The Large Hadron Collider (LHC) and CERN Neutrino to Gran Sasso (CNGS) projects require the construction of a new fast-extraction system in the long straight section LSS4 of the Super Proton Synchrotron (SPS) at CERN. A conventional DC septum magnet will be used, in conjunction with the installation of horizontal and vertical extraction bumpers, main quadrupoles with enlarged apertures, extraction kicker magnets and additional hardware protection, instrumentation, controls and electronics. The extraction channel must be able to accept the bright LHC proton beam at 450 GeV/c, and also the high intensity, large emittance fixed target CNGS proton beam at the nominal 400 GeV/c extraction momentum. This paper describes the extraction channel to be installed in 2003, and shows how the requirements for both the LHC and CNGS project can be met

Goddard, B

Knaus, P

Schröder, G

Uythoven, J

Weterings, W

CERN Document Server

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHCERN – SL DIVISIONCERN-SL-2000-036 BTTHE NEW SPS EXTRACTION CHANNEL FOR LHC AND CNGSB. Goddard, P. Knaus, G. Schro¨der, W. Weterings, J. UythovenAbstractThe Large Hadron Collider (LHC) and CERN Neutrino to Gran Sasso (CNGS) projectsrequire the construction of a new fast-extraction system in the long straight section LSS4 ofthe Super Proton Synchrotron (SPS) at CERN. A conventional DC septum magnet will beused, in conjunction with the installation of horizontal and vertical extraction bumpers, mainquadrupoles with enlarged apertures, extraction kicker magnets and additional hardwareprotection, instrumentation, controls and electronics. The extraction channel must be ableto accept the bright LHC proton beam at 450 GeV/c, and also the high intensity, largeemittance fixed target CNGS proton beam at the nominal 400 GeV/c extraction momentum.This paper describes the extraction channel to be installed in 2003, and shows how therequirements for both the LHC and CNGS projects can be met.Presented at EPAC2000, 26-30 June 2000Vienna, AustriaGeneva, SwitzerlandJuly 2000THE NEW SPS EXTRACTION CHANNEL FOR LHC AND CNGSB. Goddard, P. Knaus, G. Schröder, W. Weterings, J. Uythoven,CERN, Geneva, SwitzerlandAbstractThe Large Hadron Collider (LHC) and CERN Neutrinoto Gran Sasso (CNGS) projects require the constructionof a new fast-extraction system in the long straightsection LSS4 of the Super Proton Synchrotron (SPS) atCERN. A conventional DC septum magnet will be used,in conjunction with the installation of horizontal andvertical extraction bumpers, main quadrupoles withenlarged apertures, extraction kicker magnets andadditional hardware protection, instrumentation, controlsand electronics.  The extraction channel must be able toaccept the bright LHC proton beam at 450 GeV/c, andalso the high intensity, large emittance fixed target CNGSproton beam at the nominal 400 GeV/c extractionmomentum. This paper describes the extraction channelto be installed in 2003, and shows how the requirementsfor both the LHC and CNGS projects can be met.1  FAST EXTRACTION REQUIREMENTSThe extraction channel to be installed in SPS LSS4 [1]has to accept the high brightness beam for the LHCcollider, and also the high intensity, large emittanceCNGS beam for the neutrino production target. Therelevant nominal beam parameters are summarised inTable 1. Note that round beams are assumed for bothLHC and CNGS, and that the numbers in parenthesis forLHC refer to the ultimate beam parameters. Table 1: Main parameters of CNGS and LHC beams  LHC CNGS Number of spills  1  2 Inter-spill gap (ms)  -  50 Protons per spill (1013)  3.2 (4.9)  2.25 Spill length (   s)  <7.8  10.5 Emittance (1   norm.)  3.5  12 p inject (GeV/c)  26  14 p extract (GeV/c)  450  400The design has to satisfy the following conditions. The channel should provide a large enough verticaland horizontal aperture for injected, bumpedcirculating and extracted beam. The rise times and flat-top duration should becompatible with the above figures. The influence of the various field errors and supplyripples should be low enough for acceptance by theLHC injection system and CNGS target. The extraction magnet stray field should not give asignificant emittance blow up of the stored beam. The extraction system should be adequatelyprotected against mis-steered beams.2  CONCEPTSThe extraction region optics is shown in Figure 1.Figure 1. Optics functions in the extraction region.A conventional fast extraction will be used in LSS4with horizontal closed orbit