Marek GASIOR - Home page

Home >> Professional >> 3D-BBQ >> SPS Results >> "Damper measurement" #1

Here I present a comparison of two measurements done with the LHC pilot beam on 2/11/04 (intensity ca 5e9). The goal was to study the influence of the transverse damper system on the tune path width and this is the only beam for which the horizontal (H) damper can be easily turned off. The operators adjusted an impressive triangular H tune path along the cycle and the H damper was switched off for the first measurement (10h01) and turn on for the second (10h07); vertical (V) damper was always off. The gain was 23dB, one H damper was on, the second off. It means that the damper influence could be still stronger with the two dampers working in parallel. I saw self-excited oscillations for the whole cycle on the H plane; the V plane tune path was hardly seen at all and only with the H damper on; I will return to this topic later. The signals were quite small. I had to operate the BBQ system at full blast, with some 100 dB of gain.

Below are links to the WAV files. You can hear the effect of the damper: when the damper is off, injection betatron oscillations last longer. With the damper on you can hear more noise, in addition having a slightly different timbre (headphones may be necessary). You can see all this on the signal waveforms.

First I show H plane results with the damper off (left) and on (right). Plots for V plane will follow.

Below are time domain signals, normalized to the same value. Note a faster damping and an increased signal amplitude with the damper on.

Fig. 1a. H plane time domain signal, damper OFF.

Fig. 1b. H plane time domain signal, damper ON.

Samples of the H and V signals, sampled with the frequency of fs=96kHz, were divided into segments N=19200 long (t=N/fs=0.2s), with offset m=9600 samples (t=m/fs=0.1s), so each two adjacent sections overlap by 50%. Samples of each segment were Hanning windowed prior to calculating their discrete magnitude spectrum. The bin spacing of the discrete spectra is df=fs/N=5Hz.
The two plots below are normalized to the highest bin from all segments of both signals (i.e. to the same number).

Fig. 2a. H plane magnitude spectra, damper OFF.

Fig. 2b. H plane magnitude spectra, damper ON.

Fig. 3a. H plane magnitude spectra, damper OFF. Each spectrum segment is normalized separately.

Fig. 3b. H plane magnitude spectra, damper ON. Each spectrum segment is normalized separately.

Fig. 4a. Contour plot corresponding to Fig. 2a. Damper OFF.

Fig. 4b. Contour plot corresponding to Fig. 2b. Damper ON.

Fig. 5a. Contour plot corresponding to Fig. 3a. Damper OFF.

Fig. 5b. Contour plot corresponding to Fig. 3b. Damper ON.

Fig. 6a. Linear scale contour plot corresponding to Fig. 2a. Damper OFF.

Fig. 6b. Linear scale contour plot corresponding to Fig. 2b. Damper ON.

Fig. 7a. Linear scale contour plot corresponding to Fig. 3a. Damper OFF.

Fig. 7b. Linear scale contour plot corresponding to Fig. 3b. Damper ON.

Fig. 8a. Linear scale cross-sections of plots in Fig. 3a and 5a in moments specified on the plots. Damper OFF.

Fig. 8b. Linear scale cross-sections of plots in Fig. 3b and 5b in moments specified on the plots. Damper ON.

Fig. 9a. Log scale cross-sections of plots in Fig. 2a and 4a in moments specified on the plots. Damper OFF. Plots normalized to the same value as the plots to the right with the damper on.

Fig. 9b. Log scale cross-sections of plots in Fig. 2b and 4b in moments specified on the plots. Damper ON. Plots normalized to the same value as the plots to the left with the damper off.

Top | More V plane plots with the damper ON | Bottom

Here I show a few plots for the V plane. Note that the V damper was always off.

Below are time domain signals. They look very similar.

Fig. 10a. V plane time domain signal, damper OFF.

Fig. 10b. V plane time domain signal, damper ON.

V plane magnitude spectra are shown only for each segment normalized separately. The fact that you will see a weak V plane tune path with the H damper on and nothing with the damper off may not be just a coincidence. I checked another 9 measurements with the H damper off and I did not see any measurement bearing signs of a tune path presence. Also I checked another 11 measurements with the damper on, and I would say that the tune path is present to some extent on 7 of them.
Here I show these 11 additional "damper on" measurements on linear scale contour plots. It seems that this type of plot is the best to see slightest traces of tune paths. I agree that the difference is very small, but it could mean that the H damper influences a bit also the V plane. See these plots and judge them yourself.

Fig. 11a. V plane magnitude spectra, damper OFF. Each spectrum segment is normalized separately.

Fig. 11b. V plane magnitude spectra, damper ON. Each spectrum segment is normalized separately.

Fig. 12a. Contour plot corresponding to Fig. 3a. Damper OFF.

Fig. 12b. Contour plot corresponding to Fig. 3b. Damper ON.

Fig. 13a. Linear scale contour plot corresponding to Fig. 3a. Damper OFF.

Fig. 13b. Linear scale contour plot corresponding to Fig. 3b. Damper ON.

Fig. 14a. Linear scale cross-sections of plots in Fig. 3a and 5a in moments specified on the plots. Damper OFF.

Fig. 14b. Linear scale cross-sections of plots in Fig. 3b and 5b in moments specified on the plots. Damper ON.

Top | V plane plots | Bottom

Below I show linear scale V plane spectra on contour plots for another 11 measurements with the H damper on to support hypothesis that the H damper influences also V plane. It was only one H damper on with the gain of 23dB. I consider plots a, b, e, f, g, and k as containing traces of tune paths. With the measurement shown before that gives 7 out of 12 measurements with the damper on yielding some tune paths. I analyzed another 9 measurements with the damper off and I did not find any tune paths.

Fig. 15a. Linear scale contour plot of V plane magnitude spectra for measurement done at 9h47. Damper ON.

Fig. 15b. Linear scale contour plot of V plane magnitude spectra for measurement done at 9h50. Damper ON.

Fig. 15c. Linear scale contour plot of V plane magnitude spectra for measurement done at 9h52. Damper ON..

Fig. 15d. Linear scale contour plot of V plane magnitude spectra for measurement done at 9h52. Damper ON.

Fig. 15e. Linear scale contour plot of V plane magnitude spectra for measurement done at 9h53. Damper ON.

Fig. 15f. Linear scale contour plot of V plane magnitude spectra for measurement done at 9h54. Damper ON.

Fig. 15g. Linear scale contour plot of V plane magnitude spectra for measurement done at 10h08. Damper ON.

Fig. 15h. Linear scale contour plot of V plane magnitude spectra for measurement done at 10h09. Damper ON.

Fig. 15i. Linear scale contour plot of V plane magnitude spectra for measurement done at 10h09. Damper ON.

Fig. 15j. Linear scale contour plot of V plane magnitude spectra for measurement done at 10h10. Damper ON.

Fig. 15k. Linear scale contour plot of V plane magnitude spectra for measurement done at 10h11. Damper ON.

Top | V plane plots | More V plane plots with the damper ON