The High Luminosity Large Hadron Collider (HL-LHC) Project at CERN calls for increasing beam brightness and intensity. In such a scenario, critical accelerator devices need to be redesigned and rebuilt. Impedance is among the design drivers, since its thermo-mechanical effects could

lead to premature device failures. In this context, the current work reports the results of a multiphysics study to assess the electromagnetic and thermo-mechanical behaviour of the Target Dump Injection Segmented (TDIS). It first discusses the outcomes of the impedance analysis performed to characterise the resistive wall and the high order resonant modes (HOMs) trapped in the TDIS structures. Then, their

RF-heating effects and the related temperature distribution are considered. Finally, mechanical stresses induced by thermal gradients are studied in order to give a final validation on the design qualit

Calviani, Marco

Carbajo Perez, David

Gilardoni, Simone

Giordano, Francesco

Lamas Garcia, Inigo

Mazzacano, Giacomo

Migliorati, Mauro

Perillo-Marcone, Antonio

Teofili, Lorenzo

English

The High Luminosity Large Hadron Collider (HL-LHC) Project at CERN calls for increasing beam brightness and intensity. In such a scenario, critical accelerator devices need to be redesigned and rebuilt. Impedance is among the design drivers, since its thermo-mechanical effects could
lead to premature device failures. In this context, the current work reports the results of a multiphysics study to assess the electromagnetic and thermo-mechanical behaviour of the Target Dump Injection Segmented (TDIS). It first discusses the outcomes of the impedance analysis performed to characterise the resistive wall and the high order resonant modes (HOMs) trapped in the TDIS structures. Then, their
RF-heating effects and the related temperature distribution are considered. Finally, mechanical stresses induced by thermal gradients are studied in order to give a final validation on the design qualit

