Ion Detection System - Thermo Scientific Surveyor MSQ Plus Hardware Manual

2
Functional Description
MS Detector
Figure 19. Schematic of the RF/dc prefilter, mass analyzer, and ion detector
Source
entrance
cone
M-Path

Ion Detection System

28 Surveyor MSQ Plus Hardware Manual
Source
extraction
cone RF/dc prefilter
Forepump
The Surveyor MSQ Plus MS detector is equipped with a high sensitivity, off-axis ion
detection system that produces a high signal-to-noise ratio and allows for voltage polarity
switching between positive ion and negative ion modes of operation. The ion detection
system includes a 10 kV conversion dynode and a channel electron multiplier. The ion
detection system is located at the rear of the vacuum manifold behind the mass analyzer. See
Figure 20.
The conversion dynode is a concave metal surface that is located at a right angle to the ion
beam. A potential of +10 kV for negative ion detection or -10 kV for positive ion detection is
applied to the conversion dynode. When an ion strikes the surface of the conversion dynode,
one or more secondary particles are produced. These secondary particles can include positive
ions, negative ions, electrons, and neutrals. When positive ions strike a negatively charged
conversion dynode, the secondary particles of interest are negative ions and electrons. When
negative ions strike a positively charged conversion dynode, the secondary particles of interest
are positive ions. These secondary particles are focused by the curved surface of the conversion
Square Quadrupole
quadrupole mass analyzer
Split flow
turbomolecular pump
Ion
detector
Bounded ions successfully
transmitted by the mass
analyzer reaching ion detector
Unbounded, neutralized ions
being pumped away by the
vacuum system
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