Meeting with ph dt di @ cern 26 march 2013
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Meeting with PH-DT-DI @ CERN-26 March 2013. P rinciple of protection Scheme of KATRIN Magnets. A. Hervé /UW. 4482- Principle of Protection of Katrin Coils. KATRIN is an experiment at KIT to measure the mass of the electron neutrino. and CPS. CPS.

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Meeting with ph dt di @ cern 26 march 2013
Meeting with PH-DT-DI @ CERN-26 March 2013

Principle of protection Schemeof KATRIN Magnets

A. Hervé/UW

4482-Principle of Protection of Katrin Coils


KATRIN is an experiment at KITto measure the mass of the electron neutrino

and CPS

CPS

Needs line of small solenoids to guide electrons


Wgts small currents large inductances
WGTSSmall currents - Large Inductances




Principle of a coil and a cold diode
Principle of a coil and a cold diode


Apparition of a resistive zone r
Apparition of a resistive zone r

Quenchpropagatesveryquicky and generates a voltage that open the diode.

Then the coildischargessafely on itself.

This system is intrinsically safe


Typical self decay in 5 s
Typical self decay in ≠ 5 s

It is safe if the coil by construction can supportthe generated hot spot.One can spread more the energy by triggeringthe quench-heaters of the long quenched coil.


Two-coil set up

  • Quench of one coil near nominal current is likely to trigger quench of the other coil



Possible problem

  • If coupling is not sufficient, one can use the quench-heaters to induce quenches of the other coils (but one needs a Quench-Detector).

  • However, at reduced current ( < 2/3rdIc) the quench-heaters are not efficient because the coils are much more stable.

  • This is where is the real risk for the multi-coil systems.


If second coil does not quench

  • Current of the unquenched coil continues to circulate through the opened diode of the quenched coil for a long time!


Real case of unquenched coil
Real case of unquenchedcoil


First risk is to over heat the connecting wires
First risk is to over heat theconnecting wires

One can show that the temperature of a givenwireat time t, is a directlydependent of:

Called the currentload in MIITS

( In adiabatic conditions!)


Second risk is to overheat the cold diode connected to its heat sink
Second risk is to overheat thecold diode connected to its heat-sink

Diodes

( Also considered in adiabatic conditions!)


Two-coil set up - final

  • The trick is to add a dump resistor to make sure the residual current will disappear in a time safe for the cold wires and the diodes


LHC quench analysis

  • This protection scheme is the one adopted by the LHC with 154 magnets in series!


LHC quench protection

  • Simplify powering an protection scheme 1/8 of LHC




Conclusions

  • Each coil is self protected by its cold diode that allows discharge on itself.

  • Detection of quench stops the power supply, and powers the quench-heaters of the quenched coil to better spread the thermal energy in it.

  • If another coil quenches it is treated in the same way but how many coils quench in cascade is uncertain, as it depends for example of the current level.

  • After some time (≠ 30 seconds) the breaker is opened so that all currents disappear in a time safe for the cold wires and the cold diodes


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