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If you are interested to get a cloud chamber, here is some informations about my buildings.

 

Choice of technology

A diffusion cloud chamber requires a cool source of about -30°C with a good coefficient of performance. There are 3 technologies that can achieve that : dry ice, thermoelectric cells or gaz compressors. This page compares the pros and cons of each of these technologies.

I don’t build thermoelectric cloud chambers anymore, a technology you can see in the ‘experiences page’ (I started them in 2010).  With thermoelectric cells, it’s impossible to have an interaction surface bigger than 130 cm², because it requires a nuclear power plant and a truck to move ! In the long term, I’m not convinced about their reliability because peltier cells need to be periodically replaced by new cells to keep good cooling performance (and they are more and more costly). On the contrary, thermoelectric machines are very easy to build thus are perfect for Do It Yourself projects.

Now, I rather focus on cloud chambers cooled by a compressor (like a fridge). The building of a compressor-cooled cloud chamber is MUCH more complicated than doing a thermoelectric machine but it has some advantages : almost no maintenance, years of reliability (even a decade), any dimensions of surfaces can be reached and power consumption and price remain acceptable. 

About the design of a compressor-cooled cloud chamber

There are lot of designs possible which depend on how is used the machine.  On the market one can find several ‘museum class’ compressor-cooled cloud chambers (Phywe for example). The looks are perfect and theses machines can run continuously through days. They are really exceptional. But they have big drawbacks : they are heavy, voluminous, thus impossible to move alone; they are costly (starting price about 30/ 40.000 euros) ; they are limited in their functions (difficulty to introduce specifics radioactive sources and unable to use magnetic fields to see the deviations of particles); they are slow to display particles in the first run (you need to wait about 15-20 min before observing something of interest due to inertia) and they use complicated mechanisms that prove costly to replace in case of failure.

I’m not interested to be a competitor of ‘this market’. I’m focused in building ‘low cost machines’ with the best experience possible. ‘Low cost’ means that my designs will suffer from a lack of aesthetics : there will be some scratches from the construction, cable management would not be perfect, the cuts will not absolutely be straight ; so the overall construction will look a bit like ‘craftmanship’ (oh that solder could have been better…), … In a nutshell, I don’t attach much importance to the look, rather on the reliability of the machine.

For me, a cloud chamber remains a scientific experiment. It should have the 2 following features :

  • 1) As a machine : Simpler is better. The construction must be built with the minimum necessary while keeping a good quality of visualization of the particles. 
  • 2) As a scientific experiment.  To observe the interactions of particles in matter it’s essential to use a magnetic field in the chamber. Also, the machine should allow the introduction of different radioactive sources in the chamber.

 

1) Simpler is better

The machine should be built with the simplest materials without loosing the quality of the tracks displayed. A minimalist design results in a machine of low weight, easy to move around by a single person. One particular point is the design of the chamber, made of glass. In ‘museum class’ cloud chambers, there are always 2 glass containers. The first is the chamber surrounding the active surface and the second glass container encapsulates the first. The air space between the 2 glass container is heated to ~30°C which prevents the formation of condensation along the walls of the primary glass container. A double glass chamber allows to use the machine in cold temperatures conditions and in non-stable temperature rooms. Thus, long operations can be reached with this design : the machine can run for days without being impacted by the environment.

Schematic of a Phywe PJ45 cloud chamber, using 2 glass containers.

Unfortunately viewing through 2 layers of thick glass deteriorates the quality of observation. The observer is far from the interaction surface and there are losses of contrast from glass-absorption and parasitic reflections. Double glass enclosure adds extra weight for the machine and it’s difficult to introduce radioactive sources inside the chamber because you have to cross 2 layers of glass.

Knowing this, I prefer using single-glass enclosure like all the physicists of the last century used to. But this implies that the top of the primary container has to be heated by an external thermal source. Indeed, the bottom of the chamber is at -35°C so the top glass of the chamber freeze over time resulting in the formation of condensation reducing the visibility. The condensation act like another source of evaporation of alcohol which perturb the equilibrium by inducing turbulences. So it’s important to not let some condensation form on the top glass.  For this, the surface has to be warmed by an external thermal source like an infrared lamp or a fan heater. If the top surface is heated, the machine can work several hours even if the room temperature is very cold. You can see that below with the machine working 7 hours in a room temperature of 13°C :

Modern electronics are fantastic and omnipresent in our world but I don’t trust them. I’m still impressed to see an old fridge working after 30 years and this is what I want to achieve when designing my cloud chambers. So my machines use basic electronics features, mechanical switches and theses components are easily replaceable at reasonable cost in case of failure. Reasonable means a few dozen euros, and easily means that you can buy these common components from any source like ebay or amazon, any time in the next 15 years and thus avoid any vendor-locking.

