On the Prospects of Open-Source DIY High Power Particle Beam Physics

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If you have been following my work and progress on social media, this website, and other project sharing forums and groups, you are already aware that I am undertaking an immense particle accelerator build. It is no secret that I am a major proponent for pulsed power and its application to vacuum physics systems, and have actively worked to promote, share resources, and mentor others in this field. From my own interests and desires to build high power particle beam systems, I have dived deep into the world of accelerators, and have come across an extraordinary class of accelerators. Pushing further into this area, I have also found that these accelerators have the potential to revolutionize access to far more particle beam physics for the amateur experimenter than previously accomplished before. I have not shared the full details yet of my accelerator build, but have been slowly leaking hints and glimpses of what is to come. Should it work, it will revolutionize access to high power and high energy beam physics that have not yet been explored before at the amateur level, and would have been impossible prior with other types of accelerator builds. The build will also be fully open-source, and I will be providing immense details into the history, use, design, application, and testing of this unique type of accelerator. Let us however first dive into a bit of the field of amateur accelerators and see where this leads us in relation to the work done here at Applied Ion Systems.

Homebuilt particle accelerators is no new idea. Amateurs have been constructing various types of accelerators for decades. When I refer to a true, hobbyist, homebuilt accelerator, I am referring to efforts that are independently conceived and constructed by the amateur themselves, with their own resources, in their own home, without external system builds or setup at universities (however, salvage and scavenging of parts from universities can still fall into the category of amateur builds.) Up until now, there have been two major approaches to these efforts.

The first is perhaps the simplest – the DC electrostatic accelerator. This is simply a high accelerating potential applied across two electrodes separated by some distance with an insulator, causing particles to be accelerated to an energy equal to the DC potential. The most simple example is that of the cathode ray tube found in old television sets. This is a very simple and easy device to construct, and is often made either from scratch, or re-tasking old CRTs. Other examples in the amateur effort includes simple beam on target (BoT) systems, often for accelerating deuterium ions into a self loading target to create neutrons via fusion processes. These guns are very basic and simple in design, and also relatively easy to construct. More advanced guns that have shown up in the amateur field includes the anode layer ion source, as well as RF excited ion sources. Higher voltage amateur builds often employ either Cockcroft-Walton multipliers, or Van de Graaff machines. In all, amateur DC electrostatic machines have ranged in the tens of keV to maybe 150keV energy range at most, with currents generally in the microamp region. Such DC accelerators can be used for either electron or ion beam generation.

Next, we move to the second class of accelerators explored at the amateur level, and perhaps the ones that have garnered the most interest and excitement over the years, and is one of the oldest approaches for hobbyists – RF accelerators, primarily via cyclotrons. While RF linear accelerators are the most common and dominant type of accelerator out there, due to the extreme design, machining, and fabrication complexity of the RF cavities required, in addition to costly and complex RF modulators using high power pulsed magnetrons or klystrons, such accelerators are beyond the realm of the amateur. However, cyclotrons offer a very simple and relatively lower cost means of accelerating particles with applied RF fields. Numerous cyclotron builds have appeared over the years, and there is even now a small but enthusiastic amateur cyclotron community. The first amateur cyclotron build was reported in the 50s by a high school student and a teacher mentoring him, and since then, numerous amateur cyclotron builds have popped up all over the world. These machines are much more costly and complex than their DC accelerator counterparts at the amateur level, and requires a good deal more planning and investment, particularly with the large electromagnet and RF power supplies employed with these accelerators. Cyclotrons are used to accelerate ions, with hydrogen atoms, or protons, as the primary particle of interest, with helium being the next runner up. Like the DC accelerator, energy levels of homebuilt systems have been typically limited to 150keV range, at microamps of current.

Both efforts have a range of uses, and any accelerator attempt is commendable. However, both of these approaches have also been inherently severely limited based on a few key, fundamental limitations available to the home experimenter.

One is power. Both DC and RF accelerators require large amounts of continuous power to run at higher operating levels. While lower voltage DC power supplies at 10s of kV can be obtained at 10s to 100s of mA, getting such currents in the 100kV range is largely infeasible to the home experimenter. Cyclotrons require significant amounts of power to run the large electromagnet needed, in addition to the RF supply. A serious amateur cyclotron build can easily expect power requirements past 10kW.

Unfortunately, due to the nature of scaling for DC and RF accelerators, higher energies beyond 150keV becomes very difficult and costly as well. For DC accelerators, the issue is first finding or making a suitable high voltage power supply. Such supplies can be costly, and once you start breaking the 100kV level, corona losses and insulation becomes a significant issue. For DC guns, the major issue is the feedthrough or insulation for such a gun. Numerous hobbyists have proposed Van de Graaff accelerators over the years. However, almost no one takes into account the issue of beam loading. Regular belt-driven Van De Graaffs are inherently extremely limited in the amount of current they can supply. As such, while it is easy to generate a million volt potentials, as soon as a load is attached to the output, voltage will massively sag to pitiful levels if not properly engineered. Often in the physics field and industry, this is overcome via more efficient methods such as the Pelletron variation, as well as utilizing additional high voltage supplies to charge the belts more effectively and supply larger operating currents. Neither of these approaches for a more true-engineered VDG accelerator have been demonstrated at the amateur level.

