Pickup for a turnbyturn feedback loop
Parallel capable? : yes
GPU capable? : no
Backtracking capable? : no
Parameter Name  Units  Type  Default  Description 
ID  STRING  NULL  System identifier 

PLANE  STRING  x  ”x”, ”y”, ”delta”, or ”phase” 

RMS_NOISE  M  double  0.0  RMS noise to add to position readings. 
A0  double  0.0  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 

A15  double  0.0  Filter coefficient 

A16  double  0.0  Filter coefficient 

A17  double  0.0  Filter coefficient 

A18  double  0.0  Filter coefficient 

A19  double  0.0  Filter coefficient 

A20  double  0.0  Filter coefficient 

A21  double  0.0  Filter coefficient 

A22  double  0.0  Filter coefficient 

A23  double  0.0  Filter coefficient 

A24  double  0.0  Filter coefficient 

A25  double  0.0  Filter coefficient 

A26  double  0.0  Filter coefficient 

A27  double  0.0  Filter coefficient 

A28  double  0.0  Filter coefficient 

A29  double  0.0  Filter coefficient 

UPDATE_INTERVAL  long  0  Interval in turns for sampling data and updating filter output. 

TFBPICKUP continued
Pickup for a turnbyturn feedback loop
Parameter Name  Units  Type  Default  Description 
START_PASS  long  1  If positive, first pass on which to perform computations. 

END_PASS  long  1  If positive, last pass on which to perform computations. 

REFERENCE_FREQUENCY  double  0.0  Reference frequency for computing phase offsets. 

DX  M  double  0.0  Horizontal offset (subtracted from pickup signal). 
DY  M  double  0.0  Vertical offset (subtracted from pickup signal) 
BUNCHED_BEAM_MODE  short  1  If nonzero, run in bunched beam mode. 

GROUP  string  NULL  Optionally used to assign an element to a group, with a userdefined name. Group names will appear in the parameter output file in the column ElementGroup 

This element is used together with the TFBDRIVER element to simulate a digital turnbyturn feedback system. Each TFBPICKUP element must have a unique identification string assigned to it using the ID parameter. This is used to identify which drivers get signals from the pickup.
A 30term FIR filter can be defined using the A0 through A29 parameters. The input to the filter is the turnbyturn beam centroid at the pickup location. The output of the filter is simply ∑ _{i=0}^{29}a_{i}C_{i}, where C_{i} is the centroid from i * U turns ago, where U is the value specified by the UPDATE_INTERVAL parameter. Note that ∑ _{i=0}^{29}a_{i} should generally be zero. Otherwise, the system will attempt to correct the DC orbit. The output of the filter is the input to the driver element(s).
The PLANE parameter can take four values: “x”, “y”, “delta”, and “phase”, specifying what centroid property of the beam is measured by the pickup. The “delta”mode pickup is nonphysical, but could have applications to simulations where is not convenient to put a pickup in a highdispersion area.
See Section 7.2.14 of Handbook of Accelerator Physics and Engineering (Chao and Tigner, eds.) for a discussion of feedback systems.
TMCF