1. Real-time orbit control @ the LHC
An introduction
J. Wenninger AB-OP-SPS
AB-CO TC / J. Wenninger

2. LHC layout 2 inter-leaved proton rings. For each ring :
Pt.5
CMS
Pt.4
Pt.6 RF
Beam Dump
BEAM 1
clockwise
BEAM 2
counter-
clockwise
Pt.3
Momentum
Betatron
Pt.7
cleaning
cleaning
2 inter-leaved proton rings.
For each ring :
Horizontal & vertical beam position (orbit) sampled at 500 points by Beam Position Monitors (BPMs).
For each plane there are ~ 250 steering magnets with individual Power Conveters (PCs) to adjust the beam position.
ALICE
LHC-B
Pt.2
Pt.8
ATLAS
Pt.1
Injection
Injection
BEAM I
BEAM II
from SPS
from SPS
AB-CO TC / J. Wenninger

3. Stored beam energy
Energy stored in each LHC beam exceeds existing machine by 2 orders of magnitude
x 200
Energy stored in the beam [MJ]
Sufficient to melt
500 kg of Cu
Momentum [GeV/c]
AB-CO TC / J. Wenninger

4. Vacuum Chamber
Beam must remain centered inside the vacuum chamber that is surrounded by the super-conducting magnets :
Margin  4 mm
Stabilitity  mm
50.0 mm
Beam screen
Expected perturbations may exceed 20 mm….
36 mm
Beam 3 s envel.
~ TeV
AB-CO TC / J. Wenninger

5. Collimators
Large amplitude particles are ‘cleaned’ by collimators – very tight requirements
on beam stability :
~ 50 mm r.m.s. stability at top energy (and full intensity).
AB-CO TC / J. Wenninger

6. Real-time orbit control
The aim of real-time orbit control system is to stabilize the orbit of the LHC beams during ALL operational phases within the required tolerances.
It is a real-time system in the sense that the system must be deterministic – this important during critical phases.
The LHC system is ‘unique’ among accelerators because it is distributed over a large geographical area and because of the large number of components.
Very schematically - we have 5 players :
BPM system
Network
‘Controller’
Network
PC system
Beams
AB-CO TC / J. Wenninger

7. Preferred architecture
Concentration of all data in a central point
entire information available.
all options possible.
can be easily configured and adapted. …
network more critical : delays and large number of connections. IR FB IR IR IR IR IR IR IR
AB-CO TC / J. Wenninger

8. Beam Position Monitor Control
Hardware :
500 position readings / ring / plane ~ 1000 BPMs for the 2 rings
Front-end crates (standard AB-CO VME) are installed in 8 surface buildings around the ring :
68 crates in total  8-10 crates / point
Data streams :
Nominal sampling frequency is 10 Hz – but I hope to run at 25 Hz…
Average data rates per IR :
18 BPMs x 20 bytes ~ 400 bytes / sample / crate
140 BPMs x 20 bytes ~ 3 kbytes / sample / IR
@ 25 Hz – from each IR :
Average rate ~ 0.6 Mbit/s
Instantaneous rate ~ 25 Mbit/s (1 msec burst)
40 ms
AB-CO TC / J. Wenninger

9. Magnet & PC Control Architecture : WorldFip Gateway FGC PC
Each PC is controlled by one Function Generator Controller (FGC).
Up to 30 FGCs (PCs) per Worlfip bus segment.
1 gateway controls a given Worldfip segment.
Orbit correctors are accessed over ~ 40 gateways.
FGC PC
Gateway 1 2 3 30
WorldFip
Timing & access :
The WorldFip will 50 Hz – 20 ms cycle
 the sampling frequency must be fs = 50 Hz / n n=1,2,3….
The delay (WorldFip + PC set) is ~ ms.
Present idea is to send all settings to some ‘central’ PO gateways that will dispatch the data to the lower level gateways & Worldfip.
AB-CO TC / J. Wenninger

10. Schematically… Present architecture, as seen
BPM FE
BPM FE
Present architecture, as seen
by the parties that are involved
FB ‘servers’
PO gateways to hide HW details from the clients PC Gw PC Gw PC Gw
Remove this layer ? WF
PC FE WF
PC FE WF
PC FE WF
PC FE
AB-CO TC / J. Wenninger

11. Network delay and packet losses
The orbit system only uses a small fraction of the LHC technical network bandwidth, but the exact load is not really known today.
If IT agrees we may use a special network profile to get a higher priority – present fallback in case of difficulties.
We can accept some packets losses, as long as we only lose a sample ‘now and then’ (< 1 in 100/1000 ?) – criticality depends on the machine phase and beam intensity.
AB-CO TC / J. Wenninger