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

CPS

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

and CPS

Needs line of small solenoids to guide electrons

WGTSSmall currents - Large Inductances

M1 in WGTS

CPS

Principle of a coil and a cold diode

Apparition of a resistive zone r

Quench propagates very quicky and generates a voltage that open the

diode.

Then the coil discharges safely on itself.

This system is intrinsically safe

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

Quench-back effect

• 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 ( < 2/3rd Ic) 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.

Possible problem

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

First risk is to over heat theconnecting wires

One can show that the temperature of a given wire at time t, is a directly dependent

of:

Called the current load in MIITS

( In adiabatic conditions!)

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

WGTS

CPS

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