Radiofrequency and Mechanical Tests of Silver Coated CuCrZr Contacts for the ITER Ion Cyclotron Antenna

TL;DR

This study evaluates silver-coated CuCrZr RF contacts for ITER's ion cyclotron antenna, demonstrating high current capacity, durability under RF conditions, and wear characteristics through mechanical and RF testing.

Contribution

It provides new insights into the material performance and durability of silver-coated CuCrZr contacts under ITER-relevant RF and mechanical conditions.

Findings

Peak currents of 1.2-1.3 kA achieved without damage

Severe damage observed at 1.9 kA in 300s pulse

Silver coating wears off after ~100 cycles

Abstract

The ITER Ion Cyclotron Resonance Heating (ICRH) system is designed to couple to the plasma 20 MW of RF power from two antennas in the 40-55 MHz frequency range during long pulses of up to 3600 s and under various plasma conditions with Edge Localized Modes. Radio-Frequency (RF) contacts are integrated within the ITER ICRH launcher in order to ensure the RF current continuity and ease the mechanical assembly by allowing the free thermal expansion of the Removable Vacuum Transmission Line coaxial conductors during RF operations or during 250{\textdegree}C baking phases. A material study has been carried out to determine which materials and associated coatings are relevant for RF contacts application in ITER. In parallel, RF tests have been performed with a new prototype of Multi-Contact (r) LA-CUT/0,25/0 contacts made of silver-coated CuCrZr louvers. During these tests on a RF vacuum resonator, currents between 1.2 kA and 1.3 kA peak have been reached a few tens of times in steady-state conditions without any visible damage on the louvers. A final 62MHz pulse ending in a 300s flat top at 1.9kA resulted in severe damage to the contact. In addition, a test bed which performs sliding test cycles has been built in order to reproduce the wear of the contact prototype after 30 000 sliding cycles on a 3 mm stroke at 175{\textdegree}C under vacuum. The silver coating of the louvers is removed after approximately a hundred cycles whilst, to the contrary, damage to the CuCrZr louvers is relatively low.