Kain, V

CERN Document Server

What is required to safely fill the LHC?V. Kain, CERN, Geneva, SwitzerlandAbstractMachine protection consisting of passive and active sys-tems will be used to prevent damage during the LHC in-jection process. Concerning beam 2, parts of the SPS ex-traction and transfer line beam interlock system has al-ready been successfully tested during the TI 8 commis-sioning. Key elements of the final system for beam 2 willbe validated during the LHC Sector Test with low inten-sity beam, together with parts of the passive protection sys-tem, the TDI and at least one transfer line collimator TCDI.The remaining issues after the sector test will be discussedin detail, where the entire injection protection system to-gether with post mortem, management of critical settings,sequencer and software interlocking system must be testedwith beam, for different intensities and filling patterns dur-ing the LHC beam commissioning. Requirements fromother systems and interdependencies for test modes, suchas inject & dump, are important input for the overall LHCcommissioning strategy and will be discussed.SYSTEMS CONCERNEDThe different systems required for adequate injectionprotection are described in detail in [1].Besides the actual injection into the LHC the injectionprotection system also has to cover extraction from the SPSin LSS4 and LSS6 and the transfer via the transfer linesTI 2 and TI 8, Fig. 1.SPS-Extraction Transfer LHC-InjectionFigure 1: Overview of the injection process: extractionfrom the SPS in LSS6 and LSS4, transfer via the transferlines TI 2 and TI 8 and injection into the LHC in IR 2 andIR 8.The machine protection system consists of activeand passive systems - active protection in the form ofsurveillance systems and interlocking to inhibit extrac-tion/injection in case of failure; - passive protection withcollimators and absorbers. The main characteristics of theprotection systems are briefly summarised below.Passive Protection: TCDITransfer line collimators (TCDI) are needed to protectthe LHC aperture, assumed to be 7.5   at 450 GeV, fromany failures upstream of the collimation section. They pro-vide full phase space coverage with 3 double-jawed colli-mators per plane and a setting of 4.5  . The expected phasespace coverage was simulated including nominal errors forsetting-up, optics and trajectory and amounts to about 6.9  maximum amplitudes escaping the system, Fig. 2.In total there will be seven collimators per line. Themomentum collimator is at the beginning of the lines andthe 6 betatron collimators are located in the last 300 m,mostly downstream of the last beam dump (TED), Fig. 3.This means that these TCDI need the LHC beam permit forsetting-up. Concerning the commissioning this means thatthe LHC has to be ready to complete the beam commis-sioning of the collimators. In case of TI 8 the TCDI canalready be tested with beam during the LHC Sector Test.051015202530356.4 6.5 6.6 6.7 6.8 6.9 7max. amplitude [σx]0510152025306.4 6.5 6.6 6.7 6.8 6.9 7max. amplitude [σy]Figure 2: Expected phase space coverage with TCDI col-limators as fraction of seeds versus maximum amplitudesescaping the system.TED TED TDIMKE MKITCDIMOM TCDIH/VSPS TT40/60 TI 8/2 LHCFigure 3: The momentum transfer line collimator is at thebeginning of the line, the 6 betatron collimators are locatedin the last 300 m.Passive Protection: TDI-TCDD-TCLIThe other passive protection system involved in the in-jection process is located in the injection regions in theLHC and consists of the 4.25 m long injection stopperTDI, the mask TCDD(M) and the auxiliary collimatorsTCLIA/B. This system protects the LHC against injectionkicker (MKI) failures, the required setting is 6.8  .The TDI will be installed 90Æ downstream of the MKI,followed by the mask TCDD in front of the superconduct-ing dipole D1, Fig. 4. The TCLI collimators are locatedLHC Project Workshop - 'Chamonix XV'88on the other side of the IP and complement the protectionwith the TDI in case of phase changes between the injectionstopper and the MKI. TCLIA will be installed downstreamof the experimental area close to the D1 and TCLIB closeto the Q6 downstream of the insertion. A mask (TCLIM)is required to shield the superconducting quadrupole frompossible showers generated in the collimator jaws.Figure 4: Horizontal overview of the injection regionaround IP2.Active ProtectionActive protection has to guarantee correct settings forSPS extraction, transfer lines and LHC injection via thesurveillance of e.g.:  magnet currents with ROCS surveillance and FastMagnet Current Change Monitor (FMCM)  collimator positions  beam position in SPS extraction region  SPS extraction septum girder position  kicker charging voltageActive protection also has to make sure that high