Andrew Seltzman

Compilations of the works of significant long term members of the site. Induction into this area is by long term contribution and by nomination only.
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Andrew Seltzman
Posts: 748
Joined: Mon Feb 02, 2004 1:02 am
Real name: Andrew Seltzman

Andrew Seltzman

Post by Andrew Seltzman » Sat Feb 22, 2020 4:31 am

I'll have to update this to a more detailed description and bio over the next few weeks or so but here is a start:
  • I was born and grew up in Raleigh, NC
  • I went to Georgia Tech for undergrad and received BS degrees in Physics and Electrical Engineering. I built three fusors in my dorm room, the latest of which I still have and have been upgrading since
  • I went to grad school at University of Wisconsin - Madison and received a MS in electrical engineering, and a PhD in Plasma Physics
  • I am currently (as of 2020) a postdoc at Massachusetts Institute of Technology, where I work on lower hybrid current drive in tokamaks
Advice to new fusioneers:
  • e-Bay is your friend, search for vacuum parts at a discounted price there
  • Avoid thermocouple gauges, they are temperamental and only go down to ~1mTorr, and then only at lower resolution and accuracy. Instead use a more modern multi sensor gauge. I recommend the MKS-901p, you can find them on e-bay for about $40. They are compact, have analog and digital rs-232 computer output, set-point relays, and gas type correction. They measure from atmospheric to 1e-5torr.
  • If you can afford it, invest in a dry turbo pump system early on. You won't regret it and will never go back to any other vacuum pumping method. This combination pairs an oil free (dry) diaphragm vacuum pump with a turbomolecular-drag hybrid turbopump. To run with a diaphragm pump (typically 1Torr vacuum) it MUST be a turbomolecular-drag hybrid. My recommended pump brand for turbos is Pfeiffer (I think they are a bit higher quality and more reliable). Turbomolecular-drag hybrids from pfeiffer are denoted by the TMH (ISO flange), TMU (conflat) prefix or TPD(molecular drag only; it's a lower pumping speed but more than sufficient for fusor use unless your vacuum chamber is huge), I would recommend buying a TMH-071P or TPD011 Pump (these will usually cost <$1000 used). Buy a pump that has the model TC100 or TC110 integrated controller.
  • Avoid pipe threads where ever possible, instead invest in NW or KF type hoses for your vacuum runs, particularly after your high vacuum pump
  • If you are serious about building a neutron producing fusor, start off with buying conflat flanges hardware for your vacuum chamber, and use them with copper o-rings where ever possible. Viton o-rings slowly permeate air and water vapor; large numbers of o-rings will affect gas purity, particularly at lower pumping rates and will decrease neutron numbers.
  • Radiation safety is important, particularly as you start to get to lower vacuum (<20mTorr) and higher voltage (>15kV). The hazard is x-rays not neutrons. Use a lead glass shielded viewport (I recommend the Lesker VPZL-275XLG, it's about $162. With a 0.24" thick lead glass insert it will screen out all x-rays in the typical armature fusor voltage operating range). This will provide x-ray hazard free viewing of your plasma. At 40kV, 18mA my fusor produces ~40R/h at the surface of a borosilicate glass viewport (this attenuates rapidly with distance due to inverse square law and air absorption of the lower energy soft x-rays) with the lesker lead glass viewport (in conjunction with a 1/8" thick stainless vacuum vessel), dose rate is reduced to <1mR/h
  • Use macor for the in-vacuum insulator. Alumina insulators tend to arc near the grid (but are generally a good starting place for most people before moving to more advanced ceramics), boron-nitride absorbs and water and releases it as it is heated, and quarts can be cracked by arcing at the lips if your power supply has large enough filter capacitors (most switching power supplies do). A field control cap over the top of the ceramic insulator just under the grid will reduce arcing. /list]

    Links to highlights my work:
    My personal website:-----------------------------
    My google scholar profile with publication list: ... by=pubdate
    Thread on my latest fusor:------------------------viewtopic.php?f=6&t=10294
    Thread on my ion source design:-----------------viewtopic.php?f=12&t=5011
    Thread on thermal imaging of the fusor grid:--viewtopic.php?f=6&t=8734&hilit=Mark3
Andrew Seltzman

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