Inficon HAPSITE ER, Руководство по эксплуатации

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INFICON Introduction | 7
074-471-P1E HAPSITE ER Operating Manual 25 / 436
The inlet flow from the membrane isolation valve is brought directly to the ionizer.
Within the ionizer, the compound introduced from the inlet flow is subjected to a
bombardment of electrons which are boiled off the hot filament. Collisions with the
energetic electrons remove one electron from some of the gas molecules, leaving
them with a net positive charge. This process is termed ionization. Other gas
molecules are fractured into smaller molecules, some of which are also ionized. The
remaining stream of gas is pumped away by the vacuum pump system.
The ionized molecules, or ions, are driven from the ionizer toward the mass selector
by the different voltages on the ion volume and focusing plates. As the ions move
through the orifices in these plates, the ions are formed into a nearly parallel beam of
mixed ions of nearly the same energy.
The mass selector (or mass filter) is a quadrupole analyzer. The quadrupole analyzer
is comprised of four parallel rods, mounted with precise alignment and spacing.
Opposing rods are electrically connected together. The two pairs of rods are
connected to a radio frequency (RF) voltage 180° out of phase with each other. In
addition, the two pairs of rods have a direct current (DC) voltage applied to them;
positive on one pair, negative on the other.
The ion beam is directed down the center of the array of rods. At any specific
combination of RF and DC fields, some ions are light enough to oscillate harmonically
with the RF field. This oscillation causes them to increase in energy and in speed until
the ions impact one of the rods and are neutralized. The DC field acts upon the
heavier ions resulting in their movement from the center towards the rods. Once on
the rod, the heavier ion is neutralized. At a specific combination of RF and DC fields,
ions of a specific mass will be able to transit the rod structure and emerge at the exit
where detection occurs.
When the ions emerge from the mass selector, the ions are directed to the detector.
The active element of the detector is an electron multiplier. The electron multiplier
responds to the arrival of each individual ion with a cascade of electrons, each of
which generates more electrons. The result is a small burst of electrical current in
response to each ion emerging from the mass selector. The signal from the electron
multiplier is connected to the electronic amplifier and data-handling system outside the
vacuum.