1 interlock logic for lhc injection: intensity limitations jörg wenninger ab-op-sps outcome of the...

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Interlock logic for LHC injection:intensity limitations

Jörg Wenninger AB-OP-SPS

Outcome of the join Machine-Experiments Workshop on Machine Protection

29/01/2008 LHCCWG - J. Wenninger

Experiments worries

29/01/2008 LHCCWG - J. Wenninger 2

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:>> 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.

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

MP ‘Remedies’


1. Software Interlock System (SIS) :The settings errors required to hit the detectors are very large (many %)

>> 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…]). >> already implemented in the LHC SIS, but tolerances and references need to be defined during the commissioning.

2. Extraction interlock logic :Addition of a new Interlock Flag in the SPS for more flexibility at the level of injection interlocking.

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 < 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 < fx1011 protons, 0 < 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 < 1012 protons at 450 GeV

for I < 1010 protons at 7 TeV

The LHC Beam Presence Flag (BPF) indicates if beam is circulating in the LHC. BPF is TRUE when I > ~2x109 protons

SPS Extraction/LHC Injection Logic

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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 !

Consequence for injection…

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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).


SPS Extraction Ingredients : LSS4/Ring 2


LSS4/TT40 TI 8 LHC injection LHC SPS

MKE MKI

TT41

TT41

TE

D T

T4

0

TE

D T

I8

TD

I IR

8

IR8 BEAM2

CN

GS

ta

rget

MBSG

SPS

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

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

+ SPS SBF

“Beam flags”

SPS Extraction Ingredients : LSS6/Ring 1


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

LSS6/TT60 TI 2 LHC injection LHC SPS

TE

D T

T60

TE

D T

I2

TD

I IR

2

MKE MKI

IR2 BEAM1

SPSLH

C

BEAM1

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.

LSS6 master inputs

+ SPS SBF

“Beam flags”

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)



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

Actual Master Output

Predicted Master Output



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.

1 interlock logic for lhc injection: intensity limitations jörg wenninger ab-op-sps outcome of the...

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