FONT HardwareFONT Hardware
Processing electronics and Processing electronics and current beam testscurrent beam tests
Stephen MolloyStephen Molloy
Queen Mary, University of Queen Mary, University of LondonLondon
FONTFONT• Fast feedback scheme to maintain Fast feedback scheme to maintain
luminosity at GLC/NLC.luminosity at GLC/NLC.• FONT 1FONT 1
– NLCTA, September 2002.NLCTA, September 2002.– ΔΔ//ΣΣ of pickoff signals mixed to baseband. of pickoff signals mixed to baseband.
• FONT 2FONT 2– NLCTA, January 2004.NLCTA, January 2004.– Log ratio of pickoff signals mixed to Log ratio of pickoff signals mixed to
baseband.baseband.
• FONT 3FONT 3– Currently conducting beam tests at ATF.Currently conducting beam tests at ATF.
FONT 1FONT 1
• BPM with resonant BPM with resonant pickoffs.pickoffs.
• Used splitters and Used splitters and phase shifters to phase shifters to create create ΔΔ and and ΣΣ..
• 1/1/ΣΣ calculated digitally calculated digitally so this was from an so this was from an earlier pulse.earlier pulse.– First order correction to First order correction to
account for this.account for this.
FONT 1 – Processing circuitFONT 1 – Processing circuit
FONT 2 – First stage FONT 2 – First stage processingprocessing
• Same BPM hardware as FONT 1, but new Same BPM hardware as FONT 1, but new processing electronics.processing electronics.
• First stage of processing.First stage of processing.– Attenuate X-band signal to suitable level.Attenuate X-band signal to suitable level.– Mix to 400MHz.Mix to 400MHz.– Amplify to suitable level for second stage.Amplify to suitable level for second stage.
FONT 2 – Second stageFONT 2 – Second stage• Synchronous demodulator mixes 400MHz to Synchronous demodulator mixes 400MHz to
baseband.baseband.
• Use log amplifiers to give:Use log amplifiers to give:– Log(top pickoff)Log(top pickoff)– Log(bottom pickoff)Log(bottom pickoff)
• The difference of these is the normalised position.The difference of these is the normalised position.
Processor installed in tunnelProcessor installed in tunnel
Monitor electronics outside Monitor electronics outside tunneltunnel
ResolutionResolution
Resolution =~ 14μm
ATF beam testsATF beam tests
• Two purposes of present beam tests:Two purposes of present beam tests:– Analysis of extraction line jitter.Analysis of extraction line jitter.– Tests of processing electronics for a Tests of processing electronics for a
future feedback experiment at ATF.future feedback experiment at ATF.
• Jitter measurement:Jitter measurement:– Jitter between trains.Jitter between trains.– Jitter within a train.Jitter within a train.
• Processing electronics:Processing electronics:– Two variations of a Two variations of a ΔΔ//ΣΣ scheme. scheme.
Jitter monitorJitter monitor
Jitter monitor - componentsJitter monitor - components
• Irregular coupler:Irregular coupler:– Striplines with coupling:Striplines with coupling:
• F(z)=0.5 [1+cos(2F(z)=0.5 [1+cos(2ππ(z/L))](z/L))]
– Delta function produces ~500MHz sine out.Delta function produces ~500MHz sine out.– Matches to 50Matches to 50ΩΩ impedance at a broad range of impedance at a broad range of
frequencies.frequencies.– Diode switch between outputs:Diode switch between outputs:
• Provides possibility of shorting outputs.Provides possibility of shorting outputs.
• Allows measurement of common mode rejection of Allows measurement of common mode rejection of hybrid.hybrid.
Jitter monitor - componentsJitter monitor - components
• PIN diode controller:PIN diode controller:– Forward bias diode with 12V to close switch.Forward bias diode with 12V to close switch.– Reverse bias with -12V to open switch and Reverse bias with -12V to open switch and
insure low coupling between channels.insure low coupling between channels.– 12V is supplied to the diode via coupler output 12V is supplied to the diode via coupler output
lines.lines.
• 180° Hybrid:180° Hybrid:– Gives Gives ΔΔ and and ΣΣ of coupler output. of coupler output.
• Final amplifier to increase resolution.Final amplifier to increase resolution.
Coupler output – first bunchCoupler output – first bunch
Coupler output - multibunchCoupler output - multibunch
Processing electronicsProcessing electronics
• Position output is mixed down Position output is mixed down ΔΔ..• Difference lies in LO source:Difference lies in LO source:
– Mix with 714MHz reference.Mix with 714MHz reference.• Requires stable reference phase.Requires stable reference phase.
– Mix with Mix with ΣΣ..• Requires flat charge profile over Requires flat charge profile over
train.train.
714MHz reference stability714MHz reference stability
Next weekNext week• Further jitter measurementsFurther jitter measurements
– Calibration using upstream correctors.Calibration using upstream correctors.– Full multi-bunch measurement with ballistic Full multi-bunch measurement with ballistic
trajectory between the BPMs (ML8 and trajectory between the BPMs (ML8 and ML13).ML13).
• Stability of 714MHz reference is Stability of 714MHz reference is promisingpromising– Calibrate and measure resolution.Calibrate and measure resolution.– Latency is important for feedback experiment Latency is important for feedback experiment
and should be measured.and should be measured.
• Test “self-mixing” schemeTest “self-mixing” scheme– Simulations suggest this may be less Simulations suggest this may be less
sensitive to errors in cable lengths.sensitive to errors in cable lengths.