Shimadzu ICPE-9000, Инструкция по эксплуатации

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4 Basic Principles
4-8
4.5 Principle of RF Power Supply
4.5.1 Outline
The energy used to generate ICP is applied to the plasma in the form of RF electric power. This RF
electric power is generated by an RF power supply, which is configured as shown in "Fig. 4-4".
(1)
Oscillator
(2)
Exciter
(3)
Power
amplifier
(4)
Matching
box
Coaxial cable
Plasma
Fig. 4-4 Configuration of RF Power Supply
(1) Oscillator
This unit sets the frequency of the RF output. Fluctuations in the frequency affect the analysis
precision and so many ICP power supplies use a crystal oscillator because of the high level of
frequency stability.
(2) Exciter
This unit amplifies the radio frequency generated by the oscillator to the magnitude enough to excite
the PA (power amplifier (3)).
(3) Power Amplifier
This unit amplifies the power from the exciter to the output of kW order enough to ignite and
maintain the ICP.
(4) Matching Box
The power amplified by the PA is allowed to the plasma through a coaxial cable with the
characteristic impedance Z0. However, because the impedance of the plasma and the characteristic
impedance of the cable are different, a matching circuit is required. The box incorporating the
matching circuit is called the "matching box".
4.5.2 Principle of Matching Box
When the RF power reaches the load (impedance Zr) via the cable (characteristic impedance Z
0
), the
reflection expressed by the following equation occurs.
P P
Z Z
Z Z
r f
r
r
=
−
+





 0
0
2
Pr: Reflected power
Pf: Incident power
As shown by this equation, the reflected power, Pr, is zero only when the impedance of the load, Zr, is
equal to characteristic impedance of the cable, Z
0
.