We have calculated the electric field around and on the surface of an open thick-wall carbon
nanotube (CNT) of height h, external radius R, and wall thickness w. To accomplish that we
simulate the CNT as a vertical array of touching toroids, each of external radius R and cross
section radius w/2, and then we express the problem in toroidal coordinates. From our
calculations we obtain the enhancement factor γ as a function of h, R, and w. By fitting to our
numerical results we obtain an empirical but simple formula for γ, which extrapolates to that …