Backyard Nuclear Fusion

Methods

Summary

Fusor Design 

A simple diagram of the full Fusor

The Farnsworth Fusor is essentially a particle accelerator that operates within a chamber with a level of voltage being applied to ionize the deuterium. There are 6 main sections that all play a crucial role in the Fusor operation. They are:

1. Vacuum Chamber

2. Vacuum System

3. High Voltage Supply

4. Deuterium Gas-Line

5. Radiation Detection

6. Observation

Vacuum Chamber

The first major section is the vacuum chamber. The vacuum chamber is where all of the other systems meet and where Inertial Electrostatic Confinement takes place making the fusion possible. The chamber must be metallic, stainless steel is the best choice as it has a high heat resistance and will not corrode. The chamber must include at least 5 ports and a central point of collision for the reactions. Plausible shapes for fusors include, spheres, crosses, and cylinders. The shape of the chamber is extremely important, too big in volume and the amount of pressure increases exponentially and the cost of the equipment would increase drastically. Too small and high voltage arcing issues will occur and cause the temperature of the plasma to increase, putting into effect possible grid meltdown risking damage to the grid components. In light of these dangers, a guideline for chamber diameter goes by a minimum of a 2.75” chamber with the maximum being 8”.

 After shape and size comes the ports, they are the entry points in which the other systems come together to cause fusion. These ports include:

1. A vacuum port

1. The vacuum port is the largest port and should be on the bottom of the chamber. This is for convenience as this design will allow for the chamber to rest on top of the diffusion pump.

2. A high vacuum gauge port

1. The high vacuum gauge port may be placed anywhere of convenience. It is used to measure the chamber’s pressure.

3. A high voltage feed through port

1. The high voltage feedthrough port should be facing away from any point that can be easily accessed, especially concerning the view port, for safety reasons.

1. A gas line port for deuterium

1. The deuterium port may be placed anywhere that is not directly beside the vacuum port, as this will lead to the waste of deuterium.

2. A view port, to visually analyze the reactions

1. The viewport should be facing a thick wall or be on an angle towards the ground as a cone shaped beam of x-rays will be passing through the glass, it should not be facing towards a thin wall or window.

Careful design comes into play when planning a layout for the vacuum chamber, the high voltage feedthrough, viewport and vacuum port are the ports requiring the most attention. The chamber must have a stable and strong base to hold the chamber in place. The chamber should have a protective hydrocarbon surrounding to stop radiation, this must especially be applied to the view port, as this is where the most radiation will be emitted.

Vacuum System

The purpose of the vacuum system is to reduce the chamber’s pressure down to at least one micron with the purpose of clearing the way for the gas ions to accelerate and collide. The vacuum system consists of:

1. A gate or bellows valve

1. Separates the vacuum system from the chamber

2. Fore line/ roughing mechanical pump (Primary Pump)

1. Begins the vacuum process

3. A diffusion pump or turbo pump (Secondary Pump)

1. Scientific pump that brings the vacuum down to it’s ultimate lowest level

4. Throttle Valve

1. Controls the connection between the secondary pump and primary pump

5. High Vacuum tubing or a fore line pump connection

1. Connects the secondary pump output flange to the fore line valve and Primary Pump inlet

The primary/ fore line pump or roughing pump is a dual stage mechanical pump that must have a minimum pumping power of 5 Cubic Feet per Minute (CFM). The primary pump plumbs the vacuum pressure down to around 40 microns, at this stage the secondary pump, which must be a fully functional diffusion or turbo pump is turned on and the chamber pressure reaches less than 1 micron. At this point the deuterium needle valve is opened and the deuterium gas starts filling the chamber causing the pressure rises to 5-15 microns. Skilled operation takes place here as the operator must be sure to not put too much deuterium into the chamber while also ensuring that he/she is not wasting deuterium. If too much deuterium is leaked into the vacuum chamber then the gate valve must be opened, reestablishing dynamic equilibrium. This is why the gate valve is so crucial in a vacuum system.

