Space charge neutralization

The challenges of overcoming space charge neutralization to increase low-energy beam transport are described in the following section. Novel approaches, such as molecular ion implantation, are also discussed. 

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As one example of a coupled-currents theory, the growth of very thick oxide films under local space-charge neutrality conditions will be considered in detail in the following section. 

If local space-charge neutrality can be assumed, which has been justified by extensive numerical calculations [46] for the present case, then we can write... 

Equation (180) for local space-charge neutrality requires that the oppositely charged mobile defect species concentrations have a very special relationship. Solving for C2 gives... 

Since local space-charge neutrality does not hold at the oxide interfaces, the above expression for the current is restricted to the interior zone [28] where local space charge neutrality has been found [46] to be a good approximation. This is illustrated for the case of cation vacancy (or anion interstitial) and electron-hole diffusion by Fig. 17. Thus, the domain of validity is not 0 but instead is 5 < [Pg.75]

To evaluate C](5 ) and C1(L ), we introduce what has been designated [28, 29] the interfacial zone equilibrium approximation the concentration profiles of all charged defect species within the two interfacial regions (0interior zone (5 local space-charge neutrality can be approximated by... 

These values for Cs(8 ) and C (L ) are likewise appropriate at the respective edges of zone 2, since defect concentrations are continuous functions of position within the oxide layer. The subscript s can have the value 1 or 2 in the above relations, corresponding respectively to the ionic or electronic species concentrations. Substituting eqn. (196) for Cs(8 ) into the local space-charge neutrality relation [eqn. (180)] gives... 

Next we substitute eqn. (197) into the local space-charge neutrality relation [eqn. (180)] to obtain... 

However, applying an appreciable electric field must destroy the space-charge neutrality of the combustion system because of electron depletion. Therefore, the recombination of chem-ions with electrons will be diminished, and the total positive-ion concentration will increase sub-... 

The increase of output current in the unignited mode operation due to the illumination can be explained by the impovement of the space charge neutrality a. As mentioned above, a is usually smaller than unity at the low emitter temperature so that most electrons emitted from the emitter cannot reach the collector. However, the illumination creates so many electrons and ions by photoionization that a approaches to unity [2]. Though the remarkable effect of illumination on the output current is observed at the operation of the low emitter temperature, the increase of a does not contribute to the increase of the output current at the higher emitter tern-... 

We can put this value of U into Eq. (9). Since the bulk region is field free, we can also assume space-charge neutrality, n = p. Then the applicable diffusion equation becomes... 

X 10l6 ions and (ii) reduction in background pressure, perhaps by the use of preionized plasma in the cusp region for prompt space-charge neutralization. 

The RECE-Christa, RECE-Berta, and more recently CHIP experiments (see Table 3) provided the first successful demonstration of the formation of field-reversed rings using relativistic electron beams. A schematic of the RECE experiments is shown in Fig. 15. The REB is injected tangentially in the presence of high-pressure neutral gas (p = 0.1-1 Torr) which ionizes to produce space-charge neutralization but remains highly resistive during field-line reconnection. 

Before the formation of an anode spot, the metal vapor and plasma density in the positive colunm are so low that the mean free path of the electrons is comparable to the dimensions of the arc. Thns, thermal ionization and space-charge neutralization must be minimal. However, in the region of the cathode spots the metal vapor density is very high and ionization can readily occm. 

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