RE: Wireless power transmission (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 20 Jun 2007 17:54:06 +0100
From: Colin Dancer <colind@xxxxxxxxxxxxxx>
To: 'Tesla list' <tesla@xxxxxxxxxx>
Subject: RE: Wireless power transmission (fwd)

Hi Dave,

An interesting question which I'll do my best to answer (though it is a long
time since I've done detailed work in this area).

Beta is defined as the ratio of the thermal and magnetic pressures in the
plasma.  

The thermal pressure proportional to the particle density and the effective
particle temperature.  This is very similar to the way pressure is derived
for a normal gas, with the collisions from more, faster moving gas particles
exerting a higher pressure on a bounding box than a smaller number of colder
particles.

The magnetic pressure is a bit harder to describe, but is a volume integral
of the square of the field strength divided by twice the relevant
permeability. 

The ratio of the two, beta, gives a measure of how well a magnetic field
"confines" or "restricts" a plasma.  

The underlying method of the constriction is that a charge particle moving
in a magnetic field experiences a force at right angles to the motion and
field (classic "motor rule" stuff).  This force  is therefore effectively
inward pointing towards the field lines and while the ion can move
unconstrained parallel to the field line, in the other directions it will
tend to "gyrate" round the field line.

The higher the magnetic field the smaller the gyration radius and the
tighter the plasma is bound to the field lines.  

Increasing temperature and densities, increase the gyro radius and also
increase the random interactions between particles allowing them to be
knocked off their gyro trajectories and slip away from the field lines.

Beta is important in a range of plasma physics from fusion research (high
beta good, low beta bad), to the formation of shock waves in interstellar
plasmas, to Earth bound aurora (where charged particles from the sun spiral
round the lines of the earth's magnetic field and finally impact near the
poles where the field lines come into the atmosphere).

Hope that helps,

Colin.

---------- Forwarded message ----------
Date: Wed, 20 Jun 2007 08:50:29 -0500
From: David Thomson <dwt@xxxxxxxxxxxx>
To: 'Tesla list' <tesla@xxxxxxxxxx>
Subject: RE: Wireless power transmission (fwd)

Hi Colin,

> I'm sorry if I misunderstood about the large scale electrostatic 
> forces, but if these aren't present then your scheme does just depend 
> on ions vibrating (and waves
> propagating) due to the electrostatic repulsion between the ions.

Plasma physics is something I am interested in learning.  While researching
the physics of ion densities, I came across the phrase, "ion beta."  Can you
explain what ion beta is and how it applies to plasma physics?

Dave