  Superfluid vortices pinned to nuclear lattice sites or magnetic flux tubes in
a neutron star evolve abruptly through a sequence of metastable spatial
configurations, punctuated by unpinning avalanches associated with rotational
glitches, as the stellar crust spins down electromagnetically. The metastable
configurations are approximately but not exactly axisymmetric, causing the
emission of persistent, quasimonochromatic, current quadrupole gravitational
radiation. The characteristic gravitational wave strain $h_0$ as a function of
the spin frequency $f$ and distance $D$ from the Earth is bounded above by $h_0
= 1.2\substack{+1.3 \\ -0.9} \times 10^{-32} (f/30\;{\rm Hz})^{2.5} (D/1\;{\rm
kpc})^{-1}$, corresponding to a Poissonian spatial configuration (equal
probability per unit area, i.e. zero inter-vortex repulsion), and bounded below
by $h_0 = 1.8\substack{+2.0 \\ -1.5} \times 10^{-50} (f/30\;{\rm Hz})^{1.5}
(D/1\;{\rm kpc})^{-1}$, corresponding to a regular array (periodic separation,
i.e.\ maximum inter-vortex repulsion). N-body point vortex simulations predict
an intermediate scaling, $h_0 = 7.3\substack{+7.9 \\ -5.4} \times 10^{-42}
(f/30\;{\rm Hz})^{1.9} (D/1\;{\rm kpc})^{-1}$, which reflects a balance between
the randomizing but spatially correlated action of superfluid vortex avalanches
and the regularizing action of inter-vortex repulsion. The scaling is
calibrated by conducting simulations with ${N_{\rm v}} \leq 5\times10^3$
vortices and extrapolated to the astrophysical regime ${N_{\rm v}} \sim 10^{17}
(f/30\;{\rm Hz})$. The scaling is provisional, pending future computational
advances to raise ${N_{\rm v}}$ and include three-dimensional effects such as
vortex tension and turbulence.
