Meddahi, Malika

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Instrumentation Needs for LTIM. Meddahi, SL Division, CERNAbstractThe general layout of the LHC injection transfer lines, TI 2and TI 8, is presented, together with the other beam linesbranching off from TI 2 and TI 8. The instrumentationneeds for the beam transfer to LHC are reviewed. The lo-cation of the beam instrumentation in the lines is discussed,from the extraction in the SPS to the injection into the LHC.1 INTRODUCTIONThe general layout of the LHC injection transfer lines(TI 2 and TI 8) is sketched in Fig.1, together with thetransfer line (TT41) to the CERN Neutrino to Gran Sasso(CNGS) target. In the following an overview of the beamFigure 1: Overall layout of the LHC injection transfer linesTI 2 and TI 8 and of the proton beam line TT41 of theCNGS facility.instrumentation foreseen for the beam transfer to LHC isgiven. The required instrumentation will be first presentedfor the extraction channels in the SPS (in LSS4 and LSS6),then for the transfer lines TT40 and TT60, followed by thetransfer lines TI 2 and TI 8, and finally for the injectionchannels into LHC. The list of the required equipment,their mandatory precision, and their position in the linesare presented.2 BEAM CHARACTERISTICSIn the two LHC injection transfer lines TI 2 and TI 8, theLHC beam structure will vary from a single pilot bunch to4 trains of 72 bunches, which in terms of intensity variesfrom 5*109 (pilot) to 1.7*1011 protons per bunch (ulti-mate). In addition to this large dynamic range, the SPSextraction channels (LSS4 and LSS6) and the beginningof the LHC transfer lines (TT40 and TT60) will be sharedwith different beam structures. The LHC beam has a 40MHz structure (25 ns bunch spacing), the fast extractedbeam for the CNGS has a 200 MHz structure (5 ns bunchspacing), and finally the slowly extracted beam impingingthe T1 target has no RF structure. In these common partsonly few beam instrumentation equipment is concerned andmost of them will be recuperated equipment. It is proposedto use separate signal processing for each different beamstructure, which shall provide homogeneity in interpretingthe results over the full length of the lines, and ease opera-tion.3 REQUIRED INSTRUMENTS ANDPRECISION3.1 Beam position monitors3.2 Beam position monitors in TI 2 and TI 8In Fig. 2, the beam position monitor (BPM) set up for TI 2and TI 8 is shown. Each BPM will be equipped with 4 but-Figure 2: Transfer line BPM and support.tons, which are recuperated from the LEP BPMs. Howevermost of the BPMs will only have one plane equipped withcabling and read-out. Their precision is ± 0.1 mm within aradius of 20 mm [1]. Few BPMs will be equipped in bothplanes, permitting intensity measurements with good pre-cision, as discussed later. For each BPM, it is foreseen tohave a small crate near the quadrupole where the BPM isattached and to transport the beam position information byoptical fibers to the surface buildings. The BPM body andsupport are new and will be built in 2001. The contract willbe awarded early 2001, the pre-series finished in Septem-ber 2001 and the complete delivery is expected by January293Chamonix XI2002.Bunch by bunch reading is provided, as long as the sameelectronics as used in LHC is installed. There will be twoprocesses running in parallel, one accumulating the averagedata, and one for a particular bunch or all bunches individ-ually.3.3 Beam position monitors for TT40 and TT60For the lines TT40 and TT60 (transferring different beamstructures) short directional couplers (BPCK) will be re-cuperated during the shutdown 2000/2001 from TT10 andmeanwhile decommissioned beam lines (TT70, TI12 andTI18). It has been proposed [2] to short-circuit the elec-trodes in the middle part to obtain two independent sig-nal sources (Fig. 3). This modification is foreseen dur-ing the year 2001, the installation in TT60 in the shutdown2001/2002 and in TT40 in 2002/2003. It has to be notedthat the double signal source will only be used in TT40. InTT60 the slowly extracted beam has no structure and there-fore the existing SEM foils will be continued to be used.However the proposal to modify all the BPCKs needed inboth the TT40 and TT60 lines was taken in order to stan-dardize the equipment. The feasibility of this proposal re-110340110 BPCKD (double)short circuitsBEAMpresentmodifiedFigure 3: Recuperated short directional couplers (BPCK).mains to be studied (depending on the radiation level ofthe recuperated equipment). The precision (ratio signal tonoise) and the calibration of the system (always difficult fortransfer lines) need to be evaluated.3.4 Intensity measurementsThe beam intensity will be mainly measured by the beamcurrent transformers (BCT) for which a very good absoluteprecision is difficult to obtain. This is mainly due to thedifficult calibration for a single path system. The intrinsicprecision (calibration of the integrators) is about 1-2 %, thegeneration, transmission and measurements of calibrationpulse add an error of about 1-2 %. Finally unpredictablecapture of parasitic signals (i.e. kicker firing) might furtherdegrade the precision [3]. The relative precision given bythe beam current transformer is