Lorenzo Teofili

Marco Calviani

David Carbajo Perez

Simone Gilardoni

Francesco Giordano

Inigo Lamas Garcia

Giacomo Mazzacano

Mauro Migliorati

Antonio Perillo-Marcone

Archivio della ricerca- Università di Roma La Sapienza

ANALYSIS ON THE MECHANICAL EFFECTS INDUCED BY BEAMIMPEDANCE HEATING ON THE HL-LHC TARGET DUMP INJECTIONSEGMENTED (TDIS) ABSORBERL. Teofili∗12, M. Migliorati12, Sapienza University of Rome, Rome, ItalyM. Calviani, D. Carbajo Perez, S. S. Gilardoni, F. Giordano, I. Lamas,G. Mazzacano, A. Perillo, CERN, Geneva, Switzerland1also at CERN, Geneva, Switzerland, 2also at INFN, Rome, ItalyAbstractThe High Luminosity Large Hadron Collider (HL-LHC)Project at CERN calls for increasing beam brightness andintensity. In such a scenario, critical accelerator devicesneed to be redesigned and rebuilt. Impedance is among thedesign drivers, since its thermo-mechanical effects couldlead to premature device failures. In this context, the currentwork reports the results of a multiphysics study to assessthe electromagnetic and thermo-mechanical behaviour ofthe Target Dump Injection Segmented (TDIS). It first dis-cusses the outcomes of the impedance analysis performedto characterise the resistive wall and the high order resonantmodes (HOMs) trapped in the TDIS structures. Then, theirRF-heating effects and the related temperature distributionare considered. Finally, mechanical stresses induced by ther-mal gradients are studied in order to give a final validationon the design quality.INTRODUCTIONThe CERN accelerator complex has been upgrading toimprove its performance. In the framework of the LIU(LHC Injection Upgrade) [1] and HL-LHC (High Lumi-nosity LHC) [2] projects an increase of the beam brightnessand intensity is foreseen [1]. Several systems have to beredesigned and rebuilt to face the new situation.Devices impedance, i.e. electromagnetic beam equip-ment interaction, is among the systems design drivers. Thisinteraction causes a power deposition on the equipment (RF-Heating), proportional to the square of the beam intensityand to the device impedance [3]. The deposition, due to thepresence of trapped high order modes, can be highly irregu-lar, so leading to an uneven temperature distribution. As aresult, temperature gradients may induce intense mechanicalstresses causing failures or other undesired effects [4, 5].In this context, this paper presents the results of the multi-physics simulations performed to assess the electro-thermo-mechanical behaviour of the Target Dump Injection Seg-mented (TDIS) [6], that could experience RF-heating ashigh as its predecessor, the Target Dump Injection [4, 6].The TDIS will protect downstream LHC equipment dur-ing the injection phase, absorbing the injected beam in caseof malfunctions of the injection kicker in the Super ProtonSynchrotron (SPS)-to-LHC injection lines [6]. The geome-try of the device is presented in Fig. 1 and described in detail∗ lorenzo.teofili@uniroma1.itRF-ShieldingDetail 1: front ViewDetail 3: z-x PlaneSection ViewDetail 2Movable JawsLongitudinal RF-Fingersbetween modules gapsxyzLateral RF-Fingersx-y PlaneTankINJECTEDModule 3: Copper and Titanium JawsModule 1 and 2: Graphite JawsSegmentation; gaps between modulesInjected BeamReference OrbitBEAMRF-ShieldingLateral straightLateral curvedFigure 1: Geometry of the TDIS, detail on the RF-fingersconfigurations and transverse section.in [6]. Six vertically movable jaws of different materials arethe core of the TDIS. During the injection phase they have ahalf-gap of 4 mmwith respect to the injected beam referenceorbit, Fig. 2 bottom detail. Thus, if the orbit of the actualinjected beam differs more than the allowed tolerance, it willimpact the jaws so it is stopped. After the injection phasethe jaws are completely open (half gap 55 mm).METHODOLOGYThe current investigation involved electromagnetic sim-ulations to estimate the device impedance and the associ-ated deposited power. This power was used as an input forthermo-mechanical simulations to assess the device globalbehaviour.Excluding an impact due to beam dumping, the mainsources of heat loads for the TDIS are: direct beam load dueto the scraping of secondary halo, and impedance heating.The latter can be further divided in resistive wall heating andHOM RF-Heating. The beam halo heat load can be easilycomputed analytically [7]. Regarding the impedance heat-ing, Teofili, Lamas and Migliorati have recently proposed amethod able to simulate its mechanical induced effects ona device [8]. It interfaces two commercial programs, CSTParticle Studio® [9] a CERN standard for impedance compu-tation [10, 11], and ANSYS Mechanical® [12] widely usedfor thermo-mechanical simulations [13–16]. For this work,we adopted a slightly modified version of the method addingthe contribution of the secondary halo heat load. We fol-Thisisapreprint—thefinalversionispublishedwithIOP9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW PublishingISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-THPAK092THPAK0923448ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2018).