Zentralabteilung Forschungstecnik
Abteilung Elektronische Messtechnik (FWFE)
Microphonics Measurements at the ELBE Accelerator
Introduction
Microphonics measurements at the ELBE accelerator were already made in
2002 and published in [1]. The widespread use of the Rossendorf accelerator
module which is manufactured in license by ACCEL and the recent
development of energy recovery Linacs created new interest in microphonics
measurements. With the further completion of the ELBE accelerator significant
changes were made. In 2002 only one cryomodule with 2 cavities was in
operation. The measurements in 2002 were done with the second cavity. Now
we did quantitative measurements at the forth cavity (the second cavity in the
second cryomodule) and qualitative measurements at all 4 cavities.
FEL 2: 25 - 100 µm
FEL user labs
Neutrons
FEL 1: 5 - 25 µm
Accelerator: SRF linac, 4 TESLA cavities
During the measurements the RF feedback signal of the phase lock loop was
recorded in two ways. First with a data recorder and second with a sound card.
Both methods have shown advantages and drawbacks. The data recorder has
DC coupling and is better suited for quantitative measurements, the sound card
measurements are easier to evaluate, but the frequency response needs a
calibration and is only suited above 1 Hz.
Klystrons
MeV Bremsstrahlung
Accelerator
electronics
Module 1
Positrons
10 - 100 keV Xrays channeling
Module 2
Radiation Source ELBE – 40 MeV, 1 mA CW LINAC
Measurements
Sound Card Measurements
Data Recorder Measurements
Measurements were made for every of this 4 cavities at different gradients.
C1
C1
C1
C1
C1
C1
C1
C1
C1
1
amplitude / V
10
0.1
4.0MV/m
5.0MV/m
6.0MV/m
7.0MV/m
7.5MV/m
8.0MV/m
8.5MV/m
9.0MV/m
9.2MV/m
100
1000
1
1
Cavity 1
0.1
0.01
0.01
10
C2
C2
C2
C2
C2
C2
1
amplitude / V
1
4.0MV/m
5.0MV/m
6.0MV/m
7.0MV/m
7.5MV/m
8.0MV/m
100
Measurements were made only for cavity 4 at different gradients.
1000
1
Cavity 2
3
12
10
2.75
8
2.5
6
2.25
4
2
2
Δf
0.1
0.1
Hz
1.75
0
Avg
1.5
Hz
2
1.25
4
1
6
0.01
0.01
0.75
8
0.5
10
0.25
12
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95
1
0
t
100
1E-3
1000
100
1000
1E-3
1
10
1
10
1E-3
1
10
frequency / Hz
Cavity 3
10
C4
C4
C4
C4
C4
C4
C4
C4
C4
C4
C4
C4
1
1
0.1
0.1
0.01
1000
15
10
100
150
200
1
10
250
300
350
400
450
500
Averaged spectrum of the frequency deviation for
10 MV / m, 31 mBar
3
2.75
5.0MV/m
6.0MV/m
7.0MV/m
8.0MV/m
9.0MV/m
10.0MV/m
10.5MV/m
11.0MV/m
11.5MV/m
12.0MV/m
12.3MV/m
12.5MV/m
Cavity 4
2.5
2.25
5
2
0.1
Δf
0.01
2.5 •A i0 , m
0
1.75
Avg
5
Hz
1.5
1.25
10
1
0.75
15
1E-3
1E-3
1E-4
1E-4
1000
0.5
20
0
100
200
300
400
500
600
700
800
900
1000
0.25
m•T
,
s M •s
1
100
f
t
1E-3
1000
1E-3
50
Hz
Frequency deviation for 10 MV / m, 31 mBar
100
0.01
0.01
0
s
frequency / Hz
1
amplitude / V
amplitude / V
0.1
1E-3
1000
Hz
C3 8.0MV/m
C3 9.0MV/m
C3 10.0MV/m
C3 11.0MV/m
C3 12.0MV/m
C3 13.0MV/m
C3 14.0MV/m
C3 15.0MV/m
1
100
1
10
100
frequency / Hz
frequency / Hz
Averaged spectrum of the RF feedback signal for Cavity 1 to 4
0
cavity 1 maxima
cavity 2 maxima
cavity 3 maxima
cavity 4 maxima
1
24.6
24.4
7.7
7.0
2
69.5
69.6
49.0
49.2
3
74.2
75.6
