Inficon Transpector XPR 3+ User Manual

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Transpector XPR 3+ Operating Manual
The sensitivity for Transpector XPR 3+ instruments operating in Faraday Cup
mode is typically > 4x10
-7
amps per Torr. The minimum detectable partial
pressures, therefore, can be as small as 1x10
-9
Torr in Faraday Cup mode.
3.4.3.2 The Electron Multiplier (EM) Detector
The Electron Multiplier (EM) acts as an in situ preamplifier for improved sensitivity.
Although there are several different types of EM, their operating principals are the
same. Incoming ions are accelerated into the input of the EM by a high negative
voltage. When an ion strikes the surface of the EM, one or more secondary
electrons are emitted. These electrons are accelerated to a second surface which
is at a more positive potential, where additional electrons are generated.
This process repeats itself until a pulse of electrons emerges from the output of the
EM and is collected on a Faraday Cup. The result is that as many as a million
electrons or more can be produced by each incident ion. The current from a
Faraday detector is positive (for positive ions) while an EM detector puts out a
negative signal.
The ratio of the electron output current to the incident ion current is known as the
EM gain. The gain primarily depends on the EM type, the voltage applied to the EM
input, the voltage applied across the EM, the condition of the EM, and, to a lesser
extent, the mass and chemical nature of the incident ion. In general, the EM gain
decreases as the ion mass increases.
The advantage of the EM Sensor is its higher sensitivity, thus making it possible to
measure lower partial pressures. A typical Transpector XPR 3+ has an FC
sensitivity of about 4x10
-7
amps/Torr, resulting in a minimum detectable partial
pressure of 1x10
-9
Torr. Operating in EM mode, the Transpector XPR 3+ Sensor
has a sensitivity of greater than 4x10
-3
amps/Torr, resulting in a minimum
detectable partial pressure of 6x10
-12
Torr.
The main disadvantage of the EM Sensor is that the EM gain is less stable and is
less precisely known for quantitative measurements.
3.4.3.3 The Transpector XPR 3+ Microchannel Plate,
High Pressure Electron Multiplier
Transpector XPR 3+ uses a Microchannel plate (MCP) High Pressure Electron
Multiplier (HPEM)/Faraday Cup detector. The MCP is a small plate (approximately
1/2" (12.7 mm) square by 1/16" (1.6 mm) thick) consisting of an array of over
10,000 very small continuous dynode multipliers, each with a 0.001" (0.03 mm)
inside diameter. Refer to Figure 3-2 on page 3-6.
The main advantage of the MCP over other multiplier designs is its smaller size.
Also, the required operating voltage is lower.
The MCP does not have to be kept under a vacuum. However, because of the large
surface area, the MCP can absorb water vapor and should be protected from
exposure to high levels of moisture over extended periods.

Inficon Transpector XPR 3+ Specifications

General

Brand	Inficon
Model	Transpector XPR 3+
Category	Measuring Instruments
Language	English