Re: [TCML] magnetic quenching / neodymium magnets

["Gary Peterson" <g.peterson@xxxxxxxxxxxx>]

D.C.,

Of course Tesla used a single electromagnet with the poles protected by mica 
sheets.

> From Experiments with Alternate Currents of High Potential and High 
Frequency, IEE Address, London, February 1892

   In connection with the coil I use either the ordinary form of discharger 
or a modified form.  In the former I have introduced two changes which 
secure some advantages, and which are obvious.  If they are mentioned, it is 
only in the hope that some experimenter may find them of use.

       Fig. 4. http://www.tfcbooks.com/images/lectures/1892-02-03/004.gif

   One of the changes is that the adjustable knobs A and B (Fig. 4), of the 
discharger are held in jaws of brass, J J, by spring pressure, this allowing 
of turning them successively into different positions, and so doing away 
with the tedious process of frequent polishing up.
   The other change consists in the employment of a strong electromagnet N 
S, which is placed with its axis at right angles to the line joining the 
knobs A and B, and produces a strong magnetic field between them.  The pole 
pieces of the magnet are movable and properly formed so as to protrude 
between the brass knobs, in order to make the field as intense as possible; 
but to prevent the discharge from jumping to the magnet the pole pieces are 
protected by a layer of mica, M M, of sufficient thickness, sl sl and s2 s2 
are screws for fastening the wires.  On each side one of the screws is for 
large and the other for small wires.  L L are screws for fixing in position 
the rods R R, which support the knobs.
   In another arrangement with the magnet I take the discharge between the 
rounded pole pieces themselves, which in such case are insulated and 
preferably provided with polished brass caps.
   The employment of an intense magnetic field is of advantage principally 
when the induction coil or transformer which charges the condenser is 
operated by currents of very low frequency.  In such a case the number of 
the fundamental discharges between the knobs may be so small as to render 
the currents produced in the secondary unsuitable for many experiments.  The 
intense magnetic field than serves to blow out the arc between the knobs as 
soon as it is formed, and the fundamental discharges occur in quicker 
succession.
Instead of the magnet, a draught or blast of air may be employed with some 
advantage.  In this case the arc is preferably established between the knobs 
A B, in Fig. 2 (the knobs a b being generally joined, or entirely done away 
with), as in this disposition the arc is long and unsteady, and is easily 
affected by the draught.

       Fig. 5. http://www.tfcbooks.com/images/lectures/1892-02-03/005.gif

   When a magnet is employed to break the arc, it is better to choose the 
connection indicated diagrammatically in Fig 5, as in this case the currents 
forming the arc are much more powerful, and the magnetic field exercises a 
greater influence.  The use of the magnet permits, however, of the arc being 
replaced by a vacuum tube, but I have encountered great difficulties in 
working with an exhausted tube.

Source: http://www.tfcbooks.com/tesla/1892-02-03.htm

I'll get back to you about that other thing shortly.

Regards,
Gary

> Magnets but must be close to do so effectively (high field strength).
>
> A spark has very high heat with the high peak currents.  This rapidly
> damages the magnet. 



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