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI.05 Beam Dynamics and EM FieldsD04 Beam Coupling Impedance - Theory, Simulations, Measurements, Code Developmentslowed a conservative approach, considering the worst casescenario: the load of the three sources is at a maximum dur-ing the injection phase, when the jaws of the TDIS are at theirminimum half-gap, 4 mm, and in the pessimistic assumptionof a failure of the longitudinal RF-fingers between the jawsmodules gaps (they are little silver coated beryllium-coppercomponents which reduce device impedance guaranteeingthe electrical connection among all the device parts, Fig. 1Details). Indeed, the power deposited by the beam halosand by resistive wall effects decrease further from the beam,and in the next section we will prove that in the outlinedconfiguration the HOM load is also maximum.Please note that since the TDIS functional specificationsare currently preliminary the outlined device characteristiccould change slightly in the future. In this context, the fol-lowing simulations were performed with a value of 5 mmfor the minimum half gap instead of the current acceptedvalue of 4 mm. However, this can be considered a minordeficit given the small difference between the values.ELECTROMAGNETIC SIMULATIONSIn order to evaluate the TDIS longitudinal couplingimpedance and its heating effects, electromagnetic simu-lations were performed. The geometrical model for CST®simulations (Fig. 2), was obtained carefully simplifyingthe complex mechanical TDIS drawing, preserving only thefeatures important for the electromagnetic computations, soreducing simulations time.The TDIS was analyzed with different finger configura-tions and with different half-gap apertures. In Fig. 3 resultsof CST wakefield [17] simulations for 5 mm half-gap arereported for the cases with and without longitudinal RF-fingers with the HL-LHC beam spectrum. For the scenariowith fingers, there are no trapped resonant modes inside thestructure below 1.25 GHz. Indeed, electric contacts preventtrapped modes below the cutoff frequency of the LHC pipe.In the scenario without RF fingers, several trapped modesare presents below 1.25 GHz. There is a clear contribution tothe longitudinal impedance in the beam spectrum frequencyrange. The impact of the absence of longitudinal fingerswas then further investigated: the shunt impedance of everytrapped mode obtained by the CST eigenmode solver [18]was compared with the results of the wakefield solver, Fig.4. The two different methods provide similar results.Full Gap Half GapInjected BeamReference OrbitTankRF-ShieldingCopperTitaniumGraphiteGaps Between ModulsFigure 2: TDIS Model in CST.0 0.5 1 1.5100102104f [GHz]Re(Z)[Ω]No RF-FingerFinger00.20.40.60.81BNS[a.u.]Figure 3: Beam normalized spectrum (BNS) in black andlongitudinal impedance real part in log scale, 5 mm half-gap.0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.600.51·104f [GHz]Re(Z)[Ω]Eigenmode SolverWakefiled SolverFigure 4: Longitudinal impedance real part, 5 mm half-gap.Following the conservative approach, to compute theimpedance HOM deposited power we used the eigenmoderesults in the scenario without RF-Finger. The power wasnumerically computed for the HL-LHC beam following thework of Furman, Lee and Zotter [3]. Furthermore, a sensitiv-ity analysis of the impedance induced power was performed.For each considered jaw aperture an impedance curve wasestimated. The impedance peaks (i.e the high order modes)were individually moved from their original frequencieswithin a range of ±10 MHz to obtain the maximum couplingwith the HL-LHC beam spectrum, i.e. the maximum powerloss. Figure 5 shows the HOM RF-Heating spectrum fordifferent TDIS half-gap configurations. Despite the similarappearance, the 5 mm half gap configuration is the most crit-ical with a total deposited power on the device of 1003 W(704 W for the 25 mm half gap case). Analyses of the re-sistive wall impedance heat load have demonstrated that, asexpected, the worst case scenario is at 5 mm half gap with atotal dissipation of 798.3 W in addition to the HOM load.THERMOMECHANICAL SIMULATIONSFollowing [8], the thermo-mechanical simulations on theTDIS were carried out in ANSYS®. The main goal was toverify that in the worst case scenario the TDIS local me-chanical stresses were at least 20% lower than the yield (forductile material) or the ultimate strength (for brittle material)and that the graphite blocks temperature remained below50 ◦C, in order to avoid outgassing issues [20].The heat loads considered are listed in Table 1, they occurfor the duration of the injection phase (around 30 minutes)simultaneously. Other heat loads are negligible, e.g. heatingThisisapreprint—thefinalversionispublishedwithIOP9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW PublishingISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-THPAK09205 Beam Dynamics and EM FieldsD04 Beam Coupling Impedance - Theory, Simulations, Measurements, Code DevelopmentsTHPAK0923449ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2018).