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<sb0>
whitequark, where did you get the voltages for the "accelerating plates" on the mass spec?
<sb0>
also how are those plates organized inside the device?
<whitequark>
sb0: there are three plates equally spaced with a hole at the center
<whitequark>
the plate voltages are roughly what most mass spec designs i've seen use
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<sb0>
whitequark, and those go between the ionizer and the rods?
<whitequark>
yes
<sb0>
so you have the ionizer with filament at -70V, then a first plate at 0 that receives the electrons, then the other plates at increasingly negative voltages, then the rods?
<sb0>
isn't the potential supposed to be near 0 when entering the rods?
<whitequark>
hmm, that's a good question, let me look at a reference
<sb0>
what are those mass spec designs, exactly? where you got the voltages from
<sb0>
whitequark, in the Batey2013 paper I don't see the two accelerating voltages
<whitequark>
it also has information on ionizers, and this time with references
<whitequark>
sec
<whitequark>
bottom of page 5.
<whitequark>
"A voltage, usually in the range 5 to 10 volts, is applied to the source electrode. The extractor electrode is
<whitequark>
driven with a negative voltage, typically in the range -50V to -130V. "
<sb0>
there is the grid/source electrode, then one 'extractor' electrode, then one grounded electrode
<whitequark>
that's not the same as what is in my lab note because they use a different point for 0V
<whitequark>
you can just go with Batey2013, these should be equivalent
<sb0>
you want 0V to be the faraday cup
<whitequark>
sb0: there's another plate right before the faraday cup in Batey2013
<whitequark>
see page 20
<sb0>
so there are only three plates in the ionizer? and one is connected to the grid, and one is grounded
<sb0>
the source is at some positive voltage 5-100V above ground, filament is some 70V below source, extractor is some negative voltage 100-150V below ground
<sb0>
damn, that's going to be another annoying set of power supplies to build
<whitequark>
that sounds about right
<whitequark>
note that in our case the three plates are independent
<sb0>
independent?
<whitequark>
so you can put the filament and the grid and the plates anywhere you want
<whitequark>
I mean noe of them are grounded
<sb0>
so your "accelerating plate 3" is the grounded quadrupole entrance?
<sb0>
it's not accelerating then
<sb0>
well
<whitequark>
right, should be just "plate"
<sb0>
also the voltages are wrong
<sb0>
if you put the zero at the source then it's -300V and -150V, in that order
<sb0>
but I'd recommend using the same zero as Batey2013. also because this puts the faraday cup at 0
<whitequark>
let's follow with Batey2013
<whitequark>
I was writing the lab note in a hurry and likely made mistakes in it
<whitequark>
it's by no means an authoritative source...
<sb0>
with small currents like this you want to shield everything
<sb0>
e.g. the vacuum chamber should be at the same potential as the faraday cup electrode, to reduce leakage current via the feedthrough
<sb0>
not doing that created lots of problems with my early ion gauge designs
<whitequark>
ack
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<sb0>
whitequark, also, two amplifiers are needed, right?
<sb0>
or a transformer
<sb0>
_florent_, have you looked into multi-channel GTH transceivers for DRTIO?
<sb0>
have them all transmit with the same clock, and each generating its RX clock
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<hartytp>
rjo: sorry, had to take a break from the AD9910 for most of today to deal with some stuff that came back up in the lab