Results are presented of losses and stability measurements in a small
superconducting (SC) coil with an alternating current at frequencies u
p to 2.5 kHz. The mutual influence of losses and instability on the ma
ximum attainable current is studied and discussed. It is shown that th
ere are different modes of quench. SC wire can go to the normal state
due to the development of instability with almost no overheating over
the ambient temperature. In another mode, overheating over the current
sharing temperature occurs due to losses under stable conditions. The
experimental results agree with a recently developed stability theory
for composite wires, taking into account the smoothness of the transi
tion characteristic and its influence on stability. This theory explai
ns why cryogenically unstable SC wires work at currents close to the c
ritical current, why SC wires are more stable at lower rates of field
change and current charge rate and why wires with a smoother transitio
nal characteristic are generally more stable than SC wires with sharp
transitions to the normal state. The theory thus allows us to approach
the problem of the relationship between losses and stability.