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI.0.6 0.8 1 1.2 1.4050100f [GHz]Ploss[W]5 mm Half-Gap25 mm Half-GapFigure 5: Power Losses due to HOMs.Table 1: Applied Heat LoadsSource Heat load [W] Affected ElementSecondary halos 580 [21] Jaws free surfaceResistive Wall 798.3 Jaws free surfaceRF-Heating 1003.6 Entire TDISeffect due to e-cloud phenomena at a jaws half-gap of 5mm [19], or not associated with the injection phase.For the HOM RF-heating, the 3D map obtained following[8] was used. In the thermo-mechanical simulations the samegeometrical model of the electromagnetic simulations wasused with slight modifications. In particular, the RF-fingerswere reintroduced in order to have a realistic representationof the contact failure case, i.e. the fingers are present inthe device but they lose physical contact with device partson their non fixed side. Both secondary halo and resistivewall impedance heating was applied as a constant heat fluxon the beam facing jaws surfaces, Fig. 2. The former wasconsidered as evenly spread on the surfaces while the latterwas applied according to the resistivity of the material (i.e.75% of the load on the jaw graphite free surfaces and 25% onthe jaw titanium-copper free surfaces). The heat dissipationsystems considered were: conduction, radiation, on all thefree surfaces, and convection, only on the external surfaces ofthe tank. Furthermore, the TDIS cooling apparatus, a systemof pipes identical for each jaw in which 0.135 m3/s of waterat 27 ◦C flows, was also simulated. The global temperaturemap is plotted in Fig. 6. In this figure the component with thehighest temperature have been removed to optimize the scalefor readability. Remarkably, the graphite remains below the50 ◦C threshold.The peak temperature at the end of the injection stage isobserved on the lateral straight RF-shielding (Fig. 1 Detail1) on the longitudinal RF contacts between the two graphitemodules and is reported in Fig. 7. Regarding mechanicalstresses, the maximum value is localized on the same com-ponent on which the maximum temperature develops somecentimeters downstream: at the connections of the lateralstraight RF-shielding with the tank, Fig. 8. This is dueto the fact that the maximum temperature is at a gap. Atthis point the material is unconstrained and free to expand;whereas, the connection points between the tank and thestraight shielding fully constraint rotational and translationaldegrees of freedom. This limits deformations and increasesTemperature ◦CFigure 6: Global temperature distribution.Temperature ◦CFigure 7: Temperature distribution maximum. Lateralstraight RF-shielding, gap between the graphite modules.Von Mises Stress MPaFigure 8: Stresses distribution maximum. Lateral straightRF-shielding, gap between the graphite modules.stresses on the lateral straight RF-shielding. However, themaximum Von Mises stress value is well below the yieldstrength of the material: 250 MPa (stainless steel 314L).CONCLUSIONSIn this study, through electromagnetic and thermo-mechanical simulations, we have assessed the quality ofthe TDIS design, a key component in the LHC machine,under critical working conditions. We explored its electro-magnetic behaviour, we found the design robust given theabsence of trapped HOM in the structure up to 1.25 GHz.We further investigated a pessimistic scenario of longitu-dinal RF-Fingers failure, and we explored the mechanicaleffects of the power deposited by the electromagnetic beam-device and nuclei-matter interactions. Despite the fact thatour findings have highlighted some possible critical areas,neither the developed temperatures or the related mechanicalstresses seems to be high enough to cause problems, demon-strating the high quality of the design. Future studies shouldadopt the final minimum half-gap and further investigatethe highlighted critical zones with a more refined model tounderstand even better stress and temperatures distributions.Thisisapreprint—thefinalversionispublishedwithIOP9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW PublishingISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-THPAK092THPAK0923450ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2018).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI.05 Beam Dynamics and EM FieldsD04 Beam Coupling Impedance - Theory, Simulations, Measurements, Code DevelopmentsREFERENCES[1] J. Coupard et al., “LHC Injectors Upgrade Projects at CERN",in Proc. 7th Int. Particle Accelerator Conf. (IPAC’16), Busan,Korea, May 2016, paper MOPOY059, pp. 992–995.[2] G. Apollinari, A. Bejar, O. Bruning, M. Lamont, L. Rossi,“High-Luminosity Large Hadron Collider (HL-LHC) :Preliminary Design Report", CERN, Geneva, Switzerland,Rep. CERN-2015-005, Dec. 2015.