Runaway electrons

The most essential plasma device characteristics that are needed in order to obtain impurity release rates are the fluxes of photons and of charged and neutral particles to the wall. It will be necessary to have detailed information on the energy spectra and fluxes to walls, limiters and beam dumps of thermal electrons and ions, photons, a-particles, runaway electrons, charge exchange neutrals, neutral beam and impurity neutrals and ions. The effects of sheath potentials, secondary electron emission and unipolar arcing need to be included in these calculations. 

Although much has been done to improve the data base in these areas in the last decade, little is known about low energy (E < 400 eV) charge exchange neutrals, a-particle, and thermal and runaway electron fluxes. 

The ratio of electron drift velocity to ion thermal velocity is also similarly dependent on the line density, and in the example here is 0.96. The line density is therefore just above the critical value that could lead to ion acoustic turbulence or runaway electrons. ... 

In fusion reactors, heat load on their first wall often reaches 5-10 kW/cm for several reasons, such as the existence of abnormally accelerated runaway electrons, arcing between plasma and... 

CNTs are also valuable as field emitters because they have a small virtual source size [30], a high brightness, and a small positive temperature coefficient of resistance [31]. The latter means that they can run hot under high emission currents, but not go into thermal runaway. Emission from nanotubes can be visualized by electron holography in a TEM [32],... 

The experimental techniques described above of charge—discharge and impedance are nondestructive. Tear-down analysis or disassembly of spent cells and an examination of the various components using experimental techniques such as Raman microscopy, atomic force microscopy, NMR spectroscopy, transmission electron microscopy, XAS, and the like can be carried out on materials-spent battery electrodes to better understand the phenomena that lead to degradation during use. These techniques provide diagnostic techniques that identify materials properties and materials interactions that limit lifetime, performance, and thermal stabiity. The accelerated rate calorimeter finds use in identifying safety-related situations that lead to thermal runaway and destruction of the battery. 

Fig. 6.2 Energy-transfer curves for increasing applied fields, showing the onset of electron temperature runaway. After Frohlich (1947), by courtesy of the Royal Society.

One disadvantage of the low beta approach is the possibility of a runaway discharge. In order to avoid the microinstabilities associated with a large electron drift velocity V, it is desirable to keep this velocity less than 2-5 times the the ion sound velocity (V = y V ). 

Theoretically, the maximum attainable accelerating field in the superconducting cavity is determined by a magnetic breakdown which takes place when the magnetic component of the hf field is equal to the critical field of the superconductor. However, in practice the breakdown is caused by other effects such as electronic load or, more often, a thermal runaway related to the formation of weak zones of superconductivity caused by defects and limited thermal conductivity of the cavity walls. 

Overcharging a lithium-ion cell is a severe abuse that can lead to the thermal runaway and catastrophic failure of a battery pack. Redox shuttles are intrinsic chemical overcharge protection mechanism for lithium-ion cells. Several stable redox shuttles have been identified to provide long-term overcharge protection, without the drawbacks of other technologies, which include complex electronic control systems for external voltage regulation and... 

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