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V6
Protection Current
Tbl. 5:
3.3 Mass filter
The correct material selection and highly precise manufacturing methods ensure a high degree of line-
arity and reproducibility.
3.3.1 QMA 430
The 8 mm rod system made of stainless steel can be used up to mass number 300.
3.3.2 QMA 400
For higher mass ranges as well as optimum stability and reproducibility, 8 mm molybdenum rods are
used, because of the superior electrical and thermal properties of the material.
3.3.3 QMA 410
The QMA 410 has rods made of molybdenum, with a diameter of 16 mm. At the same frequency, the
transmission increases as the rod diameter increases, but the mass range decreases. The impact of the
filtered ions on the rod surfaces is reduced, and thus also the susceptibility to contamination.
3.4 Secondary electron multiplier
The multiplier consisting of 17 discrete stages with focusing dynode geometry is a fast ion current am-
plifier that is located between the mass filter and electrometer pre-amplifier. Thanks to its high amplifica-
tion, the downstream electrometer pre-amplifier can be operated with a lower amplification; this results
in smaller time constants and thus make it possible to measure fast signals with low intensity.
3.4.1 SEV 217
In normal operation, with negative high voltage at HV- and ground at HV+ of the SEV 217 secondary
electron multiplier, the SEV 217 detects positive ions. The "SEM Voltage" parameter for the SEM oper-
ating voltage determines the amplification and is simultaneously the post-acceleration energy of the
ions.
Fig. 5:
Typical values of the grid ion source
HV-
0...-3.5kV
-
+
HV 701
HV 702
SEV 217
Inner Deflection
W
YO
-Ir
x
EP 422
EP
HV+
Product description
200 V
4.2 A
3.5 A
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