[3] M. Furman, H. Lee and B. Zotter, “Energy loss of bunchedbeams in RF cavities”, Lawrence Berkeley Laboratory,Berkeley, California, Rep. SSC-086, 1986.[4] B. Salvant et al., “Beam Induced RF Heating in LHC in 2005”,in Proc. 7th Int. Particle Accelerator Conf. (IPAC’16), Busan,Korea, May 2016, paper MOPOR008, pp. 602–605.[5] D. Lipka, “Heating of a DCCT and a FCT due to wake lossesin PETRAIII, simulations and solutions”, presented at theSimulation of Power Dissipation & Heating fromWake LossesWorkshop, Diamond Light Source, Oxfordshire, UK, Jan.2013, unpublished.[6] D. Carbajo Perez et al., “Operational Feedback and Analysisof Current and Future Designs of the Injection ProtectionAbsorbers in the Large Hadron Collider at CERN", in Proc.8th Int. Particle Accelerator Conf. (IPAC’17), Copenhagen,Denmark, May 2017, paper WEPVA108, pp. 3517–3520.[7] B. Goddard, V. Kain, M. Lamont, "Function and OperatingConditions of the TDI Beam Absorber". CERN, 2004, EDMS508735, pp. 8.[8] L. Teofili, I. Lamas and M. Migliorati, “A Multi-PhysicsApproach to Simulate the RF Heating 3D Power MapInduced by the Proton Beam in a Beam Intercepting Device”,presented at the 9th Int. Particle Accelerator Conf. (IPAC’18),Vancouver, Canada, May 2018, paper 2578, this conference.[9] CST Studio Suite, https://www.cst.com/products/csts2[10] C. Zannini, “Electromagnetic Simulation of CERN accelera-tor Components and Experimental Applications”, Ph.D. thesis,Phys. Dept., Ecole Polytechnique, Lausanne, Switzerland,2010.[11] B. Salvant, “Impedance model of the CERN SPS and aspectsof LHC single-bunch stability”, Ph.D. thesis, Phys. Dept.,Ecole Polytechnique, Lausanne, Switzerland, 2013.[12] ANSYS, https://www.ansys.com/[13] A. Dallocchio, “Study of Thermo-mechanical effects inducedin Solids by High Energy Particle Beams: Analytical andNumerical Methods”, Ph.D. thesis, Phys. Dept., Politecnico diTorino, Torino, Italy, 2008.[14] C. Torregrosa, “Comprehensive Study for an OptimizedRedesign of the CERN’s Antiproton Decelerator Target”,Ph.D. thesis, Eng. Dept., Universidad Politecnica de Valencia,Valencia, Spain, 2017.[15] G. Romagnoli et al., “Design of the New PS Internal Dumps,in the Framework of the LHC Injector Upgrade (LIU) Project”,in Proc. 8th Int. Particle Accelerator Conf. (IPAC’17),Copenhagen, Denmark, May 2017, paper WEPVA109, pp.3521–3523.[16] I. Lamas et al., “LHC Injection Protection Devices, Thermo-mechanical Studies through the Design Phase”, in Proc. 7thInt. Particle Accelerator Conf. (IPAC’16), Busan, Korea, May2016, paper THPMY019, pp. 3698–3701.[17] CST Studio Suite: Wakefield Solver, https://www.cst.com/products/cstps/solvers/wakefieldsolver[18] CST Studio Suite: Eigenmode Solver, https://www.cst.com/products/cstmws/solvers/eigenmodesolver[19] G. Skripka and G. Iadarola, E-cloud in TDIS, https://indico.cern.ch/event/707491/contributions/2904336/attachments/1607146/2550476/TDIS_HiLumi_updated.pdf[20] J. M. Jimenez, "VACUUM REQUIREMENTS FOR THELHC". CERN, 2003, EDMS 428155, p. 6.[21] D. Carbajo, A. Perillo, L. Teofili, private comunication, Nov.2017.Thisisapreprint—thefinalversionispublishedwithIOP9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW PublishingISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-THPAK09205 Beam Dynamics and EM FieldsD04 Beam Coupling Impedance - Theory, Simulations, Measurements, Code DevelopmentsTHPAK0923451ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2018).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI.

Analysis on the mechanical effects induced by beam impedance heating on the HL-LHC target dump injection segmented (TDIS) absorber

The High Luminosity Large Hadron Collider (HL-LHC) Project at CERN calls for increasing beam brightness and intensity. In such a scenario, critical accelerator devices need to be redesigned and rebuilt. Impedance is among the design drivers, since its thermo-mechanical effects could lead to premature device failures. In this context, the current work reports the results of a multiphysics study to assess the electromagnetic and thermo-mechanical behaviour of the Target Dump Injection Segmented (TDIS). It first discusses the outcomes of the impedance analysis performed to characterise the resistive wall and the high order resonant modes (HOMs) trapped in the TDIS structures. Then, their RF-heating effects and the related temperature distribution are considered. Finally, mechanical stresses induced by thermal gradients are studied in order to give a final validation on the design quality

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Analysis on the Mechanical Effects Induced by Beam Impedance Heating on the HL-LHC Target Dump Injection Segmented (TDIS) Absorber

https://iris.uniroma1.it/bitstream/11573/1156646/2/thpak092.pdf

Analysis on the mechanical effects induced by beam impedance heating on the HL-LHC target dump injection segmented (TDIS) absorber

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