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

2. 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

3. 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

4. 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

5. 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

6. “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

7. 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

8. “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

9. “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

10. 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

11. 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