Author: Taborelli, M.
Paper Title Page
TUXA03 Progress in Mastering Electron Clouds at the Large Hadron Collider 1273
 
  • G. Iadarola, B. Bradu, L. Mether, K. Paraschou, V. Petit, G. Rumolo, L. Sabato, G. Skripka, M. Taborelli, L.J. Tavian
    CERN, Geneva, Switzerland
  • K. Paraschou
    AUTH, Thessaloniki, Greece
  
  Dur­ing the sec­ond op­er­a­tional run of the Large Hadron Col­lider (LHC) a bunch spac­ing of 25 ns was used for the first time for lu­mi­nos­ity pro­duc­tion. With such a spac­ing, elec­tron cloud ef­fects are much more se­vere than with the 50-ns spac­ing, which had been used in the pre­vi­ous run. Beam-in­duced con­di­tion­ing of the beam cham­bers mit­i­gated the e-cloud for­ma­tion to an ex­tent that al­lowed an ef­fec­tive ex­ploita­tion of 25 ns beams. Nev­er­the­less, even after years of con­di­tion­ing, e-cloud ef­fects re­mained very vis­i­ble, af­fect­ing beam sta­bil­ity and beam qual­ity, and gen­er­at­ing strong heat loads on the beam screens of the su­per­con­duct­ing mag­nets with puz­zling fea­tures. In prepa­ra­tion for the High Lu­mi­nos­ity LHC up­grade, re­mark­able progress has been made in the mod­el­ing of the e-cloud for­ma­tion and of its in­flu­ence on beam sta­bil­ity, slow losses and emit­tance blow up, as well as in the un­der­stand­ing of the un­der­ly­ing be­hav­ior of the beam-cham­ber sur­face. In this con­tri­bu­tion, we de­scribe the main ex­per­i­men­tal ob­ser­va­tions from beam op­er­a­tion, the out­come of lab­o­ra­tory analy­sis con­ducted on beam screens ex­tracted after the run, and the main ad­vance­ments in the mod­el­ing of these phe­nom­ena.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXA03  
About • paper received ※ 19 May 2021       paper accepted ※ 12 July 2021       issue date ※ 29 August 2021  
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WEPAB338 Amorphous Carbon Coating in SPS 3475
 
  • W. Vollenberg, P. Chiggiato, P. Costa Pinto, P. Cruikshank, H. Moreno, C. Pasquino, J. Perez Espinos, M. Taborelli
    CERN, Geneva, Switzerland
  
  Within the LHC In­jec­tor Up­grade (LIU) pro­ject, the Super Pro­ton Syn­chro­tron (SPS) needs to be up­graded to in­ject into the LHC higher in­ten­sity and brighter 25-ns bunch spaced beams. To mit­i­gate the Elec­tron Mul­ti­pact­ing (E.M.) phe­nom­e­non, a well-known lim­it­ing fac­tor for high-in­ten­sity pos­i­tively charged beams, CERN de­vel­oped car­bon coat­ings with a low Sec­ondary Elec­tron Yield (SEY). Dur­ing the 2016 & 2017 year-end tech­ni­cal stops, such coat­ings were de­posited on the inner wall of the vac­uum cham­bers of some SPS quadru­pole and di­pole mag­nets by a ded­i­cated in-situ setup. A much larger scale de­ploy­ment was im­ple­mented dur­ing the Long Shut­down 2 (2019-2020) to coat all beam pipes of fo­cussing quadrupoles (QF) and their ad­ja­cent short straight sec­tions. In this con­tri­bu­tion, we re­mind the mo­ti­va­tion of the pro­ject, and pre­sent the re­sults and the qual­ity con­trol of the car­bon coat­ing cam­paign dur­ing the lat­ter phase of im­ple­men­ta­tion.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB338  
About • paper received ※ 19 May 2021       paper accepted ※ 16 June 2021       issue date ※ 13 August 2021  
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WEPAB339 Beam-Induced Surface Modification of the LHC Beam Screens: The Reason for the High Heat Load in Some LHC Arcs? 3479
 
  • V. Petit, P. Chiggiato, M. Himmerlich, G. Iadarola, H. Neupert, M. Taborelli, D.A. Zanin
    CERN, Geneva, Switzerland
  
