It's been a few weeks since a thruster update, but I think I've got a direction to move forward on for the next phase of the Pico Hall development. Got some new background info relevant to the overall tech as well as new design mods in the works. Details in the thread below.
1
1
0
14
First off, some additional background, which has both positive and negative implications. Anode layer ion sources (ALIS) running in a self-igniting "vacuum mode" were originally developed for implementing large area racetrack channel ion beam surface modification sources (1/)
1
1
0
3
Due to the larger channel and overall track size, neutralizer flow rates would have to be significant, which has major implications for not only vacuum infrastructure but overall system power, size, and complexity, and such flow rates would be very unwieldy for big sources (2/)
1
0
0
2
Using a self igniting mode, gas flow rates could be kept minimal, allowing the large sources to operate with significantly reduced gas at much lower pressures. This means self igniting beam down to 10^-5 Torr on residual background gases alone (3/)
1
0
0
1
However, there is a price to pay. First, beam self-neutralization is not complete, and gets worse at lower gas flow rates. While there is some neutralization due to secondary electrons, the beam is not fully neutralized. The upside is that a neutralizer is not needed to run (4/)
1
0
0
1
This can be compensated however with either larger flow rates, or more recently and specifically to micro-Hall development, the use of low work-function material inserts in the housing to increase secondary electron emission yields (5/)
1
0
0
1
The second and perhaps bigger issue is efficiency. While you gain significant gas efficiency (and hence ISP), beam efficiency takes a massive hit. While normal ALIS can achieve 80-90% discharge/beam current conversion, in self-igniting mode this drops to 10% or less (6/)
1
0
0
1
Since thrust is directly related to beam current, this means to operate without a neutralizer, while very much possible on very low fuel flow, you take a huge hit in thrust efficiency, even worse than end-Hall, which is already quite low (7/)
1
0
0
1
This means that the thrust I was originally anticipating would be far, far lower as a result. So there is a tradeoff to consider. A highly simplified, small scale, low-power, and low cost Hall, but performance will undoubtedly be quite poor. (8/)

3:55 PM ยท Oct 19, 2021

1
0
0
1
Now, using this Hall on a Cubesat with say something like a CNT neutralizer (like demonstrated by Busek, which showed operation in excess of 10k hours with a Hall thruster) would mitigate these losses. However at the PQ level, high efficiency losses would have to be accepted (9/)
1
0
0
1
Moving forward, despite the new insight on further performance issues, I will still be pushing forward with this Hall. I think it could still open many new doors and really want to bring this tech to a level anyone could deploy and use (10/)
1
0
0
3
For the next iteration, I am almost finished with the new mods. Looking back, it makes sense why the original design wouldn't work. Too narrow anode surface, too narrow channel, too shallow channel depth, on top of insulation, flow, and magnetic issues already addressed (11/)
1
0
0
2
As a result, I am looking to maximize these features as much as possible in the space I have, rather than minimize like I was prior. Larger anode, channel width, channel depth, improved insulator design, and using a copper anode are the major changes moving forward (12/)
1
0
0
3
Hopefully if I can get these designs wrapped up in the next few days and sent out for fabrication, I could expect the new round of testing to begin within the next month. Progress is slower than usual, but I hope this new step forward will be the one needed to get running (13/)
0
0
0
2