better (about 1 %).As already mentioned, intensity measurements can alsobe provided by the beam position monitor system, if it isequipped with read-out in both planes. In this case the pre-cision on the intensity is ± 1 % within a radius of 15 mmand ± 2 % within a radius of 20 mm. If the BPMs areonly equipped in one plane, the intensity measurement isnot recommended due to lack of precision. It is proposedto equip some BPMs in both planes, as they will providemeans to check the intensity along the line, where lossesmight occur. Therefore, in order to monitor the intensity,the LHC injection transfer lines shall be equipped with twobeam current transformers (at the entrance and exit of eachline) and with few BPMs equipped with read-out systemsin both planes.3.5 Beam Loss detectionTo detect beam losses, it is foreseen to use ionization cham-bers (Fig. 4). Their sensitivity and resolution are aboutFigure 4: Ionization chambers.3000 electrons per primary charge [4]. Their dynamicrange is very broad and with the lowest gain, intensity ofthe order of 0.1 % of 5*109 can be detected, as with thehigher gain up to the full intensity can be measured. Tocover this large dynamic range, different capacitors (from1 nF to 100 nF) will be used depending on the beam inten-sity, as well as different gains, depending on the noise level.The gain level could also be linked to the cycle used (as itis done for the SPS cycle). About 30 beam loss monitorswill be installed along each beam line at strategic location.The electronics will be located on both sides of the line, inthe surface buildings (BA4 and SR8 for TI 8 and BA6 andSR2 for TI 2).3.6 Profile measurementsFig. 5 represents the setup which will be installed in thetransfer lines in order to locate the beam, to get the beamprofile values and to finally obtain a measurement of theemittance [5]. For the transfer line setting up, with the pi-lot beam, the Alumina screen (1 mm width) will be used.For the pilot beam there will not be enough signal to use theoptical transition radiation (OTR) monitors. For the nomi-nal beam, OTR monitors will be used. The mirror is madeof Titanium (12 µm) or Mylar (12 µm and a slice of 250A0 of Alumina) [6].The profile measurements will be essential for the opticalparameter checks. The precision on the sigma, for the pilotbeam (with the Alumina screen) was estimated to 5 % [5].Chamonix XI294Nominal beams Set-up or bad days60 x 6042O T R Free passage Al2O 3  [Cr]3060Beam60Figure 5: Screens (dimensions in mm).The precision is affected by a halo of light which adds upto about 0.5 mm to the 1 σ width. This effect can be es-timated and corrected, such that the residual error is about5 %. For the nominal beam, if the beam is Gaussian, thesigma is estimated by a fit to a proper Gaussian, taking intoaccount the beam tails, and the precision is estimated toabout 4 %. This precision comes from the statistical errors(2 %, mainly because the light distribution is not fully rep-resenting the particle distribution, but these errors can bediminished by averaging over many measurements) and thecalibration of the camera optics (2 %). If the beam is non-Gaussian, the r.m.s. will be measured (ignoring the tails)and can be provided with a better precision. ConcerningKickers SeptaBumper 2 Bumper 3Bumper 1 Bumper 4418419417x (m)s(m)Figure 6: SPS LSS4 extraction layout and horizontal ex-tracted trajectory.the selection, it will be possible to select the pilot (20 msintegration) or to integrate over a full batch of 3 or 4 trainsof 72 bunches. If a particular bunch within a train, or aparticular train within a batch needs be selected, then thescreen will have to be equipped with a photomultiplier oran electronic shutter.The emittance can be deduced, taking into account the er-ror on the size and on the Twiss parameters. From the ex-perience accumulated with measurements in TT10, it is as-sumed that the emittance could be measured to a precisionof about 10 % [7].4 BEAM INSTRUMENTATION LAYOUT4.1 SPS extractionThe fast extraction is done by establishing a horizontalclosed orbit bump in the SPS (4 dedicated bumpers) andby fast pulsed extraction kicker magnets and slowly pulsedmagnetic septa (Fig. 6) [8]. A vertical closed orbit bump isalso necessary. The measurement of the bumped beam po-sition is essential [9] and the confidence in the absolute po-sition with respect to the centre of the adjacent quadrupoleis mandatory. It was suggested to use two separate cou-plers, the first one electrically centered at the position ofthe bumped beam and the second one electrically centeredon the quadrupole axis. The simultaneous horizontal andvertical orbit acquisition at quadrupoles 417, 418, 419 isnecessary. This is where the horizontal bump is and wherethe vertical steering through the channel is tight.The extracted beam profile and position at the entrance andexit of the septum are required. In terms of constraints onthe instrumentation, the most challenging issue is the spe-cial BPM required in front of the septum magnet. At thislocation the aperture radius is 100 to 200 mm and the re-quired precision and linearity is 100 to 200 µm over 50 %of the aperture, i.e 0.1 to 0.2 %, which is a factor 20 lowerthan what is currently