bunch measurement with ballistic trajectory between the BPMs (ML8 and ML13).Stability of 714MHz reference is promisingCalibrate and measure resolution.Latency is important for feedback experiment and should be measured.Test self-mixing schemeSimulations suggest this may be less sensitive to errors in cable lengths.