Historical research guide · 0937 · 2017
Study on discharge plasma in a cylindrical inertial electrostatic confinement fusion device
N. Buzarbaruah · N.J. Dutta · D. Borgohain · S.R. Mohanty · H. Bailung
In one minute
A cylindrical inertial electrostatic confinement device is about the simplest fusion machine anyone builds: a vacuum chamber holding a little deuterium, with a see-through cylindrical wire cage down the middle held at a large negative voltage. Ions formed in the gas fall towards the cage, shoot through the gaps, and keep recirculating through the centre. Buzarbaruah, Dutta, Borgohain, Mohanty and Bailung ran their machine two ways — with a heated filament supplying electrons, and without one — and read the plasma with an electrostatic probe. The two modes trade against each other. The cold-cathode discharge makes the hotter plasma, about ten electron volts; the hot-cathode discharge makes a cooler one, about three electron volts, but two orders of magnitude denser. The same probe caught something the device does on its own: ions sloshing back and forth in the negative potential well that forms between the cage and the chamber wall, oscillating spontaneously, and doing so at harmonics of the fundamental as well.
Connection
Chapter 9 is about plasma that organises itself — and here a benchtop machine with one voltage knob produces a potential well that rings on its own, harmonics included. Chapter 12 keeps the ledger of fusion routes, and this is the measurement that tells a builder which discharge mode buys density and which buys temperature in the cheapest confinement geometry there is.
From the source
Deuterium plasma was produced in a cylindrical inertial electrostatic confinement fusion device in two distinct ways — a hot cathode discharge and a cold cathode discharge — and the plasma parameters of each were determined with an electrostatic probe.Abstract, sentence 1; Physics Letters A 381, 2391 (2017)
At optimum experimental conditions the plasma temperature is about 3 electron volts in the hot cathode discharge and about 10 electron volts in the cold cathode discharge, so the mode that needs no filament is the one that makes the hotter plasma.Abstract, sentence 2
The trade runs the other way for density: the plasma density measured in the hot cathode discharge is two orders of magnitude greater than in the cold cathode discharge, which is the figure of merit that matters for reaction rate in a device of this kind.Abstract, sentence 3
A negative potential well forms in the space between the cathode grid and the chamber wall acting as anode, and the probe was used to observe ions oscillating inside that well — the recirculating motion that defines the inertial electrostatic concept, seen directly rather than inferred.Abstract, sentence 4
The oscillation is spontaneous rather than driven, and it appears together with its harmonics, so the discharge is self-organising a resonance and not merely following the applied voltage.Abstract, final sentence
What to watch: the same group later modelled this machine particle by particle and matched the probe measurements, finding a core ion density around ten to the sixteenth per cubic metre, a virtual anode built from trapped ion charge, and grid transparency as the design parameter that sets core density — so the open question this paper leaves, which discharge mode and which grid geometry give the best neutron yield per watt, now has a validated simulation to answer it.Read against the same group’s Physical Review E 102, 063205 (2020), held on this site at stm-0b806244cb
The way in
https://doi.org/10.1016/j.physleta.2017.05.029How to cite it
N. Buzarbaruah, N.J. Dutta, D. Borgohain, S.R. Mohanty, H. Bailung (2017) Study on discharge plasma in a cylindrical inertial electrostatic confinement fusion device doi:10.1016/j.physleta.2017.05.029