The Polomac

Deutelio proposes to address fusion with the Polomac, a magnetic confinement where the field lines have a dipole shape, like those of a stick magnet or those of the magnetospheres of the Earth.

These lines run from the North pole to the South pole, along the so-called “poloidal” direction, instead in the Tokamak and Stellarators the magnetic lines bend about the axis spanning a toroidal space.
The Polomac includes a poloidal magnetic configuration with some magnetic tunnels in the outboard, to serve the coil surrounded by the plasma. The tunnels solve the problem of keeping in place the internal coil, providing it with electric current and water coolant, while avoiding the plasma particles to collide with the connections.

This idea of shielding the supports of the coil inside the plasma in the poloidal configuration is not new; however earlier attempts were partially successful because they lack of modern analysis tool and CAD systems. These inefficiencies led to abandon the research on the poloidal magnetic confinement and to concentrate on the Tokamak.
Deutelio instead developed an engineered solution of the shield (called “magnetic tunnels”) which can be tested and tuned quickly on small prototype.

The tunnels are achieved by segmenting in four parts the external coils which are then bridged by radial segments thus arcs and segments form a set of four-side coils. The interest on reviving the poloidal magnetic confinement lays on the possibility of obtaining a confinement efficiency much higher than in the Tokamak and Stellarator.

The confinement efficiency is the ratio of the energy density of the plasma respect to the energy density of the confinement system. A burning plasma at 10 keV and density 10²⁰ particles per cubic meter reaches 0.16 MJ per cubic meter, i.e. 0.16 MPa. Remember that energy density corresponds to pressure. The energy density corresponding to the toroidal field of ITER 5.3 T is 11.17 MPa. The energy efficiency of the Tokamak is then 0.16 MPa over 11.17 MPa equal to 1.4%. This parameter is normally known as Beta.

Instead, the Polomac should replicate the efficiency of the theta pinch and operate with Beta up to 0.7-0.8. Already with Beta 0.5 and a magnetic field of 3 T it could trap plasma at 100 keV.

While operating at high Beta with an increase by 10 of the confinement time respect to the present values of the Tokamaks, i.e. from 5 to 50s, the Polomac can produce energy from the D-D reaction, without provision of external tritium.

According to the Lawson criterion for burning plasma, the triple product of density, temperature and energy confinement time, for D-D reaction must be almost 200 times larger than in the D-T reaction, which is the current reference in ITER and in DEMO. The increase of temperature from 10 to 100 KeV and of the confinement time from 5 to 50 s along with few higher density can accommodate the Lawson criterion.

Since the cross section of the D-D reaction is about 100 times lower than D-T, the size of the corresponding reactor could be larger, although better confinement and higher operating parameters expected in the Polomac should allow for a power density 1-3 MW/m³, as assumed at present in the Tokamak rector studies. Surely a D-D reactor is simpler, because it does need any breeding blanket to produce Tritium.

The construction of a large Polomac is not demanding as a Tokamak, because there is only one system of flat coils working at 3T. The superconductor is Nb-Ti instead of Nb-Sn, thus coil fabrication is less demanding.

Comparison with other Fusion lines

The Tokamak is a model designed to study and advance nuclear fusion technology. Its toroidal, or doughnut-shaped, chamber uses magnetic fields to confine a superheated plasma, creating conditions similar to those found in the sun’s core. The hard work done to improve the Tokamak since the 1970 led to scarce results because the plasma is disturbed by the large toroidal current, involving mutual forces with the other coils and triggering instabilities.

The Stellarator is another type of experimental device designed to explore nuclear fusion. Unlike the Tokamak, which uses a toroidal shape with magnetic fields generated by external coils and plasma currents, the Stellarator relies on twisted magnetic fields generated solely by external coils. This design aims to maintain a stable, helical magnetic field configuration that confines the plasma without requiring a current to flow through it. The primary advantage of the Stellarator is its potential for steady-state operation, as it does not rely on the transient plasma currents needed in Tokamaks.

One of the major challenges facing Stellarators is their complex design and engineering. The twisted magnetic fields needed for plasma confinement require a highly intricate arrangement of coils, which makes the construction and alignment of Stellarators technically demanding and expensive

The Polomac, compared to the Tokamak, works in a stable and continuous way and it is simpler to build than the Stellarator. In addition, the Polomac is based on the same physics, and experiences accumulated over decades of research around the world.

The Polomac takes up the scheme of the poloidal magnetic field studied and experimented all over the world in the years 1960-70, then abandoned in favor of the Tokamak, but re-proposed in 2005 by the MIT in Boston with an incredible super-conductive magnet suspended in a vacuum by magnetic levitation. This recent and innovative application has highlighted the very high efficiency of the poloidal magnetic scheme, even if magnetic levitation introduces a complexity that has discouraged further developments towards industrial application.

The Polomac differs from earlier closed poloidal magnetic tests ( i.e. Levitron, Stator, Spherator, JFT-1, Intrap, LDX ) in the magnetic tunnels, a new feature which could finally bring us to nuclear fusion energy. The tunnels allow the passage of the supports and the electrical and hydraulic connections for the conductor held inside the plasma. Therefore, the Polomac is assembled with conventional flat magnets and works with a magnetic field 4-5 times less intense than that one needed for the Tokamak.