Abstract Prime Candidate Alloy (PCA) for the near term fusion reactor is irradiated with dual ions to examine the microstructural changes under high helium production rate. Cavity density is found to increase with increasing He/dpa ratio. Few cavities are observed in the specimens irradiated with heavy ions only. He/dpa ratio does not change cavity diameter significantly. It is also found that helium has strong effects on the radiation induced precipitate fomation.