High Voltage Supply

The high voltage system is what ionizes the gas and accelerates the deuterium ions so they have enough energy to fuse. The high voltage system requires some understanding of electrical engineering and physics, it is an extreme safety hazard and will kill or extremely harm the operator if it is used with poor knowledge. The high voltage system does two things:

1. Ionizes the gas into plasma by stripping away the electrons from the deuterium nucleus, turning the deuterium atoms into deuterium ions causing it to have one proton and one neutron, positively charged.

2. Accelerates the newly formed deuteron ions towards a spherical anode, the inner grid, due to coulomb attraction (deuterons are positively charged, so they accelerate towards the negatively charged anode) all of the deuterons meet near this anode and have a chance of colliding and fusing.

The Fusor needs at least 10mA at 30kV to produce detectable fusion, the current must be direct current. The Fusor needs two high voltage connections: the first one is to the negative hot lead, the inner grid connection, which is what will attach to the high voltage feed through. The second output must be positive ground, which will be hooked up to the Fusor chamber shell, outer grid. If the polarity specifications are not met, then fusion will not happen. There are many different ways to achieve the 30kV 10mA minimum power supply for the Fusor. The easiest way is to buy an industrial power supply that outputs the exact power requirements needed for fusion, unfortunately these tend to cost thousands of dollars new. The more economic option is to make your own power supply, there are many different ways to do this with the most common method being the X-Ray transformer method, the parts required for this method include:

1. X-Ray transformer

1. The most common option when choosing a high voltage power transformer, the X-Ray transformer is what provides the tens of thousands of volts needed within the Fusor, it boosts the household outlet 120 volts to often more than 50,000 volts.

2. Variable Transformer

1. Controls the voltage being outputted from the X-Ray transformer as the X-Ray transformer has no controller knob of its own. Required for safety and smooth operation.

3. Ballast and resistors

1. limits the amount of current passing through to the Fusor for the purpose of avoiding setting off a breaker or melting the inner grid.

4. Rectifier

1. Since transformers output AC and the Fusor requires DC, a rectifier must be added to the high voltage circuit to ensure proper functioning. This usually comes in the form of a half wave or full wave rectifier made of high voltage diodes.

5. Voltmeter

1. Used to measure the voltage level

6. Ammeter

1. Used to measure the current

7. High Voltage Wiring

1. Connects all of the components together

Deuterium Gas-Line

The deuterium gas line is the most simple out of all of the systems, the gas-line is what supplies chamber with the fusion fuel, deuterium, to the chamber. The gas-line consists of 5 main components:

1. Deuterium Lecture Bottle

1. Contains and stores the deuterium itself

2. Pressure Regulator

1. Regulates and measures the high pressure gas within the lecture bottle

3. Stainless Steel Capillary

1. Thin stainless steel tube to limit the flow of gas

4. Needle Valve

1. The main control valve used to precisely regulate the flow of gas

5. Gas-Line fitting and adapter

1. Connects the gas line capillary to the vacuum chamber

Although the deuterium system is simple, the sealing and flow rate, must all be met with precision. The reason for this being that the required deuterium pressure within the chamber must be 1*10^-2 torr, a very precise pressure. To meet this, a very low flow rate must be used as to not fill the chamber with deuterium too quickly, a flow rate of 1 Standard Cubic Centimeters/ Minute (SCCM) is ideal. Establishing a dynamic equilibrium is a much easier task when careful care is taken with the gas line.

Radiation Detection

The radiation detection system is the only system that is not needed to produce fusion and attached to the chamber. Yet without it there would be no way to prove that fusion is taking place at all. In the fusor system there are 2 main detectors:

1. X-Ray detection Components

1. Measures the amount of x-rays being produced, they are a byproduct of electrons slamming into the chamber walls. Constant monitoring during operation is needed to ensure that a lethal amount is not being produced. It is purely for safety reasons. The x-ray detection is usually measured by a Geiger counter.

