Next generation nano pattern transfer processing require manufacturing of cylindrical nano stampers with the length of up to 1 meter. KERI has been developing proprietary nano patterning technology based on treatment of magnetically levitated large cylindrical substrate. Prior to patterning, the cylinder should be superfinished to R_a and R_max within few nanometers. An ion beam at glancing angle and cluster ion beam at normal incidence are capable to reach the goal. However, conventional sources are rather ineffective, complex and difficult to scale up. To address the problem, we applied a novel Plasma Immersion Ion Milling (PI²M) process for smoothing of large cylindrical workpieces. In the method, the vacuum chamber is filled with high-density uniform argon plasma produces by an interior antenna ICP source. The cylindrical substrate is placed at the chamber axis and covered with a special multislot 2-electrode ion extracting house. The slots are arranged along cylindrical workpiece so that extracting ions impinge the surface at a predetermined angle. Thus high-rate uniform smoothing of a cylindrical surface is achieved by simultaneous bombardment of the surface by a number of ribbon ion beams at a desired angle (patent pending). PI²M experiments were carried out on the developed multiplex ICP tool NN500 intended for etch/deposition/smoothing of a cylindrical workpiece of up to 500-mm length. Details of the system design and dependence of treatment results on process parameters are presented and discussed in the paper.