Interlock logic for LHC injection: intensity limitations

1
Interlock logic for LHC injectionintensity
limitations
Jörg Wenninger AB-OP-SPS
Outcome of the join Machine-Experiments Workshop
on Machine Protection
2
Experiments worries

• At the common Machine-Experiments Workshop on
  Machine Protection Issues for the LHC
  Experiments, held in June 2007,
• All LHC experiments expressed their concern about
  the maximum intensity that may be injected into
  an EMPTY LHC ring
• gtgt Failures may generate very high instantaneous
  fluxes that may damage Vertex detectors
• Basic message the intensity limit for injection
  into an EMPTY ring should be for as low as
  possible. The experiments felt quite
  uncomfortable with our limit of 1012 p.
• Following the Workshop, modifications were made
  to the Extraction Interlock logic from the SPS to
  address the experiments worries, discussed at an
  LTC in December 2007.

3
Concerns beam injected into a ATLAS

• Wrong setting of D1
• Bunch scrapes TAS towards IP
• 1 pilot bunch deposits 5x10-3 Gy in Pixel B-Layer
• 107 particles per cm2
• 107 times more than during normal operation at
  design luminosity

• Wrong setting of MCBX
• Bunch hits beam pipe close to Pixel detector
• Factor of 30 - 40 more

S. Wenig MPWG Nov. 07, simulations by D. Bocian
4
MP Remedies

• Software Interlock System (SIS)
• The settings errors required to hit the
  detectors are very large (many )
• gtgt monitor the currents of critical
  elements (D1,D2, MCBX, etc) at 1 Hz with SIS
  and inhibit injection if the settings are out of
  tolerance (few permill on D1,D2, some margin for
  MCBX steering defined by operation).
• gtgt already implemented in the LHC SIS, but
  tolerances and references need to be defined
  during the commissioning.
• Extraction interlock logic
• Addition of a new Interlock Flag in the SPS for
  more flexibility at the level of injection
  interlocking.

5
Extraction/Injection Interlock Ingredients

• The SPS Safe Beam Flag (SBF_SPS) defines the safe
  beam limit for masking interlocks for the
  extraction interlock system.
• SBF_SPS TRUE for I lt 1x1012 protons (assumes
  450 GeV)
• The SPS Probe Beam Flag (PBF_SPS) defines the
  safe beam limit for injection into an EMPTY LHC
  ring.
• PBF_SPS TRUE for I lt fx1011 protons, 0 lt
  f 1. Default f 0.1
• The LHC Safe Beam Flag (SBF_LHC) defines the safe
  beam limit for masking interlocks for the
  extraction interlock system.
• SBF_LHC is TRUE for I lt 1012 protons at 450
  GeV
• for I lt 1010 protons at 7 TeV
• The LHC Beam Presence Flag (BPF) indicates if
  beam is circulating in the LHC.
• BPF is TRUE when I gt 2x109 protons

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SPS Extraction/LHC Injection Logic
Following the June Workshop the logic for
extraction from the SPS was modified to take into
account some worries and still provide some
flexibility for us. The new logic decouples what
is safe for masking from what is safe for
injection. The extraction logic is based on the
Probe Beam Flag PBF_SPS TRUE ?
Extraction/injection is ALWAYS allowed. PBF_SPS
FALSE ? Extraction/injection only if BPF
TRUE, i.e. there must be measurable beam in
the ring.

• Injection into an empty LHC ring
• For regular operation, only possible if the beam
  intensity in the SPS is 1010 p.
• For MD injection of up to 1011 p is possible.
  Under what conditions the limit may be increase
  from the regular OP value still needs to be
  defined !

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Consequence for injection

• Empty ring nominal limit 1010 p, exceptional
  limit 1011 p.
• This logic will affect measurements
• in INJECT-DUMP mode,
• with screens (optics matching, injection region
  steering) since screens can only be used IN
  ABSENCE OF CIRCULATING BEAM,
• Filled ring no limitations, but the LHC Safe
  Beam Flag must be forced FALSE to inject an
  unsafe beam.
• To study high intensity injection, it is
  necessary to have at least one circulating pilot
  present in the ring before the high intensity is
  injected. Injecting over the pilot should also be
  minimized
• ? not a stopper, but more complicated procedure
  ( slow down due to injectors switching between
  beams).

8
SPS Extraction Ingredients LSS4/Ring 2

• Extraction from the SPS in LSS4 is controlled by
  a special MASTER BIC module that takes into
  account
• the beam (type intensity CNGS LHC),
• the dump states,
• LHC injection BIS state,
• all transfer line BIC inputs.
• Specially designed logic (combination of ANDs and
  Ors) that applies ONLY to the LSS4 master.

LSS4 master inputs
1 E450(LHC)
2 E400(CNGS)
3 BIC TT40 A
4 BIC TT40 B
5 TED TT40 IN
6 BIC TT41 A
7 BIC TT41 B
8 BIC TI8 up
9 BIC TI8 down
10 TED TI8 IN
11 Injection Permit IR8
12 Probe Beam Flag
13 Beam Presence Flag
14 LHC Safe Beam Flag
SPS SBF
Beam flags
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SPS Extraction Ingredients LSS6/Ring 1
LSS6 master inputs

• Extraction from the SPS in LSS6 is also
  controlled by a special MASTER BIC module that
  takes into account
• the beam (intensity),
• the dump states,
• LHC injection BIS state,
• all BIC inputs.
• Specially designed logic (combination of ANDs and
  Ors) that applies ONLY to the LSS6 master.

1 BIC TT60 A
2 BIC TT60 B
3 TED TT60 IN
4 BIC TI2 up
5 BIC TI2 down
6 TED TI2 IN
7 Injection Permit IR2
8 Probe Beam Flag
9 Beam Presence Flag
10 LHC Safe Beam Flag
11 Free
12 Free
13 Free
14 Free
SPS SBF
Beam flags
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Diagnostics / commissioning (1)

• To ease the diagnostics for extraction with a
  large number of rapidly varying interlock
  signals, a special monitoring program
• monitors all state transitions in one SPS cycle,
• analyses the time sequence of all signals,
• provides a summary of the extraction interlock
  system over the last 15 selected SPS cycles,
• provides detailed diagnostics in case of
  problems,
• CNGS LHC extraction versions, SPS ring
  version.

Extraction interlock summary
PC surveillance USER-PERMIT (2 ms long)
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Diagnostics / commissioning (2)
Actual Master Output

• A special diagnostics panel will be used to
  commission the master BIC
• the master logic will be applied to the inputs to
  predict the output

Predicted Master Output
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Diagnostics / commissioning (3)

• The FULL commissioning of the master BIC
  requires
• SPS super-cycle with CNGS LHC,
• LHC beams of varying intensity (pilot, few
  bunches, 1 or more batches),
• All BICs with at least one input that may be
  toggled between TRUE and FALSE,
• Possibility to move all TEDs ? LHC access system
  !!!
• Commissioning of the LSS4 master BIC must be done
  for mid-May for CNGS operation/TI8 extraction
  (?)
• Validation of the master BIC inputs,
• Validation of the full (?) logic (pretested in
  the lab - tbc).
• Commissioning of the LSS6 master BIC must be done
  for TI2 extraction.