Gridless ion mirrors with smooth fields

The ion mirror of any preceding claim, further comprising an entrance lens, the entrance lens optionally comprising one of the group:

• (i) an accelerating lens;
• (ii) a retarding lens;
• (iii) a multistage lens;
• (iv) a dual lens formed on both ends of an elongated lens electrode;
• and (v) an immersion lens.

An ion mirror for reflecting ions along an axis (X) comprising:

• a first axial segment, within which the turning points of the ions are located in use, and a second axial segment, wherein the first and second axial segments are adjacent each other in a direction along said axis (X);
• and
• voltage supplies configured to apply electric potentials to electrodes of the first axial segment for generating a first linear electric field of a first strength within the first axial segment, and to apply electric potentials to electrodes of the second axial segment for generating a second linear electric field of a second strength within the second axial segment;
• wherein the voltage supplies and electrodes are configured such that the second linear electric field penetrates into the first axial segment so that the axial electric field in an axial portion of the first axial segment is non-linear where the turning points of the ions are located, and such that an axial electric field strength E0 at a mean ion turning point within the first axial segment is related to the strength E2 of the first linear electric field by the relationship 0.01≤(E0−E2)/E2≤0.1.

An ion mirror for reflecting ions along an axis (X) comprising:

• an entrance end for receiving ions;
• a first axial segment (E2), within which the turning points of the ions are located in use, and a second axial segment (E3) adjacent the first axial segment in a direction along said axis (X);
• and
• voltage supplies for applying different voltages to different electrodes of the ion mirror for generating electric fields that perform said reflecting of the ions;
• wherein at least the first axial segment is defined between inter-segment electrodes that are spaced apart along said axis, each of said inter-segment electrodes being an electrode to which one of said voltage supplies is connected to, wherein the first axial segment comprises a plurality of electrodes spaced apart from each other along said axis (X) and arranged between the inter-segment electrodes, wherein the plurality of electrodes are electrically connected to the inter-segment electrodes and interconnected with each other by electronic circuitry such that when the voltage supplies apply voltages to the inter-segment electrodes, this causes the plurality of electrodes to be maintained at different potentials so as to generate said electric fields;
• wherein said plurality of electrodes define windows arranged in a plane (Y-Z plane) orthogonal to said axis (X) through which the ions travel in use, wherein the windows have a minimum dimension H in said plane (Y-Z plane);
• and
• wherein the mirror is configured such that the distance (X3) along said axis from a mean ion turning point within the first axial segment to the inter-segment electrode nearer to an entrance end of the mirror is selected from the group of:
• ≤2H;
• ≤1.5H;
• ≤1H;
• ≤0.5H;
• in the range 0.2H≤X3≤1.7H;
• or in the range 0.1H≤X3≤1H.

A mass spectrometer comprising:

• at least one ion mirror as claimed in any preceding claim;
• an ion source for providing ions into the ion mirror;
• and
• an ion detector.

A method of mass spectrometry comprising:

• providing an ion mirror or spectrometer as claimed in any preceding claim;
• supplying ions into said ion mirror;
• reflecting ions at ion turning points within said first axial segment (E2);
• and
• detecting the ions.

Within time-of-flight, or multi-reflecting time-of-flight, or isochronous electrostatic trap mass spectrometers, an isochronously reflecting gridless ion mirror, comprising:

