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