intensitybeam can only be injected into the LHC when beam is al-ready circulating (beam presence condition). BCT signalsfrom the SPS and the LHC are required to verify this con-dition:  SPS safe beam intensity  LHC beam presenceThese two intensity signals (in the form of flags) alongwith the User Inputs from the surveillance systems are in-put to the Beam Interlock System (BIS) via Beam InterlockControllers (BIC). A schematic of the BIS for the injectionprocess of beam 2 as well as CNGS can be seen in Fig. 5.LHC inject permitSPS extract permitSPS MKDdumpSPS MKE extractLHC MKIinjectLHC MKDdumpSPS ringBICSPS LSS4MASTERBICSPS LSS4/ TT40BICTI 8 upstreamBICTI 8 downstreamBICLHC IR8 injectionBICLHC ringBICSPS beam permitLHC beam permitSPS ring UPsLSS4/TT40 UPsTI8 upstream UPsTI8 downstream UPsTED TT40TED TI8TDI IR8SPS safe intensity flagIncludes TI 8 after TEDTT40/CNGS/TI 8 and injection interlockingTT41 & CNGSTT41CNGSBICUPsMBSGSwitch+ MB PC switchLHC safe parametersLSS4/TT40 TI 8 down LHC injection LHC SPS TI 8 up?LHC injection UPsLHC ring UPsSPS timingFigure 5: Schematic of the interlock system for the injec-tion process of beam 2 and CNGS.SoftwareBesides hardwired active and passive protection also anumber of software ingredients are required for adequateinjection protection.Software interlocking system (SIS)Beam quality aspects like trajectories along the transferlines, but also screen positions and other less safety criticalissues are covered by the software interlocking system.Management of critical setting (MCS)The MCS is a software to remotely manage interlock set-tings in a secure way. It needs the SIS for full functionality.The MCS will be used for a lot of surveillance systems ofdevices involved in the injection process, examples are theMKI, MKE, TDI, TCLI, TCDI, ROCS, BLMs, BPCE andMSE. The first version of this software is planned to beready for the extraction and transfer tests in 2006.Extraction/transfer/injection data analysis and di-agnosticsA tool for extraction, transfer and injection data anal-ysis and diagnostics is required. It will have to covershot-by-shot beam quality checks to allow the next ex-traction/injection as well as post mortem analysis afterabnormal situations e.g. in case of an interlock.LHC injection sequencerSetting up of the TDI and TCLI collimators needs tobe driven by the LHC injection sequencer to guaranteecoherency with the different injection preparation andfilling steps. The sequencer will also have to provide theLHC machine mode inject & dump, which is required forsetting up the transfer line collimators, as will be discussedbelow.LHC Project Workshop - 'Chamonix XV'89WHEN DO WE NEED INJECTIONPROTECTION?Injection protection must be in place and working cor-rectly when the injected intensity exceeds the damagelimit. The damage limit is assumed to be about     protons at 450 GeV, corresponding to about 5 % of a nom-inal full batch extracted from the SPS towards the LHC.According to the “overall commissioning strategy forprotons” [2], injection protection is absolutely mandatoryfrom commissioning stage II onwards.Before a beam intensity above the damage limit canbe authorised, formal tests and acceptance of the protec-tion system performance are needed. Injection protectionshould hence be operational for 156 on 156 bunches and becommissioned at latest during the operation with 43 on 43bunches.The only exception are the TCLI collimators. They en-hance the protection performance against injection kickerfailures, the main protection however is provided by theTDI. The TCLIs are needed above an injected intensity of50 % of nominal and can be commissioned later than therest of the protection system.There will also be some earlier milestones before theLHC start-up. The SPS extraction will be commissionedwith high intensity during the commissioning of CNGS in2006, TI 8 will be commissioned with higher intensity in2006 and finally the LHC Sector Test will allow to test andverify procedures.ISSUES AFFECTING THECOMMISSIONING STRATEGYBefore showing the time-line indicating when the differ-ent protection systems have to be in place and work prop-erly, issues which might affect the commissioning strategyare discussed.Transfer Line CollimatorsThe setting-up procedures for TCDI centering, align-ment and beam size measurement for single pass in thetransfer lines have to be defined. A possible single-passmethod for the alignment was already tested during the TI 8commissioning in 2004. This method is based on a trans-mission measurement with BCTs and non-local BLMs.The promising results of the tests can be seen in Fig. 6.In test phase 3 one of the jaws was moved into the beamand its tilt was varied by 300 rad. This variation had aclear effect on the transmitted intensity on the