My cloud chamber have the following electrical components :

  • An isolated cooling circuit. It provides an active surface cooled at about -30°C to -40°C. This circuit is designed to work for years without maintenance, it has the same components of an old fridge : a compressor, a filter drier, a condenser with fan and the evaporator (interaction surface). 
  • A standard 30A DC power supply. It converts the main supply from 220V AC to 12VDC. The 12V feeds the LCD temperature controller, the led light and some resistive wires for heating. 
  • A mechanical main switch to ON or OFF the machine. The 220V supply the compressor, the condenser’s fan, the DC power supply, the IR lamp and the high voltage circuit.
  • A temperature controller. It shows the temperature of the active surface and the temperature inside the alcohol gutter tank in the chamber. The controller keeps the temperature to the desired value at any time thanks to a relay and a resistive wire that heat or let cool the alcohol tank. 
  • A 12V led light bar to provide illumination in the chamber. Life expectancy is supposed to be a few thousand hours. Led bars are commonly sold for 4WD vehicles to provide additional outdoor lights and are quite heavy-duty. 
  • A high voltage circuit to provide about 2500 VDC in the top wire of the chamber, located above the alcohol gutter. If you ever happen to touch this circuit with your hands, you will feel a spike like an electrostatic discharge. « High voltage » here does not mean it is a danger to you, because the amperage is just a few microamps ! The shock is identical to a mosquito electric racket. In normal use you can’t physically access the HV wires because they are inside the glass container.

 

2) A scientific experiment

 The machine should allow the use of magnetic fields to observe the deflection of light particles (electrons, positons, slow muons).  A magnetic field allows to discriminate between positive and negative particles just by looking at their direction of deviation. The magnetic field B is created by a NdFeB magnet put 30 mm under the active surface. The intensity of magnetic field in the chamber is about 50 mT.

The North face of the magnet (direction of B) is located under the active surface and pointing ‘to us’. According to the right hand rule , a charged particle will curve perpendicularly to both the velocity vector v and the B field. So a positon (+q) will curve to the right and an electron (-q), to the left

Examples with some pictures taken from the videos in this page. Without a magnetic field it’s impossible to say if we are observing an electron or a positon, unless we are looking at a delta ray, which is an electron ejected from an atom by an incoming particle. So we must find a delta ray to check the directions of motion of negative particles in the chamber :

We have to find a recognizable negative particle to determinate the direction of curvature. Only delta ray (electron coming from the ionization of an atom) can give this information.

The above picture is taken at 1 min 12 from the video, after 2 hours of run. At the position 1 above we have a particle travelling downward and at 2, it produces a delta ray (ionization of an atom). The ejected electron is going towards left making a curve at position 3. So, as we said, electron indeed moves « to the left » in the chamber, according to the direction of B field.

Let’s now study another picture :

Find this event at 1 min 36 seconds in the video « after 2 hours of run »

Above : An electron of high energy at point 1 is moving upward and undergo a hard electrostatic collision with a nucleus at point 2 (we described this event there). The nucleus can be from an atom of O,C,N,H… In the collision, the electron loses a great amount of energy by Bremsstrahlung as the angle of diffusion is about 140°, so it almost bounced back ! In 3 as the Lorentz force is bigger with particles of few kinetic energy (low velocity), the electron is strongly deflected towards the left and end in point 4, when all it’s kinetic energy is depleted. As we previously observed in the last picture that an electron is deflected towards the left, we are now certain that the whole track was an electron and not a positon. Can you see something new in the same picture? Just look the beautiful curve at the middle-left. The particle is deflected to the…right, it’s a positon ! (produced from a gamma annihilation). 

Proton moving upward with a delta ray. Find this event at 1 min 20 seconds in the video « after 2 hours of run ».

