Nuclear Fission(Radioactive decay) is a First Order Reaction. What is the Order of Reaction of Nuclear Fusion?

"Light element fusion requires the product of density, time, and temperature exceed a critical value. Fusion spontaneously disembles without propagation (second order reaction) unless actively confined - implosion, gravitation, external EM fields, possibly inertia. Deuterium is nobody's idea of inertial confinement - including deuterated polyethylene. You only have a few shakes (tens of nanoseconds) to get the job done before the m thermally expands, reaction rate dropping as the inverse square of concentration."