Can I simplify AC calculating by using one period data repeatedly?

I'm trying to calculate an alternating electric field and simulate how charged particles move in it. Through my calculating, I find that it takes much time to calculate the AEC(alternating electric field)(about 40 mins for 200ns's calaulating), but relatively few to track particles(within 1 mins). So I have an idea that since the AEC is quite the same in every period, if I can use the data repeatedly, it will help me save a lot of calculating resources. BUT I don't know how to haddle it, I'll be grateful if anyone can help me with it. Or there will be other better methods to solve it, I expect them too.!