Microwave Measurement of Recycler Electron Cloud:

1. Microwave Measurement of Recycler Electron Cloud: Jeffrey Eldred 12/19/14

2. Microwave Measurement Schematic • ~ 2 GHz carrier frequency is propagated through beampipe. • The presence of ecloud causes a phase-delay • The phase modulation occurs at the beam harmonics ~90 kHz. • The spectrum analyzer should see 90 kHz sidebands on either side of the carrier frequency.

3. S21 Measurement: Comparison of setups & amplifiers

4. S21 Measurements • Previously, the microwave setup was connected to BPMs VP201 and VP203; • Now we are connected to VP130 and VP202 which should the same distance and have a similar sequence of accelerator components. • Somehow this came with a significant drop in transmission in the measurement range 1.97 - 1.99 GHz. • Its not an error in the way the cables are connected and its not a fault in the amplifier. • For the result presented today, we use 2.06 GHz as our carrier frequency.

5. Fig. 1-1: Transm. at Old Setup and New Setup

6. Fig. 2-1: Transm. with each Amplifier

7. Spectrum Measurement: 90 kHz sidebands of 2.06 GHz signal

8. Fig. 2-1: Spectrum at 2.06 GHz • Blue line: Carrier signal sent while beam running • Red line: Beam running but no carrier signal.

9. Fig. 2-2: Spectrum at 2.06 GHz • Green line: Measurement made from subtract “beam only” background from “signal + beam”.

10. Zero Span Measurement: Sideband height over the ramp cycle

11. Data-taking procedure • Previously, I showed a frequency spectrum with a carrier frequency, sidebands, and noise at beam harmonics. • The measurements track the (lower) sideband amplitude over the course of the Recycler cycle. “Zero-span” trace. • The carrier frequency is 2.060 GHz. • Measurements performed at four different time intervals. • Measurements taken with and without carrier signal. • Each measurement is an average of 50 Recycler cycles. • Four such averages are taken for each condition. • Next I take the average and standard deviation of these four datasets and each point is calculated independently. • In order to see the sidebands more clearly and test their statistical significance, its necessary to subtract the beam background.

12. Fig. 3-1: Sideband Height over RR cycle • Blue line: Carrier signal sent while beam running • Red line: Beam running but no carrier signal.

13. Fig. 3-2: Sideband Height over RR cycle (current) • Green line: Measurement made from subtract “beam only” background from “signal + beam”.

14. Fig. 3-4: Sideband Height after first injection • Blue line: Carrier signal sent while beam running • Red line: Beam running but no carrier signal.

15. Fig. 4-4: Sideband height after first injection • Green line: Measurement made from subtract “beam only” background from “signal + beam”.

16. Notes • Like all other RR ecloud measurements, the ecloud signal is composed of a series of peaks right after a batch injection that are gradually decreasing in height and separated at half-synchrotron periods. • In this case the signal appears solely after the first batch injection and no significant signal after other injections. • When there is no beam, the spikes at injection (in the beam background) completely disappear.

17. Comparison to Previous Microwave Measurement

18. Fig. 3-2: Sideband Height over RR cycle (current) • Green line: Measurement made from subtract “beam only” background from “signal + beam”.

19. Fig. 5-1: Sideband Height over RR cycle (prev.) • Green line: Measurement made from subtract “beam only” background from “signal + beam”.

20. Fig. 3-4: Sideband after first injection (current) • Blue line: Carrier signal sent while beam running • Red line: Beam running but no carrier signal.

21. Fig. 5-2: Sideband after first injection (prev.) • Blue line: Carrier signal sent while beam running • Red line: Beam running but no carrier signal.

22. Comparison to Previous Microwave Measurement • In current microwave measurement, only the peaks after the first injection are significant. • In previous microwave measurements, the peaks after the second injection is highest, then the first, then the rest. • The carrier frequency and the BPM location changed, but that wouldn't be responsible for this difference. • In the previous measurement the first batch was at lower intensity and in the current measurement all batches are at the same intensity.

23. Comparison to Recycler Instability • The batch-dependence of the microwave electron cloud measurements matches the batch-dependence of the Recycler instability (although the threshold is now much higher). • There is no straightforward way to connect them: • Originally our ecloud models had the instability be batch-selective, not the ecloud density. • Recent measurements showed the instability does not depend on the separation between batches. • The instability threshold is now much higher.

24. Comparison to Simultaneous RFA measurement

25. Fig. 3-2: Sideband Height over RR cycle (current) • Green line: Measurement made from subtract “beam only” background from “signal + beam”.

26. Fig. 6-1: RFA signal at the same time.

27. Comparison to Simultaneous RFA Measurement • In the Microwave measurement the ecloud signal appears only after the first batch injection • In the RFA measurement, the ecloud signal that appears after the first batch injection is always small than the ecloud signal that appears after subsequent injections. • Neither batch-dependence matches the loss monitor. • There is a lot of variability in the RFA measurements, but they all keep this same general structure. • Why don't they match? • The beampipe around the RFA is still scrubbing. • The RFA is only in a field-free region. • Neither fact really explains the difference.

28. Fig. 7-1: Beampipe outgassing by RFA.

29. No Conclusion; Just Discussion!