Performance of the transverse coupled-bunch feedback system in the SRRC Page: 2 of 5
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Submitted to the Fifth European Particle Accelerator Conference, EPAC'96
Barcelona. Spain. 10 to 14 June 1996
with 10 kHz-250 MHz bandwidth. Each kicker electrode
is driven by an independent power amplifier. The
advantage of using high power amplifier in the system is
to provide the capability of suppressing large transverse
beam instability and reducing transient disturbance to the
stored beam during injection.
At present, transverse feedback system is in
operation for routine user shifts. One can also choose to
disable the system from control console for machine
3. SYSTEM PERFORMANCES
The transverse feedback system was put into
operation since last October. Its performance is
described in the following categories as status summary.
3.1 Transverse beam profile
Vertical coherent oscillation was observed during
the commissioning of SRRC storage ring in 1993. The
excited coherent oscillation was observed with a
synchrotron radiation profile monitor and is shown in the
upper part of figure 2. When the feedback system was
turned on, the stored beam was stabilized and its vertical
dimension was reduced as indicated in the lower part of
figure 2. The vertical beam size was effectively reduced
to less than 100 gm.
Figure 2. Synchrotron radiation beam profile versus
feedback effect. The upper profile was with
feedback off, the lower one was with feedback
3.2 Damping time observation
Since this feedback system is bunch-by-bunch
correlated, the suppression of instant betatron excitation
can be much faster than that of the radiation damping
case in the ring. This behavior was studied and verified
with either the transverse feedback system was turned on
or turned off. The stored beam damping time was
measured with a digitized oscilloscope which was
synchronized with the excitation pulse generated by an
impulse generator. Figure 3 gives betatron sideband
amplitude variation as a function of time when the
transverse feedback turn off and on. Feedback loop
control signal is shown as upper trace for comparison.
The time evolution of the betatron sideband amplitude
with mode number n=1 are displayed together on lower
trace. Although the lattice transverse damping time was
10 ms, the measured growing time of sideband amplitude
was observed to be 30 ms at the beginning of the
feedback loop open. On the other hand, the
corresponding damping time right after close the
feedback loop was found to be about few millisecond.
This observation indicated that the transverse feedback
system was able to suppress instability built up in the
stored beam and to reduce the damping time effectively
whenever there was a transverse beam disturbance
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Figure 3. Growth versus damping of mode number n = 1
for feedback loop open and close.
3.3 Betatron sideband suppression by
Figure 4 shows comparison spectra of the undamped
and damped vertical betatron sideband. It is clear that the
vertical betatron sideband disappears after turning on the
feedback system. These spectra were taken without and
with the feedback system.
3.4 Lifetime effect due to feedback system
Figure 5 shows typical lifetime changed with and
without the feedback system in operation. Although the
transverse feedback system provided reproducibility in
terms of beam orbit and stability between injection
cycles, it was clear that the smaller the beam size was in
the ring, as shown in figure 2, the shorter the beam
lifetime it would be, as pointed out in figure 5. This
feature indicated that the storage ring beam lifetime is
predominatedly Touschek limited.
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Hsu, K.T.; Kuo, C.C.; Kuo, C.H.; Lin, K.K.; Ueng, T.S. & Weng, W.T. Performance of the transverse coupled-bunch feedback system in the SRRC, article, October 1, 1996; Upton, New York. (digital.library.unt.edu/ark:/67531/metadc687399/m1/2/: accessed August 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.