Report from KEK (High gradient study results from Nextef)

Most up-to-date high gradient test of the CLIC prototype structures as of September 2011 is described in this report. The "T24" undamped structure showed fast processing time, still-decreasing breakdown rate and its breakdown rate was estimated to be as low as the CLIC requirement. The "TD24" damped structure showed not so excellent high gradient performance as undamped "T24" but the characteristics was much improved than the damped "TD18" structure with higher magnetic field. Further R&D is needed and we present some of the present efforts at KEK.