Thermal stability of superconducting magnet

system in a tokamak

Dr hab. inż. Leszek Malinowski, prof. PS

Dr inż. Monika Lewandowska

Elevation of the ITER magnet system

TF coil conductor design

PF coil conductor design

CS coil conductor

Conductor quantities for ITER magnets

Heat loads

• Conductors made of pure superconducting material are thermally unstable

• Cables constituted of the superconducting material embeded in the normal metal can operate stable.

Thermal stability

Full stabilizationq > Q

1max

cI

I where oc

c

TThPRI

2

Imax - maximum stable operating current, R - normal state resistance, h - heat transfer

coefficient, P - cooled perimeter, Tc - critical temperature, To - coolant temperature.

Main disadvantage of fully stable wires is large amount of stabilizer. This implies:

• low overall current density of the conductor• large size and big cost of a superconducting device

Modern superconducting wires are partly stable.

It implies limited amount of energy which can be dissipated in a cable without disturbing its safe operation.

Critical energy

crEE

E - energy of dissipationEcr - critical energy of the conductor.

Critical energy - the minimum energy of the thermal disturbance destroying the superconductivity

Mathematical model of normal zone

quu

gu

au

m

sxxxt

e

h

h

h

n

I

T

p

V

T

u

Tn - temperature of the n thermal component

Vh - volumetric flow in the h cooling channel

ph - pressure in the h cooling channel

Th - temperature in the h cooling channel

Ie - current in the e conducting component

Main goals of studies and anticipated results

• Identification and quantification of energy disturbances and heat sources in superconducting magnet system in a fusion reactor.

• Analysis and modelling of heat transfer phenomena in cable-in-conduit-conductors (CICC) used in fusion reactor magnets.

• Development of an analytical model of a normal zone in CICC.

• Formulation of stability criteria for CICC.• Performance of sample calculations and validation

of the results by comparison with experimental results.