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Building The Torilux - Part I

Riccardo Fagiolo
July 22, 2025

Not long ago, I stumbled upon a fascinating project on Hackaday. The project showcased the design and construction of circuitry capable of generating a rotating magnetic field, which in turn shapes ionized gas into plasma forms using electromagnetic fields. I was immediately drawn to it, not only because of the inherent coolness of ionized gas, but also due to the connection to power electronics (my area of expertise) and the potential to create unique, visually striking plasma displays. I decided to develop my own version of the device as an affordable lighting fixture, which I’ve decided to name Torilux. I decided to start this article series as a log and guide for anyone interested in building their own version of this fascinating device.

Original Plasma Toroid Image

Original Plasma Toroid Image | Credit: Hackaday (sky_guided)

The Operating Principle

Let's assume that we have a coil and we have some sort of circuit capable of pushing a sinusoidal current through it - this coil would be a standard air-core inductor, producing an alternating magnetic field in its center. Let's try to play with some numbers to understand the behavior of the system.


Let's say we are pushing a sinusoidal current with an amplitude of 100A100 A through a coil with N=8N = 8 turns and a radius of r=8cmr = 8 cm. The amplitude of the magnetic field at the center of the coil can be easily estimated to be:

B^=μ0NI^2r=6.283  mT\hat{B} = \frac{\mu_0 N \hat{I}}{2 r} = 6.283 \; mT
Magnetic Field

Concept | Magnetic Field

The time-varying magnetic field induces an electric field in the surrounding space, which can be calculated using Faraday's law of induction:

∇×E⃗=−∂B⃗∂t⇒∣∇×E⃗∣=∣dB⃗dt∣=ωB0⇒E0=ωB0⋅l\nabla \times \vec{E} = -\frac{\partial \vec{B}}{\partial t} \quad \Rightarrow \quad \left| \nabla \times \vec{E} \right| = \left| \frac{d\vec{B}}{dt} \right| = \omega B_0 \quad \Rightarrow \quad E_0 = \omega B_0 \cdot l
Electric Field

Concept | Electric Field

With the circumference of the coil and the amplitude of the magnetic field already determined, the frequency of the current flowing through the coil remains as the main variable we can adjust. As we've just seen, increasing this frequency directly increases the strength of the resulting electric field.

E0(100  kHz)=2π⋅100  kHz⋅6.283  mT⋅2π⋅8  cm=1.984  kV/mE0(10  MHz)=2π⋅10  MHz⋅6.283  mT⋅2π⋅8  cm=198.43  kV/m\begin{aligned} E_0 (100 \; \text{kHz}) &= 2 \pi \cdot 100 \; \text{kHz} \cdot 6.283 \; \text{mT} \cdot 2 \pi \cdot 8 \; \text{cm} = 1.984 \; \text{kV/m} \\ E_0 (10 \; \text{MHz}) &= 2 \pi \cdot 10 \; \text{MHz} \cdot 6.283 \; \text{mT} \cdot 2 \pi \cdot 8 \; \text{cm} = 198.43 \; \text{kV/m} \end{aligned}

At a pressure of 20  Torr20 \; \text{Torr} - a typical value for neon display tubes - the electric field required to ionize Neon is about 250  kV/m250 \; \text{kV/m}, while for Xenon it is around 400  kV/m400 \; \text{kV/m}.


The frequency of the current flowing through the coil is directly related to the switching losses in the circuit components used to generate it. For this reason, it's best to use a frequency that is only as high as necessary to achieve the required electric field strength.


Maintaining an electric field strong enough to ionize atoms is quite challenging. Achieving this would require a larger coil with more turns, which would significantly increase power losses beyond what is practical. After all, the goal is to have a device that can run on a desk without consuming excessive power or generating too much heat.


So what purpose does our electric field serve? It is used not to ionize, but to accelerate the ions that must be produced in the gas some other way.

Producing Ions

In order to produce ions, we need to create a high electric field that can overcome the ionization energy of the gas atoms. This can be achieved by increasing the frequency of the current flowing through the coil, which in turn increases the strength of the resulting electric field.

Accelerating Ions