Home built mass spectrometer

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Jan Ohlsson
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Home built mass spectrometer

Post by Jan Ohlsson »

Hi, I am situated in Stockholm, Sweden. I have a vacuum system and am learning a little scientific glass blowing for producing Crooke´s tubes and other discharge tubes. I am not into fusion for the moment, but could perhaps be later on.

At this moment I have just put together a working DIY mass spectrometer. Please visit my website for the spectrometer, and feel free to comment.

https://diy-masspectrometer.se/

Kind regards,
Jan
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Richard Hull
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Re: Home built mass spectrometer

Post by Richard Hull »

A really nice little system! I have been thinking about building a beta energy spectrometer using variable magnet strength coil magnets.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Dan Knapp
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Re: Home built mass spectrometer

Post by Dan Knapp »

Richard, Most electron spectrometers used in surface analysis use electrostatic deflection with either a cylindrical or hemispherical analyzer. A cylindrical electrostatic analyzer spectrometer would probably be easier to build than a magnetic deflection machine. There is a huge literature on these analyzers, but I don’t recall ever having seen a DIY version. Many research labs build their own instruments, so it is certainly doable with normal shop capabilities.
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Richard Hull
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Re: Home built mass spectrometer

Post by Richard Hull »

I would think to turn 2.1mev electrons electrostatically you would need a gang o' voltage or a larger device. Electromagnetic deflection requires a gang o' gauss easily obtained in a small gap electromagnet. Instead of a gang o' volts you need a gang o' amps, much easier to work with and easy to control.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Dan Knapp
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Re: Home built mass spectrometer

Post by Dan Knapp »

Richard, My mistake. I overlooked that you said beta energy. The spectrometers I was talking about are for much lower energy electrons.
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Richard Hull
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Re: Home built mass spectrometer

Post by Richard Hull »

Spectrometers are definitely in the fusor column as there are many spectrometers that can be brought to bear on this work and nuclear work in general. Unfortunately the best are expensive or present a would-be builder with a steep learning curve. Lucky surplus finds can reduce the cost of professional instrument, though.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Jan Ohlsson
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Re: Home built mass spectrometer

Post by Jan Ohlsson »

Hi, and thanks for the friendly comment.
I have added two spectrograms to the site, and will add more in the coming days.
They look rather awful at the moment, as I still use the triangle sweep waveform and get double peaks. Hopefully this will disappear when I install the sawtooth sweep oscillator.
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Joe Gayo
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Re: Home built mass spectrometer

Post by Joe Gayo »

Why do you think there's hysteresis in the measurements (the double peaks not lining up exactly)?
Jan Ohlsson
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Re: Home built mass spectrometer

Post by Jan Ohlsson »

I think the hysteresis is caused by my DC/DC converters, as there is much more from the one taking care of the low mass range. But I will not spend so much energy thinking about this, as I expect the hysteresis to go away with the sawtooth oscillator and the sweep going in just one direction.
John Futter
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Re: Home built mass spectrometer

Post by John Futter »

You get double peaks with your magnets remanence ie it remembers a bit of field when at zero current.
There are techniques to buck this but using a field probe is the best way and close the magnetic loop ie your electronics will automatically buck the remanence.
so peaks going up in current are shifted compared to peaks when going down in current.
If you use a sawtooth (this is not easy as your magnet takes finite time to reset) you can blank the display for the return trace (just like an oscilloscope does)
Jan Ohlsson
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Re: Home built mass spectrometer

Post by Jan Ohlsson »

Hi John, I use a sweep of the acceleration voltage for the X-axis. I did think about sweeping the magnetic field at first, but I did not go down that road, for the reasons you mention. So the magnetic field is supplied by neodymium magnets.
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Re: Home built mass spectrometer

Post by John Futter »

Ok thanks for the update on how you are doing it
The double peaks might be from not having a load on your acceleration voltage so that what is commanded to the power supply is not the actual voltage due little load and some stray capacitance in your system keeping the actual acceleration voltage higher than what you think. Work out what your max accel voltage is and load the accel psu to half of its current capability with a resistor to earth, and do your scans much slower to allow the voltage to track correctly especially if you are using coaxial cables to supply your acceleration voltage from the PSU to the accel stage ( remember about 100pF per meter)
Jan Ohlsson
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Re: Home built mass spectrometer

Post by Jan Ohlsson »

Thanks John, that could very well be the case. Will look into that.
ChristofferBraestrup
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Re: Home built mass spectrometer

Post by ChristofferBraestrup »

Great work!

This might be the highest resolution mass spectra I've seen on a DIY instrument!

Sweeping a magnetic field is difficult, and requires a lot of heavy iron and coiling to get a uniform field, I can understand using permanent magnets.

Have you considered a quadrupole mass analyzer? The geometry of the parallel rods is tricky, but afterwards it should be pretty easy to operate.

-An ion shutter could be used to remove the return sweep peaks. Another option is to try and do a VERY slow ramp from min to max, over many minutes. That might also give good resolution.
Jan Ohlsson
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Re: Home built mass spectrometer

Post by Jan Ohlsson »

Hi Christoffer, thanks for the kind remarks!
I have changed to a slower sweep now (15 s per sweep), as you suggest, which does not cause double peaks any more. It is still quick enough for helium leak detection. But the triangle wave still causes some differences in peak height on forward and reverse sweeps, so I will go for a sawtooth waveform as soon as I get delivery of an oscillator capable of that.

Regards,
Jan
Jan Ohlsson
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Re: Home built mass spectrometer

Post by Jan Ohlsson »

Yes, the quadropole. I thought abut it, but the demand for absolute parallell rods are beyond my machining and mechanical skills...

Jan
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