2. Neutron Detector Components

1. Needed to prove that fusion is happening, the neutron detector system is much more costly than a simple Geiger counter because neutrons have no charge and are therefore much harder to detect compared to other rays or particles. The cheapest method for neutron detection is the bubble detector, which detects neutrons through bubble formation within a liquid containing tube. The detector is placed directly beside the chamber to detect the neutrons at their strongest flux.

Neutron detection is no easy task and is crucial within the Fusor system, cheaper neutron detectors will have less accuracy when detecting neutrons and are not as reliable for data collection and more expensive detectors. Simple bubble detectors will be used during the first stage of Fusor testing, but as we began analyzing the fusion reactions in greater detail then better detectors will be used.

Observation

This section serves no other purpose than to observe the plasma and inner grid within the chamber. This is done through a silica view port attached to one of the chamber ports, from there a camera connected to a monitor is needed as direct observation cannot be done because x-rays easily pass through glass. 

Challenges

The construction of the Fusor itself is the easy part, the analyzation of data from test runs and implementation of our own theory, which will be used to conceptualize various engineering designs, is the real challenge. This will be overcome through thorough discussion and hypothesizing of various engineering designs based off of the grounds of IEC to match with the concepts of collisional cross section and kinetic theory. There also imposes a major safety risk that comes along with the high voltage equipment and radiation. Safety protocols will be taken to prevent injury or death from either of these risks including; electrical insulation and radiation absorbing materials.

Pre Analysis Plan

In this project, we plan to test the capabilities of neutron production and power output of our Farnsworth-Hirsch Fusion Reactor. Study of fusion through Inertial Electrostatic Confinement will be divided into 4 main areas of data analysis:

1. Current

2. Voltage

3. Vacuum Pressure

4. Neutron Counts

Current will be monitored through the use of an ammeter within the high voltage circuit. Current measures the amount of electrons present per amount of time. The higher the current the more electrons will be present meaning more ionization and more energy, along with this is the risk of overheating the grid or circuit so caution must be taken while testing the limits. Current is a crucial factor when it comes to fusing atoms, the analysis of current will help to determine how the flux of electrons affects the number of fusion reactions.

Voltage will be monitored through the use of a voltmeter within the high voltage circuit. Voltage or potential difference, is what provides the electrons with enough energy to create an ionizing field within the confinement chamber, creating the plasma and accelerating the atoms so they can fuse. The study of voltage within the fusor allows us to monitor the amount of energy the deuterium ions will be gaining and releasing when fusing.

Vacuum Pressure is measured through the use of an ionization gauge which is attached to the chamber. This gauge provides precise measurements in microns, allowing us to monitor the vacuum operation during air evacuation as well as during fusor operation. Pressure is important as it prominently contributes to the behavior of the plasma within the chamber.

Neutron Detection is the only means of data analysis in which the data being analyzed is a direct product of the fusion reactions, it is also the most important. This is because neutrons are the only particles being ejected from the fusion reaction that can pass through the stainless steel chamber and be detected from the outside world. Neutron detection comes in two forms:

1. Neutron Emission (Neutrons ejected per second)

   1. Neutron emission is used to decipher how many neutrons are being created per second, and thus how many reactions are taking place per second. For a bubble detector dosimeter, one can easily figure out emission rates based of off the rate of bubbles created per mrem of absorption for that specific detector.

2. Neutron Flux (Neutrons present per square unit of area)

   1. Neutron flux is the amount of neutrons present per unit of space squared per second. For a bubble detector dosimeter, neutron flux can be figured based of off the rate of bubbles created per mrem of absorption for that specific detector.

The testing of our fusor will allow us to collect and analyze data directly, which will in turn be used to hypothesize on how the fusor may be upgraded or entirely changed to produce more reactions and thus more power.