Satellite bunches in the LHC

1
Satellite bunches in the LHC
J. Wenninger AB/OP

• Satellite definition
• Satellite luminosity
• Satellite detection tolerances

2
Nominal proton filling
3
Satellites

• LHC bunch filling and RF
• Bunches are separated by a multiple of 25 ns.
• 400 MHz LHC RF system 1 RF bucket every 2.5 ns.
  
• ? room for 9 satellite bunches between the
  nominal ones, spaced by 2.5 ns.
• Satellite bunch formation
• Transfer from one machine to the next (PS ? SPS,
  SPS ? LHC)
• Un-captured beam ? lost at the beginning of
  acceleration.
• Beam captured in unwanted locations ? satellite
  bunches.
• Amount of un-captured beam /satellites depends on
  
• RF settings
• Longitudinal parameters emittance, bunch
  length
• Finally satellites must survive the ramp not
  guaranteed.

4
LHC beam _at_ injection into SPS
injection
injection 1 second
Uncaptured beam
72 bunches from PS

• Un-captured beam up to 10
• Satellite bunches possibly level -
  difficult to measure !

Note The main SPS RF system runs at 200 MHz.
5
Satellite bunch collisions luminosity

• IP1, IP2, IP5, IP8 collisions between
  satellites every 2.5 ns (same vertex as nominal
  bunches worst case 9 times more frequent than
  normal collisions).
• per collision Lsat r2 L r
  satellite bunch int./normal bunch int.
• IP8 / LHCb additional possibility of collision
  between satellites normal bunches at the
  beginning and end of each 72 bunch train.
• per collision Lsat r L
• At all other encounters (upstream downstream of
  IP) ? beams separated.
• Totem no crossing angle ! Possible additional
  collisions between satellite and normal bunches
  every 37.5 cm on either side of IP.

6
Satellite Detection

• LHC
• A high sensitivity longitudinal profile monitor
  should detect satellites at the per-mill level
  within minutes.
• Either level is OK, or re-filling (and possibly
  retuning of the SPS and/or LHC RF system) may be
  required.
• For a good RF capture in the LHC there are
  stringent requirements on transfer conditions
  SPS-LHC (energy, time jitter, emittance, bunch
  length).
• SPS
• Satellite bunches present in the SPS are likely
  to create satellites in the LHC.
• So far measurements in the SPS are difficult and
  limited to level.
• Detection of satellites in the SPS may be used to
  prevent injection into the LHC but that would
  require new instrumentation / detection methods
  that are so far not foreseen.

7
SatelliteTolerances

• Sensitivity of machine components
• So far the main concern is for the beam position
  monitor (BPM) system. Systematic position errors
  of 0.1 mm possible with r 5-10. Depends
  strongly on the exact pattern. r 1-2 should be
  acceptable
• Note that errors on the BPM system may have
  consequences on other systems (collimation).
• Sensitivity of the Experiments
• Are satellites at level acceptable ? What is (a
  reasonable) maximum ?
• TOTEM must probably be considered a special case
  that may need more careful treatment.

• Acceptable intensity levels for satellites have
  consequences on requirements for instrumentation
  (and eventually on beam quality interlocks) in
  the SPS.