bumpers, extraction kickerand conventional DC magnetic septum located just afterthe focusing quadrupole 418.The beam will be moved close to the extraction septumusing the horizontal closed orbit bump, and is then kickedhorizontally across the septum during a gap in thecirculating beam. The extraction septum then deflects thebeam out of the SPS vacuum chamber and into thetransfer line TT40, with the required position and angle.A vertical closed orbit bumper system (in fact a set ofstrong orbit correctors) will also be used for precisevertical beam steering at high energy.3  SYSTEMS AND PERFORMANCE 3.1  Extraction bumpers Four horizontal bumper magnets, located atquadrupoles 414, 416, 420 and 422, allow the circulatingbeam to be bumped by the required 40 mm at theextraction septum next to quadrupole 418, with amplemargin for additional orbit correction at 450 GeV/c. Four vertical 'bumper' (strong corrector) magnets arelocated at defocusing quadrupoles. The obvious locationat position 417 would require the construction of a special-50-2502550751001251503937 3969 4001 4033 4065 4097-1-0.500.511.522.53BETYBETXDXBeta (m)Dx (m)QF420QDA419QFA418QDA417QF416MKE 1-6DILUTERMSE1-6H-BUMPMB415H-BUMPQD415magnet with an enlarged aperture - for standardisationpurposes the correction will be done using magnets at thepositions 413, 415, 421 and 423. This configurationallows a  10 mm vertical orbit correction at the extractionseptum. 3.2  Extraction Kicker System MKEThe bumped stored beam will be deflected by six fastpulsed kicker magnets by a total angle of 0.5mrad. Thekicker magnets are of travelling wave type with externalmatching capacitors. There will be six or seven cells permagnet. The CNGS beam will be extracted in two batchesrequiring a rise and fall time of the kicker pulse smallerthan 1.1  s. An additional clipper and dump switch on thePulse Forming Network are used to obtain the rapid falltime. Studies are ongoing to replace the thyratron of thedump switch by fast diodes. The layout of the kickersystem, most likely two families of magnets withdifferent apertures to combine maximum magnetic fieldand sufficient vertical aperture, is presently under study.Measurements on a prototype magnet installed in the SPSshowed a temperature rises of more than 20 K due toheating of the ferrites by the beam. Extrapolation to finalCNGS and LHC beam currents indicates the necessity ofwater-cooling of the magnet. This needs to be designedwith great care as the whole system is part of the machinevacuum. 3.3 Extraction Septum Magnet MSEFor the extraction septum magnet an alternative to theconventional DC septum (MSE) was evaluated [2]. Thefast-pulsed septum (MSP) takes advantage of the short(maximum 10.5  s) flat top required for the fastextraction. The magnet is powered by a 250  s longsinusoidal pulse with a superimposed 3rd harmonic to givethe required flat-top precision of about  0.02 %. TheMSP septum uses a yoke of tape wound silicon steel of50  m thickness. The septum element is a passive electro-magnetic eddy current screen of 5 mm thickness, notconnected to the excitation current loop. The developmentof this magnet has made significant progress, and is nowat a stage where a full sized magnet can be built.However, for reasons of planning, resources andcompatibility, and also because of the cost savings whichcan be made by reusing existing equipment, the LSS4extraction channel will be equipped with the conventionalMSE magnet.The main parameters of the MSE magnet are shown inTable 2 [3]. Six magnets will be required to provide the12 mrad deflection necessary, and these will be mountedon a rigid retractable girder for alignment purposes and toease the setting up of the SPS. Table 2. MSE septum magnet parametersSeptum thickness mm 17.25Gap height mm 20Maximum field T 1.508Kick at 450 GeV/c mrad 2.249Magnetic length m 2.237B.dl max Tm 3.373Peak current A 24,000B.dl / I Tm/A 1.41 10-4Total resistance m  2.9Total inductance  H 84Peak voltage V 80Minimum rise/fall time ms 200Magnet spacing (centre) mm 3,234 3.4  Septum Protection Direct impact of the extracted beam would destroy theseptum magnet coils. A comprehensive interlock systemwill be required to survey the beam positions, losses,bumper and septum currents, kicker charging voltages,etc. However, operator error can never be excluded, andseveral other modes of failure are also possible. Aphysical protection element (diluter) will therefore berequired. This will be placed immediately upstream of thefirst septum coil, and will reduce the particle flux on thecoil to a safe level, such that the temperature does notexceed 100   C. The diluter will be a composite shieldmade up of graphite, graphite/copper composite andaluminium. Monte Carlo simulations with the FLUKAcode have determined that a length of 3 m should beadequate for this element. Figure 2 shows a simulatedtemperature profile for an LHC-type beam impact along a3 m graphite/aluminium diluter and in the first part of theMSE coil. The coil temperature is kept to about 100   C. Figure 2. Simulated temperature profile in diluter andMSE coil (4.1 1013 protons, 450 GeV/c, 3.5 	 m nh). 