done with the available technolo-gies. The use of OTR around the septum magnet is in-vestigated (difficulties from the demanding dynamic rangeand radioactive environment). The beam loss monitors willalso be an important instrument for the setting up of theextraction (low intensity), for post mortem of the extractedbeam and for interlocking with the beam dump for circu-lating beam (bad bumper setting or septum position).4.2 TT40 and the Start of TI 8The layout of the requested beam instrumentation for TT40and TI 8 is presented in Fig. 7 [10]. It has also been donefor TT60 and TI 2 but the philosophy being the same, it isonly explained for one line. The extracted beam will be firststopped on the first TED (beam dump) of TT40. Upstreamof this TED, it is proposed to install a BCT as well as threeOTRs, which can be used to check the optical parameters.The OTRs have been positioned at a phase advance differ-ence of about 60 degrees. Beam loss monitors are also fore-seen around the dipole magnets at the entrance of TT40, inorder to monitor the quality of the extracted beam. Threemodified short directional couplers will provide the beamposition information in TT40. At the entrance of TI 8, twoother OTRs have been installed, one being at a maximumhorizontal dispersion (also a good place for momentum col-limation if required).295Chamonix XIs(m)D(m)BPM (2-in-4 scheme)BCTBLMModified BPCK (LHC and CNGS  beam)CNGSTT40 and TI 8MSIMKITED TEDOTRFigure 7: Proposed instrumentation layout for TT40 and TI 8.4.3 TI 8In the regular cell structure, the trajectory correction willbe done using monitors and correctors which are arrangedin a 2-in-4 scheme (per plane), which means that 2 adja-cent short straight section per plane will be equipped out of4 [11]. Three OTRs screens are foreseen after three con-secutive quadrupoles (phase advance of about 60 degreesin both planes) for a second optical check. Beam loss mon-itors have regularly been installed along the beam line.4.4 Injection into LHCThe last TED downstream of TI 8 will be used as a fi-nal check point before the injection into the LHC. Anotherthree sets of OTRs have been positioned between the lastset of tilted dipoles and the TED. In front of the TED, itis proposed to install the second BCT. From this last TEDonwards, each quadrupole will be equipped with BPMs.The septa and kicker magnets will be equipped with OTRscreens at their entrances and exits. The TDI, injectionbeam stopper, (protection against miskicked bunches), willbe equipped with an OTR at its entrance and a beam lossmonitor which will check the quality of the injected beaminto the LHC. An additional collimator for the protection ofD1, in addition to TDI is the TCDD. This additional pro-tection allowed to reduce the size of the TDI.5 SUMMARYThe baseline layout of the beam instrumentation for theTI 2 and TI 8 lines has been presented. The list of thenecessary equipment (beam position, intensity, beam lossand profile monitors) and their required precision is given.The presented instrumentation scheme reflects the equip-ment needed in order to monitor the beam for its transferto the LHC. If there is a need for more detailed measure-ments (i.e. for a better knowledge of the LHC beams forthe collider), the addition of more beam instrumentationcan be considered. For example, it has been mentionedfor the profile monitors that the selection of one particularbunch or train within a batch is not envisaged in the frameof the beam instrumentation required in the transfer lines.If it would be needed to check the beam properties for theLHC ring, it would require to equip some screens with aphotomultiplier.6 ACKNOWLEDGEMENTSThe author would like to thank E. Weisse and V. Mertensfor many fruitful discussions. I am grateful to W. Herr forChamonix XI296very interesting discussions and I would also like to thankcolleagues from OP (G. Arduini and K. Cornelis) and BI (J.Borer, J. Camas, D. Cocq, F. Ferioli, C. Fischer, R. Jung,J.P. Papis, H.J. Schmickler) for their help in preparing thistopic. Thanks to J. Ramillon for providing some of the fig-ures and transparencies and to S. Bidon for the photographsof the BPM set up.7 REFERENCES[1] D. Cocq, private communication.[2] J-P. Papis contribution, Summary notes of the BI discussionon BPM in TT40, TT41 and TT60, 24 August 2000.[3] H.J. Schmickler, ”Proton Beam Instrumentation for CNGS”,Proc. 2nd Workshop on Neutrino Beam Instrumentation, Fer-milab, 6-9 September 2000[4] F. Ferioli, private communication.[5] R. Jung, private communication.[6] J. Camas, private communication.[7] G. Arduini, M. Giovannozzi, D. Manglunki, M. Martini,”Measurement of the Optical Parameters of the Transfer LineUsing Multi-Profile Analysis”, CERN/PS 98-032 (CA).[8] B. Goddard, ”Fast Extraction from the SPS LSS4 for the LHCand NGS Projects”, SL-Note-98-066 (SLI).[9] B. Goddard, Summary notes of a discussion on beam instru-mentation in the LSS4 extraction channel held on the 6 ofJune 2000.[10] G. Arduini, K. Cornelis, private communication.[11] A. Hilaire, V. Mertens, E. Weisse, ”Trajectory Correction ofthe LHC Injection Transfer Lines TI 2 and TI 8”, LHC ProjectReport 122.297Chamonix XI

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