downstreamBCT. For a realistic set-up a complete scan of transmis-sion versus tilt would have to be carried out with about 10measurement points. The optimum alignment would thencorrespond to the maximum in the obtained transmissioncurve [3].As already mentioned, the TCDIs need the LHC beampermit for setting-up and hence the LHC inject & dump 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.11:55 am1:30 am1:05 am12:40 am12:15 am11:50 pm11:25 pm11:00 pmtransmission I TI8/I SPS jaws out➁first jaw injaws outsecond jaw infirst jaw in +tilt variation➂b0b1b2b3➀Figure 6: The transmitted intensity at the BCT at the down-stream TED in TI 8 during a setting-up test of a collimator.mode. Thus the whole of the LHC has to be ready, the in-ject & dump mode working (interplay between sequencer,timing, BIS etc.) and the beam dump has to be commis-sioned, before the TCDIs can finally be commissioned withbeam.The transfer line collimators will be installed in the partof the transfer line which is already close to the apertureof the LHC superconducting magnets. Beam losses onthe TCDI during nominal operation, during setting-up ofthe collimators or during accidental loss of a full batchon one collimator jaw could lead to quenches of the adja-cent LHC magnets. FLUKA simulations were carried outwhere 70 m of TI 8 with the adjacent LHC were modeledand loss scenarios studied, Fig. 7. Preliminary results showthat even for an accidental loss of a full ultimate batch theLHC magnets do not quench (assuming a quench limit of38 ). The results for an accidental loss onTCDIV.87804 can be seen in Figs. 7 and 8.TCDIV.87804MB.A9R8TI 8LHCFigure 7: The FLUKA model to study losses on the TCDIand the resulting energy deposition in the adjacent LHCmagnets. In this case a full ultimate batch was lost at TC-DIV.87804.TDIThe setting-up procedures for the TDI, the injectionstopper, have not been defined yet. As this diluter is al-ready in the LHC it can either be set up on the circulatingLHC Project Workshop - 'Chamonix XV'90RR88TI8Coil: max. 8 mJ/cm3MB.A9R8Figure 8: Energy deposition in MB.A9R8 for an accidentalloss of a full ultimate batch at TCDIV.87804 in the TI 8transfer line.beam or on the injected beam. During the Sector Test it is(obviously) planned to set it up on injected beam.The halo load on the TDI from the circulating beam is ofconcern. The baseline TDI does not include cooling and theout-scattered particles could lead to D1 quenches. In caseof unacceptable heat load on the TDI or the D1, retractingthe TDI further might be considered. In this case the TCLIcollimators would be needed earlier than discussed beforeto provide sufficient protection of the LHC aperture, seealso [4].The reproducibility of optics and orbit at the location ofthe TDI (TCLI) is an issue and data from the Sector Test iseagerly awaited. Orbit feedback might be necessary.The TDI is fixed in the horizontal plane and not muchspace is left for the non-injected beam, Fig. 9. The aperturefor the non-injected beam has been validated according tothe standard procedure for LHC apertures, Fig. 10, never-theless care has to be taken as the TDI is a movable device.Non-injected beamCorrectly injected beamFigure 9: Cross-section of the TDI.Figure 10: TDI at IP2: the available aperture for the non-injected beam corresponds to n1  7.TCLIOne of the two TCLI collimators per injection inser-tion, TCLIA, will be installed in an area of the LHC whereboth beams share a common beam pipe. A special col-limator design is required to accommodate two beams inone collimator tank. The TCLIs are vertical collimators,TCLIA however will most probably also need to be set upin the horizontal plane to provide enough aperture for theother beam. Special setting-up procedures will be required,where crosstalk between the beams might be of an issue.Collimator Control SystemAll movable devices in the LHC and also the transfer linecollimators will eventually be under a common collimatorcontrol system. It is not clear yet when this will be avail-able. A rudimentary version of this system is required forthe TI 8 tests and the Sector Test towards the end of thisyear to be able to test the TCDIs and the TDI.The interplay of the MCS and the collimator control sys-tem has to be defined. One question to answer is whether tostore absolute or normalised interlock settings for the col-limators in the MCS. In the case of normalised settings theorbit at the device locations might be locally folded into theinterlock setting.At a later stage automatic setting-up procedures will berequired (e.g. for 43 on 43 bunches). The automatic pro-cedures developed by the collimation project for the ringcollimators will be reused as much as possible.Active ProtectionInterdependencies are a general issue. As an example,for