Historical research guide · 0786 · 2014
Fusion proton diagnostic for the C-2 field reversed configuration
R. M. Magee · R. Clary · S. Korepanov · A. Smirnov · E. Garate · K. Knapp · A. Tkachev
In one minute
Tri Alpha Energy — the California company now called TAE Technologies — built its C-2 machine to hold a field reversed configuration, a plasma that makes its own magnetic bottle out of its own circulating current. Richard Magee and six colleagues describe a new instrument for reading what happens inside it. When two deuterium nuclei fuse they sometimes produce a proton of about three million electronvolts, and because the fusion rate climbs steeply with ion energy, counting those protons is an unusually sensitive way to measure how energetic the ions are. Their detector is a large silicon diode, fifty square centimetres, run so that every arriving proton registers as one countable pulse. The scintillator neutron detectors already on the machine are fast but positionally blind. This one resolves ten centimetres along the machine, which is exactly what is needed to test whether the fast ions injected by the neutral beams settle where classical theory says they should, or whether some other scattering mechanism is at work. The paper closes with first data from a neutral beam test chamber.
Connection
Chapter 9 is about self-organised plasmoids, and the field reversed configuration is the laboratory version of one: a plasma ring that holds its own shape with its own currents. Chapter 12 is about getting fusion out of a confined system, and this is the instrument that tells you whether the fast ions are behaving — the measurement that has to work before any claim about confinement or gain can be trusted.
From the source
Measurements of the flux of fusion products from high temperature plasmas provide valuable insight into the ion energy distribution, because the fusion reaction rate is a very sensitive function of ion energy. That steep dependence is what makes counting fusion products a thermometer rather than merely a tally.Abstract, first sentence
In C-2, field reversed configuration plasmas are formed by the collision of two compact toroids and are partially sustained by high power neutral beam injection — the architecture reported by Binderbauer and colleagues in Physical Review Letters 105, 045003 (2010) and by Tuszewski and colleagues in Physical Review Letters 108, 255008 (2012).Abstract, second sentence, with the two Physical Review Letters citations it carries
Measurements of the deuterium-deuterium fusion neutron flux are already used on C-2 to diagnose ion temperature and to study fast ion confinement and dynamics.Abstract, second sentence
The new instrument is a 3 MeV proton detector built to complement the existing neutron detectors: a large area, fifty square centimetre, partially depleted, ion implanted silicon diode operated in a pulse counting regime.Abstract, third and fourth sentences
The scintillator-based neutron detectors allow high time resolution of about 100 kHz but have no spatial or energy resolution; the proton detector supplies 10 cm spatial resolution instead.Abstract, fifth and sixth sentences
What to watch is the measurement the detector was built to make: whether the axial distribution of fast ions is consistent with classical fast ion theory, or whether anomalous scattering mechanisms are active. The paper presents the diagnostic design and initial data from a neutral beam test chamber; the answer comes from the machine.Abstract, sixth and final sentences
The way in
https://doi.org/10.1063/1.4892861How to cite it
R. M. Magee, R. Clary, S. Korepanov, A. Smirnov, E. Garate, K. Knapp, A. Tkachev (2014) Fusion proton diagnostic for the C-2 field reversed configuration doi:10.1063/1.4892861