----- 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). >> 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) Michel
