MOOC04
LBNL, Berkeley, California, USA
The ALS upgrade project (ALS-U) consists in the replacement of the existing ALS storage ring with a new storage and accumulator rings. Due to the reduced lifetime of the ultra-low emittance beam circulating in the new storage ring, trains of 25/26 bunches have to be swapped between storage and accumulator every 30-60 seconds. The depleted train swapped out to the accumulator is topped back to its nominal charge from the injector and swapped back into the storage ring at the next injection cycle. Monitoring the bunch charge and parasitic bunches is necessary to minimize stored current variations in the storage ring and beam losses during the injection/extraction process. We present a bunch charge monitor based on a broadband analog-to-digital converter that allows to sample the signal obtained from a beam pickup at a frequency resulting in a scan of the entire ring with a ~60 ps resolution every 60 microseconds. Hundreds of scans are accumulated to obtain the necessary charge resolution. The beam pickup has been designed to be insensitive to the beam transverse position and its response to a bunch passage decays so rapidly that the readout is not affected by adjacent bunches.
