Runaway-Breakdown

Runaway Breakdown, called in German also runaway discharge is a physical effect of the electrical discharge, probably in the lightning formation plays a role. The resistance, learn the accelerated electrons in air by collisions decreases above a certain speed, instead of continuing to rise.

Problems in the examination of the flash origin

From the pioneering studies of lightning by Benjamin Franklin, it was assumed that lightning as spark discharges were to be treated. These are manifested, for example, by small electric shock that one gets when one has become electrostatically charged and then touching a doorknob. For such a flashover can occur, electric field strengths of about three million volts per meter must occur in the air. In thunderclouds, these field strengths, however, were not even begin to measure. Clearly, therefore, the mechanism that leads to the emergence of a flash, no easy unloading.

Runaway Breakdown

A solution to the problem could be the runaway breakdown, an unusual type of electrical breakdown, carry with you. This theory was first proposed in 1961 by Alexander Gurevich of the Lebedev Institute in Moscow.

In a conventional discharge, electrons move relatively slowly, because they constantly collide with molecules of air. This resistance is greater the faster the electrons. However, speeds in excess of 6 million meters per second (about two per cent of the speed of light), the resistance decreases in spite of increasing speed. The reason is that the measure of the probability of an electron - impact ionization, the so-called cross-section, with the first electron energy above the ionization increases until at approximately three times the maximum threshold is reached ( Lotz formula). In the cross section decreases again ( Bethe- Heitler formula). Electrons, which are accelerated in a strong electric field beyond this point, therefore, be faster and can reach almost the speed of light. They are called runaway electrons ( in German also as an outlier - electrons). This gives rise to high energies that make some researchers responsible for the flash development. Assuming a runaway breakdown, so rich already 150,000 volts per meter of electrical field strength from to make a lightning occur. This value is actually measured in thunderclouds.

Detection of Runaway -Break Downs

When the highly accelerated runaway electrons collide with gas molecules in the air, braking radiation is emitted in the form of X-ray and gamma radiation. The best so far yielded evidence for the correctness of the theory of runaway breakdown is that it is in 2001 actually succeeded in measuring these radiations in flashes.