Michel Jullian wrote: > > ----- Original Message ----- > From: "Harry Veeder" <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Saturday, February 24, 2007 10:12 PM > Subject: Re: [Vo]: Re: Lifter electrode geometries > >>> In Sigmond's derivation d is the z- (usually vertical) distance traveled by >>> the single ion under study. Since the highest density of ions takes the >>> shortest route, for most (but not all) lifter designs one can make the >>> approximation of the same z-distance d (the gap length) for all ions, hence >>> the I*d/mu thrust formula obtained by summing all the q*d/mu momentums >>> contributed by all the ions crossing the gap in one second. In those lifters >>> the exact shape of the collector doesn't matter, whether wing shaped or >>> round >>> tube or plane mesh. >> >> If the thrust can be increased by increasing the gap distance, how large can >> the gap be made? > > As large as you wish, but if you increase the gap you must also e.g. increase > the voltage and the wire-to-wire spacing, the parameters are interdependent so > you must calculate them in the right order (cf the multiwire-plane design > guide).
Ok. >>> But there are exceptions, e.g. in my trough shaped mesh design as I >>> explained >>> the ions fan out, so they travel very different z-distances, so the >>> X-to-plane >>> I*d/mu formula doesn't apply. If you do the (simple) maths you find: >>> >>> Thrust(line to half cylinder) = 2/pi * I*d/mu >> >> It doesn't depend on the width of the trough? > > It does, via the d parameter (the trough width is 2*d, it's a half cylinder > with the wire on its axis) > OK. Harry
