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

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.

S21 Measurement: Comparison of setups & amplifiers

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 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.

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

Fig. 2-1: Transm. with each Amplifier

Spectrum Measurement: 90 kHz sidebands of 2.06 GHz signal

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

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

Zero Span Measurement: Sideband height over the ramp cycle

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 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.

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

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

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

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

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.

Comparison to Previous Microwave Measurement

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

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

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

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

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.

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.

Comparison to Simultaneous RFA measurement

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

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

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.

Fig. 7-1: Beampipe outgassing by RFA.

No Conclusion; Just Discussion!