YOU CAN BUILD YOUR OWN FLOATING RING OF PLASMA IN A GLASS SPHERE
A glowing purple-white ring of plasma floats freely inside a glass sphere, touching nothing — held only by an electromagnetic field.
by Simon Liu
ScienceWorkshop
- difficulty
- ●●●●○
- time
- a weekend-plus
- license
- MIT
- repo
- repo ACTIVE143 stars
●●●●○ · a weekend-plus · MIT · 143 stars · repo ACTIVE
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COMPAREE VERDICT
This is a plasma toroid generator — a floating ring of ionized xenon gas, held by an electromagnetic field inside a low-pressure glass sphere. The effect is magnetic: purple-white light, no contact, a miniature cousin of fusion tokamaks. The circuit is a self-oscillating class-E amplifier driving an induction coil beneath the sphere. Simon Liu's design is complete — schematic, PCB, BOM, theory — but it assumes you can source or adapt a vacuum sphere, pump it down to a few torr, and backfill it with xenon. That is the hard part. If you have never worked with vacuum systems or high-voltage RF, this will be a steep weekend. The xenon itself is not exotic (welding suppliers stock it), but filling a small sphere to the right pressure without contamination is fiddly. The PCB is straightforward to order and assemble, the coil is wound by hand, and tuning the resonance is done with a scope and a trimmer cap. The single biggest trap is the sphere: the repository does not specify a source, and most generic vacuum chambers are steel, not glass. You will spend more time solving that than soldering. If you have the vacuum tooling and a source for a borosilicate sphere, this is a spectacular build. If you do not, budget another weekend for that problem alone.
IN THE REPO
NOT IN THE REPO
- —Repository contains schematic, PCB design, and bill of materials.
- —No CAD files — the sphere and base are machined or adapted, not printed.
- —No firmware — the circuit is analog, self-oscillating at 10-13 MHz.
- —Documentation covers theory, construction steps, and tuning procedure.
- —Licence is MIT, allows commercial use.
- —Missing: assembly photos, vacuum pump guidance, xenon filling procedure beyond text.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
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Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Read the theory document in the repository to understand the resonant LC circuit and plasma formation.(This explains why the coil geometry and sphere pressure range matter — skip it and you will tune blind.)
- 2.Source or adapt a vacuum-capable sphere — borosilicate preferred, acrylic possible if you keep power low.(The repository does not specify a supplier. Lab glassware vendors and vacuum chamber resellers are your best options.)
- 3.Order the PCB from the Gerbers in the hardware folder and buy the BOM components.(Standard through-hole and SMD parts, nothing exotic. The MOSFET and trimmer caps are the tuning heart.)
- 4.Wind the induction coil per the specs, assemble the PCB, and tune to resonance with an oscilloscope.(Resonance will be 10-13 MHz depending on coil and stray capacitance. This step takes patience.)
- 5.Pump the sphere down to a few torr and backfill with xenon, seal, power on, and adjust trimmer for stable toroid.(Too much pressure and the plasma will not form a ring; too little and it will not sustain. The sweet spot is narrow.)
KNOWN ISSUES
- The vacuum sphere is not included or specified — most builders will spend more time sourcing this than assembling the electronics.
- Xenon filling without contamination is fiddly — even trace air will shift the glow colour and stability. A proper gas handling valve or syringe port is essential.
- Resonance tuning is sensitive — a few picofarads on the trimmer cap or a turn on the coil will shift the toroid from stable to collapsed. Expect an afternoon with the scope.
- High-voltage RF at resonance can exceed 500V on the coil — touching it while powered will deliver a painful shock and possibly break the circuit. Power off before adjusting anything.
- Acrylic spheres are cheaper than borosilicate but can melt or deform under prolonged high-power operation — keep duty cycles short if using acrylic.
- The repository does not include assembly photos — you will infer coil placement and sphere mounting from the schematic and your own setup.
Can I use a different noble gas instead of xenon?
Yes — argon, neon, and krypton all work, but the glow colour and ionization threshold will change. Xenon is chosen for its purple-white colour and lower breakdown voltage. Neon will glow orange-red, argon pale blue. Adjust pressure and power accordingly.
Do I need a vacuum pump, or can I use a syringe to evacuate the sphere?
A vacuum pump is strongly recommended — you need to reach a few torr (low-pressure regime) for the toroid to form cleanly. A syringe or aspirator will not pull low enough. Borrow or rent a rotary vane pump if you do not own one.
What size sphere should I use?
The repository does not specify a diameter, but typical plasma toroids are stable in 10-15 cm spheres. Smaller spheres make tuning harder; larger ones need more power. Start in that range.
How much power does this draw?
The circuit runs on 12-24V DC input and draws a few watts in steady state, spikes higher during initial plasma formation. Total draw is modest, but the RF field is intense locally around the coil.
Is this safe to run continuously?
Continuous operation is possible if the sphere and coil do not overheat, but most builders run it in short bursts — a few minutes on, a few minutes off. The high-voltage RF is present whenever powered, so treat it as live.
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FROM THE COMPAREE TEAM
The hardest part is not the circuit — it is sourcing a vacuum-capable sphere and filling it with xenon without contamination. Where would you start: lab glassware suppliers, a vacuum bell jar, or a custom blown sphere?
Simon Liu
Simon Liu designed the plasma toroid as a demonstration of inductively coupled plasma and resonant RF circuits. The project combines high-voltage electronics, vacuum science, and plasma physics into a visually striking tabletop experiment.
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CompareeTEAM1mo agoedited
Practical notes from our verification: the repository contains schematic, PCB Gerbers, and a detailed BOM, but no photos of the assembled unit or the coil winding in situ. The theory document is thorough and explains why the resonant frequency and pressure range matter. The single biggest gap is the vacuum sphere — no part number, no supplier, no guidance beyond 'low-pressure glass or acrylic'. If you have never worked with vacuum systems, budget a full weekend just to solve that piece. The xenon is straightforward (welding suppliers carry it), but filling to the right pressure without air contamination will test your patience. The circuit itself is elegant and well-documented; the mechanical and vacuum side is where most builders will stumble.