Electrons are extracted from the selected heated Thoria coated tungsten filament. The filament material ensures that even under high emission a long lifetime is achieved. The focusing ring and nose cone shape ensure that the electrons hit the selected active anode face at the correct spot. By switching between either of the filaments a different anode face may be excited. The standard DAR 400 twin anode source has aluminium and magnesium facets.

The anode internal design creates turbulent water flow conditions, optimised to prevent the aluminium or magnesium surfaces from evaporating and to minimise sample heating via the source. The X-rays generated at the anode surface pass through a thin Aluminium window designed to maintain a partial vacuum barrier between source and sample.

The window allows the source to be differentially pumped and to reduce Bremsstrahlung radiation. The profiled nose cone has been designed to minimise mechanical clashes and allow the DAR 400 to operate as close as possible to the sample, whilst other techniques are in use.