TFBDRIVER

Driver for a transverse feedback loop

Parameter Name	Units	Type	Default	Description
ID		STRING	NULL	System identifier
STRENGTH		double	0.0	Strength factor
KICK_LIMIT	$RAD$	double	0.0	Limit on applied kick
DELAY		long	0	Delay (in turns)
OUTPUT_FILE		STRING	NULL	File for logging filter output and driver output
A0		double	1	Filter coefficient
A1		double	0.0	Filter coefficient
A2		double	0.0	Filter coefficient
A3		double	0.0	Filter coefficient
A4		double	0.0	Filter coefficient
A5		double	0.0	Filter coefficient
A6		double	0.0	Filter coefficient
A7		double	0.0	Filter coefficient
A8		double	0.0	Filter coefficient
A9		double	0.0	Filter coefficient
A10		double	0.0	Filter coefficient
A11		double	0.0	Filter coefficient
A12		double	0.0	Filter coefficient
A13		double	0.0	Filter coefficient
A14		double	0.0	Filter coefficient

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 $\sum_{i=0}^{14} a_i P_i$, where $P_i$ is the pickup filter output from $i$ 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 $a_0=0, a_1=1$ with a delay of 0 is equivalent to $a_0=1, a_1=0$ 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.