  All over Run 2, the LHC beam-in­duced heat load ex­hib­ited a wide scat­ter­ing along the ring. Stud­ies as­cribed the heat source to elec­tron cloud build-up, in­di­cat­ing an un­ex­pect­edly high Sec­ondary Elec­tron Yield (SEY) of the beam screen sur­face in some LHC re­gions. Dur­ing the Long Shut­down 2, the beam screens of a low and a high heat load di­pole were ex­tracted. Their inner cop­per sur­face was analysed in the lab­o­ra­tory to com­pare their SEY and sur­face com­po­si­tion. While find­ings on the low heat load beam screens are com­pat­i­ble with ex­pec­ta­tions from lab­o­ra­tory stud­ies of cop­per con­di­tion­ing and de­con­di­tion­ing mech­a­nisms, an ex­tremely low car­bon amount and the pres­ence of CuO (non-na­tive sur­face oxide) are ob­served on the high heat-load beam screens. The az­imuthal dis­tri­b­u­tion of CuO cor­re­lates with the den­sity and en­ergy of elec­tron im­pinge­ment. Such chem­i­cal mod­i­fi­ca­tions in­crease the SEY and in­hibit the full con­di­tion­ing of af­fected sur­faces. This work shows a di­rect cor­re­la­tion be­tween the ab­nor­mal LHC heat load and the sur­face prop­er­ties of its beam screens, open­ing the door to the de­vel­op­ment of cu­ra­tive so­lu­tions to over­come this crit­i­cal lim­i­ta­tion.  
poster icon Poster WEPAB339 [2.247 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB339  
About • paper received ※ 19 May 2021       paper accepted ※ 22 June 2021       issue date ※ 16 August 2021  
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WEPAB361 New Generation CERN LHC Injection Dump - Assembly and Installation (TDIS) 3548
 
  • D. Carbajo Perez, E. Berthomé, C. Bertone, N. Biancacci, C. Bracco, G. Bregliozzi, B. Bulat, C. Cadiou, M. Calviani, G. Cattenoz, A. Cherif, P. Costa Pinto, A. Dallocchio, M. Di Castro, P. Fessia, M.I. Frankl, R. Franqueira Ximenes, J.-F. Fuchs, H. Garcia Gavela, J.-M. Geisser, L. Gentini, S.S. Gilardoni, M.A. Gonzalez De La Aleja Cabana, J.L. Grenard, J.M. Heredia, S. Joly, A. Lechner, J. Lendaro, J. Maestre, E. Page, M. Perez Ornedo, A. Perillo-Marcone, D. Pugnat, E. Rigutto, B. Salvant, A. Sapountzis, K. Scibor, R. Seidenbinder, J. Sola Merino, M. Taborelli, E. Urrutia, A. Vieille, C. Vollinger, C. Yin Vallgren
    CERN, Geneva, Switzerland
  
  Funding: Work supported by the Hilumi Project
Dur­ing CERN’s LS2, sev­eral up­grades were per­formed to beam in­ter­cept­ing de­vices in the frame­work of the HL-LHC Pro­ject. Up­graded equip­ment in­cludes two in­ter­nal beam dumps (TDIS) in­tended for ma­chine pro­tec­tion lo­cated at the in­jec­tion points from the SPS to the LHC. These two de­vices have been as­sem­bled, tested, and in­stalled around LHC Point 2 and Point 8 and are cur­rently ready to get com­mis­sioned with the beam. They are 5.8m-long, three-mod­ule-seg­mented vac­uum cham­bers, with large aper­ture to ac­com­mo­date the in­jected and cir­cu­lat­ing beam and equipped with ab­sorb­ing ma­te­ri­als, These com­prise graphite and higher Z al­loys that are em­bed­ded on sub-as­sem­blies re­in­forced with back-stiff­en­ers made of TZM. The cur­rent con­tri­bu­tion cov­ers three main mat­ters. First, it de­tails the TDIS de­sign and its key tech­ni­cal fea­tures. The sec­ond topic dis­cussed is the out­come of an ex­per­i­ment where a pro­to­type mod­ule was tested under high-en­ergy beam im­pacts at CERN’s Hi­Rad­Mat fa­cil­ity. To con­clude it is pre­sented the re­turn of ex­pe­ri­ence from the pre-se­ries con­struc­tion, val­i­da­tion and in­stal­la­tion in the LHC tun­nel. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB361  
About • paper received ※ 18 May 2021       paper accepted ※ 11 June 2021       issue date ※ 17 August 2021  
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