Real-time orbit control @ the LHC An introduction J. Wenninger AB-OP-SPS 11.12.2003 AB-CO TC / J. Wenninger

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 11.12.2003 AB-CO TC / J. Wenninger

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] 11.12.2003 AB-CO TC / J. Wenninger

Vacuum Chamber Beam must remain centered inside the vacuum chamber that is surrounded by the super-conducting magnets : Margin  4 mm Stabilitity  0.5-1 mm 50.0 mm Beam screen Expected perturbations may exceed 20 mm…. 36 mm Beam 3 s envel. ~ 1.3 mm @ 7 TeV 11.12.2003 AB-CO TC / J. Wenninger

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). 11.12.2003 AB-CO TC / J. Wenninger

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 11.12.2003 AB-CO TC / J. Wenninger

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 11.12.2003 AB-CO TC / J. Wenninger

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 11.12.2003 AB-CO TC / J. Wenninger

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 run @ 50 Hz – 20 ms cycle  the sampling frequency must be fs = 50 Hz / n n=1,2,3…. The delay (WorldFip + PC set) is ~ 30-40 ms. Present idea is to send all settings to some ‘central’ PO gateways that will dispatch the data to the lower level gateways & Worldfip. 11.12.2003 AB-CO TC / J. Wenninger

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 11.12.2003 AB-CO TC / J. Wenninger

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. 11.12.2003 AB-CO TC / J. Wenninger