73.3
73.2
4
99.9
100.1
259.7
259.7
5
132.2
132.2
292.4
292.0
6
164.2
164.2
--
--
7
169.6
169.2
--
--
8
193.5
193.5
--
--
9
300.1
300.1
--
--
Peaks in spectrum of the RF feedback signal for Cavity 1 to 4
Conclusions
50
100
150
200
fLow..fhigh
20 mBar 10 MV/m
12 MV/m
31 mBar 10 MV/m
12 MV/m
250
300
350
400
450
500
f
Hz
Averaged spectrum of the frequency deviation for
10 MV / m, 20 mBar
Long time frequency deviation for 10 MV / m, 31 mBar
overlayed with the amplitude of the 7.7 Hz component
total pk-pk
number
0
sec
3
5..11 48..50 68.77 130..137 163..169 188..196 223..226 265..272 292..295 298..301
[Hz] [Hz] [Hz] [Hz]
[Hz]
[Hz]
[Hz]
[Hz]
[Hz]
[Hz]
[Hz]
[Hz]
3.8 33.0 2.70 1.04
0.46
0.40
0.51
0.64
0.04
0.43
0.08
0.47
4.0 36.8 2.47 0.51
0.93
1.82
0.61
0.49
0.21
0.39
0.21
0.45
3.8 30.2 3.07 0.58
0.35
0.84
0.39
0.46
0.04
0.28
0.05
0.38
9.3 134.8 3.62 0.53
3.19
2.36
2.05
1.00
0.40
0.43
0.60
0.65
Total, peak to peak and RMS frequency deviations for the
10 biggest components
2.75
2.5
2.25
2
1.75
Avg
Results:
• No significant correlation between the frequency components was
found
• The 7.7 Hz component changes strongly over time with a period of
~ 45 seconds
• Working at the limit of the Helium machine increases mainly the
135 Hz and 75 Hz components
• No influence on microphonics was seen by using the tuning system
• No influence was seen by switching off a membrane pump at the
module
Hz
1.5
1.25
1
0.75
0.5
0.25
0
0
50
100
150
200
250
300
350
400
450
500
f
Hz
Averaged spectrum of the frequency deviation for
12 MV / m, 31 mBar
Acknowledgement
Cavity 1 shows significant energy dependency for low frequencies at energies
from 9 MeV and above. Cavity 1 / 2 and also cavity 3 / 4 have very similar peaks.
The peaks are not corresponding to calculated values for the self resonances of
the cavities [2] without housing. In Module 2 a significant component at 7.7 Hz
could be observed. It would be useful to reduce this to the levels of module 1 and
to reduce the hum components at 50 and 100 Hz.
The next step in research would be to identify the sources of excitation by using
real time cross-spectra.
This work has been partially supported by the EU Commission in the Sixth Framework Program,
Contract No. 011935-EUROFEL and Contract No. RII3-CT-2003-506395-CARE. And we acknowledge
the support of the German Federal Ministry of Education and Research grant 05 ES4BR1/8.
References
[1] A. Büchner, F. Gabriel, H. Langenhagen, “Noise Measurements at the RF System of the ELBE
Superconducting Accelerator” EPAC’2002, Paris, June 2002.
[2] T. Schilcher, “Vector Sum Control of Pulsed Accelerating Fields in Lorentz Force Detuned
Superconducting Cavities” TESLA Report 98-20, DESY, August 1998.
Autoren: Dr. Andree Büchner und Prof. Frank Gabriel (FWF), Rico Schurig und Dr. Gerald Staats (FWL)
Member of the Leibniz Association y Bautzner Landstr. 128 y 01328 Dresden/Germany y http://www.fzd.de
Contact: Dr. Andree Büchner y Department of Research Technology y Email: a.buechner@fzd.de y Phone: +49 351 260 – 2809
Dr. Gerald Staats y Division of Radiation Physics y Email: g.staats@fzd.de y Phone +49 0351 260 – 2469