MgB2 superconducting particles in a strong electric field

Comment on “Spherical agglomeration of superconducting and normal microparticles with and without applied electric field”

“…5,6 When we worked with Pb, other low temperature superconducting particles, and MgB 2 , the experiments were performed in a helium dewer, which was completely isolated. 13,15 In addition, our experiments found that superconducting particles as large as 60 μm could be aggregated into balls under an electric field.…”

“…However, the most important issue is that the water induced ball formation by shaking has nothing to do with the electric field-induced superconducting ball formation. [12][13][14][15][16] When we used liquid nitrogen to work with high temperature superconducting particles, the particles were dried, and the experiments were always conducted in a glove bag with dry nitrogen. No open air was in contact with our particle samples.…”

Explanation of the Tao Effect: Theory for the Spherical Aggregation of Superconducting Microparticles in an Electric Field

“…However, subsequent experiments reported in 2002 for conventional superconducting materials (Pb, V, V 3 Ga, Nb-N, and Nb 3 Sn) all showed the same behavior [2], and the same behavior was observed in MgB 2 [3]. Briefly the remarkable observation is: when the applied electric field exceeds a critical value, typically of order 0:5-1 kV=mm, millions of superconducting microparticles each of size 5 m spontaneously aggregate into spherical balls of millimeter size.…”

Reply to “Comment on ‘Spherical agglomeration of superconducting and normal microparticles with and without applied electric field’ ”

“…This demonstrates that indeed large electric fields exist in our capacitor with insulating electrodes, contrary to the statements in the Comment, hence that no spurious charges appear that would screen the electric field in the capacitor for fields of up to at least 15 000 V cm −1 . These fields are substantially larger than what would be needed to induce ball formation according to Tao's claims, [3][4][5][6] and no ball formation is seen with insulating electrodes as discussed in our paper 2 and not disputed by Tao et al Tao et al attributed their findings to the hypothesis 5,6 that the electric field penetrates the surface of the superconductor and destroys Cooper pairs that are within a distance ξ = coherence length of the surface thereby increasing the energy, and spherical agglomeration avoids this energy cost. This would be consistent with BCS theory, as they state in the abstract of their Comment.…”