OLMAT

OLMAT (Optimization of Liquid Metal Advanced Targets) is a High Heat Flux (HHF) device to expose different types of armor to heat and particle loads similar to those expected in a future fusion nuclear reactor like DEMO.

Figure 1. Sketch of the OLMAT facility.

Irradiation


OLMAT can irradiate samples with two types of beams, see Figure 1.

NBI
A neutral beam injector (NBI) from the stellarator TJ-II is used to irradiate samples in a separate diagnosed chamber under high vacuum conditions. It has a maximum beam power of 705 kW (with 33% ions), H+ energy: 30-40 keV; H+ flux: 1.45·1022 1/m2s. In this way, heat fluxes relevant for steady state and slow transients,  8±2 to 40±15 MW/m2, in pulses of up to 180 ms every 30-120s (depending of power) are achieved. One of its main advantages is the size of the beam, 20 cm diameter, which allows the irradiation of large targets or multiple small samples. A cold plasma is developed in front of the target which has been used for plasma physics studies: Te: ~2eV; ne: 1018 m-3.

CW laser
The high-energy CW laser is a unique addition. It allows the simulation of continuous heat fluxes of 10 MW/m2 in a tens mm2 area, steady state at DEMO, and smaller areas, few mm2, for slow transients (tens MW/m2). At the same time, in ms pulsed mode, it can perfectly simulate fast, powerful transients like disruptions of 1 GW/m2 in a few mm2 area. It can also simulate fast, mild transients like mitigated ELMs (tens MW/m2 of up to 2 kHz frequency) in very large areas, hundreds mm2.

Diagnostics
Additionally, the facility is equipped with a wide range of diagnostics for analyzing the thermal response of the targets (thermocouples, Infrared pyrometry and IR thermography with 1 ms resolution) and monitoring atomic/plasma physics phenomena (fast camera, optical spectroscopy and langmuir probes). In this way, OLMAT combines pure technological material research with the investigation of physical phenomena such as vapor shielding, thermal sputtering, crater formation during laser ablation, formation and characterization of plasma plumes and the detection of impurities in front of the studied targets.

Samples
Solid samples, or liquid metal based ones (like CPS, Capillary Porous System) may be tested at OLMAT. In fact, OLMAT team is a world reference in liquid metal studies, and the facility was specifically designed for its use. Samples or targets may be exposed in three ways at OLMAT

  1. Manipulator: sample holder with heating, biasing, translation, and rotation capabilities as can be seen in Figure 2. CPS targets, or a group of smaller samples, of up to 70 mm diameter may be exposed. Heating up to 550 ºC is possible by a resistance heater allowing its use for liquid metal studies.
  2. Actively-cooled sample holder: fixed sample holder at the refrigerated beam dump as can be seen in Figure 1. It allows the exposure of a great number of samples at the same time as the whole, 20 cm diameter, NBI beam is taken advantage of for thermal fatigue studies. Due to the bigaussian profile of the NBI beam, samples of the same material may be exposed at different power densities.
  3. Free: the wide NBI beam allows large mock-up exposure when inserted at the bottom with their own refrigeration.
Figure 2. OLMAT manipulator with a CPS consisting of liquid Sn embedded on a 3D-print porous W substrate.

Publications

  1. D. Alegre, E. Oyarzabal, D. Tafalla, M. Liniers, A. Soleto, F.L. Tabarés, Design and Testing of Advanced Liquid Metal Targets for DEMO Divertor: The OLMAT Project, J Fusion Energy 39 (2020) 411–420.
  2. F.L. Tabarés, E. Oyarzabal, D. Alegre, D. Tafalla, K.J. McCarthy, A. de Castro, E. Ascasíbar, A. Soleto, I. Fernández-Berceruelo, R. Carrasco, F. Martin, J.A. Sebastián, J. Gómez-Manchón, A. Pereira, A. de la Peña, Commissioning and first results of the OLMAT facility, Fusion Engineering and Design 187 (2023) 113373.
  3. E. Oyarzabal, F.L. Tabarés, M. Liniers, D. Alegre, D. Tafalla, K.J. McCarthy, A. de Castro, T.W. Morgan, J.G.A. Scholte, M. Iafrati, E. de la Cal, I. Voldimer, E. Ascasíbar, A. Soleto, Comparative study of different Sn wetted W CPSs exposed to NBI fluxes in the OLMAT facility, Fusion Engineering and Design 190 (2023) 113711.
  4. A. de Castro, E. Oyarzábal, D. Alegre, D. Tafalla, M. González, K.J. McCarthy, J.G.A. Scholte, T.W. Morgan, F.L. Tabarés, the OLMAT team, Physics and Technology Research for Liquid-Metal Divertor Development, Focused on a Tin-Capillary Porous System Solution, at the OLMAT High Heat-Flux Facility, J Fusion Energ 42 (2023) 45.
  5. D. Alegre, D. Tafalla, A. De Castro, M. González, J.G. Manchón, F.L. Tabarés, T. Hernández, M. Wirtz, J.W. Coenen, Y. Mao, E. Oyarzábal, First thermal fatigue studies of tungsten armor for DEMO and ITER at the OLMAT High Heat Flux facility, Nuclear Materials and Energy 38 (2024) 101615.