Multi-reflection mass spectrometer

A method of operating a multi-reflection time of flight mass spectrometer comprising:

• two ion-optical mirrors, each mirror elongated generally along a drift direction away from an ion injection point (a Y direction), each mirror opposing the other in a Z direction, the Z direction being orthogonal to the Y direction, and wherein the two mirrors are tilted such that a separation between the mirrors in the Z direction decreases as a distance along the Y direction increases;
• and
• at least two correction electrodes extending along at least a portion of the Y direction in or adjacent the space between the mirrors;
• and
• wherein:
• each correction electrode has a surface substantially parallel to the Y-Z plane and has a shape such that the surface is separated from one of the mirrors by a distance that varies along the Y direction and in which the correction electrodes are, in use, electrically biased with voltages so as to produce, in at least a portion of the space extending between the opposing mirrors, a combined voltage offset which varies as a function of the distance along the Y direction, wherein the voltages include a first component to correct for an intended aberration arising from the an intended tilt angle of the mirrors and a second component to correct for unintended aberrations arising from a range of perturbations to an ideal time of flight extending from a maximum perturbation to a minimum perturbation, wherein the second component varies between a maximum value and a minimum value;
• and
• the shapes of the at least two correction electrodes are such that some or all the at least two correction electrodes may be energised with the voltages including the first component and the second component, that varies between a maximum value and a minimum value, to generate a range of combined voltage offsets that compensate for a range of time of flight aberrations corresponding to the intended aberration arising from the intended tilt angle of the mirrors and the unintended aberrations arising from the range of perturbations to the ideal time of flight extending from the maximum perturbation to the minimum perturbation;
• wherein
• the method comprises:
• energising the mirrors to provide electric fields to cause ions to follow a zig zag path through the mirrors;
• energising each of the at least two correction electrodes with a voltage including the first component and/or the second component such that the at least two correction electrodes generate a combined voltage offset that compensates for the intended aberration and the aberrations;
• injecting ions from an ion source into the mirrors;
• and
• detecting the ions with an ion detector located at the same end of the mirrors as the ion source.

A method of designing a multi-reflection time of flight mass spectrometer, comprising:

• configuring an ideal arrangement of an ion source, an ion detector and two ion-optical mirrors, each mirror elongated generally along a drift direction away from an ion injection point (a Y direction), each mirror opposing the other in a Z direction, the Z direction being orthogonal to Y, such that ions provided from the ion source enter mirrors at the ion injection point and then follow a zig zag path through the mirrors when the mirrors are energised to provide electric fields;
• configuring at least two correction electrodes extending along at least a portion of the Y direction in or adjacent a space between the mirrors, wherein each correction electrode has a surface substantially parallel to the Y-Z plane and has a shape such that the surface is separated from one of the mirrors by a distance that varies along the Y direction and in which the correction electrodes are, in use, electrically biased with voltages so as to produce, in at least a portion of the space extending between the opposing mirrors, a combined voltage offset which varies as a function of the distance along the Y direction, wherein the voltages include a first component to correct for an intended aberration arising from an intended tilt angle of the mirrors and a second component to correct for unintended aberrations arising from a range of perturbations to an ideal time of flight extending from a maximum perturbation to a minimum perturbation, wherein the second component varies between a maximum value and a minimum value:
• determining maximum and minimum perturbations away from the ideal arrangement of the mirrors, and the resulting maximum and minimum aberrations in time of flight of ions through the mirrors;
• and
• determining the shape of the at least two correction electrodes such that some or all the at least two correction electrodes can be energised with voltages including the first component and the second component, that varies between a maximum value and a minimum value, to generate a range of combined voltage offsets that compensate for a range of time of flight aberrations corresponding to the intended aberration arising from the intended tilt angle of the mirrors and the unintended aberrations arising from the range of perturbations to the ideal time of flight extending from the maximum perturbation to the minimum perturbation.