The total current density J ≡ | J| (left two columns) and total particle density n (right two columns) in a slice y = 5 λ _p. In each pair of columns, the first column shows times t = (37.5, 47, 56, 65.5, 75) τ _c0 and the second column shows t = (84.5, 94, 103, 112.5, 122) τ _c0 . The particle density n, which is not used directly in the PIC code, is calculated from particle positions using a uniform kernel of half-width two grid lengths. The same kernel is used to smooth the current density J.