3.5  ApertureThe layout of the LSS4 extraction channel has beenoptimised with the present equipment parameters, tomaximise the aperture available for the injected,circulating and extracted beams.Figure 3 shows the horizontal trajectories through theLSS4 extraction for the CNGS beam at injection, bumpedand during extraction. A  3   beam envelope is plotted.0 1000 2000 3000 4000length [mm]0100200300400500600T[oC]Temperature Profile in 2.5m C, 0.5m Al, 0.827m gap, 0.5m CuFigure 3. Trajectories of CNGS beam (  3  ) in the LSS4extraction channel.The minimum vertical and horizontal  half-aperturesand half-openings, in both mm and numbers of beamsigma, are given in Table 3 for both CNGS and LHCbeams. Note that only the extracted beam has any verticallimit imposed by the extraction channel, due to the20 mm gap height of the MSE. Table 3. Minimum half-apertures (numbers of sigma) andhalf-openings for CNGS and LHC beams. h    v mm h mm vCNGS inject 5.6 - 45.4 -CNGS bump 8.0 - 12.9 -CNGS extract 6.5 6.7 10.5 10LHC inject 14.1 - 45.4 -LHC bump 12.4 - 11.2 -LHC extract 8.2 13.3 8.0 10 3.6  Effect of Stray Field The stray field of the MSE magnet was measured in theregion traversed by the circulating bumped beam. Amultipole expansion with just dipole and decapolecoefficients gave a good fit, Figure 4. Figure 4. Measured MSE stray field (points) and fit(solid line) using dipole and decapole coefficients. These values were used in MAD to make tracking over104 turns, corresponding to about 200 ms. For the largestbeam (CNGS), the emittance increase in this case wasbelow 1%, with a small effect seen on the closed orbit.This effect was measured in the SPS with low energybeams bumped close to the existing MSE septa. Theeffect observed on the orbit agreed with the simulations. 3.7  Stability and field errorsIt is assumed that the static field errors (e.g. caused byalignment tolerances, different gap heights, etc.) arereproducible and will be corrected for. These are notconsidered in this analysis. For LHC injection [4], theimportant parameter isx /    =   k  (  1    /  n) = 1.17 104  k  (  1)where  x is the relative error produced by  k the kickerror, at the location with horizontal beta of  1. Asexpressed above, the total contribution of all pulsedextraction elements must be less than 0.5. The systems contributing to this error are the bumpermagnets, the kicker magnets and the extraction septum.The kicks, betas, power supply ripples and resultinginjection error contributions are given in Table 4.  Table 4. Contributions to LHC injection errors.System   av.) (m) k (mrad) ﬀ ﬀ I/Imax ﬀ ﬀ x/ ﬁ ﬁBumpers 77.3 1.04 0.00055 0.059MKE 75.3 0.5 0.005 0.254MSE 54.2 12.0 0.00025 0.259 Assuming that the contributions from the differentsystems add quadratically, the total contribution is ﬂ x / ﬃ  =  (0.0592 + 0.2542 + 0.2592) = 0.37 3  CONSTRUCTION TIMESCALE The installation of the extraction channel begins in the2000/2001 SPS shutdown, and is expected to becompleted at the end of the 2002/2003 shutdown. Themodification of the existing MKE kicker system isexpected to be the critical element in the planning.REFERENCES[1] P.Collier et al., “The SPS as Injector for LHC –Conceptual Design”, CERN SL 97-07 (DI), 1997.[2] G.Schröder et al., “A Novel Eddy Current SeptumMagnet for SPS Extraction towards LHC andCNGS”, these proceedings.[3] J.Dupin, “Extraction Septum Magnets for the SPS –List of Parameters”, CERN/SPS/ABT/EX/JD/ph/81-42, 1981.[4] A.Hilaire et al., “Beam Transfer to and Injection intoLHC”, CERN/LHC/Project-Report 208, 1998.0501001502002503003969 3985 4001 4017 4033 4049 4065050100150200250300x (mm)s (m)x (mm)MKE 1 -6 MSE 1-6Injected Bumped Extracted 20 40 60 80 100x [mm]11.522.53B sdl[10-3 Tm]MSE Stray Field Vs Distance

The New SPS Extraction Channel for LHC and CNGS

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