1. CRYOGENICS AND POWERING
L. Serio
AT/ACR

2. Contents Cryogenic system introduction
What does the cryogenic system need to do its job?
Conditions to start powering: CRYO_START
When do we have to stop powering: CRYO_MAINTAIN
Quench and quench recovery
How operators get an overview of the cryo process
What instrumentation is available to understand quenches?

3. LHC Cryogenic system operation
8 sectors
8 refrigerators
8 cold compressor systems
Cold interconnecting boxes (QUI [8], QURC[8])
25 km of cryostats in superfluid helium
1400 control loops for c.l. control [powering]
320 control loops for magnets T control [powering/beam]
600 control loops for beam screen T control [beam]
few 1000’s control loops for cryo operation

4. LHC cryogenic system layout
Odd point
Even point
Odd point
MP Storage
MP Storage
MP Storage
1.8 K
New
Existing
1.8 K
Refrigeration
4.5 K
4.5 K
Refrigeration
Unit
Refrigerator
Refrigerator
Unit
Warm
Warm
Warm
Warm
Warm
Surface
Compressor
Compressor
Compressor
Compressor
Compressor
Station
Station
Station
Station
Station
Upper
Upper
Cold Box
Cold Box
Cold Box
Cold Box
Shaft
Lower
Lower
Cold Box
Cold Box
Cold
Cold
Cold
Cavern
Compressor
Compressor
Compressor
box
box
Interconnection Box
box
Distribution Line
Distribution Line
Tunnel
Magnet Cryostats, DFB, ACS
Magnet Cryostats, DFB, ACS
Magnet Cryostats, DFB, ACS
Magnet Cryostats, DFB, ACS
LHC Sector (3.3 km)
LHC Sector (3.3 km)

5. LHC Cryogenic Components in Tunnel
4 circuits:
The cooling and filling circuit : Line C and D
The thermal shield circuit : Line E and F (no control valves for the standard cell, line E pass across the ARC)
The cold support and beam screen circuit : Line C and D
The superfluid helium circuit: line C and B

6. LHC magnets cooling scheme

7. Tunnel components cooled by the cryogenic system

8. What does each sector cryogenic system need?
Electric power
about 4 MW; 3 GWh/month
150 kCHF/month
Cooling and ventilation
600 m3/h of water
Cooling towers
Compressed air
Helium and nitrogen
15 t of He – 0.5 MCHF
1260 t of LN2 – 0.2 MCHF
Frequently, presenters must deliver material of a technical nature to an audience unfamiliar with the topic or vocabulary. The material may be complex or heavy with detail. To present technical material effectively, use the following guidelines from Dale Carnegie Training®.
Consider the amount of time available and prepare to organize your material. Narrow your topic. Divide your presentation into clear segments. Follow a logical progression. Maintain your focus throughout. Close the presentation with a summary, repetition of the key steps, or a logical conclusion.
Keep your audience in mind at all times. For example, be sure data is clear and information is relevant. Keep the level of detail and vocabulary appropriate for the audience. Use visuals to support key points or steps. Keep alert to the needs of your listeners, and you will have a more receptive audience.
In your opening, establish the relevancy of the topic to the audience. Give a brief preview of the presentation and establish value for the listeners. Take into account your audience’s interest and expertise in the topic when choosing your vocabulary, examples, and illustrations. Focus on the importance of the topic to your audience, and you will have more attentive listeners.
Vacuum
10-3 mbar
CRYO
Controls:
Networks, fieldbuses,
PLC, SCADA

9. State diagram and cryogenic system process
Powering:
Change toTT891=50K

10. CRYO_START (authorization for powering) considerations
The CRYO_START is a start interlock. Therefore once the conditions are met the powering is authorised without any further acknowledgement. It requires a manual intervention (operator request) by the cryogenic operator. It will also modify the control temperature of the HTS leads.
The CRYO_START ensures that the required conditions to power the magnets are met.
It gives sufficient margins to “safely” operate cryogenic equipment (temperatures, pressures, levels).
It does not protect equipment (it does not replace the quench protection system, the voltage taps, the beam monitors, etc.).
If the CRYO_START disappears the machine can still safely run for several minutes.