the testing of the interlocking functionality of parts ofthe surveillance equipment, the MCS and also the SIS haveto be available.About 15 magnet families involved in the injection pro-cess have to be equipped with FMCMs to guarantee safeinjection [5, 6]. Three out of the 5 required for CNGS willbe installed for CNGS commissioning, not all are available.TI 8 needs six in total. Whether TI 8 commissioning withhigher intensity 2006 should/can take place if not all FM-CMs are ready, has to be clarified.LHC Project Workshop - 'Chamonix XV'91Passive ProtectionActive ProtectionSoftwareOthersInject & Dump modepost mortemInj. SequencerMCSTL intlkLHC beam presenceSPS safe beamLHC energySIS SPSSIS TL/LHCFMCM I surv.ROCS I surv.TCDDSPS extract intlkLHC Inj intlkTCDITDITCLIColl. Control HWColl. Control SW43/43 156/156 stage IILHC Inj TI2-lo TI2-hi LHC startCNGS LSS6 TI8-lo TI8-hiFigure 11: Time-line: systems required for the different commissioning stages. Each row is divided into a beam 1 anda beam 2 row. Colour code: green = installed & prototype test; orange = needed, but may not be fully available; red =installed & fully operational.The protection level of the TCDIs depends on the mo-mentum offset of the extracted beam. Sufficient phasespace coverage can only be guaranteed for a momentumoffset Æ    , due to the partly large dispersion atthe TCDI locations (e.g. TCDIH.87441: 	  m). Aninterlock on the SPS energy has to be in place.With safe beam intensity, interlock signals like collima-tor positions can be masked. For the time being the valuefor the safe beam intensity is set to     protons at450 GeV. This leaves more than a factor of 2 margin tothe assumed damage limit for nominal emittance. For runswith smaller emittance the safe beam intensity will proba-bly need to be reduced.SYSTEMS REQUIRED FOR THEDIFFERENT COMMISSIONING STAGESFig. 11 shows when the different protection systems haveto be ready. On the left side of the table in Fig. 11 thesystems involved in injection protection can be found andthe top row lists the commissioning stages.Many injection protection systems will already have tobe operational a long time before the actual start-up of theLHC due to the tests in 2006, like the CNGS high intensitycommissioning and the Sector Test. The passive protectiondevices belong to the last systems becoming fully opera-tional, as they need the whole LHC ready for the final beamcommissioning.DiscussionTesting procedures and criteria to declare systems com-missioned after each commissioning stage have to be de-fined (e.g. ready for pilot or ready for 43 on 43 bunches).How and where to represent, store and “move” betweenthe allowed operating conditions (e.g. maximum current inthe LHC, minimum emittance, number of bunches) has notbeen decided yet. A possibility would be to use the MCS tostore the operating conditions for the current commission-ing stage and the SIS as surveillance system to guaranteethat the previously authorised operating conditions are re-spected.CONCLUSIONSInjection protection must be fully operational for 156on 156 bunches in commissioning stage I. The main unre-solved issues concern the machine protection state controland the passive protection system. For the machine pro-tection state control the sequencer, the interplay betweensequencer, MCS and SIS and the formalisation of the com-missioning pathway have to be defined. The passive pro-tection systems need setting-up procedures and a workingcollimator control system.A lot of important tests of the injection protection systemand procedures can and will be done during the TI 8 testsin 2006 and the Sector Test. A prerequisite however is thatthe TCDIs, the MCS, injection post mortem, the collimatorcontrol system, the injection sequencer for setting up theTDI, the safe beam intensity flag from the SPS etc. areavailable.REFERENCES[1] V.Kain, “Safe Injection into the LHC”, Proc. Chamonix XIV,CERN, Geneva, Switzerland, 2005.LHC Project Workshop - 'Chamonix XV'92[2] R.Bailey, “Summary of Overall Commissioning Strategy forProtons”, these proceedings.[3] V.Kain et al., “Beam based Alignment of the LHC TransferLine Collimators”, Proc. PAC 2005, Knoxville, Tennessee,USA.[4] G.Robert-Demolaize, “Critical Beam Losses during Com-missioning and Initial Operation”, these proceedings.[5] V.Kain et al., “Protection Level during Extraction, Transferand Injection into the LHC”, Proc. PAC 2005, Knoxville,Tennessee, USA.[6] M.Zerlauth et al., “Requirements for the Fast Magnet Cur-rent Change Monitors (FMCM) in the LHC and the SPS-LHCTransfer Lines”, LHC-CIW-ES-0002-00-10, CERN, Geneva,Switzerland, 2005.LHC Project Workshop - 'Chamonix XV'93

What is required to safely fill the LHC ?

Abstract

Similar works

Full text

Available Versions

CERN Document Server