PlasmaQuant MS Series
Mass
Spectrometer
121
The function of the three extraction lenses is to gather the plasma from the rear of the
skimmer cone, accelerate it and direct it into the mirror lens. Approximately ninety
percent of the ions formed in the plasma are lost as they pass through the skimmer
cone therefore the extraction lens design is critical. They ensure the sample beam has
sufficient energy to survive a ninety-degree change in direction into the mass analyzer.
As the plasma emerges from the back of the skimmer cone its velocity and
temperature decrease rapidly from the supersonic speeds it had reached as it passed
through the sampler cone. E1 controls the spread of the beam. Greater negative
voltage applied to E1 will compress the beam, increasing signal intensity and
interferences. E2 accelerates the beam, keeps it parallel and directs it toward E3. The
interaction between E3, the mirror segments and the corner lens controls the field to
reflect the ion beam.
The extraction lens voltages change significantly when tuning between high and
normal sensitivity modes. Typically high sensitivity mode requires that they run at
larger negative voltages.
The adjustable range is for each lens is from -1000 to zero volts.
The extraction lenses vary in shape. The first has an almost conical shape while the
second and third are more representative of hollow disks. They are positioned on axis
with the cone orifices’. E1 is located approximately 12 mm behind the skimmer cone
orifice and E2 is positioned directly behind E1. E3 is attached to the mirror lens
assembly and separated from E2 by the gate valve.
Figure 8-11 - Extraction lenses # 1 and # 2
After removing the cones the extraction lenses can be removed using a tool. The same
tool is used to remove both extraction lenses.
The extraction lenses