• (a) a set of parallel conductive electrodes having or forming mutually aligned windows oriented orthogonal to the ion reflection axis X to form a two-dimensional electrostatic field in the XY-plane within Cartesian XYZ coordinates;
• the characteristic smallest transverse size H of said windows is defined as either the window diameter for ring electrodes, or the smaller Y-dimension for rectangular windows;
• (b) electrodes are grouped into at least two segments denoted as E2 and E3;
• wherein segments E2 and E3 are adjacent and are separated by a “knot” electrode with an open window, not having mesh;
• wherein distinct potentials are applied to the “knot” electrodes on segment boundaries;
• and wherein electrodes of each segment are interconnected with a uniform resistive chain to form a linear potential distribution on electrodes within segments with corresponding potential gradients E2 and E3 on electrodes;
• wherein segment E3 is located upstream of E2 segment, i.e. closer to the mirror exit;
• (c) potentials U2 and U3, applied to the “knot” electrodes surrounding E2 segment, are chosen to contain mean potential U0, also defining the X-axis origin X=0:
• U2>U0>U3, U0=K0/q, where K0 is the mean ion energy and q is the ion charge, this way ensuring that the mean ion turning point is contained within the E2 segment;
• (d) wherein said applied potentials are chosen to provide non equal potential gradients in the segment E2 and E3 to form a non uniform axial field at segments' boundary;
• (e) at least in the E2 segment, the electrodes thickness and spacing in the X-direction are uniform and spatial period P of electrodes is P≤H/5;
• (f) wherein to provide for advanced isochronous and spatially focusing properties at ion reflection, the mirror satisfies the following set of conditions:
• (i) field strength E2 is 4.3U0/D≤E2≤5U0/D, where D is the distance from mean ion turning point to a first order energy focusing time focal point;
• (ii) the distance X3 (in the positive X-direction from the ion turning point to the exit from the ion mirror) from the mean ion turning point (X=0;
• U=U0) to the nearest “knot” electrode plane is 0.2H≤X3≤1.7H in case of planar mirror symmetry and is 0.1H≤X3≤1H in case of cylindrical mirror symmetry;
• (iii) the ratio of field strengths E3/E2 is linked to the X3 distance by the relation E3/E2=A*[0.75+0.05*exp((4X3/H)−1)] for ion mirror with planar symmetry, where 0.5≤A≤2 to provide for a controlled non-linearity of axial field distribution, demonstrated to enhance the energy acceptance of the ion mirror.

An ion mirror for reflecting ions in an X-direction, comprising:

• (a) two parallel printed circuit boards, aligned in the XZ plane and spaced in the orthogonal Y direction by a distance H;
• said boards are formed of epoxy, ceramic, or quartz substrate;
• (b) wherein said printed circuit boards have periodic structure of conductive stripes aligned with the Z axis with a period P being less or equal than H/5;
• (c) wherein said stripes are interconnected by uniform resistive chains and wherein individual potentials are applied to selected “knot” conductive stripes, forming boundaries and separating at least three segments of uniform potential gradient;
• wherein said potential gradients are different between said segments;
• (d) wherein the X-length of an intermediate segment is less than 2H and wherein potentials U2 and U3 on the boundaries of this intermediate segment are chosen to contain the mean ion specific energy U0:
• U2>U0>U3;
• and
• (e) wherein said printed circuit board has an antistatic feature formed either with periodic structure of parallel fine conductive lines between said conductive stripes and/or an antistatic coating with resistance in the range from 1 GOhm/square to 10 TOhm/square.

A multi-reflecting time-of-flight mass spectrometer with at least two ion mirrors comprising:

• (a) at least two segments of uniform two-dimensional electric field in the XY-plane, formed within channels of equal height, merged and open to each other for mutual field penetration in the X-direction of ion reflection;
• (b) wherein the ion energy, said segments dimensions and fields are chosen to provide for locating the ion turning point within said penetrating field and distant from the field boundary by less than N calibers of smallest channel transverse dimension H;
• and
• (c) wherein N is one of the group:
• (i) N≤2;
• (ii) N≤1.5;
• (iii) N≤1;
• and (iv) N≤0.5.

A method of forming electrostatic field of ion mirror comprising the following steps:

• (a) forming open and adjacent segments with a uniform electrostatic field;
• (b) forming different field strength in said segments to produce mutual field penetration and curvature of equipotential lines in transition regions between segments;
• (c) arranging ion energy and field strength and lengths so that the ion turning point appears in a segment E2, and wherein for the purpose of high quality isochronicity and wide spatial acceptance of said reflecting field, the field penetration of at least one adjacent segment is arranged for the field E0 at ion reflecting point deviating from the field strength E2 in one range of the group:
• (i) 0.01≤(E0−E2)/E2≤0.1;
• (ii) 0.015≤(E0−E2)/E2≤0.03.