  It is shown that electric current flowing along an axially non-uniform
magnetic flux tube produces an associated non-linear, non-conservative axial
MHD force which pumps plasma from regions where the flux tube diameter is small
to regions where it is large. In particular, this force will ingest plasma into
the ends of a fat, initially potential flux tube and then pump the ingested
plasma towards the middle bulge, thereby causing mass accumulation at the
bulge. The ingested plasma convects frozen-in toroidal magnetic flux which
accumulates at the middle as well. Flux accumulation at the bulge has the
remarkable consequence of causing the bulge to diminish so that the flux tube
becomes axially uniform as observed in coronal loops. Stagnation of the
convergent plasma flow at the middle heats the plasma. A small number of tail
particles bouncing synchronously between approaching fluid elements can be
Fermi-accelerated to very high energies. Since driving a current along a flux
tube is tantamount to helicity injection into the flux tube, this mass
ingestion, heating, and straightening should be ubiquitous to helicity
injection processes.
