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James Doherty | Open University | United Kingdom

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Physics + wine = plasma + fun

Ever fancied making your own particle accelerator? Fermilab posted a great blog entry last month (here) showing how anyone can make a particle detector for viewing cosmic rays. In this post, I will explain how particle accelerators can also be hacked so that you can make your very own cathode ray tube (CRT).

I came across this experiment when attending an accelerator school at the Australian Synchrotron last year. To read more about my adventures down under please see Accelerating Down Under and If you can’t stand the heat, get into the Synchrotron!.

What is a cathode ray tube?

Good question. It consists of a vacuum chamber containing some electrodes between which a high voltage is applied. Electrons are accelerated from the negatively charged cathode to the positively charged anode. But some electrons fly past the anode to hit a glass wall. CRTs were utilised in old television sets to form images on a fluorescent screen.

Ingredients

You will need:

  • – a clear wine bottle
  • – a vacuum pump
  • – a rubber hose
  • – epoxy resin
  • – mini chrome-plated metal doorknob
  • – a piece of steel brake line
  • – a piece of steel wire several centimetres long
Empty wine bottles at the Australian Synchrotron.

Experimental preparation at the Australian Synchrotron: GRAPE 1, 2 & 3. Image credit: Ralph Steinhagen.

Recipe

A detailed method for this experiment may be found (here) but I summarise the main steps below:

  1. Drink a bottle of wine. Wash out the wine bottle with warm soapy water and remove all labelling from the exterior.
  2. Drill a hole about 1/2 way down the wine bottle which is big enough to fit the metal wire through. This will act as the mount for the anode. If your bottle cracks, throw it away and return to step 1.
  3. Drill a hole through the metal doorknob. Use epoxy to attach the break line to the doorknob’s screw mount. This will act both as the cathode and vacuum port. Apply epoxy to the rim of the mouth of the wine bottle and attach the cathode to form an airtight seal.
  4. Bend the steel wire into a C-shape and thread it through the hole you drilled in the wall of the wine bottle. This is your anode. Orient it so that all points on it are equidistant from your cathode. Secure it with epoxy and ensure it is airtight.
  5. Attach the rubber hose to your anode and the other end to the vacuum pump. Attach the anode and cathode to a high voltage power supply. Turn on the power supply and vacuum pump and enjoy!

 

GRAPE 2

The GRAPE 2 experiment: a vacuum pump is connected to the experiment via the rubber tube to the right of the bottle. The anode and cathode, which are connected to a high voltage supply, are seen to glow. Image credit: Ralph Steinhagen.

Safety

A word of warning: using high voltages, creating vacuums and drilling holes in glass bottles are all inherently dangerous activities. If you attempt this experiment please observe all safety advice. In particular, wear protective clothing and safety glasses, don’t use cracked bottles for the experiment – you risk implosion – and apply the voltage for a maximum of 30/40 seconds.

And please leave adequate time between consuming the wine and carrying out the experiment to sober up.

Plasmatastic!

The video below shows what happened when the switch was flicked on the GRAPE 2 experiment at the Australian Synchrotron:

 

Initially there is a clear purple electric discharge between the anode and cathode. This discharge excites the atoms in the gas in the bottle causing a burst of liberated free electrons. The electrons are travelling much faster than the positive ions they leave behind and so diffuse to the cathode and bottle walls. Thus a plasma (or ionised gas) is created.

The plasma stabilises as more ionisation occurs, then begins to glow as electrons and ions recombine and emit photons. This process of ionisation and recombination is continuous. The instabilities or fluctuations observed indicate that different proportions of the remaining gas are being excited as the experiment proceeds. Can you think of why this happens? If so, please comment below.

When a magnet is placed near the bottle the plasma is visibly distorted. This phenomenon is known as magnetic deflection and is described by the Lorentz force law. The plasma’s charged particles experience a force when they travel through the magnetic field which is perpendicular both to the path they follow and to the applied magnetic field, that is the magnet causes the particles to follow a curved path. This effect is used in circular particle accelerators, such as the Large Hadron Collider, where strong dipole magnets are used to steer the particles around the machine.

A cross section of the LHC showing the dipole magnets which are used to bend the path followed by protons.

A cross section of the LHC showing the dipole magnets which are used to bend the path followed by protons. The magnets may be seen flanking the left-hand beam pipe. Image credit: James Doherty

What are you waiting for?

Particle physics is not a game that only elite scientists at well-funded institutions can play. With a little effort, determination and ingenuity, it is possible to make your own particle accelerator or detector. So what are you waiting for? Give it a go and let us know how you get on in the chat box below. Good luck!

The GRAPE 2 experiment was carried out by Kaitlin Cook, Paul Bennetto and Tom Lucas under the supervision of Ralph Steinhagen at the 2014 Australian Synchrotron Accelerator School. The above photos and video are courtesy of Ralph Steinhagen.

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