On the cyclotron side, a fundamental limitation is the magnetic field required for acceleration, as well as overall dee size. Ion energy in a cyclotron is governed by the simple relationship KE = (R^2*q*B^2)/2m, where KE is the kinetic energy, R is the dee radius, q is the fundamental particle charge, B is the magnetic field strength, and m is the particle mass. Here we see the major issue with such a build. In order to increase particle energy, either large radii are needed, and/or high magnetic field strengths. However, for iron-core electromagnets, there is a fundamental limit of around 1.5-2 Tesla due to core saturation. Therefore, one must rely heavily on larger electromagnets for higher energies. Unfortunately, such a required electromagnet can way several tons, and becomes impractically large for the average amateur to handle. Bigger magnet also means bigger power budget. A decent size magnet that will allow for several hundred keV can easily require over 10kW of power. This also requires magnet cooling, and stable high current supplies.

Regardless whether DC or RF acceleration is used, ultimately amateur efforts until this point have been limited to maybe a couple hundred keV at microamps at most. While these accelerators are excellent and powerful learning tools, and can provide a good variety of simple demonstration experiments in the realm of particle physics, or in the case of lower voltage BoT systems, good compact neutron sources, they are fundamentally limited to simpler physics experiments and demonstrations. Unfortunately, from the power level (maybe a few watts peak beam power) and energy level (couple hundred keV) perspectives, these builds cannot rise to the next level of industrial or academic research-class accelerators. But there is no reason that such systems cannot be built, enjoyed, and explored at home by the dedicated hobbyist.

There is however, another class of accelerators!

A third class of accelerators includes the pulsed accelerator. When I am talking about pulsed accelerators, I am not talking about pulsed injectors for DC or RF accelerators (where one could very easily pulse a VDG accelerator or cyclotron to get a few amps of current), but extremely high power, intense pulsed beam direct-drive systems that can deliver many kiloamps of beams at hundreds of keV to a couple of tens of MeV, at peak power levels of TWs. These systems can drive both electron and ion beams, and have historically been the most powerful beam systems ever built. It is this class of intense pulsed accelerators I am currently after and in the process of constructing, aiming at a beam system that can handle kiloamps of beam current at peak power levels of hundreds of MWs.

Why the push for such high peak power beams? For one, at a certain intensity, a new and diverse array of beam physics opens up across a wide range of fields. This is a key advantage of pulsed high power accelerators, in their shear versatility for driving many types of high-power physics systems. Second, at the amateur level for a reasonable budget and available resources, pulsed accelerators can easily far surpass the capabilities and versatility of DC electrostatic or RF cyclotrons which have been the two major dominant amateur accelerator builds until this point. This includes beam power, beam current, beam energy, and overall system versatility. Not only are beam powers in the range of hundreds of MWs well within the reach of the amateur experimenter, but unprecedented beam energies in the low-MeV range are achievable as well, utilizing a very niche and now-forgotten type of accelerator in this area. Such an accelerator can easily run off the wall outlet at less than 1kW total electrical energy due to the fundamental nature of pulsed power and its ability to achieve extremely high power compression ratios from very low starting power and stored energy. While DC and RF accelerators far surpass the capabilities in terms of achievable beam energy in the research field, for the amateur level, pulsed systems have distinctly dominant advantages for equivalent cost and complexity. However, regardless if the system is amateur or professional, pulsed systems dominate in terms of beam power. In fact, pulsed power systems are the fundamental key for modern high power and high energy physics, as it would be otherwise impossible to generate the immense currents and voltages simultaneously with regular DC or AC systems in a compact and feasible manner.

I have continuously pushed the idea, and still firmly submit, that the pulsed accelerator approach is the ultimate way to achieve a research class system for an amateurs budget at home, and bring amateur particle physics to the next level. Using simple and dirt cheap pulsed power techniques pioneered by exceptional hands-on DIY experimenters decades ago, unmatched beam power and energy levels can be attained with relative ease and compactness that would be otherwise impossible at home with DC and RF approaches.

Yet despite these advantages, a true, high power pulsed accelerator has not been built or attempted at the amateur level before. Such ideas have floated around very briefly in various internet forums and discussions, but no one has taken the initiative to combine pulsed power systems and vacuum systems specifically for the application of intense beams at home. While these two groups of home experimenters, the pulsed power and vacuum groups exist separately, they very rarely cross or merge efforts at this level. There have been some efforts for pulsed plasma systems at this level, but very rarely accomplished – pulsed beam systems are even more rare. In certain DIY groups, pulsed power is even seen as something to be feared, or far too advanced for the amateur to explore. I say this is utter nonsense. Pulsed power was historically developed specifically for such intense beam systems, and born from intensely DIY approaches. Making arcs, sparks, and loud bangs is easy and trivial with high voltage and pulsed systems, such as the commonly built Marx generator. These demonstrations may be fun at first, seeing how far of an arc you can draw, but at the end of the day, it is wasted energy to what could be applied to driving real physics loads to do some real physics experiments. Pulling vacuum and igniting a DC plasma just for show, while involved and somewhat more costly, is also fundamentally not a terribly challenging effort. What is the true challenge in such fields is manipulating raw power at tens to hundreds of kV at thousands of amps, in incredibly short time periods of tens of nanoseconds, to a highly critical matched-impedance loads, to extract tremendous beam power or driven plasmas for a brief moment. And in those brief moments, incredible amounts of experimental data and exciting physics applications can be generated and explored.

And perhaps the best part about all of this is, is that one does not need multi-million or billion dollar budgets at prestigious facilities to pursue such efforts. One does not need a PhD to design and build such systems. One does not need massively complex state-of-the-art equipment to explore the understudying principles in these areas of physics. It is a challenging and tough road, that requires tremendous passion, dedication, and resourcefulness, but the willing and determined hobbyist can accomplish smaller-scaled research-class systems themselves. The beauty of pulsed power is that it can be fully scaled, from tabletop units to monstrous machines, and accomplish incredible feats at all levels.

And I will demonstrate this with EXEDA…