The 'Crown of Nobles' Noble Gas Tube Display (2024)

Source: Hacker News

Desktop Display for Noble‑Gas Tubes

I work with ion thrusters for spacecraft. These electric‑powered rockets expel xenon gas at extremely high speeds to generate thrust and adjust a satellite’s orbit.

• Xenon is a heavy, noble gas that doesn’t react with engine components, making it ideal for in‑space propulsion.
• It is the heaviest non‑radioactive noble gas (radon and oganesson are radioactive).
• Lighter noble gases such as helium, neon, argon, or krypton can be used, but xenon delivers the best performance.

Alternative Propellants

Some cutting‑edge ion engines are experimenting with reactive fuels that can be stored as solids, eliminating the need for high‑pressure tanks:

• Iodine
• Zinc
• Bismuth

These alternatives reduce the risk of leaks or tank ruptures, but xenon remains the most proven, high‑performing propellant today.

Why a Desk Display?

Working with xenon in the lab feels abstract:

• The gas is stored in large metal cylinders.
• It travels through a complex network of tubes, valves, and pressure gauges.
• Hot‑fire tests are performed in massive vacuum chambers, where the thruster’s electromagnetic fields make direct interaction impossible.

I wanted a hands‑on desktop display to:

1. Visualize the behavior of ionized gases.
2. Have a tangible “scapegoat” for troubleshooting propulsion issues.

Amazon sells noble‑gas illumination tubes (no xenon‑only option). I purchased a 5‑pack of all the noble gases:

HMME 99.999% Luminous Noble Gas Collection (5‑Pack)

The only missing piece was a mount for the tubes, so I designed and built a custom stand myself. Below is a long‑exposure photograph of the finished setup:

Figure: Custom‑built stand holding the five noble‑gas tubes.

Building the Gas Tube Display

After acquiring the gas tubes, the stand required three things:

1. A high‑voltage RF power source to ionize the gas.
2. An electrical coupling between the power source and the tubes.
3. A structure to hold the tubes.

1. High‑Voltage RF Power Source

The easiest (and, in my opinion, safest) way to obtain a high‑voltage RF source was to repurpose the base of a plasma ball toy.

• Why a plasma ball?

  • Cheap, portable, and can be battery‑powered.
  • Wikipedia cites that plasma lamps typically output 35 kHz currents at 2–5 kV.
  • From a 5 W supply the maximum current is roughly 5 W / 2000 V ≈ 2.5 mA, well within the safe exposure zone for AC currents.

• Safety checks

  • I measured the output with a high‑voltage probe on an oscilloscope.
  • The frequency was in the low‑20 kHz range, and the peak‑to‑peak voltage was at least ≈ 1.5 kV (the reading fluctuated due to RF coupling).
  • Even though this is “safe enough,” the voltage is only an order of magnitude away from the dangerous >30 mA region, so extreme caution is required.

⚠️ Warning: Opening a plasma ball and working with high‑voltage RF can be hazardous. I do not provide CAD files for this part, and I do not recommend anyone attempt it without proper test equipment and safety precautions.

2. Electrical Coupling to the Gas

Directly touching the high‑voltage wire to the tubes does nothing; the energy must be capacitively coupled through the glass.

• In a standard plasma ball, a hollow post filled with crumpled metal mesh (similar to steel wool) acts as an antenna. The high‑voltage wire contacts this mesh, and the antenna radiates energy into the surrounding gas.
• For the gas tubes, I inverted the concept: a metal “antenna” (made from a small piece of tinfoil) was wrapped around each tube, allowing the RF field to couple through the glass and ionize the gas.

Switching Between Tubes

I wasn’t sure the system could ionize all five tubes simultaneously, so I added a dial switch to select one tube at a time.

• The switch sits between the power supply and each tinfoil cap.
• Hot‑glue was used to prevent arcing at the solder joints, and high‑voltage wire from my DIY laser cutter was used to avoid breakdown.
• The design is a weak point: there is noticeable crosstalk, but it works well enough for a simple demonstration.

3. Mechanical Structure

The holder was designed in CAD and 3‑D printed. The process involved:

1. Measuring the plasma‑ball base, gas tubes, and switch.
2. Iterating the design a few times to achieve a snug, aesthetically pleasing fit.

The final assembly shows:

• Left: Early prototypes and the number of attempts required.
• Center: Wire exits from each tube holder; the gas tubes (with tinfoil caps and rubber gaskets) are pressed onto these posts.
• Right: The completed stand, achieving the desired “mad‑science” look.

Final Thoughts

The project demonstrates a low‑cost way to create a gas‑tube display using a repurposed plasma ball, simple capacitive coupling, and a 3‑D‑printed holder. While the electrical design is functional, it is not optimized for RF performance or safety. Anyone attempting a similar build should:

• Verify voltage and current levels with appropriate high‑voltage measurement tools.
• Insulate all high‑voltage connections and keep a safe distance from the RF source.
• Consider using proper RF components (e.g., matching networks, shielding) if higher reliability or multiple‑tube operation is desired.

Lighting the Crown of Nobles

Here’s a video of the crown in action, switching between lighting the different gases. It can be fairly hard to see anything but the neon during the day, but at night in a dark room all the gases come alive.

This thing is an RF beehive and doesn’t always work as cleanly as in the video above:

• Heavier‑element gases (especially xenon) don’t always ionize when you flip the switch. I have to fiddle with the tube—touching it or grabbing the base—to encourage it to light up. You can see me do this briefly in the video when the xenon doesn’t ignite immediately. My theory is that my hand acts as a better capacitive ground than the surrounding air, allowing more of the voltage drop to occur across the gas tube.
• Neon is the easiest gas to ionize, and it often “steals” the signal from its neighboring helium or argon tubes. This is visible in the video when the switch is set to argon. The crosstalk and RF coupling in the wiring cause this behavior. I don’t fully understand why this happens—intuitively I would have thought xenon would be the easiest to ignite because it has the lowest ionization energy of the gases involved. The discrepancy may be due to different pressures in the tubes. If anyone can explain this phenomenon, I’d love to hear about it in the comments.
• There are plenty of reports of plasma balls emitting enough RF energy to interfere with nearby electronics. You also have to keep the ionized gas away from metal objects that might capacitively couple to it and cause arcing, which can start fires. See, for example, this video of someone burning their fingernail by wrapping a plasma ball in tinfoil.

Ultimately, I’m very pleased with the whole project. The xenon is especially beautiful, with its yellow core fading out to blue, and touching the tubes to make the beams bend and dance never gets old. It’s a fun little desk toy, and I get to play with my “propellant” as much as I want now—great for building hands‑on intuition about the nature of these ionized noble gases.