R&D activities on RF contacts for the ITER ion cyclotron resonance heating launcher

Abstract

International audienceEmbedded RF contacts are integrated within the ITER ICRH launcher to allow assembling, sliding and to lower the thermo-mechanical stress. They have to withstand a peak RF current up to 2.5 kA at 55 MHz in steady-state conditions, in the vacuum environment of themachine.The contacts have to sustain a temperature up to 250°Cduring several days in baking operations and have to be reliable during the whole life of the launcher without degradation. The RF contacts are critical components for the launcher performance and intensive R&D is therefore required, since no RF contactshave so far been qualified at these specifications. In order to test and validate the anticipated RF contacts in operational conditions, CEA has prepared a test platform consisting of a steady-state vacuum pumped RF resonator. In collaboration with ITER Organization and the CYCLE consortium (CYclotronCLuster for Europe), an R&D program has been conducted to develop RF contacts that meet the ITER ICRH launcher specifications. A design proposed by CYCLE consortium, using brazed lamellas supported by a spring to improve thermal exchange efficiency while guaranteeing high contact force, was tested successfully in the T-resonator up to 1.7 kA during 1200 s, but failed for larger current values due to a degradation of the contacts. Details concerning the manufacturing of the brazed contacts on its titanium holder, the RF tests results performed on the resonator and the non-destructive tests analysis of the contacts are given in this paper

Characterizations of thermal stability and electrical performance of Au-Ni coating on CuCrZr substrate for high vacuum radio-frequency contact application

“…Electrical contacts that operate under alternating current (AC), e.g., radio-frequency (RF) contacts, are commonly employed on large-scale scientific research devices in several fields such as high-energy physics and nuclear fusion [1,2]. Electrical contacts employed on accelerators or nuclear-fusion-related research devices differ from general commercial electrical contacts mainly in terms of the specific working conditions: electrical contacts operate under conditions of long periods of high-temperature (250 °C) baking to attain ultrahigh vacuum and are subjected to high heat loads owing to ohmic losses during operation.…”

“…Sliding in high vacuum makes selection of the material of the RF contact more challenging since severe wear can occur on the RF contact. An RF contact that can be operated safely for 1200 s with a maximum current load of 2 kA under high-vacuum and high-temperature conditions is presently under development at the Commissariat à l'Énergie Atomique (CEA) in France for the International Thermonuclear Experimental Reactor (ITER) project, which is the world's largest fusion experimental facility [1]. The first prototype of an RF contact whose louvers were made of Cu with a 4 µm Au coating was tested.…”

Study of thermal ageing effects on Rh coating's mechanical performance upon CuCrZr substrate through modeling and experimental methods

“…On the Large Hadron Collider (LHC) accelerator, Rh coatings on Cu and CuBe (C17410) were evaluated based on their electrical performance for sliding RF contact application [8][9][10]. On ITER tokamak, RF sliding contacts [11][12][13] are being developed on which Rh is expected to be electroplated on the CuCrZr substrate to improve its wear and corrosion resistance.…”

Multifunctional tribometer development and performance study of CuCrZr-316L material pair for ITER application

“…In order to ease the ICRH antennas' assembly, enhance the maintainability, realize radial sliding and release thermal stresses, few flexible electrical contacts (RF contacts) will be installed on the RF transmission lines [3 5]. During operation, these RF contacts will be working under high temperature (>130 C) and high vacuum (<10 À3 Pa), and one of the RF contacts is designed to be operated under the current of 2 kA with current density of 4.8 kA/m [2,6]. In addition, wear phe nomenon will occur on the RF contact louvers during operation.…”

“…In the lifetime of ITER, the machine components will be baked for outgassing at 250 C during an estimated time of 850 days. Copper is an interesting material with high electrical conductivity, however, creeping issues make it unsuitable as contact louver material [6]. On the Large Hadron Collider (LHC) RF contact which works under the nominal beam current of 0.6A, CuBe was applied to manufacture the contact fingers [7,8].…”