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Author: Thomas Schilcher
Phone: +41 56 310 4593
Updated: 09.09.2015


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FOFB Feed Forward Properties


Date: 12 September 08

Introduction

The fast orbit feedback system at the SLS provides the possibility to add feed forward (FF) tables to the corrector magnets. Due to memory restictions on the FOFB system (DSP card) only one set of feed forward tables can be added to one corrector. However, independant tables for each plane (x/y) are possible. The update rate of the FOFB is equal to the DBPM output rate which is
fDBPM = fRF / NCLKDIV / NDDC = 4066 Hz
with
  • fRF = 499.637 MHz (main RF frequency)
  • NCLKDIV = 16 (RF clock divider: division ratio)
  • NDDC = 7680 (Digital Down Converter decimation ratio for closed_orbit mode)
The feed forward table size for each corrector plane has been set to 4066 elements which results in a one second time window. The FF table is written to the corrector power supply in a circular manner.
Attention:
Due to the circular buffer any excitation signal programmed into the FF tables is repeated with 1 Hz frequency. Watch out for continuous excitation signals!
All properties of the FF can be controlled with GUIs. An expert GUI is available at

launcher -> System Expert Applications: Diagnostics -> RI Diagnostic Expert: FOFB

Launch the related display with label "Expert Control: Control", then launch the required sector panel "Sector expert: sector #". A list of available EPICS channels is given at the end of this page.

The normalized FF tables ($(SEC):CORRX-FF / $(SEC):CORRY-FF) are scaled with a scaling factor $(SEC):FF-SCALE-X / $(SEC):FF-SCALE-Y and directly added to the corrector signal. Therefore, the units of the scaled FF tables are [A]! The corrector to which the FF table should be added can be selected by the channel $(SEC):FF-CORR-SEL which is a linear index of the correctors within a sector (e.g. SEC2: 01SD, 01SE, 01SB, 02SB, 02SE, 02SD). FF tables can be enabled/disabled for each plane individually by the channels $(SEC):FF-X-REQ / $(SEC):FF-Y-REQ.
A predefined set of normalized, sinusoidal excitation signals can be found in
/exchange/home/schilche/ff_tables.

Downloading these files to the according EPICS channels can be achieved easily with matlab.

Feed forward tables are added to the corrector magnet currents only if the FOFB is running. In case that one wants to excite the beam with FF without fast orbit feedback the FOFB has to be set to passive mode either by the GUI (FOFB expert panel: FOFB mode -> passive) or by setting the EPICS channels ARIDI-BPM:FOFB-MODE-X / ARIDI-BPM:FOFB-MODE-Y to passive.

Operator Properties


The EPICS channel name is obtained by concatenation of the device name (sector names, $(SEC)) and the property.


<EPICS channel name>=<$(SEC)>:<property>


The sector device names are:

 
$(SEC)
DI RACK
ARIDI-BPM-SEC1
.19.0.14 (DI-1A)
ARIDI-BPM-SEC2
.24.0.3 (DI-2)
ARIDI-BPM-SEC3
.28.0.3 (DI-3)
ARIDI-BPM-SEC4
.31.0.3 (DI-4)
ARIDI-BPM-SEC5
.37.0.12 (DI-5A)
ARIDI-BPM-SEC6
.42.0.3 (DI-6)
ARIDI-BPM-SEC7
.48.0.3 (DI-7)
ARIDI-BPM-SEC8
.50.0.3 (DI-8)
ARIDI-BPM-SEC9
.55.0.21 (DI-9)
ARIDI-BPM-SEC10
.2.0.3 (DI-10)
ARIDI-BPM-SEC11
.6.0.12 (DI-11)
ARIDI-BPM-SEC12
.14.0.17 (DI-12)

 
EPICS channel
(PROPERTY)
DESCRIPTION
EPICS record type
$(SEC):FF-X-REQ horizontal feed forward request (enable request)
bo
$(SEC):FF-X horizontal feed forward granted (indicates FF activity)
bi
(SEC):FF-Y-REQ vertical feed forward request (enable request)
bo
$(SEC):FF-Y vertical feed forward granted (indicates FF activity)
bi
$(SEC):FF-CORR-SEL select corrector for feed forward;
corr. magnets are selected by ascending numbers within a sector (1..7)
ao
$(SEC):FF-BPM-SEL select BPM for feed forward readback;
BPMs are selected by ascending numbers within a sector (1..7)
ao
$(SEC):FF-COUNTER feed forward counter;
indicates present position within the feed forward table
ai
$(SEC):FF-COUNTER-C clear feed forward counter;
(reset to zero)
ao
$(SEC):FF-SCALE-X horizontal scaling factor for feed forward table;
normalized feed forward tables are multiplied by this factor, the result is interpreted as A (Ampere) and directly added to the corrector current output
ao
$(SEC):FF-SCALE-Y vertical scaling factor for feed forward table;
normalized feed forward tables are multiplied by this factor, the result is interpreted as A (Ampere) and directly added to the corrector current output
ao
$(SEC):CORRX-FF horizontal feed forward table (normalized); 4066 elements
aao
$(SEC):CORRY-FF vertical feed forward table (normalized); 4066 elements
aao
$(SEC):WF-CORRX-FF scaled horizontal feed forward table ($(SEC):CORRX-FF x $(SEC):FF-SCALE-X); 4066 elements
waveform
$(SEC):WF-CORRY-FF scaled vertical feed forward table ($(SEC):CORRY-FF x $(SEC):FF-SCALE-Y); 4066 elements
waveform
$(SEC):WF-BPMX-FF horizontal, synchronous BPM reading of BPM no. $(SEC):FF-BPM-SEL; 4066 elements
waveform
$(SEC):WF-BPMX-FF vertical, synchronous BPM reading of BPM no. $(SEC):FF-BPM-SEL; 4066 elements
waveform

 
Author: Thomas Schilcher   Phone: +41 56 310 4593   Updated: 09.09.2015