#3191, 14 oct 2012

#3191, 14 Oct 2012 • Cabling installed to allow fast BPM electronics on injector BPMs• System is flexible enough to allow different INJ-BPMs to be used (not

simultaneously) • We looked at

– INJ-BPM-03 (first post-booster BPM , before any dipoles)– INJ-BPM-01 (first BPM, after gun + sol1)– And examined the frequency content

• INJ-BPMS are CIRCULAR rather than RECTANGULAR – software adjustments required.

• BPMs calibration is a guess, 13 mm scale factor for BPM1 and BPM3• Also .. Closing the dispersion in AR1.• We used a FEL-like set up from previous day’s shift.

WARNING !!!

• The y BPM data in this file is all incorrect due to software bug present at the time.

• The code used to compute y was

• The correct code should be

• However the raw A, B, C, D data is still there in the file so all the data can be reconstructed

(B-P2)-(D-P2)/((B-P2)+(D-P2))

((B-P2)-(D-P2))/((B-P2)+(D-P2))

INJ-BPM-03• Nominal FEL set-up. ‘Typical’ 1-shot BPM train measurement

100 KHz obvious in xy very similar to sum_pickup voltage6 Mhz present, smaller than 100 KHz‘usual’ 300 KHz present

x (mm), y (mm), sum voltageFourier transform vertical axis amplitude^2horizontal axis frequency in MHzFourier transforms done after subtracting mean values

Shot-by-shot variation

• I THINK (not enough data to prove) that the DFT power spectrum might vary quite a bit from train to train

• The variation might be big enough to obscure some effects when trying to judge effect of scanning each accelerator param– i.e. is the parameter (magnet strength etc) changing the DFT, or is the

DFT changing in time anyway?

INJ-BPM-03 Buncher OFF• On EVERY shot with buncher OFF, the x trace is

a lot ‘hairier’ than with buncher ON

6 MHz looks enhanced ‘hairier’ and fourier confirms. But 100 kHz also enhanced

Any 100 kHz in y ?• Another shot with nominal set-up

Some 100 kHz in y here.

Other Parameters Variation on BPM3

• We varied several other injector parameters (apart from buncher power) – 2 quads between booster and BPM3– Booster entrance correctors. – Solenoids

• General, crude observations– No parameter enhanced 100 kHz (some

suppressed it very strongly)– SOL-02 seemed to enhance the 6 MHz the most

INJ-BPM-01• Took 1 shot as a reference

Is there 100 KHz here or not?Note scale change here

Parameters Variation on BPM1

• Varied HVCOR-01, SOL-01, and Gun HV (changed to 230 kV, rather arbitrarily)

• Crude observations again– Difficult to see 100 kHz, but perhaps it is there (I

see small peak on y on some of the shots)– Gun HV didn’t seem to drastically change the

frequency content of x, y, charge– 6 MHz stronger on x than y generally.

Other observations

• The amplitudes of the frequency components vary shot to shot.

• Need to be careful when changing parameters and concluding “this parameter enhances the oscillation at X Mhz”, you can probably trick yourself into observing effects.

General Conclusions

• I think there is enough evidence here to say that the 100 kHz seen in AR1 (on x AND y) cannot be solely due to ALICE dipoles (as PHW simulated). 100 KHz comes certainly in injector before any dipoles.

• Y is very similar to SUM_CHARGE.

Dispersion at AR1 Exit

• Use AR1-BPM-06 and measure x/E for different AR1Q1/4 values

ERROR, DUPLICATED DATA

Despite the error, the closed arc condition can be interpolated

FCUP-01 Frequency Analysis• Record FCUP-01 trace using high-res scope

(20 Gsamples/sec == 1 sample every 50 ps)

• 100 uS bunch train == 100 Mbytes. Mathematica has problems with this size of data

• Took 1 in every 10 points (1 sample every 0.5 ns) to help things.

• The DFT frequency spectrum ranges from 10 kHz to 1 GHz, although only part of this spectrum is meaningful due to fcup time response

• However, you can see the individual bunches on the scope!

• To do DFT, first take off similar transient to the transients we have been removing in BPM DFT (100 bunches ~ 6 μs)

• Then subtract mean charge and perform DFT

16 humps in 1 μs == 16 MHz, these are the bunches

FCUP-01 Frequency AnalysisVarious regions of the frequency spectrumHorizontal axis is in Hz in all plots

Bunch frequency 16 MHz + harmonics due to “triangle” shape of bunches on FCUP

Bunch frequency 16 MHz

6MHz we have seen in the BPM charge signal and x and y

This is also an artefact of the 6MHz, it is the sideband 16 MHZ – 6 MHz. i.e. the envelope

6MHz we have seen in the BPM charge signal and x and y

300 kHz we have seen in the BPM charge signal and x and y

FCUP-01 Frequency Analysis300 kHz we have seen in the BPM charge signal and x and y

MHz

Compare with IBIC data from #3121 Fourier transform of summed ARC1 BPM signal

No 100 kHz visible

If 100 kHz (seen on the BPM x signals) was electrical noise on the cables, wouldn’t it be visible in both the FCUP signal and the BPM individual button voltage signals?