Parallel Plate Pulsed Proton Beam Generator (Thought Experiment)

[BrandonBerchtold]

I am trying to come up with a design for a device with which to generate a rapidly pulsed proton beam (on the order of 1 pulse per ms). My thought was to apply a 10 kV potential between two parallel plates (each with a hole in their center) and inject a steady stream of hydrogen gas through the parallel plate system with the gas contained within a ceramic tube inserted through the holes of the parallel plates (see "No Electrode.jpg" below). The gas travels from left to right and would be ionized some how (either via an electron beam knocking electrons off the atoms or via the use of ionizing radiation) right after it passes the 10 kV plate, causing the hydrogen to be separated into electrons and protons. The protons would be accelerated to the right and the electrons would be accelerated to the left (albeit not for very long as they would be quite close to the 10 kV plate upon their formation).

My question is: how can the liberated electrons be managed. I assume if they are not removed, they will distribute them selves over the walls of the ceramic tube and possibly interfere with the electric field used to accelerate the protons. Would it be practical to use an electrode connected to a capacitor connected to the 10 kV plate to drain the electrons from the system (see "With Electrode.jpg"). Assume the electrode is at a potential slightly higher than the 10 kV plate and the capacitor has a capacitance of slightly more than the charge carried by the liberated electrons.

Side note: I'm a mechatronics student so sorry if there are any glaringly obvious miss-assumptions in my design. I am very open to suggestions :)

 

[mfb]

You can remove the capacitor and use the walls of the tube as electrode.
Your accelerated protons might hit hydrogen atoms and lose energy that way.
With 10 kV discharges are a serious concern.

The whole approach comes with the usual issues (safety and otherwise) from vacuum and high voltage. Add safety concerns from ionizing radiation if applicable.
What is the purpose of the beam?

 

[BrandonBerchtold]

You can remove the capacitor and use the walls of the tube as electrode.
Your accelerated protons might hit hydrogen atoms and lose energy that way.
With 10 kV discharges are a serious concern.

The whole approach comes with the usual issues (safety and otherwise) from vacuum and high voltage. Add safety concerns from ionizing radiation if applicable.
What is the purpose of the beam?

Won't using the walls of the tube as an electrode interfere with the acceleration field between the plates (See "Field Lines.jpg"). Will there still be a voltage gradient inside the tube for the particles to be accelerated with? I assumed this would put all particles within the tube at the same electrical potential.

Also, what if the ionization yield is nearly 100% (side note: how difficult is it to get such ionization yields?). That would get rid of the issue of accelerated protons hitting hydrogen atoms since there would be no unionized hydrogen atoms in the path of proton acceleration, right? I don't have that much experience with ionization processes but if a large and fast enough pulse of electrons or x-rays would hit the hydrogen gas, that should ionize most of the hydrogen atoms at effectively the same time, right?

Side note: I am assuming the surrounding environment is under high vacuum.

I plan to have the pulses occur such that once the hydrogen gas begins to enter the acceleration gradient, it is ionized and accelerated creating the first pulse, then the next pulse occurs when new hydrogen gas has reached the same location along the tube at which the first pulse was ionized. The flow of hydrogen should be constant and the pulsing would be tuned so that no unionized hydrogen should exit the tube.

I am well aware of the safety concerns that come with projects like this, so I will not be attempting to make any physical version until I have a much better understanding of how to do it safely.

The purpose of the beam is for an accelerator based fusion reactor. I read several reports on various accelerator based fusion reactor designs, and I wanted to get a better understanding of if they would or would not work in practice. I am leaning towards the latter since accelerator based reactors have a plethora of issues that come along with them (bremsstrahlung, rarity of collision events, high energy investment to reach fusion conditions, small fusion cross section, etc.). Basically, I expect there to be some problems that cannot be overcome that would yield an accelerator based reactor fully impractical, but as a learning exercise I want to go through each component and understand some of their potential short comings and issues.

 

[mfb]

Not the whole wall, just up to the point where you go through the +10kV plate.

Also, what if the ionization yield is nearly 100%

It won't be.

Making pulses with the gas sounds impractical, pulsing the ionization source is easier.

Accelerator-based fusion devices work - as neutron sources. They are commercially available.
The scattering cross section is just so large that most particles lose their energy before fusing. This is something you can calculate - no need to get into details of the proton source.

 

[ZapperZ]

http://physics.princeton.edu/~mcdonald/examples/patents/cleland_us8508158_13.pdf
Zz.