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If you are interested to get a cloud chamber, here is some information 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 action 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, they are very easy to build.

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 to 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 particle in the first run (you need to wait about 15-20 min before observing something of interest) 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 rather 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 (hidden with paint ^^), cable management would not be perfect, the overall construction will look a bit like ‘craftmanship’ (oh that solder could have been better…). But in a nutshell, the ‘low cost’ approach only impacts the look, not the safety or reliability of the machine.

For me, a cloud chamber is a powerful teaching tool but first remains a scientific experiment. It should have the 3 following feature:

1) 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 chamber. The air space between the 2 glass container is heated to ~25°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 (< 20°C) 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 with double glass chambers, viewing through 2 layers of thick glass (about 5 mm each) 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 ; in these conditions it’s difficult to use a camera to capture the events. It also adds extra weight for the machine (+5 or 6 kg). 

I prefer using single-glass enclosure like all the physicists of the last century used to (example of older reviews). With this design, it’s easier to access the interaction surface (to put radioactive substances for example). But a single-glass approach implies that the cloud chamber should be used in room temperature > 22°C . It can work in cold rooms but only during a short amount of time (~1-2 hours) before condensation starts appearing on the top or side walls. The condensation can be removed with a hair dryer, gently heating the surface from a distance for a few seconds, but this operation perturbates the equilibrium inside the machine. That’s why my machines are not designed to work for a day in cold environment, but they are very powerful when used during a window of a few hours (this time is far enough for a presentation, a lecture or a demonstration). If the outside temperature is > 24°C, the machine can work several hours without condensation effect.

2) The machine or ‘the experience’ should be easily usable and easy to modify for anyone with minimal knowledge.

3) The design should allow the use of magnetic fields to observe the deflection of light particles (electrons, positons, slow muons). It’s a good practical exercise for students because measuring the angle of curvature of a particle allows to calculate its energy. The magnetic field B is created by a strong NdFeB magnet put under the active surface. A magnetic field can display beautiful examples of interactions of particles with matter. It also allows to discriminate between positive and negative particles just by looking at the direction of deviation. Examples of pictures below, with some shots taken from the videos below the page. In the machine, the north face of the magnet is located 30mm under the active surface. The intensity of magnetic field in the chamber is thus about 50 mT. According to the right hand rule, a charged particle will curve perpendicularly to both the velocity vector v and the B field. In the chamber, the North face of the magnet is pointed ‘to the sky’. So a positon will curve to the right. An electron, to the left (you can use your left hand to figure out the vectors for negative particles).  Let’s check that in the pictures. First, 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 (which are electrons) 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 or upward it doesn’t matter) 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 if you missed it). 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 stronger with particles of few kinetic energy (low velocity), the electron is subject to the Lorentz force and thus is 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 with electron being deflected towards the left, we are now certain that the whole track was an electron. 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. 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 about 107 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, in a city, so 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 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 presents in the chamber.

It is truly nice to describe so many events with just a single picture and a magnet!

The machine of 2020

I made a 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 42cm. 

Here is a video showing the machine in action:

After 2 hours of running:

Modern electronics are fantastic and omnipresent in our world, but I don’t always trust them. I’m still impressed to see an old fridge working after 30 years and this is also what I want to achieve when designing my cloud chambers. In order to have reliable machines, mechanical switches and basic electronics features should be used instead. The electrical components of the machine should be easily replaceable and at a reasonable cost, in case of failure. Reasonable means here 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 (220VAC compressor + condenser with fan). It provides an active surface cooled at about -30°C to -35°C depending of the room’s temperature. This circuit is designed to work for years without maintenance. However, any pressurized circuit can have infinitesimal leaks and with a long period of time the circuit loses its charge of refrigerant and the performance of cooling decrease. Roughly, about 5 years or more, and only when there is a lack of performances (low cooling capability) it may be necessary to refill the circuit with refrigerant. It’s an operation that any HVAC technician can do through the two services valve which are presents in the machine. You can also do it yourself if you have the required hardware (a manifold gauge, a vacuum pump and a refrigerant canister, that’s about $200).  The compressor is massive and of high quality with a life expectancy of minimum 15 years ; the assembly of the refrigerating circuit is made with careful operations to not contaminate the inside circuit or to reduce the life of the compressor by overheating or overcharging ; If the condenser’s fan fails, the compressor is protected by a Danfoss pressure switch. The fan of the condenser, as a standard piece, can be easily replaced in case of failure. The design of the machine is designed so that in case of failure of the compressor, a new one can be soldered to the circuit without destroying the whole machine. The cooling circuit is only made of copper, as well as the condenser, to prevent any galvanic internal corrosion.
  • A standard 30A DC power supply. It converts the main supply from 220V AC to 12VDC. The 12V feeds the peristaltic pump, the LCD temperature controller, the two led lights and the resistive wire present in the alcohol tank gutter. The power supply is easy to replace and to re-wire according to the electric wiring diagram of the machine.
  • An optional peristaltic pump to provide alcohol in the upper gutter-tank. Two switches can control its speed and the direction of flow: pumping or putting alcohol in the tank. Easy to find and replace in case of failure. This pump is used only for very long run (> 4 hours) .
  • A mechanical main switch to ON or OFF the machine. The 220V supply the compressor, the condenser’s fan, the DC power supply 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. You can control the temperature in the tank with this controller (if you want to). 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. Easy to find and replace.
  • Two 12V led light bar to provide illumination in the chamber. Life expectancy is supposed to be a few thousand hours. Tiny fans are put on the lights to reduce heat and increase their life expectancy. These led bars are commonly sold for 4WD vehicles to provide additional outdoor lights and are quite heavy-duty.
  • 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 if I can compare. In normal use, you can’t physically access the HV wires because they are secure inside the glass container.

