Establish circulating beam: Ring 1, Ring 2, separately

Successfully completed November 2009; circulating beams re-establish without any problems February 2010

Prerequisites: first turn, lattice sextupoles, first cut b3 compensation, RF, BPM system etc. 

Exit:  Circulating low intensity beam - both rings.



  Beam Task Who How long Status    
2.1 B1/B2 Instrumentation check - multi-turn "threading" mode BI  2h OK    
2.2 B2 Establish N turns   4h      
    Integer tune from trajectory difference OP OK B2   Integer tunes OK  64/59
    Close turns OP OK B2    
    N turn average measurement/correction OP OK B2    
2.3 B2 Few turns with first corrections of following   8h      
    Fractional tune (adjusted well enough to ciruclate) OP   OK  


2.2 B1 Establish N turns   4h      
    Integer tune from trajectory difference OP      
    Close turns OP      
    N turn average measurement/correction OP      
2.3 B1 Few turns with first corrections of following   8h      
    Fractional tune (adjusted well enough to circulate) OP      


    Repeat other beam 1          
  B2 RF capture - part 1          
  • Switch on voltage - biggest possible bucket - 16 MV
  • Synchro-loop on
  • f rev - look at slip - tell OP how much to
  • trim LHC injection energy
  • adjust injection phase
    OK B2    
2.5 B2 RF capture - part 2 RF 2*4h      
  B2 Centre          
  B2 Measure frev          
  B2 Correct          
  B2 Commission phase loop     OK - nice image    
    Correct residual error          
2.7 B2 Synchro loop and RF capture RF 8h      
  B2 Commission synchro loop          
  B2 Check phasing of cavity sum          
  B2 Fine tune capture          
  B2 Measure lifetime BI        
2.5 B1 RF capture - part 2 RF 2*4h      
  B1 Centre          
  B1 Measure frev          
  B1 Correct          
  B1 Commission phase loop          
  B1 Correct residual error          
2.7 B1 Synchro loop and RF capture RF 8h      
  B1 Commission synchro loop          
  B1 Check phasing of cavity sum          
  B1 Fine tune capture          
  B1 Measure lifetime BI        
2.4 B1B2 Energy matching          
    Orbit to 1mm rms OP        
    Correction of BdL sector by sector OP        


1. Establish multiple turns:

No correction
80% dipole correction – spool pieces only
Natural Q’ corrected with lattice sextupoles

Fairly obvious that we will attempt use lattice sextupoles as per MAD and b3 as per FiDeL.

Issue is the decoherence time due to chromaticity: if no correction - measurement possible in the V-plane only (for nominal cycle). In the H-plane not feasible:


How many turns can we see with the BPMs and with RF OFF?

Main problem for the BPMs as a result of bunch length increase is the loss of linearity
The BPM system can cope with an increase from in r.m.s. bunch length sigma_t from 0.4 to 1.3 ns.

142 turns
It is possible to increase it by reducing the momentum spread at extraction from the SPS by using pilot with smaller longitudinal emittance and or reducing the RF voltage SPS extraction

Tune measurement:

Integer part from trajectory difference for two different injection settings
Fractional part from phase advance per turn: e.g. it can be measured by putting together the turn-by-turn data from two pick-ups at ~90 phase advance
Need error study?



Close the trajectory on itself to obtain closed orbit: comparison between two consecutive turns (or at least some pick-up for the second turn)  close with two closed orbit correctors
By averaging over at least 10(?) turns (QH=64.28, QV=59.31)


3. Initial RF phasing and Capture

With pilot bunch, RF off:

Adjust (at least) 2 out of the 3 variables: BLHC, BSPS, fRF :

BLHC (CODs and/or MBs):
need to assess the implication of changing the B-field in LHC
also quadrupoles, etc.
Any frequency change will require re-tuning of the SPS RF:
timing of the fine rephasing
retraining of the frequency program (for future reference: this is also true when changing cycle e.g from pilot to LHC filling)
radial position and momentum change in SPS
Philippe’s view: should not treat fRF as a “free parameter”, we should aim to minimize the number of times we change the frequency establish a “standard” frequency early on, which will then remain fixed
also quadrupoles, etc, plus transfer lines
retraining of the frequency program

Example: adjust fRF and BLHC

In theory we should be able to correct both B and fRF in one iteration:

- δR/R = -1/γtr2 ΔB/B + γSPS2/ γtr2. Δfinj/f
- δf/f = -1/γtr2 ΔB/B – [(γ2 - γtr2)/γ2 γtr2.γSPS2 + 1] Δfinj/f

Energy matching - two rings

For 2 LHC rings, a third constraint: fRF is the same but circumference may be slightly different unless we are very lucky, the beams cannot be centered in both rings: must find a compromise in which the average radial position in the 2 rings is zero
1cm length difference ~ 1.5 mm radial offset ~ 150Hz
Will have to inject fairly soon in 2nd ring to check this need to define what is the minimum set of measurements and corrections on the first ring before going to the second