ITER ECRH Upper Launcher diamond window – Qualification and testing of a Protection Important Component

Abstract

The diamond window is part of the ex-vessel waveguide system of the ITER ECRH Upper Launcher and consists of an ultra-low loss CVD diamond disk mounted in a system of metallic parts. On the one hand the window has to fulfil adequate transmission capability for high power mm-waves and on the other hand it serves, together with an isolation valve, as primary vacuum boundary of the ITER vacuum vessel, and has the function of tritium confinement. Therefore it is classified as Protection Important Component and high requirements for quality and safety apply. The window assembly cannot be entirely covered by codes and standards and thus an ad-hoc qualification program is required, including prototyping activities. The mm-wave transmission capability of the window, which is mainly defined by the dielectric loss of the diamond disk, has to be demonstrated as well as its structural integrity. For previous and current window prototypes, diamond disks with low dielectric losses have been chosen with a diameter of 80 mm and a thickness of 1.11 mm. This thickness satisfies the resonance condition (d = n*eff/2) for the 170 GHz beam, ensuring a high transmission, but it also needs to be validated with respect to the mechanical loads, especially the expected pressure loads. Investigations on the flexural strength of diamond disks (D = 30 mm, d = 1.11 mm) have been performed using a ring-onring setup and the results lead to an estimation of the failure behavior. In addition, pressure tests of a mock-up consisting of a diamond disk (D = 80 mm, d = 1.11 mm) brazed to a copper cuff are under examination. The dedicated test program includes cyclic tests at lower pressures and high pressure tests (up to 2 bar) allowing a simulation of the expected events. This paper will give an overview on the qualification activities for the ITER torus window with a focus on the qualification of the diamond disk and with respect to its mechanical properties. Respective parts of the test program, which need F4E and IO review and approval, will be described and first results will be presented.

Pressure tests supporting the qualification of the ITER EC H&CD upper launcher diamond window

“…The growth side of the diamond disks has been under tensile stress. The determined flexural strength values have differed between 295-333 MPa (314 MPa on average) [9]. The boundary conditions of these ring-on-ring tests are not completely comparable to the real conditions (disk geometry and its integration in the window assembly).…”

Effect of Laser Ablation on Microwave Attenuation Properties of Diamond Films

“…However, in general, the loss tangent of pure diamond films is only in the range of 10 −3 –10 −5 [17,18,19,20]. That means pure diamond films are a microwave transparent material, usually used in high-power microwave windows [21].…”