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| Item type: | Article | ||||
|---|---|---|---|---|---|
| Journal or Publication Title: | Review of Scientific Instruments | ||||
| Volume: | 71 | ||||
| Number of Issue or Book Chapter: | 12 | ||||
| Page Range: | pp. 4421-4430 | ||||
| Date: | 2000 | ||||
| Additional Information (public): | CAN 134:138695 73-8 Optical, Electron, and Mass Spectroscopy and Other Related Properties | ||||
| Institutions: | Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Chemistry III - Physical Chemistry (Molecular Spectroscopy and Photochemistry) > Prof. Dr. Bernhard Dick | ||||
| Identification Number: |
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| Keywords: | Particle acceleration (ion, optimization of a one-dimensional time-of-flight mass spectrometer); Ion accelerators; Optimization; Simulation and Modeling; Time-of-flight mass spectrometers (optimization of a one-dimensional time-of-flight mass spectrometer); optimization time flight mass spectrometer ion acceleration | ||||
| Dewey Decimal Classification: | 500 Science > 540 Chemistry & allied sciences | ||||
| Status: | Published | ||||
| Refereed: | Yes, this version has been refereed | ||||
| Created at the University of Regensburg: | Yes | ||||
| Item ID: | 5541 |
Abstract
Space focusing of a linear time-of-flight mass spectrometer (TOFMS) with an arbitrary no. N of ion acceleration regions, a field free drift tube, and a reflectron is analyzed. A quality function Q(d,u0) is defined as the fractional error in the flight time of an ion with initial position d and initial velocity u0 with respect to an ion with d = 0 and u0 = 0. This quality function has the form ...
Abstract
Space focusing of a linear time-of-flight mass spectrometer (TOFMS) with an arbitrary no. N of ion acceleration regions, a field free drift tube, and a reflectron is analyzed. A quality function Q(d,u0) is defined as the fractional error in the flight time of an ion with initial position d and initial velocity u0 with respect to an ion with d = 0 and u0 = 0. This quality function has the form Q(d,u0)=-u0/f(0)+F(u02-d), where the function f(y) depends on the dimensions and the field strengths chosen for the instrument, and F(y)=f(y)/f(0)-1. The quality function is optimized up to the order k by setting all Taylor coeffs. of F(y) up to and including yk equal to zero and solving this system of equations for the design parameters of the instrument. A linear TOFMS with N acceleration regions can be optimized in this way with respect to N design parameters. An addnl. reflectron will not add another optimizable parameter, i.e., no further Taylor coeff. can be made to vanish. After optimization of the TOFMS with respect to all field strengths including that in the reflectron, the quality function becomes independent of the length of the field free drift tube. Hence, the effect of the reflectron is to make space focusing independent from the drift tube length. The quality function for a fully optimized TOFMS depends only on the no. N of acceleration stages and is, for a given N, identical for the designs with and without a reflectron. However, the design contg. a reflectron has a smaller value of the factor 1/f(0) which dets. the error introduced by the initial velocity distribution of the ions. A space focused TOFMS cannot be further focused with respect to the initial velocity u0, since the 1st term in the Taylor expansion of the quality function in the variable u0 is proportional to the inverse of the total flight time. For a TOFMS with two or more acceleration regions this is the dominant source of error that remains after space focusing. This situation cannot be improved by delayed or pulsed extn. of the ions from the ionization region nor by deceleration of the ions before they enter the field free region.
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