Above : here we have something new. We know that there is a magnetic field in the left bottom corner of the chamber. But at 1 we have a track which undergo no deflection. Lorentz force says that it’s proportional to the velocity and the mass of the particle (remember that the radius of curvature = mv/Bq). So a fast or a massive particle will have R→∞ and so no curvature can be seen : the trajectory will be linear. That’s what we observe in the picture. Looking at the angle of emission of the delta ray produced in point 2, we can affirm that the particle is moving upward. The little delta ray tries to move to the left (it feels the Lorentz force because of it’s low kinetic energy) but it fails making a nice curve, because at mid range it expect a nuclear collision that bounces it upward.

Back to the primary particle 1. The absence of deflection means that the particle is massive or have a great velocity, or both. The density of ionization (number of droplets in the track) is important. We know that heavy particles are much more excitating/ionising than electrons, thus produce denser tracks. You can compare the density of the track 1 to the one of electrons present in the far left of the picture : electron’s tracks are thinier, about to 3 to 4 times less than the track 1. So it’s not an electron (or positon). Could it be a muon? Very unlikely, because we know that the horizontal flux of muons is about 300 times less than the vertical flux. The video was taken in a room above 2,5 m of the ground surrounded by buildings. The direction of motion of the particle imply that if it was a muon, it would have traversed about 500 concrete walls before coming to the cloud chamber, so it would have an enormous initial energy, which looks quite impossible from the intensity curve of muon flux at sea level. A muon has a mass of 207 me so we should have observed a very slight deflection, but there is nothing like that here. Could it be a proton? Very likely, because protons are created locally anywhere by natural neutrons. It may have been produced in the glass wall of the chamber at an energy of a few dozen MeV, and its great mass (937 me) makes it insensitive to the magnetic field.

With single picture, many physicals interactions can be explained thanks to a magnetic field. And by measuring the angle of curvature of a particle, you can also estimate it’s energy (a good practical exercise for students !).

 


The machine of 2020/2021

I made a complete new cloud chamber during the Covid events in April 2020. I didn’t have access to new materials so I made it from scratch parts so the aesthetic could be slightly better.  Here is a picture :

The weight is about 25 kg. The active surface is ~40 x 20 cm. The dimensions of the whole machine are 45 x 55 cm (including lights), with a total height of 42 cm. 

Here is a video showing the machine in action (recorded 2 months after its build) :

I made some crash tests during May-December 2020 then early 2021 I simplified the chamber. Only the glass container was modified (way to evaporate alcohol, height of the chamber, layout of the electric field and light, recovery of the condensed alcohol…). The latest version of the machine is below. This video will show you how to operate it. The equilibrium is reached 8-10 min after powering up the machine.

The last version, still a prototype, but not far from the final built. 

I’m very satisfied about the quality of the tracks and the reliability mainly because it can work in cold or hot temperature rooms. The main drawback is that the infrared light is needed during the operation (it don’t disturb the visibility of the particles for the viewers). I made other constructions which don’t need this thermal source, but the quality of seeing is not as good as with the thermal lamp. I can use a fan heater to warm the top surface but this produce an additional loud. So I decided to keep the silent thermal IR lamp in my next designs. If you remove the IR light, the machine will work with no change during a dozen of minutes, then some mist will form on the top and will deteriorate the equilibrium.

I don’t have much modifications left to do. What the next version will need is better connectors, security, cables managements, design….

I’m currently working about the CE marking to have the right to sell this machine on European market. This step is almost completed, I wrote all the documentations needed for that.

 


For this machine, still in an experimental state, the price will be ~4500 € for 220VAC@50Hz countries.

Engineering note : For a 110VAC version, I need to build a specific one and invest in heavy hardware. I can’t use simply a step-up transformer 110VAC to 220VAC and feed the machine with, because 110VAC country output 60 Hz and the compressor is designed to work at 50 Hz. This imply that the compressor will run at 220VAC@60Hz, and thus will turn 20% faster, reducing its life expectancy. So a machine working on a power grid at 60 Hz should use components designed to work at 60 Hz. To build a reliable machine working at 110VAC@60Hz living in a country where it’s 220VAC@50Hz (France), I need a powerful and costly frequency converter. For this reason I decided to not build machines for 110V 60 Hz countries :/

 

If you are interested to get such cloud chamber, you can contact me below but please note that the building time is important so I can’t respond to hurry requests.

My lab is located near Avignon, France. 

 

Please don’t ask me how to build your own cloud chamber, as I don’t have much time to help everyone and there is enough information on internet to make your own. I hope you will understand that I’ve spent nearly 10 years to have something workable so I can’t give you all the secrets of the internal working of the machine. Thanks for your interest.