relativity has fuck all to do with it.
as the partcile gets faster, mass and spped increase.
there fore a greater force is required to hold it in circular path (f=mv^2/r) hence requiring increased B, and as v increases (f=bqv)
mv^2/r=bqv
mv/r=bq
b=mv/qr
q and r are constant, and as m and v...