Test results from the SMES proof of principle experiment

Abstract

A Proof of Principle Experiment (POPE) has been constructed and conducted to demonstrate the stability and operation of the SMES conductor in the SMES-WISC team's Engineering Test Model (ETM) design. The experimental facility includes: a 100 kA DC power supply; a 4 tesla, 1 meter bore, background field split solenoid; a three turn-1 meter diameter test coil of the ETM conductoG a dewar for operation of the solenoid and test coil at 1.8 K and 1 atmosphere, and support syskms for vacuum, helium supply and recovery, and data acquisition. The test facility exactly duplicates the electric, magnetic and thermal conditions zxpected for the ETM conductor. We report on measurements of conductor stability vs. transport current, applied magnetic field, and cooling from liquid helium. The measurements characterize the conductor's stability against finite length traveling normal zones, and against quenches resulting from transient normal zones. The data qualify the conductor for dependable use at 50 kA, 4 tesla and 1.8 K.

Stability test results on the aluminum stabilized superconductor for the helical coils of LHD

“…Since there have not been enough data below the recovery current, it is hard to determine precisely the minimum propagating current a t which the propagation velocity must become zero. As was found in [7], there is a possibility of observing a traveling normal zone also for our conductor in this current range. Probably, this will be examined for longer conductor samples, i.e., representative coil samples, which will be tested in the nearest future.…”

“…For example, in the experiments for a SMES conductor, there has been observed, as it is called, a traveling normal zone [7,8], which showed that the initiated normal zone propagated forward and recovered a t the back end with a typical time scale corresponding to the current diffusion time in the aluminum stabilizer. Appearance of such a traveling normal zone should be treated as an important issue not only from the view point of cryogenic stability, but also of Manuscript received September 14, 1998. continuous heat load on a magnet system as well.…”

Asymmetrical Normal-Zone Propagation Observed in the Aluminum-Stabilized Superconductor for the LHD Helical Coils

“…With the coil current of 11.4 kA, the normal-zone propagates in two directions, the spatial profiles, however, show asymmetry as the propagation velocities differ. On the other hand, in the case of a lower current of 10.8 kA, the normal-zone propagates only in one direction, which is the downstream side of the transport current, and the spatial profile of the longitudinal resistance clearly shows a form of "traveling normalzone" which was previously observed for another type of aluminum-stabilized superconductor developed for a SMES application [9].…”

Cryogenic Stability of LTS/HTS Hybrid Conductors

“…This is due to the long magnetic diffusion time constant in the pure aluminum ( 50 ms with 5 N purity and 6 mm thickness), and asymmetrical propagation velocity was found. With a transport current just above the minimum propagation current, it has been also found that the normal-zone propagates only in one direction along the conductor by forming a "traveling normal-zone" [3], [4]. Due to this fact, partial and transient normal-transitions have been observed with the LHD helical coils [5].…”