# Homework Help: Drift speed for plasma

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1. Dec 27, 2014

### ExoP01

1. The problem statement, all variables and given/known data
I need to calculate the drift speed, drift orbital period and current density for 1eV protons and 10eV electrons. The density is 5 cm^-3
The assumption is that it is only a grad-B drift

2. Relevant equations
<V> = [6*E/(qBo*L*Re)](0,35 + 0.15sin(a))

3. The attempt at a solution
For drift speed: I assumed that <V> = [6*E/(qBo*L*Re)](0,35 + 0.15sin(a))
Where a= pitch angle = 90 degrees, L= field line= 5 in this case and Bo is 0.35*10^-4 T for equatorial plane of Earth.
q= elementary charge.
I tried and got a wrong value for the average speed when I calculated for 1 eV (proton), the answer became too small. Where did I do wrong?

For drift orbital period:
The formula is (Td=2*pi*L*Re)/abs(V) from above, bud I need V, so this should be easy

The current density for the ring current: I actually have no idea, maybe a hint from you guys?

thanks!

2. Dec 30, 2014

### Astronuc

Staff Emeritus
There seems to be some missing information in the problem statement. The B-field is missing, but later one indicates the earth's magnetic field. The particle density is 5 cm-3. How did one determine L = 5?

Please show the source of the equations, and please show one's work.

I think the problem concerns the "ring current" in the Earth's atmosphere, but the stated energies are rather low.
http://farside.ph.utexas.edu/teaching/plasma/Plasmahtml/node23.html

Last edited: Jan 2, 2015