whitequark changed the topic of #tinyqma to: design of an open hardware DDS-based QMA with a low-voltage dc/rf stage :: http://irclog.whitequark.org/tinyqma
mne has joined #tinyqma
<whitequark> bofh__: any idea which dielectric to use?
<whitequark> needs to be easily machinable and at same time with low thermal expansion coefficient
<whitequark> and rigid
<whitequark> maaaaybe macor?
<bofh__> macor would definetly work, honestly any machinable ceramic insulator should work here
<bofh__> (yes I realise "machinable ceramic" is a bit of an oxymoron)
<whitequark> wellll I am told alumina is "machinable"
<whitequark> in the sense that, say, glass is "machinable"
<whitequark> I've yet to try this bc I don't have spare alumina
<whitequark> oh
<whitequark> one of the compositions sinters in a commercial ceramic oven, and I have all the necessary oxides for it and a ball mill
<bofh__> also isn't alumina's thermal expansion coeff a bit on the high end?
<whitequark> hmm
<whitequark> well it is less than the other thing i am considering
<whitequark> which is teflon
<bofh__> I don't quite have a feel for how low we need it
<whitequark> which expands so hard you can't machine it to better than .5mm
<whitequark> solely because of the heat liberated during cutting
<whitequark> also squishy
<whitequark> alumina... hm
<whitequark> 5.4
<bofh__> I thought perhaps aluminum nitride, but that doesn't work well as a dielectric when you get to high-frequency RF
<whitequark> errr it is machinable?
<whitequark> sounds like it would be hard as hell
<whitequark> heck there are tools with AlN coatings
<whitequark> lol pine wood is 5
<whitequark> that... actually
<whitequark> ...
<whitequark> why not
<bofh__> yeah no, I wouldn't really want to machine AlN
<bofh__> rofl
<bofh__> as long as it's completely dry, it would be a suitable dielectric here
<whitequark> the trouble with it is that it's porous
<whitequark> but I want to try it solely for the sheer shock value it would have on anyone in the field
<bofh__> yeah that's basically the only reason I'm considering it
<bofh__> oh god
<bofh__> thing is we're under a kV and aren't running particularly high currents, so the dielectric properties aren't really hard to come by
<whitequark> sure
<whitequark> practically anything dielectric works here
<whitequark> I'm more concerned of mechanical properties
<bofh__> yeah that's basically the deciding factor. I wasn't even aware you *could* machine teflon, iirc it melts at like 300C or thereabouts.
<whitequark> um, duh
<whitequark> it softens way earlier
<whitequark> you don't want it to get over fifty.
<whitequark> but the thing is, you can machine acrylic
<bofh__> yeah that's what I thought.
<whitequark> it's a pain in the ass
<whitequark> but I did it
<whitequark> basically just soak it in water
<whitequark> then you can actually cut chips
<whitequark> the moment the endmill is not in water, it melts, solidifies in a cylindrical thingy on the endmill, and breaks it
<bofh__> when you say acrylic, do you mean PMMA, or?
<whitequark> PMMA.
<bofh__> wow
<whitequark> the feeds/speeds for PMMA are basically the same as for aluminium
<whitequark> people call it "transparent aluminium"
<whitequark> Al also tends to stick to endmill, though the mechanism is of course different
<whitequark> also a pain to machine
<whitequark> fun fact: PMMA and pureish Al have the same Mohs hardness
<bofh__> I assume just lasercutting it wasn't sufficient for the detail needed?
<whitequark> I don't have a laser cutter
<whitequark> but I have a mini mill
<whitequark> CNC
<whitequark> 20x30x5cm area
<whitequark> plastics all seem to have expansion coefficients of over 25, and most over 50 even
<whitequark> that's micron per meter per kelvin
<bofh__> fun thing with a CNC is if you retrofit it with a 445nM 1W laser diode (cheap as hell on ebay), you can use this to do photoresist etching of PCBs.
<whitequark> yeah I have considered this
<bofh__> yeah I'm not really considering any plastic here for exactly that reason
<whitequark> I currently do photolithography
<whitequark> using transparencies printed on a laser printer
<whitequark> the diode thing is slooooow and also doesn't give you as nice resolution unless you focus it somehow
<bofh__> I've done this, it works well, and you can route traces much more precisely than by doing toner-transfer (which I have also done). More of a pain in the ass to setup, though, and slow.
<whitequark> toner transfer is shit
<whitequark> not even considering
<whitequark> I got photolithography figured out fairly well
<bofh__> you need good collimating lenses
<whitequark> down to 50 micron traces
<whitequark> ironically I have trouble etching lately. all my etchants either immediately work shitty or start working shitty after one etch or so
<whitequark> I suspect my lack of deionized water is the culprit
<whitequark> I have no clue where to get deionized water. I knew one place which sold it bottled but it no longer operates
<bofh__> so I just use Na4S2O8 for both prep and trace etchant, saves me from having to get fecl3
<bofh__> you want it more dilute for the latter
<whitequark> yeah I figured that out
<whitequark> but yu want to heat it
<whitequark> I have nothing to heat it in
<bofh__> oh so fecl3 etches slow as shit in my experience unless heated
<whitequark> faster than persulphate ime
<whitequark> marginally, perhaps
<whitequark> anyway lately I switched to just making pcbs at board houses, my needs are a tad too complex
<whitequark> the QMA board will be 4 layer obviously
<bofh__> yeah this method doesn't scale to multilayer nicely obv
<whitequark> well i have considered making multilayer
<whitequark> you can't buy prepregs
<whitequark> but you can buy .2mm copperclad fiberglass here
<bofh__> so I've done photolithography but my issue is the boards themselves (the ones with the preapplied photoresist) tend to be more expensive than I'd like
<whitequark> i use film photoresist
<whitequark> it's cheap
<bofh__> where do you get it from / what type?
