|KICK_LIMIT||double||0.0||Limit on applied kick|
||Delay (in turns)|
|OUTPUT_FILE||STRING||NULL||File for logging filter output and driver output|
|GROUP||string||NULL||Optionally used to assign an element to a group, with a user-defined name. Group names will appear in the parameter output file in the column ElementGroup|
This element is used together with the TFBPICKUP element to simulate a digital transverse feedback system. Each TFBDRIVER element must have a unique identification string assigned to it using the ID parameter. The same identifier must be used on a TFBPICKUP element. This is the pickup from which the driver gets its signal. Each pickup may feed more than one driver, but a driver can use only one pickup.
A 15-term FIR filter can be defined using the A0 through A14 parameters. The output of the filter is simply , where is the pickup filter output from turns ago. The output of the filter is optionally delayed by the number of turns given by the DELAY parameter.
To some extent, the DELAY is redundant. For example, the filter with a delay of 0 is equivalent to with a delay of 1. However, for long delays or delays combined with many-term filters, the DELAY feature must be used.
The output of the filter is multiplied by the STRENGTH parameter to get the kick to apply to the beam. The KICK_LIMIT parameter provides a very basic way to simulate saturation of the kicker output.
See Section 7.2.14 of Handbook of Accelerator Physics and Engineering (Chao and Tigner, eds.) for a discussion of feedback systems.