Stability, i.e. the possibility of self-recovery of a superconductor
after a quench, is one of the most important features of technical
superconductors. The stability of a superconductor is determined
quantitatively by some limiting parameters, called indicators or parameters
of stability, which delimit the region of safe (stable) operation of the
superconductor. The parameters of stability are used in the design and
operation of superconducting devices.
In the introductory part of the work, after a short description of
the structure and properties of the technical superconductors, there are
characterized the most often used stability parameters as well as the
methods of their determination.
The essential part of the work starts with the derivation of a heat
conduction equation of a new type which can be used for the description
of quick-changing heat processes in the superconductors. This equation
takes into account the finite velocity of heat flux propagation and
the relaxation of heat source capacity.
Further on, there are successively discussed elaborated by the author
analytical methods for calculation of the stability parameters, first
of all the critical energy of the conductor which is the most frequently
The presented method for calculation of the minimum propagating current
allows for the full boiling characteristic of the coolant and permits
any dependence of the heat conductivity of the conductor on temperature.
The proposed general analytical method for calculation of the critical
energy as equal to the enthalpy increase in the normal zone considers
both quasi stationary minimum propagating zones and transient
propagating zones. This method takes into account nucleate and film
boiling of the coolant.
The analytical method for calculation of the critical energy of thermally
insulated superconductors takes into consideration transient heat transfer
in the conductor, temperature dependent conductor properties as well as
the finite duration and finite length of heat disturbances.
The analytical method for calculation of the critical energy of the
conductor remaining in the intimate contact with the coolant allows for
transient heat transfer in the conductor and coolant, and the finite
duration and finite length of heat disturbances.
In the latter part of the work there is discussed a transient numerical
model of the normal zone taking account of the precise temperature
dependencies of the conductor thermal conductivity and heat capacity, the
current sharing region, transient heat transfer to the coolant as well as
the non-linearity of the steady boiling characteristic of the coolant.
Using the elaborated analytical and numerical methods there is also carried
out the investigation of influence of basic variables characterizing the
superconductor and its operating conditions on the value of stability
parameters. On the ground of this investigation a number of general
conclusions are drawn. The comparison of the calculated values of the
stability parameters with experimental and calculated ones taken from
literature is made as well. In most cases the agreement is good.