Interlock System ‘Flags’ for LHC Injection

1. Interlock System ‘Flags’ for LHC Injection JörgWenninger AB-OP-SPS Proposal for ‘flag’ implementations LTC - J. Wenninger

2. The issue 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 and lead to Vertex detector damage. >> Message : the intensity limit for injection into an EMPTY ring should be as low as possible. Following the Workshop, modifications were made to the Extraction Interlock logic from the SPS to address the experiments’ worries. Now we have to agree on some “numbers” ! LTC - J. Wenninger

3. Do not confuse Injection procedures or sequences based on ‘good’ operational practice, that may fail or may be modified, with injection procedures that are ENFORCED by the Machine Protection System and that cannot be ‘bypassed’ from the CCC. Example : It may be a good practice to always inject a pilot first… … but if the MPS does not force you to do so, you could inject up to the intensity that is considered safe by the MPS ! LTC - J. Wenninger

4. Concerns : beam ‘injected into a ATLAS’ • Wrong setting of D1 • Bunch scrapes TAS towards IP • 1 pilot bunch deposits 5x10-3Gy 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 LTC - J. Wenninger

5. MP ‘Remedies’ • Software Interlock System (SIS) : • Since the settings errors that are required to hit the detectors are very large (many %), it is easy to 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). • >> Will be implemented soon & (pre-)tested during HW commissioning • Extraction interlock logic : • Addition of a new Interlock Flag in the SPS for more flexibility at the level of injection interlocking. • >> Will be implemented for the SPS startup in 2008. • >> Logic must be frozen asap. LTC - J. Wenninger

6. Extraction/Injection Interlock Ingredients • The SPS Safe Beam Flag(SBF_SPS) defines the safe beam limit for masking interlocks for the extraction interlock system. • SPS_SBF = TRUE for I < 1x1012 protons (assumes 450 GeV beam) • 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 LTC - J. Wenninger

7. ‘Old’ SPS Extraction Logic • The initial extraction logic that is enforced at the interlock system leveland is acceptable from the machine point of view is : • If the beam in the SPS is safe • SBF_SPS = TRUE  Extraction/injection is ALWAYS allowed. • If the beam is the SPS is not safe (SBF = FALSE), extraction is only allowed when some beam is circulating in the LHC ring, • SBF_SPS = FALSE  Extraction/injection only if BPF = TRUE. • In this scheme: SAFE for MASKING = SAFE for injection. • The MPWG considers that this scheme is SAFE for MACHINE COMPONENTS. LTC - J. Wenninger

8. ‘NEW’ SPS Extraction/LHC Injection Logic • Following the June Workshop, we have adopted a new logic that decouples the limits for masking in the SPS from the safe beam for LHC injection. • We introduce yet another Safe Flag in the SPS, the Safe LHC Injection Flagwith an intensity limit that is decoupled from the SPS_SBF. The new logic becomes: • SLIF_SPS = TRUE  Extraction/injection is ALWAYS allowed. • SLIF_SPS = FALSE  Extraction/injection only if BPF = TRUE. • Discussion point : • SLIF_SPS = TRUE if I < ??? LHC Exp. : I ~ pilot bunch MPWG : I < 1012 p LTC - J. Wenninger

9. Injection into an empty ring • The SLIF setting will affect measurements at injection: • - define the maximum intensity • and/or • - complicate or lengthen measurements, because it may require timing sequence changes in the injector chain (>= ~ 2 minutes). • Candidates: • Measurements of screens profiles(optics matching, injection region steering) since screens can only be used IN ABSENCE OF CIRCULATING BEAM. • Injection protection/transfer line collimator setup. • MDs at injection with safe beams (< 1012 p). • Measurements in INJECT-DUMP mode. • “Controlled” quench limit experiments. • … >> Such measurements could profit if injection into an empty machine of fewx1010 p would be possible !! LTC - J. Wenninger

10. Proposal (RS & JW) • The Safe LHC Injection Flag becomes a TRIMABLE parameter: • Its maximum value is hardcodedin an FPGA: • MAXIMUM = 1011 protons ~ ONE nominal bunch • Critical parameter controlled via MCS, accessible only to a few people. • FPGA ensures that SLIF < MAXIMUM at all times. • Default setting for startup and for REGULAR (physics) operation: • SLIF = 1010 protons • No changeto the Safe Beam Flag limits. • >> Satisfy the experiments. • >> Provides flexibility for certain measurements and for the commissioning, exact conditions for changing SLIF will have to be defined. LTC - J. Wenninger