bunch current measurement at SPring-8
intorduction
To keep the bunch current constant, the bunch current of each bucket
is measured before each injection at top-up operation.
setup
We use sum signal of diagonal two button electrodes as a pick-up. The
signal is fed to the oscilloscope (TDS7404B).
The sampling rate is 20Gs/s. The analog bandwidth is 4GHz.
The trigger signla for the scope is revolution signal generated from RF
reference signal.
The data is averaged for 100 samples.
The data for 5us is transfered to the workstation. Figure 1 shows an
example of waveform from the pickup.
We use the minimum value of the waveform as a bunch current.
because the sampling rate is too slow to determin the mininum with an
accuracy of 1%, we interpolate the data between sampling points with
sin(x)/x function.
To reduce the waveform distortion, the timing is carefully adjusted for
two pickup signals. Signals are summed up using power combiner.
Attenuators are installed for both ports to reduce the effects of
reflected power. The time needed to aquire whole bunch currents is
about 30seconds; 10seconds for averaging, 5seconds for data transfer
from the oscilloscope to the workstation through Network File Server
system, 3seconds to interpolate the data and less than 1 second for
writing bunch currents to data bese.
links
2006 EPAC06 Beam Phase Measurement of Stored Bunch
2005 Particle Accelerator Society of Japan Top-up injection control using bunch current monitor at SPring-8
This page is under developement
ohshima@spring8.or.jp 10 Jul /2004