Magnetron Operation

As a consequence, the electrons which are accelerated in the cathode sheath are forced onto a closed loop drift path parallel to the target surface because of the Lorentz Force. This magnetic trapping of the electrons and the corresponding ambipolar diffusion of the ions raises the plasma density in front of the target. A much higher ion current and therefore deposition rate is possible. Furthermore, the pressure can be decreased, which improves 

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A further effect of bipolar pulsed power plasma excitation addresses the disappearing anode effect and thus the long-term stability of reactive sputtering. In conventional reactive DC magnetron operation, the anode gets coated with oxide films. These insulating films give rise to plasma fluctuations... 

Cutoff magnetic flux density In magnetrons operated under a constant anode voltage, a value of magnetic flux density at which the anode current decreases abruptly. 

Some power tubes can be operated without the need for a protective ferrite isolator. One example is the cooker magnetron (700 W) used in modern microwave ovens (57). At higher power levels, such as 25 kW, it is more common to employ a protective ferrite device, particularly in the form of a circulator (58), as shown in Figure 3. This results in a power loss equivalent to a few percentage points in system efficiency. The ferrite circulator prevents reflected power from returning to the power tube and instead directs it into an auxiHary dummy load. The pulling of tube frequency is thus minimised. 

Food. The most successful appHcation of microwave power is that of food processing (qv), cooking, and reheating. The consumer industry surpasses all other microwave power appHcations. Essentially all microwave ovens operate at 2450 MH2 except for a few U.S. combination range models that operate at 915 MH2. The success of this appHance resulted from the development of low cost magnetrons producing over 700 W for oven powers of 500-800 W (Table 3). 

Further designs of ion sources applied in plasma spectroscopy such as electrodeless microwave induced plasmas (MIPs) operating in a noble gas atmosphere at low power (mostly below 200 W) or capacitively coupled microwave plasma using Ar, He or N2 the as plasma gas (at 400-800 W) were described in detail by Broekaert.33 Microwave plasmas produced by a magnetron are operated at 1-5 GHz. Their special application fields for selected elements and/or element species are based (due to the low power applied) in atomic emission spectrometry.33... 

Fig. 5.4. (a) Operation principle of a planar magnetron cathode. The secondary electrons emitted from target surface are trapped by the magnetic field due to the Lorentz force. The result is a plasma torus in front of the target, (b) Planar magnetron cathode of 3.75 m length (from [35])... 

Process Reactive MF magnetron sputtering. Sinusoidal plasma excitation (40 kHz, Advanced Energy PEII). Static deposition. Boxcoater Pfeiffer PLS 580. Process operation in the metallic mode of the discharge. ... 

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