1. FONT Oxford FONT REPORT NOVEMBER Neven Blaskovic Kraljevic and Talitha Bromwich Friday, 27 November 2015 1

2. FONT Oxford Aims Friday, 27 November 2015 2 Find the source of the resolution-limiting static erratic feature in our IP BPM signals. Look at cavity cables, cavity reflections and possible phase sensitivity issues. (2 shifts) Set up FONT upstream feedback for IPBSM studies. (1 shift)

3. FONT Oxford Monday - day Friday, 27 November 2015 3 Check cable lengths from IPBPM dipole cavities inside the IP vacuum chamber to the hybrid prior to the processing electronics. Use TDR, with help from Naito-san and Tauchi-san, to look for mismatches, as cavities are inaccessible.

4. FONT Oxford Results Friday, 27 November 2015 4 Cable velocity 2.381 x 10 8 m/s. Calculated from 100 waveforms on the TDR.  is the phase difference in length after removing integer wavelength differences. Cavity to hybrid(ns) Error (ns) Cavity to hybrid (m) Error (m)  Length (m) Error (m)  Length / Wavelength  (m) Error (m) IPA-X19.910.022.3600.004 0.11430.00042.7420.01080.0004 IPA-X210.390.022.4740.004 IPB-X110.390.022.4750.004 0.00110.00060.0260.00110.0006 IPB-X210.390.022.4740.004 IPC-X19.920.022.3620.004 0.11210.00062.6900.01290.0006 IPC-X210.390.022.4740.004 IPA-Y19.920.022.3610.004 0.11320.00053.0560.00210.0005 IPA-Y210.390.022.4740.004 IPB-Y110.400.022.4760.004 0.00380.00060.1030.00380.0006 IPB-Y210.390.022.4730.004 IPC-Y19.910.022.3610.004 0.11320.00043.0560.00210.0004 IPC-Y210.390.022.4740.004

5. FONT Oxford Identify mismatch location We used the timing of small reflections at the feed-through into the vacuum chamber to deduce that the cable mismatches are between the cavity and the feed-throughs. Friday, 27 November 2015 5 O

6. FONT Oxford Tuesday – Swing Shift Try delaying the signal using 5.5 m delay cables before the hybrid to see if the static feature moves along the pulse, i.e. if there are reflections somewhere causing the static feature. Switch 180-degree hybrid for a splitter to observe monopole-like position- independent modes. Friday, 27 November 2015 6

7. FONT Oxford Delay cable study 5.5 m delay cables  28 ns delay . 6.5 samples for the SIS digitiser frequency of 4.2 ns per sample. Signals delayed as expected. Static feature appears to be delayed by the same amount. Friday, 27 November 2015 7 Delay cables No delay cables

8. FONT Oxford Splitter study Normal set-up Friday, 27 November 2015 8 BPM CAVITY BPM CAVITY 180° HYBRID Splitter set-up BPM CAVITY BPM CAVITY SPLITTER Extracts anti-symmetric (position-dependent) modes. Cancel symmetric modes. e.g. monopole mode. Extract symmetric modes. Cancel anti-symmetric (position-dependent) modes. Cavity BPM image credit: M. Wendt. “BPM Instrumentation: A Short Introduction for Non-Experts” (September 2000). Introductory talk given at DESY lab.

9. FONT Oxford 0-degree hybrid study Replace 180 degree hybrid with a splitter. Allows us to analyse any symmetric mode, e.g. the monopole mode. Waveform observed (similar to static signal in usual mode of operation). Perform wide mover scan. Signals do change with position, which they shouldn’t, because with a splitter it should have no position dependence. Friday, 27 November 2015 9

10. FONT Oxford Thursday – Owl Shift Try compensating for cable length mismatch using variable phase shifters. Diagnose any position sensitivity on phase by manually changing the LO phase using variable phase shifters. Friday, 27 November 2015 10

11. FONT Oxford Mismatch compensation Static feature still present. Friday, 27 November 2015 11 With phase shifters to match cables on both ports No phase shifters

12. FONT Oxford Position vs Phase study 30dB with a beam offset 1.5um apparent change over 240 degrees. Friday, 27 November 2015 12 30dB no beam offset 1.5um apparent change over 240 degrees.

13. FONT Oxford Friday, 27 November 2015 13 This wave-like pattern is only observed when sample number 52 is included in the sampling range, which is at the very beginning of the waveform – see further analysis presentation for correct sampling results

14. FONT Oxford Friday – Owl Shift Set up upstream feedback with Kano-san for IPBSM study. Friday, 27 November 2015 14

15. FONT Oxford Friday, 27 November 2015 15 Jitter amplitude vs position jitter at FONTP2 (when feedback is on & off )

16. FONT Oxford Friday, 27 November 2015 16 Jitter amplitude vs position jitter at FONTP3 (when feedback is on & off )

17. FONT Oxford Conclusions Cable length measurement: 10cm mismatch in cable lengths from pairs of ports of IP BPM cavities. For the Y-ports the mismatch is equal to three wavelengths +/- 2mm. Long delay cable study: 5.5m delay cables did not move the static waveform. Splitter study: Addition of symmetric modes using a splitter shows waveform similar to that obtained using 180-degree hybrid in normal operation. Cable matching: Compensating cable mismatch to better than 1mm did not remove the static waveform. LO phase dependence study: Dependence of apparent position on LO phase measured at 30dB and 50dB by scanning LO phase more than 180 degrees. Friday, 27 November 2015 17