What is Plasma? Why should you know?

I was recently invited to a video call interview about an opening role in digital marketing. Among SEO and PPC questions, the interviewer, an engineer, asked me “what is Plasma?”. With my surprise, although I have got a background in Electronics and Telecoms in school, I was caught unprepared. So I have decided to do a little research online. This might help you to know too… or maybe not.

Spoiler alert: No, I didn’t get the job in the end, but that is another story.

The Plasma Science and Fusion Centre department of the Massachussets Institute of Technology (AKA M.I.T.) provides the following definition of Plasma:

“Plasma is often called “the fourth state of matter,” along with solid, liquid and gas. Just as a liquid will boil, changing into a gas when energy is added, heating a gas will form a plasma – a soup of positively charged particles (ions) and negatively charged particles (electrons)”.

In another way, Plasma is an ionised gas, meaning it consists of highly charged particles known as ions and free electrons. Plasma is created when gas is subjected to extreme heat or when a strong electric field is applied, causing the gas atoms to lose electrons and become charged. In a plasma state, the atoms of the gas break apart, resulting in a mixture of positively charged ions and negatively charged electrons. This separation of charges allows plasma to conduct electricity and be influenced by magnetic fields, making it a unique and versatile state of matter.

Why Plasma is important for the Industrial applications?

Plasma can be artificially created and controlled in laboratories for various applications, such as fusion research, plasma cutting in metalworking and nano electronics. In particular:

  • Thin Film Deposition: Plasma is employed to deposit thin films of materials onto various substrates. This process is widely used in the production of microelectronics, solar cells, optical coatings, and other advanced materials.
  • Plasma Etching: In semiconductor manufacturing, plasma etching is used to remove specific layers from microchips during the fabrication process. This helps create intricate patterns and structures on the chip’s surface.
  • Plasma Sterilisation: Plasma is used for sterilisation in the medical industry and for various sensitive equipment. It provides an effective and chemical-free way to kill bacteria and other harmful microorganisms.
  • Surface Modification: Plasma treatments can alter the surface properties of materials, such as making them hydrophobic or hydrophilic, improving biocompatibility for medical applications, or enhancing wear resistance in mechanical components.

What is a Plasma sensor?

Every research, industrial processes, and technologies that involve working with plasma has a Plasma sensor to detect, measure, or analyse plasma. It can provide valuable information about plasma parameters, allowing researchers and engineers to monitor, control and calibrate plasma-based systems effectively. Some common types of plasma sensors include:

  • Langmuir Probes: Langmuir probes are widely used in plasma diagnostics. They consist of small electrodes inserted into the plasma, and by measuring the current-voltage characteristics of the plasma-electrode interaction, they can determine properties like electron temperature, electron density, and plasma potential.
  • Optical Emission Spectroscopy (OES) Sensors: OES sensors use the light emitted by excited atoms and ions in the plasma to analyse the plasma’s composition and temperature. Different elements emit characteristic wavelengths of light when excited, enabling researchers to identify the elements present and their concentrations in the plasma.
  • Electrostatic Probes: Electrostatic probes are similar to Langmuir probes but operate based on the electrostatic potential difference between the plasma and a collector electrode. These probes can provide information about plasma potential and electron temperature.
  • Magnetic Probes: Magnetic probes, also known as magnetic field probes or magnetometers, are used to measure the magnetic fields produced by currents in the plasma. These measurements can help understand the behavior and confinement of plasma in magnetic fusion devices.
  • Microwave Interferometers: Microwave interferometers measure the density of the plasma by analysing the phase shift of microwaves passing through it. Changes in density cause variations in the microwave phase, which can be used to determine the plasma density.
  • Residual Gas Analysers (RGA): RGAs are mass spectrometers used to analyse the composition of gases in plasma chambers or vacuum systems. They help identify the presence of different elements and molecules in the plasma environment.
  • Plasma Optical Density Sensors: These sensors measure the optical density of the plasma, providing information about the plasma’s opacity and its interaction with light.
  • Plasma Current Probes: Plasma current probes measure the electric current flowing in the plasma. This is particularly important in magnetic confinement devices for studying plasma stability and confinement.

If you arrived here at the end of the page, well done! Maybe now you learned something new. As for me, probably even if I knew the answer, I wouldn’t have gotten the job anyway.

Till the next weird post, take care yourself!

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