Damping rates of the SRRC storage ring Page: 2 of 4
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is much stronger in the horizontal plane than that in the
vertical plane.a'
A.
31
21. --- - --- - - - --
0.9
079 . . _ .m..t 5 . 2.
023
0 5 10 15 20 2:
Curret (mA) or hizontal ChromaticityFigure 2: Horizontal damping rate as a function of the
horizontal chromaticity with bunch current 2.7 mA or a
function of bunch current at constant chromaticity.s
C
I)1000
900
SO
700
600
500
400
300
200
100
0._ .-._ ..._ ..._- .... ..-- . _ .... . 7 . - . __ . -
0 5 10 15 20 25
Beam Current Times vertical Chromaticity (mA)0.9
0.8
0.6
0.5
0.4
0.3
0.2
0.1
0
-0.10.000 0.005
Figure 4: The decay pattern of the vertically excited beam
with bunch impurity. In the beginning the beam current is
9.3 mA and then decay to 8mA. The impurity is increased
because the main bunch current decay rate is fast due to
Touschek scattering. The beating period is increased when
impurity becomes larger. The introduction of the high
chromaticity increases the decay rate of the excited beam
centroid.
system. The system shall be of help in the suppression of
the transverse beam oscillation in the routine operation at
high current mode for the synchrotron light users. Fig. 5
depicts the damping effect with transverse damping sys-
tem. The stored bunch current was not pure, therefore the
distinct amplitude modulation appeared.30
Figure 3: Vertical damping rate as a function of bunch
current times vertical chromaticity.
In Fig. 1 the decoherence and recoherence modulation
amplitude depends on the chromaticity and the frequency
is the same as the synchrotron oscillation frequency . = 27
kHz. This is due to incoherent synchrotron oscillation.[3,
4, 5] The modulation amplitude increases as chromaticity
is larger. If the bunch purity is not good and hence there
exists satellite bunch, we observed some distinct modula-
tion frequency other than the synchrotron frequency, which
differed in each plane, corresponding to the frequency beat-
ing of the betatron sidebands. The measured vertical tune
shift as a function of bunch current was about 0.2 kHz/mA.
Hence, the modulation period becomes longer and modu-
lation amplitude is larger as the main bunch current ap-
proaches the satellite bunch current. Fig. 4 gives an exam-
ple of the modulation frequency at different current ratio
in the vertical plane.
A transverse damping system is currently under devel-
opment and test. The system is a wide band dampingV
'a0.9
0.8
0.7
0.6
05
0.4
0.3
0.2
0l
0
-0.1Figure 5: The damping effect of the transverse feedback
system.
III. LONGITUDINAL DAMPING
In the longitudinal plane, we excited the beam with
rf frequency modulation at synchrotron frequency for a
few ps and then measured the decay rate of the ampli-
tude of the synchrotron sideband. We performed the mea-
surements either in the single bunch mode or in a few-
bunch mode. Significant decrease of the damping time in4
. .............:............ l9:3mtA~irooalciy*---.
I-& mtA. zero chromaticit--"
T. aiT~ A. chomiiaiiciy:TE3 ..
_. :; ........ Y. .0.010
Time (see)0.015 0.020
------- - ------ - - -----
---------- --
. Cedbaek o - --
~o-n0.000 0.005 0.010
Trine(-e)0.015 0.020
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Hsu, K. T.; Kuo, C. C.; Lau, W. K. & Weng, W. T. Damping rates of the SRRC storage ring, article, June 1, 1995; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc707947/m1/2/: accessed April 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.