Ion and electron detector for use in an ICR spectrometer
OwnerJames C. Administrator of the National Aeronautics and Space Administration, with respect to an invention of Fletcher, Wesley T. Huntressinventors
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Abstract
A detector for detecting ions and/or electrons present in a resonance cell of an ICR spectrometer is disclosed. The detector which operates on the Q-meter principle is driven by an external rf oscillator capable of providing rf frequencies up to about 15MHz at an adjustable low rf signal level, e.g., below 20mV. The detector is connected across the resonance of the cell to detect ions by detecting their cyclotron frequency. Electrons are detectable by connecting the detector across the cell's trapping plates and thereby detect the electrons' trapping motion, the frequency of which is in the megahertz range.
Claims18
A detector for use in an ion cyclotron resonance (ICR) spectrometer of the type including a resonance cell through which ions move, the cell including first and second parallel resonance plates spaced apart along a first axis, and first and second parallel trapping plates, spaced apart along a second axis perpendicular to said first axis, said spectrometer including means for applying a magnetic field in the direction of said second axis, and means for applying a preselected potential between each of said trapping plates and a reference potential, the detector comprising:
- a coil;
- means connecting said coil substantially across said first and second resonance plates, the latter defining a capacitive element which together with said coil form a tuned circuit;
- an external radio frequency (rf) oscillator adapted to provide signals at frequencies up to the megahertz range, at relatively low adjustable (rf) voltage levels which are independent of the signals' frequencies;
- injecting means for connecting said oscillator to said tuned circuit to inject signals at a selected level and frequency from said oscillator into said tuned circuit;
- and
- means for sensing the level of the signals across said tuned circuit.
A detector for use with a resonance cell in a cyclotron resonance spectrometer to detect the presence of electrons in the cell, the cell including first and second parallel resonance plates, spaced apart along a first axis, and first and second parallel trapping plates, spaced apart along a second axis perpendicular to said first axis, the detector comprising:
- means for biasing said resonance plates whereby a midpoint between said resonance plates is at ground potential;
- means for applying a negative dc bias potential to each of said trapping plates with respect to ground;
- a coil;
- means for connecting said first and second trapping plates substantially across said coil to form a tuned circuit therewith, with said trapping plates defining a capacitive element;
- an oscillator for providing (rf) signals in the megahertz frequency range at selectable signal levels;
- means for connecting said oscillator to said tuned circuit to inject therein said signals at a selected low (rf) voltage level and at a frequency definable as f.sub.e, where f.sub.e in megahertz is substantially equal to (5.3/d) (V.sub.T).sup.1/2, where d is the spacing between said trapping plates and the spacing between said resonance plates in inches, and V.sub.T is the negative bias potential with respect to ground;
- and
- sensing means coupled to said tuned circuit, for sensing the signal level across said circuit, the signal level dropping appreciably when said oscillator provides signals at said frequency f.sub.e and electrons are present in said cell.
An arrangement for detecting the presence of charged particles in a quadrupolar field, the arrangement comprising:
- first means for establishing a quadrupolar field including first and second elements, which are at a first negative dc potential with respect to a reference dc potential definable as ground, and which are spaced apart along a firxt axis, and third and fourth elements which are at a second dc potential with respect to ground and which are spaced apart along a second axis perpendicular to said first axis;
- a coil;
- means for connecting either said first and second elements or said third and fourth elements substantially across said coil to form a tuned circuit therewith;
- an oscillator for providing (rf) frequency signals at frequencies up to the megahertz range at selectable signal levels;
- means for connecting said oscillator to said tuned circuit to inject therein said signals at a selected frequency and low (rf) voltage level, the selected frequency being a function of the type of charged particles to be detected, and the spacings of said first and second elements along said first axis, and the third and fourth elements along said second axis;
- and
- sensing means coupled to said tuned circuit for detecting the signal level across said circuit.
Dependencies are inferred from the claim text.