A large Bradbury Nielsen ion gate with flexible wire spacing based on photo-etched stainless steel grids and its characterization applying symmetric and asymmetric potentials

Bradbury Nielsen gates are well known devices used to switch ion beams and are typically applied in mass or mobility spectrometers for separating beam constituents by their different flight or drift times. A Bradbury Nielsen gate consists of two interleaved sets of electrodes. If two voltages of the same amplitude but opposite polarity are applied the gate is closed, and for identical (zero) potential the gate is open. Whereas former realizations of the device employ actual wires resulting in difficulties with winding, fixing and tensioning them, our approach is to use two grids photo-etched from a metallic foil. This design allows for simplified construction of gates covering large beam sizes up to at least 900 mm2 with variable wire spacing down to 250 μm. By changing the grids the wire spacing can be varied easily. A gate of this design was installed and systematically tested at TRIUMF's ion trap facility, TITAN, for use with radioactive beams to separate ions with different mass-to-charge ratios by their time-of-flight.

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► We present a new and simple design of a UHV compatible Bradbury Nielsen ion gate.
► The gate design is based on two photo-etched wire grids allowing exible wire spacing and large area.
► Such a Bradbury Nielsen gate was systematically tested at the TITAN experimental facility and has been used during the Penning trap mass measurement of radioactive Rb.
► An asymmetric voltage applied to the gate results in a change of the ions’ time-focus. Based on this, the time resolution of the gate can be improved at the cost of energy spread.