Reply To: Military Effects

[Joseph Chikva]

Background of the Invention

Fusion is the process by which two light nuclei combine to form a heavier one. The fusion process releases a tremendous amount of energy in the form of fast moving particles. Because atomic nuclei are positively charged – due to the protons contained therein – there is a repulsive electrostatic, or Coulomb, force between them. For two nuclei to fuse, this repulsive barrier must be overcome, which occurs when two nuclei are brought close enough together where the short-range nuclear forces become strong enough to overcome the Coulomb force and fuse the nuclei. The energy necessary for the nuclei to overcome the Coulomb barrier is provided by kinetic energies, which must be rather high.
For example, the fusion rate can be appreciable if the temperature is at least of the order of 104 eV—corresponding roughly to 100 million degrees Kelvin. The rate of a fusion reaction is a function of the temperature, and it is characterized by a quantity called reactivity. The reactivity of a D-T reaction, for example, has a broad peak between 30 keV and 100 keV.

Heating is needed during startup before alpha heating can take over.

And, so, we need to get the core of the plasma to 10keV i.e. around 100 million deg K, that for Plasma Volume 57.5-840 m3 (first number is of compact high field TOKAMAK IGNITOR, while the second is ITER’s – the largest TOKAMAK ever built) and 1020 m-3 Number Density corresponds to Plasma Stored Energy 11.9-520 MJ.

Existing (using) now plasma creation and heating methods
For TOKAMAKs and other fusion experiments using toroidal vacuum chambers (e.g. Large Helical Device – Stellarator)

Initial heating (Ohmic heating). Generated by induced electric field driving the toroidal current
When driving current using a toroidal electric field, current is initially driven at the surface (skin-effect) and then diffuses into the plasma.
Diffusion coefficient DJ = η/µ0 m2/s
Plasma resistivity (Spitzer) η=10-4Z lnΛT-3/2 Ωm and so:

DJ = ~103T-3/2 m2/s
During plasma startup some time is needed for diffusion from the edge to center. For a plasma on the scale of meters, at 10eV the timescale is 10ms and at 1keV it’s 10s of seconds [6]

Then resistive heating ηJ2 raises the temperature
But at the same time the resistivity of plasma decreases with temperature η 1/ T3/2
As the plasma heats up, the amount of energy which can be pumped into the plasma drops.

From the other side the energy losses increase by increasing the temperature – τE gets smaller.

Significant time is needed for Ohmic heating – big energy losses during that time mostly via Bremsstrahlung.

Neutral Beam Injection (NBI)
• Ions from the ion source accelerate by grids to high energy
• Then they pass through the neutraliser and become neutral high energy atoms
• The neutral beam penetrates the reactor magnetic fields. The penetration of the beam depends on the NBI energy, mass and on the plasma density
• Within plasma neutrals are ionized by collisions with thermal ions & electrons
• These fast ions are trapped by the reactor magnetic fields
Advantages
• Efficient heating of ions
• High power capability (40 MW on TFTR, 24 MW on JET, 70MW projected for DEMO)
• Drives plasma rotation (stabilizing lock modes)
• Fuelling
• Current drive
Disadvantages
• Heating not well localized
• Neutralizing cell is a gas filled chamber directly joining with vacuum vessel of reactor with long “atom conductor”. For preserving vacuum quality in a chamber vacuum absorbers on the walls of atom conductor are used which are needed desorbtion after each shot.

Ion Cyclotron Resonance Heating
Advantages
• Localised heating
• Hydrogen minority ICRH creates H minority with E> Ecrit – it heats electrons
• However, heating of IONS is also possible (e.g. 3He minority in DT plasma)
• Some current drive
Disadvantages
• Antenna inside the vessel
• Low power capability
• Plasma coupling may be a problem in, e.g. H-mode with ELMs
Concluding all three using now heating methods it can be said that all those need significant time for putting into the plasma the energy sufficient for ignition.
[em]So, today we already know how to confine plasma in toroidal reactors long enough time (3-5 sec has been really achieved) but we have not effective enough heating way: temperature limit of Ohmic heating goes not exceed 1 keV order, and RF heating and NBI have not enough power as even very powerful 70 MW NBI source will heat 840 m3 plasma in ITER with projected number density 2*1020 m-3 in 7.4 s even in 100% energy absorption case (100% is impossible by definition).

And it is proposed the conceptually new Method comprising in heating of plasma by creating in-situ in the reactor of high energetic halo-particles, with the help of which it is possible to input the required energy within only several milliseconds.[/em]

For providing of above mentioned the following procedures should be performed consistently (and corresponding hardware should be included in toroidal fusion reactor):

To create the bending magnetic field directed orthogonally to equatorial plane of toroidal vacuum chamber (vertically) penetrating only its curvilinear segments.
(As a rule the vacuum chamber of toroidal fusion reactors has a round central axis but generally round segments can alternate with the rectilinear – racetracks). And as the Method is proposing injection along the axis of high current beams, presence of racetracks would be preferable as they provide easier injection.
Such racetracks have been used in first Stellarators. Also they widely used in high energy particle accelerators for example racetrack FFAG betatron for Muon Fabric (Brookhaven National Laboratory) or Induction Synchrotron (All-ion Accelerator) developing now by KEK (High Energy Accelerator Research Organization)