<bofh__> rofl I keep forgetting Inkscape technically will try to import postscript
<whitequark> there is a reason i painstakingly compose these lists
<whitequark> INKSCAPE IS FUCKING AWFUL GARBAGE I HATE INKSCAPE
<bofh__> it's generated broken svgs every single time I've tried it
<whitequark> EXACTLY
<whitequark> IT HAS ONE JBO
<whitequark> AND IT CAN'T DO IT
<whitequark> anyway basically any photoresist which has color like that is the same as mine
<whitequark> approximately
<whitequark> there are different colored resists
<bofh__> it's not like it's a hard task, they're both text-based vector image formats and often both support the same scaling/dimensions/colourspaces/etc
<bofh__> fuck I've regexed a ps to svg before (it was a simple ps)
<whitequark> lol
<whitequark> hardcore
<bofh__> no, hardcore is applying regex on an instruction sequence in a binary and hoping you don't hit anything else with it
<bofh__> successfully worked 3/5 times so far
<whitequark> i had a crack for sublime text that consisted of dd piped into sed
<bofh__> rofl
<bofh__> also I saw your post on fixing sublime/gtk's xcompose support
<bofh__> that was pretty cool
<whitequark> yeah
<whitequark> i was at the point where pressing compose and not seeing the result just sent me into nine hours of blind rage
<whitequark> and ... apparently this is what results when that happens
<bofh__> I'm impressed you managed to do that in 10 hours not having any idea of the internals of libgtk
<whitequark> I was really angry.
<bofh__> it feels like you'd need 10 hours to just track down the sequence of calls it uses to do anything
<bofh__> gtk is kind of a mess. and huge.
<whitequark> rofl that is mostly what i was doing
<whitequark> you can't successfully use gtk without going knee deep in its source
<whitequark> when i ported solvespace to gtk, i spent like half of the time figuring out how exactly something works
<bofh__> I feel like this is a disturbingly common thing with a lot of opensource software.
<whitequark> like... filechooser? I don't remember
<bofh__> the docs are shit and often don't cover a lot of things at all
<whitequark> in case of gtk, everything in it is shit
<whitequark> right so alumina can be machined with diamond tools and water coolant
<whitequark> as expected really
<whitequark> bofh__: do you know anything about ionizer design?
<whitequark> speaking of alumina
<whitequark> you can take this
<whitequark> and put a lateral load on it
<whitequark> it will work like an "endmill"
<whitequark> it works with glass
<bofh__> what form of ionizer? air?
<whitequark> for QMA
<whitequark> usually it's an electron gun and a few accelerating electrodes
<whitequark> but I don't really know anything about fabricating these
<bofh__> so the only hard part of that is the electron gun if we need something stronger than what is used in, say, an old CRT
<whitequark> I'm not quite sure of the geometry mainly
<bofh__> most QMAs use I've seen use direct-current or inductively-coupled argon plasma ion sources, which are more complicated than just using RF arc sources
<bofh__> oh you mean for focusing the beam?
<bofh__> I have a document that describes the geometry relatively well, now if only I can find it.
<whitequark> hmm
<whitequark> which is the most common design i've encountered in literature
<bofh__> it's honestly just a bunch of plates orthogonal to x with circular apetures, focusing is done by applying HV to them
<whitequark> so I've been thinking
<whitequark> cut them from sheet metal
<whitequark> assemble in a stack using nylon washers
<whitequark> screw together with nylon screws
<bofh__> mostly because all you really need is a circular beam that more-or-less matches what your quadrupole acceptance function is
<bofh__> yeah that's pretty much what I'd do as well.
<bofh__> start from sheet metal since that's all you really need
<bofh__> that's a nice price for thoriated tungsten wire.
<whitequark> yeah not bad
<whitequark> grab it before safety nazis ban thorium completely, or something
<bofh__> LOL that site sells "Ion-sensor grade" bis(2-ethylhexyl) phthalate
<whitequark> i can understand not having thoriated tungsten in welder electrodes because you grind it all day long, so it's the literal worst case
<bofh__> it's bis(2-ethylhexyl) phthalate. just use some plastic lab equipment or something in it for a few minutes.
<whitequark> but trying to get rid of it everywhere is just silly
<bofh__> that shit is like ground loop hum for NMR spectra
<whitequark> haha
<bofh__> no, the literal worst case is using thorim dioxide as a radiocontrast agent :P (used to be a thing once)
<bofh__> though yeah, using it in welder electrodes comes close
<bofh__> wow that is a really low-energy alpha particle
<bofh__> so apparently eating a thorium gas mantle only gives you about 2mSv - 4mSv of extra radiation exposure?
<bofh__> that's... really tiny
<whitequark> huh
<whitequark> indeed that is not ... very complex machining
<bofh__> a pair of plates might even be sufficient actually
<bofh__> the beamforming is done mostly via the actual emitted EM fields, so the shape of the emitting elements isn't necessarily going to be complex, and certainly doesn't have to be.
<whitequark> right