Mass Spectrometer

The mass spectrometer is an instrument which can measure the masses and relative concentrations of atoms and molecules. It makes use of the basic magnetic force on a moving charged particle.

Circular Path from Magnetic Field

If a charge moves into a magnetic field with direction perpendicular to the field, it will follow a circular path. The magnetic force, being perpendicular to the velocity, provides the centripetal force.

Velocity Selector

A velocity selector is used with mass spectrometers to select only charged particles with a specific velocity for analysis. It makes use of a geometry where opposing electric and magnetic forces match for a specific particle speed. It therefore lets through undeflected only those particles with the selected velocity.

Applications of Mass Spectrometers

Mass spectrometers are sensitive detectors of isotopes based on their masses. They are used in carbon dating and other radioactive dating processes. The combination of a mass spectrometer and a gas chromatograph makes a powerful tool for the detection of trace quantities of contaminants or toxins. A number of satellites and spacecraft have mass spectrometers for the identification of the small numbers of particles intercepted in space. For example, the SOHO satellite uses a mass spectrometer to analyze the solar wind.

Mass spectrometers are used for the analysis of residual gases in high vacuum systems.

Display from residual gas analyzer 残余气体分析仪显示 Isotopic abundances of krypton 氪的同位素丰度

Magnetohydrodynamics

A magnetohydrodynamic generator has been described as a magnet on the tail of a jet engine. A super-hot plasma is created, ionizing the atoms of the fuel mixture. The magnetic field deflects positive and negative charges in different directions. Collecting plates for the charges provide a DC voltage.

Magnetohydrodynamics as an electricity generation process holds the possibility of very efficient fuel utilization because the extremely high temperatures at which it operates correlate to a high Carnot efficiency. Its practical application has been slow in coming because of a number of problems, including a high rate of damage to the combustion chamber by the high velocity particles.