Analysis and improvement for the residual stress of the in-vessel ELM coil in ITER

The paper mainly describes the comparative analysis and study results of the main residual stress on the ELM in-vessel coil outer-jacket (Inconel625) and the inter-conductor (CuCrZr)respectively. The hole drilling method was applied to measure the residual stress whereas the heat-treatment technology was chosen as the way to mitigate the stress on the ELM in-vessel coil. The results showed that the compaction process increased the main residual stress on the ELM in-vessel coil which could be 100% higher. However, the winding process could eliminate by around 20% residual stress of the compacted coil. When the heat-treatment technology was applied on the sample that was compacted and winded, the main residual stress on coil could decrease by about 40%. Additionally, the heat-treatment technology (keeping 550 ℃ for 2 hours and air cooling) did not only decrease the residual stress on coil but also made the residual stress distributed more homogenized. The stress difference between the outer-jacket and the inter-conductor was 27.07 MPa and 15.97 MPa, which had respectively decreased 38.98 MPa and 31.67 MPa when compared with the status after compaction and before winding. (authors)