Keeping LHC cold during LS periods Preliminary proposal TE-CRG-OP_GF 2017/05/09 TE-CRG-OP_GF

Nominal configuration during LS agenda Definitions Nominal configuration during LS Adapted configuration to fit with request “Keep LHC cold during LS” Summaries table Conclusion 2017/05/09 TE-CRG-OP_GF

Cold sector conditions means: Definitions Cold sector conditions means: At least one Cryoplant running, 80 K level Pressure in Vertical transfer line, QUI and QRL up to 18 bars. Temperature of circulating helium 80 < T < 90 [K] Temperature of cold mass 85 < T < 100 [K] for ARC excepted extremities Q7 Temperature of LSS + extremities Q7 : 90 < T < 105 [K] Temperature of DFB : Natural warmup Maximum temperature of sectors components during switch of cryoplants or major issue From Q7+1 Left to Q7+1 Right; 120 K within 7 to 10 days Q7 & standalone magnet 120 K within less than 3 days 2017/05/09 TE-CRG-OP_GF

Nominal configuration during LS Cryoplants, lines, QUI, Sector are warmed up to 300 K then depressurized than consigned for LS duration (Cryo lock-out). Under this configuration, all interventions on sector (magnet exchange, diode repair…) are free (cryogenic temperature & pressure point of view). During this LS period, the mandatory major overhauling (each 5 years) of all warm compressors and associated motors is realized. For LHC cryoplants, the duration of unavailability for major overhauling purpose is from 10 to 12 months. 2017/05/09 TE-CRG-OP_GF

Adapted configuration to fit with request “Keep LHC cold during LS” for 2 adjacent sectors Requested configuration for one point (2 adjacent sectors!) At least one Cryoplant, lines, QUI, Sectors remains around 80 K level Pressure in Vertical transfer line, QUI and QRL could be up to 18 bars Under this configuration, all interventions on cold part of the 2 sectors are forbidden. The mandatory major overhauling of all warm compressors and associated motors must be shared in phases of 2*6 months during this LS period. Note: with this configuration, no maintenance of common Cryo parts such as Vertical transfer lines, QUI, QRL… is possible. From safety point of view, only minor interventions on tunnel, above cold QRL, cold magnet & DFB should be possible after risk assessment. Major handling or massive proximity intervention will not be possible in the vicinity of cold parts! All utilities such CV, EL, network, controls, Vac… must be operational 2017/05/09 TE-CRG-OP_GF

“Keep LHC cold during LS” for 2 adjacent sectors Circulating Helium, 80K, up to 18 bars Phase 2 ~ 6 months Phase 1 ~ 6 months 1.8K unit 1.8K unit 2017/05/09 TE-CRG-OP_GF

Requested configuration to fit with “Keep LHC cold during LS” for 1 sector and intervention on the adjacent sector Requested configuration for one point (1 sector!) At least one Cryoplant, lines, QUI, Sectors remains around 80 K level Pressure in Vertical transfer line, QUI and QRL could be up to 18 bars To intervene on the adjacent warm sector, a decoupling of adjacent sector must be foreseen but is not possible without hardware heavy modifications during a preceding LS. The mandatory major overhauling of all warm compressors and associated motors must be shared in phases of 2*6 months during this LS period. Note: with this configuration, no maintenance of common Cryo parts such as Vertical transfer lines, QUI, QRL… is possible. From safety point of view, only minor interventions on tunnel, above cold QRL, cold magnet & DFB should be possible after risk assessment. Major handling or massive proximity intervention will not be possible in the vicinity of cold parts! All utilities such CV, EL, network, controls, Vac… must be operational 2017/05/09 TE-CRG-OP_GF

“Keep LHC cold during LS” for 1 sector Phase 1 ~ 6 months Already proposed, Chamonix, not approved Controlled airlock air and moisture condensation/icing not controlled Helium, 80K, up to 18 bars Atmosphere One valve to be added, see Chamonix 2010

“Keep LHC cold during LS” for 1 single sector Phase 2 ~ 6 months Atmosphere Helium, 80K, up to 18 bars air and moisture condensation/icing not controlled Controlled airlock by adding valves

OK, nominal configuration Nominal status (300K) 2 adjacent sectors remains cold 1 sector remain cold Option OK, nominal configuration Possible with no job foreseen on sectors Not possible with the present configuration Related risk na No major handling/intervention in the vicinity of the cold parts of the 2 sectors Cryo-lockout not possible Air/moisture trap on cold part of QUI Risk mitigation No access in the 2 adjacent sectors Heavy intervention in QUI to create airlock (sas) on the concerned sector. Creating airlock (sas) must be done during LS to allow this option during the following LS. Cryo maintenance Ok Refrigeration maintenance must be shared in 2*6 months No maintenance for common items Never presented, must be carefully studied 2017/05/09 TE-CRG-OP_GF

Conclusions “Keep LHC cold during LS” is not trivial. In all case the Cryo maintenance will be negatively impacted with possible effect on availability. In the hypothesis of keeping 2 adjacent sectors cold and according to the present risk assessment, major intervention on magnets will be forbidden. In the hypothesis of keeping cold one sector during LSx , QUI must be modified during the previous LS(x-1) by adding 5 valves per sector. The associated cost should be around 300 kCHF/sector (cost to be confirmed). CRG recommendation is to warmup all sectors during LS in order to allow all interventions in tunnel, caverns and to allow a complete maintenance of cryo equipment's, a guarantee of better availability over the long term. 2017/05/09 TE-CRG-OP_GF