When we think of solar sails, I guess we mostly think of using radiation pressure of our closest star to achieve thrust, gracefully leaning on it with a large area sail of incredibly light and thin reflective materials. The idea, we now know, works and there's no doubt about it. We're now way past the early days of testing torque on a tiny carbon fiber sail by "light" alone in laboratory environment, something I still vividly remember watching nearly live (in those days that meant with months of delay, but it still felt as live if the science was cutting edge).
But the emissions from our Sun aren't exactly clean, and there's much more to it than what meets the eye, apparent to most of us only through photographs (and if we're lucky enough also seeing them in person) of polar auroras, a display of lights as the highly charged particles of solar winds hit the upper layers of our atmosphere and ionize the air molecules.
Such proton flux is however everyday's business as usual in the outer space, beyond protective shroud of Van Allen radiation belt, with not much in the way of decreasing kinetic energy of these highly charged, high velocity mass particles from solar emissions, so it's hardly radiation pressure alone that actually interacts with whatever we send there. Solar sails being no exception. But as they're meant to be extremely light and thin, I imagine most of such proton emissions would just push through them, with not much matter in their way to decrease their kinetic potential, and would slowly decay the sail's fabric. So here's my question:
With current materials used for solar sails, how fast would proton flux decay them and lower their performance, if used in regions outside of Van Allen belt? What is their life expectancy, and does this mean they wouldn't be suitable for long duration missions, say as means to regain some of the velocity of Aldrin Cyclers as it would be lost during taxiing?
From this question on How much would a solar sail's usefulness be reduced by a perforation? and its answer, we know that the expected performance is directly proportional to the area ratio of damage it would sustain. Obviously, this proton decay would also be relative to total proton flux hitting it, its density depending on the distance to the source of emissions. But as far as I understand it, it should be directly proportional to solar sail's expected performance (total insolation), and also a function of time, so there should be some way to infer that regardless of where in the outer space it would be used. Additionally, would this decay rate be any different above and below the solar equator, where I expect proton emissions from the Sun are less frequent?