There is a space under the active surface to place a magnet of maximum dimensions 20 x 20 x 2,8 cm. A magnet half of this size is enough to see interesting events.

To start up the machine :

    1. Remove the glass chamber,
    2. Pour about 250 ml of alcohol in the alcohol tank. You can also keep the glass chamber in place and use the peristaltic pump. This amount of alcohol is enough for a non-stop working during 3-4 hours. I recommend using isopropanol which is costly but far less toxic than methanol. If you use methanol be sure to wear a mask to avoid breathing the vapors when you remove the glass chamber. 
    3. Put the glass chamber back,
    4. Switch on the machine with the main switch. 
    5. Wait ~7 min to observe the first particles. Here is a video showing the start-up and when the first particles appears:

I don’t know any compressor-cooled cloud chambers that can display particles in less than 5-7 minutes. Manufacturers of ‘museum class’ cloud chambers don’t publish videos of the startup of their machines.

If you want to operate the machine for a day long, you have to follow theses steps :

  1. The room temperature should not exceed 35°C, so the compressor will stay cool during the whole operation.
  2. Put 300 ml of alcohol in the gutter tank (max capacity is 350 mL).
  3. Every 4 hours: stop the machine. Wear a disposal glove and remove the glass container. The alcohol evaporates from the alcohol gutter tank and condense on the active surface. An excess of liquid alcohol on the surface reduce the effectiveness of cooling so it should be removed. The excess of liquid can be collected by a hole on the surface, which is connected through a tube to the alcohol reservoir. With your gloved hands, displace the rest of liquid present on the surface to the tiny hole, to force the alcohol to go to the reservoir. If you are in hurry you can also use a dry sponge to absorb all the liquid. Note: at this step, the surface is still very cold so the alcohol can’t evaporate.
  4. Re-fill the gutter tank with the alcohol you just collected,
  5. When the surface is free of liquid (or just wet), put back the glass container and power-on the machine. 

Drawbacks of the machine

  • The single glass design is more sensible to cold environments. It’s preferable to operate the machine during 1-2 hours, or longer in warm environments (> 24°C). In cold environments, some condensation can appear on the top glass, reducing the visibility. Condensation can be removed with a gentle heat source. A too hot heat source will modify the equilibrium and the particles will disappear for few minutes. A good heat source is to put your hand on the glass for a dozen of seconds, until the condensation is removed. Another problem is sometimes it can appear on the surface long curtains of drops which prevent the formation of any tracks in that region. This effect come from a non uniform top-glass temperature due to a cold environment. The solution is to direct a stream of warm air at the top glass. This is clearly the main drawback of this machine as it require a bit practice to master the machine. I’m working about this problem.
  • Unlike ‘museum class’ chambers, the evaporator (active surface) is not massive thus the thermal inertia is poor. That means the compressor should run continuously to create a cold surface so the machine can not be qualified as ‘silent’ as the others chambers. The advantage of using a lightweight evaporator is that it gives a good start-up time (the time needed before observing the first particles) and spare about 6 kg less on the overall weight. 
  • The top of the chamber is made of 2 mm thick glass (a low thickness improve the visibility), so this top is fragile and should be manipulated with care. In case of issue, it’s easy to replace any glass part from any hardware store. This is however not sekurit glass. The walls of the chamber are 4 mm thick.
  • The lighting is accessible from outside the chamber, like the power supply cable which can simply be removed. The corners of the top glass chamber can be quite sharp. The cap nuts can easily be removed to access the inside of the machine. So, unqualified people (children, public) should not touch the machine and this one should always be operated with the surveillance of a qualified person.
  • It’s necessary to manually remove the condensed alcohol presents on the active surface after a few hours . There is a hole that collects a bit of this excess of alcohol, but it’s not enough to collect it all (due to a problem of pressure equalization and surface tension that would require a bigger hole but affecting the viewing). ‘Museum class’ chambers use gutters placed along the peripheral of the active surface, so the alcohol falls from the sides, resulting in an efficient collection. But this setup implies to build a bigger machine.
  • A magnetic field can be put only on one third of the area of the active surface.
  • The overall dimensions of the machine are kept to a minimum so there is few room for vibrations dampening or noise reduction. 10 mm of vibration dampers are put under the compressor and condenser. It could be useful to place the machine on a vibration damping pad.
  • The machine weight 25 kg and I can move it alone through stairs, but you need to be in good condition for that. Otherwise, just use a trolley. I can’t make it lighter, without sacrificing the reliability of it.
  • The layer on the active surface can be changed if it’s damaged by scratches. It’s a simple and inexpensive operation but requires 15 min of time.
  • After hours of usage, it’s necessary to check if there is any residual condensation or drops of water on the metals parts in contact with the cold surface (for example screws which are put under the evaporator, inside the machine). It’s a routine operation. The condensation can be simply removed with a cloth.

I’m working about the CE marking, to meet safety, health, and environmental protection requirements. I’m satisfied about this version but I guess the next won’t have a peristaltic pump, an alcohol reservoir and an alcohol exit hole on the surface. It’s easier to collect the alcohol with a sponge after some hours and put it back in the gutters with a funnel. Simpler is better !

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

For a 110VAC version, I need to build a specific one and invest in hard hardware so it will be more costly. We 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 60Hz 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, I need a powerful frequency converter. So at this moment, I’m stuck with the 110V 60 Hz countries :/

If you are interested to get a cloud chamber, you can contact me below.

Note: This machine is built for teachers, speakers or researchers. It’s not designed for museum as it’s not fully automatic in operations. I can’t build many machines because it requires a lot of time for each, so the shipping time can be long.

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.