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COOLING OF THE LHC ENERGY EXTRACTION RESISTORS
G. Peón (ST/CV), K. Dahlerup-Petersen, G. Coelingh (AT/MEL)
INTRODUCTION
In the LHC, there are:
8 dipole magnet chains,

154 dipoles each
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each chain stores 1353 MJ at 13 kA

2 energy extraction systems for each chain.
The energy extraction system is mainly composed of:

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eight 4 kA d.c. breakers
a current-equalising busway,
a powering and control system

and a dump
HOW THE DUMP RESISTOR’S TANK
LOOKS LIKE
Inside the dump resistor’s tank, the air cools the resistor body by flowing through its plates and it is
cooled down by the water when passing through the air pipes
Water tank
resistor assembly.
(secondary
circuit of the
cooling
station)
The heat dissipation to the air in the LHC underground has to be minimized,
Each dipole dump-resistor assembly has a dedicated water-cooling
station.
Resistor
body
In total, there are:
8 water cooling stations in the LHC tunnel and dipole magnet chains,
8 in the UAs


Air closed
circuit
DESCRIPTION OF A COOLING STATION
Both circuits use demineralised water for cooling.

In the primary circuit (cold circuit), the quality of the demineralised water is generally
kept to values of 0.1mS/cm

In the secondary circuit (hot circuit) the electrical conductivity of the water is not an
important issue as it can rise to 300 mS/cm without any risk for the equipment.
3D MODEL OF A PROTOTYPE COOLING STATION
The main components of the cooling station are:

The heat
exchanger, the expansion vessel and the pump
There are two flow switches, one to indicate the availability of enough water flow

in the secondary circuit and a second one to indicate a major water leak.
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A pressure
switch avoids the circuit to reach a gauge pressure higher than 1 bar.

REQUIREMENTS AND DESIGN CONSTRAINTS

The expansion vessel must be at 0.25 bar for the dump resistor vertical configuration
Able to work with no cooling in the primary side
Assuming all the energy going to the secondary water circuit: 5 m3 water volume -> the increase in temperature is
33.5 K and the volume change is about 70 liters. Main input for the expansion vessel.

Maximum relative pressure in the resistor’s tanks 1 bar
This implies that the nominal pressure in the pump must be lower than 0.65 bar (a pressure relief valve will
avoid a higher pressure if the pump works at zero flow).
The pressure loss in the tank 0.15 bar,
Temperature recovery time in the resistor less than 2 hours
0.5 bar for the rest of the circuit.
(This requirement is demanding for the filter, the heat exchanger and the flow switch).
A simulation shows that for inlet water temperature in the secondary always equal to 25oC:
⇒ The hottest part in the resistor’s body gets below 50oC after 1.6 hours.
⇒ After 2 hours is 38oC.
⇒ The maximum outlet temperature is 41oC -> The maximum power needed in the heat exchanger is 100 kW.
In the real case the maximum inlet water temperature will be about 30oC.

2 dump resistors’ configurations, 2 particularities
⇒ The position in the tunnel limits the height of the equipment.
⇒ The position in the UA gallery reduces the available pressure drop in 0.2 bar.
Dimensioning of the heat exchanger and the water flow in the primary circuit.
Position in the main LHC tunnel below the beams

Radiation constraints
⇒ Bellow the beam, the expected dose is 20 Gray/year. For a 20 years
400 Gray.
⇒ According to literature, EPDM, Nitrile rubber (NBR), PVDF, Viton, PEEK, PUR, PP, PE and Nylon can withstand it.
CONCLUSIONS
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ST/CV participates in the design and construction of dedicated cooling stations for the dump resistors of the LHC dipoles
The dump resistors have very particular features that imply constraints for the different components in the cooling stations.
The delivery to CERN of the first of the 16 cooling station is foreseen for January 2004.
Position in the UA galleries