High heat flux tests of the WENDELSTEIN 7-X pre-series target elements

Abstract

The high heat flux (HHF) testing of WENDELSTEIN 7-X pre-series target elements is an indispensable step in the qualification of the manufacturing process. A set of 20 full scale pre-series elements was manufactured by PLANSEE SE to validate the materials and manufacturing technologies prior to the start of the series production.The HHF tests were performed in the ion beam test facility GLADIS. All actively water-cooled elements were tested for about 100 cycles at 10 MW/m 2 (10-15 s pulse duration). Several elements were loaded with even higher cycle numbers (up to 1000) and heat loads up to 24 MW/m 2 . Hot spots were, observed at the edges of several tiles during the HHF tests indicating local bonding problems of the CFC.The thermo-mechanical behaviour under HHF loading has been evaluated and compared to the FEM predictions. The measured temperatures and strains confirm the chosen FEM approach. This allows a component optimisation to achieve a successful series production of the W7-X divertor target elements.

Cyclic heat load testing of improved CFC/Cu bonding for the W 7-X divertor targets

“…More details of the loading conditions in GLADIS are described in the reference [8]. A pulse length of 10 s for cycling was applied because the target achieved the thermal equilibrium after 7 s of loading.…”

“…The target design is based on flat tiles made of CFC NB31 [2][3][4] as plasma facing material bonded by Active Metal Casting (AMC) [5] onto a water-cooled CuCrZr structure [6]. The excellent heat removal capability was demonstrated in previous test campaigns of more than 30 full-scale pre-series elements [7,8]. No large detachment or loss of CFC tiles occurred during previous cyclic loading tests performed in the neutral beam facility GLADIS [9], but growing local degradation of bonding at the free edges of several CFC tiles was observed.…”

Finite element based design optimization of WENDELSTEIN 7-X divertor components under high heat flux loading

“…The thermal loading is due to a surface heat flux acting continuously for 15 s on the CFC plasma facing surface ranging from a power density of 10.5 MW/m² at the half length of the component down to 1 MW/m² at the free ends, compare [3], and is subsequently followed by a cooling downphase. Surface film conditions are applied at the surface of the cooling channel with a film coefficient ranging from 75,000 W/(m²K) at a surface temperature of 60 °C to 110,000 W/(m²K) at 260 °C [4].…”

“…2. An optimization of the reference design is required due to the relatively high failure rate during high heat flux testing [3] for 20 pre-series target elements that make use of the reference design. Beside the other design parameters (compare Section 2.1) the interlayer design and material characteristics introduce additional design variables that can be adjusted correspondingly.…”

Mechanical analysis of the joint between Wendelstein 7-X target elements and the divertor frame structure

“…The HHF areas thus consist of 50 to 60mm wide target elements hydraulically and mechanically connected to each other in modules. The behavior of the attachment system of the target elements under loading has been calculated and experimentally studied prior in the HHF test facility GLADIS [3], the work presented here sets the focus to the details of the attachment system, the disc spring stack that interfaces the target element with the support frame.…”