SLS Filling Pattern Feedback (FPF) system

1
SLS Filling Pattern Feedback(FPF) system

• Charge Distribution Control in SLS Storage Ring

2
Why?
Camshaft Bucket
SLS Storage Ring

• Provide any desired bunch pattern
• Which buckets to fill
• How much charge/current

Bunch Train

• total ring length 960 ns
• each RF bucket 2 ns
• electron bunch length few tens of picoseconds

3
Better charge distribution
With filling pattern feedback
Longer lifetime in the middle of bunch train
Without filling pattern feedback
4
Better beam stability
X-BPM positions at 4S and 6S
Filling pattern feedback starts
5
How?

• Avalanche Photo Diode (APD) after bending magnet
• Sample APD reading with fast ADC
• Sort readings into buckets and integrate
• Calibrate and scale readout
• Compare to reference pattern
• Sort buckets according to charge difference
• Distribute bucket list for next injections
• Adjust electron gun trigger delay (linac timing)
• Transfer charges from BO to SR at the right time
  (main timing)

6
LAN
Linac timing IOC
DLY
C PU
EVR
Main timing IOC
E-gun trigger
FAN
C PU
EVG
3. Synchronize bucket list
EVR
C PU
2. Distribute bucket list (CA)
Pulsed magnets triggers
Injection control IOC
Filling pattern IOC
EVR
C PU
ADC
VHQ
MOT
1. Sample filling pattern
Avalanche Photo Diode
7
Filling pattern readout
Integrated bunches
Sampled bunch
8
Bucket list distribution problem
IOC_3 (main timing)
IOC_2(linac timing)
6 3 2 7 8 1
6 3 2 7 8 1
10 25 15 33 58 90
CA
Synchronization over network not reliable
10 25 15 33 58 90
IOC_1 (filling pattern)
9
Bucket list synchronization
IOC_3
current
copy
CA
IOC_2
unlock_event
current
copy
CA
unlock_event
unlock_event
CA

IOC_1
generate bucket list
recv.
?
copy
new
current
unlock_event
10
Filling pattern control panel
Ref. pattern
Actual pattern