11. CRYO_MAINTAIN (request for slow discharge)
The CRYO_MAINTAIN is a full stop interlock which cause a slow discharge. An operator acknowledgement is therefore needed to be able to power again the magnets.
Only the conditions that will directly and rapidly provoke a quench (magnets, current leads, bus-bars) will be considered.
A filtering logic on the sensor used for CRYO_MAINTAIN will be necessary in order to avoid unnecessary downtime due to failing sensors or electrical noise. In principle it will be based on the verification of 2 out of 3 sensors in the cell requesting the discharge or in the case of only 2 sensors both must be out; the conditions must be valid for at least 30 sec. Instrumentation clearly not functioning (open or short circuit) will be flagged out.

12. Cryogenics conditions for powering
There would be three logic states:
Conditions to authorize magnet powering
(CRYO_START=TRUE and CRYO_MAINTAIN=TRUE)
Conditions that do not authorize magnet powering but if there is already current in the magnets there is no request for discharge (the conditions of magnet powering were met at the time of the start of powering but have disappeared meanwhile) (CRYO_START=FALSE and CRYO_MAINTAIN=TRUE)
Conditions that do not authorise magnet powering and request a slow current discharge
(CRYO_START=FALSE and CRYO_MAINTAIN=FALSE)
Each powering subsector has one CRYO_START and one CRYO_MAINTAIN

13. CRYO_START (authorization for powering if TRUE)
Superconducting magnets OK
Magnets below threshold (1.95 K) and pressure above threshold (1 bar)
Stand alone above threshold (level above threshold)
Beam screen temperature below 25 K
Line D (T lowest point above 5 K) and Quench Tanks empty (pressure)
DFB’s OK
Liquid helium level between thresholds in DFB (to cover LTS-HTS joint and below maximum level)
Current leads temperature between threshold (48 K – 52 K)
DSL OK: temperature below threshold (5.2 K)
Sector refrigerators OK (Cryoplant Ok for powering)
Compressors
Cold compressors
Turbines
Phase separator above 50 %
Ethernet communication OK
Vacuum OK (Magnets and QRL): pressure below threshold (10-3 mbar)

14. CRYO_MAINTAIN (request for slow discharge if FALSE)
Magnets below temperature threshold or above liquid helium level (2 K or minimum level for stand alone)
Liquid helium level inside thresholds in DFB (above LTS-HTS joint or below maximum level)
Current leads temperature below threshold (60 K)
DSL temperature below threshold (5.6 K)

15. Quench and helium recovery

16. Quench propagation within two adjacent cell
Expected performances and limitations: cell quench recovery
< 3 kA
9 kA > x > 3 kA
> 9 kA 7 6 5
Cooldown K 4
Filling %
Recovery time [hours] 3
Filling 0-70 % 2
Cooldown K 1 1 2 3 1 2 3 1 2 3
Number of cells [-]
Quench propagation within two adjacent cell
More than 14 cells or full sector recovery up to 48 hours

19. Expected interfaces and interactions
Machine setting-up and performance improvement
Strong reciprocal relationship between the magnets powering and cryogenics
Magnet powering requires accurate preparation of the cryogenic system and constant monitoring during ramping to avoid operational quenches
Machine reliability and availability
Monitoring, control, recovery actions coordinated with magnet powering for reciprocal optimization and increased availability
Monitoring, control, recovery actions coordinated with technical infrastructures for start-up and recovery optimization
Magnet powering
and protection
Quenches
Ramping
Losses
Resistive
Splices
Temperature control
Network
controls
Beam
Particle
Losses
Image
Currents
Synchrotron radiation
Cryogenics
Beam
Vacuum
Cryo-pumping
E-cloud losses
Technical utilities
(water, compressed air, electricity)
Compressors, turbines, valves, instrumentation …
Insulation
Vacuum
Cryostat

20. Available instrumentation
Mid Sector TT PT TT PT TT PT TT TT
Positive Slope PT LT LT TT TT TT TT TT TT TT TT TT TT TT TT TT TT TT TT
Standard Cell
Standard Cell
Cryo Cell

21. Documentation / informations
LHC Design Report – Chapter 11 - Cryogenics
LHC-Q-ES-0004 (EDMS ): The circuit of the LHC cryogenic system
LHC-Q-ES-0003 (EDMS ): Functional analysis of the LHC cryogenic system process