Here's an example where we generate 3 replications of a time series of length 5:
replicate(3, arima.sim(n = 5, list(ar = 0.5)))
#> [,1] [,2] [,3]
#> [1,] 0.3317528 0.45128945 -0.7448801
#> [2,] -1.0320203 -0.01145362 -1.0386216
#> [3,] -0.7867396 1.13977269 -0.2131131
#> [4,] -0.2833714 2.87683788 -0.6263452
#> [5,] 0.2448601 0.04664901 -0.5471205
Created on 2020-02-26 by the reprex package (v0.3.0)