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

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

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

4. FONT 1 – Processing circuit

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

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

7. Processor installed in tunnel

8. Monitor electronics outside tunnel

9. Resolution Resolution =~ 14μm

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

11. Jitter monitor

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

13. Jitter monitor - components PIN diode controller: PIN 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: 180° Hybrid: –Gives Δ and Σ of coupler output. Final amplifier to increase resolution. Final amplifier to increase resolution.

14. Coupler output – first bunch

15. Coupler output - multibunch

16. Processing electronics Position output is mixed down Δ. Position output is mixed down Δ. Difference lies in LO source: Difference lies in LO source: –Mix with 714MHz reference. Requires stable reference phase. –Mix with Σ. Requires flat charge profile over train.

17. 714MHz reference stability

18. Next week Further jitter measurements Further jitter measurements –Calibration using upstream correctors. –Full multi-bunch measurement with ballistic trajectory between the BPMs (ML8 and ML13). Stability of 714MHz reference is promising Stability of 714MHz reference is promising –Calibrate and measure resolution. –Latency is important for feedback experiment and should be measured. Test “self-mixing” scheme Test “self-mixing” scheme –Simulations suggest this may be less sensitive to errors in cable lengths.