Y.H. Chang Studies

Y.H. Chang studied 34 gas mixtures in the magnetic fields of 0-1 T. Measurements of drift velocity of electrons in gas mixtures of and hydrocarbon gases, and mixtures and gas mixtures were done.

 
Figure 1

Figure 1 shows the + different hydrocarbon mixtures, such as methane, ethane, propane and isobutane mixtures for drift velocity vs. electric field and the behavior of the Lorentz angle with electric field. The drift velocity has been plotted against the electric field component parallel to drift direction. The above measurements shown are for a mixture of 80:20 at a B field of 1 Tesla. One can note that as the molecular weight of the hydrocarbon increases (as one moves from methane to butane) the drift velocity of the electron decreases and the Lorentz angle also decreases for such mixtures. However, the Lorentz angle is affected significantly in the lower E field regions.

 
Figure 2

Figure 2 shows the behavior of for different mixtures, the behavior of drift velocity and tangent of Lorentz angle as a function of E field. As the composition of mixture decreases the electron drift velocity in the mixture decreases. The addition of a third component gas such as reduces the Lorentz angle drastically. This is evident from Figure 3.

 
Figure 3

The electron drift velocity also decreases. At B=1 T, gas mixtures of ratios 20:60:20 and 30:60:10 seem to show a Lorentz angle of around and the electron drift velocity are around 7cm/s. These are gas mixtures also exhibit a behavior of almost linear dependence of tan with E field.

There have been studies of drift velocity and Lorentz angle in other mixtures such as , , and . Some of these mixtures have a lower breakdown voltage and most of them have a Lorentz angle greater than those gas mixtures discussed earlier.

 
Figure 4

 
Figure 5

Figures 4 and 5 show the plot of defection figure of merit (C) for a gas with the electric field component parallel to drift velocity. The gas deflection figure of merit is defined as:

For a good gas mixture one would expect C to be a constant as a function of E. If this were to be the case one can assume a linear scaling to obtain the value of at different B fields. Note for mixtures the figure of merit is fairly constant, however, the influence of a magnetic field on the microscopic drift process leads to small effects only, as seen from the scatter of the points.

Mixtures of doesn't seem to have these effects whereas in the Ar mixtures it is the worst.

Making use of the figure of merit data one could calculate the Lorentz angle for mistures of of composition 20:60:20 and 60:20:20 at different B.

These studies suggests that some of these gas mixtures used could be probable candidate gases for use in the drift and CSCs. However, further studies of the gas mixtures must be done in order to evaluate their behavior as far as gas multiplication, electron diffusion, efficiency, and stable operation are concerned.