Magnetic confinement fusion is an approach to generating thermonuclear fusion power that uses magnetic fields to confine the hot fusion fuel in the form of a plasma.

Articles:

http://mragheb.com/NPRE%20402%20ME%20405%20Nuclear%20Power%20Engineering/Magnetic%20Confinement%20Fusion.pdf

https://www.nap.edu/read/4936/chapter/8

Books:

Fusion: An Introduction to the Physics and Technology of Magnetic Confinement Fusion

By Weston Monroe Stacey, Wiley, 1991

Magnetic Confinement Fusion Driven Thermonuclear Energy

Bahman Zohuri

Springer International Publishing, 2017

 We use the magnetic field mainly to confine plasma with high temperature.

The following two books may also be useful:

1.Jeffrey P. Freidberg, Plasma Physics and Fusion Energy. New York. Cambridge University Press,2007.

2. John Wesson, Tokamaks (Oxford Engineering Science Series). Oxford University Press, October 1, 1987.

As known, magnetic insulation of the plasma is carried out for its containment in the reactor chamber. The principle of minimum magnetic field strength in the central region of the reactor is used. This allows us to eliminate the fluxes of charged particles on the walls of the reactor chamber. However, magnetic isolation does not allow the elimination of particle fluxes that appear in the plasma due to formation of electrical domains under the influence of electrons which runaway from collisions in azimutal direction. In the plasma, in the presence of a magnetic field always exists a domain instability ((see my results in Proc. EPS Conferences on Plasma Physics). Attempts to obtain a nuclear fusion reaction using hot plasma in a tokamak reactor chamber are unpromising. The thermonuclear fusion is humanity's gold dream or very deep error of theorists.

Basically, magnetic field suppresses transport of mass and energy from the plasma core (where nuclear reactions are supposed to occur) and the material walls of the chamber which contains the plasma; should this suppression fail, excessive plasma cooling would prevent nuclei to achieve fusion. The field is also supposed to prevent particles coming out of the wall to enter the plasma core; indeed, the slightest contamination of the core raises X.ray radiation to unacceptable leve, leading once again to plasma cooling. Trouble is, the system made of the plasma and the magnetic field is often far from stable, as plasma itself is an excellent electric conductor, and even small electric currents flowing across it modify the field. Research on stability is one of the oldest topics in fusion research; ot date, it has been only partially successful.

We may wonder how large is the magnetic field required for successful nuclear fusion. Sadly, it is not really a matter of intensity, but of shape of the magnetic field lines. Open field lines are easily to design and to be put in practice, but obviously confine plasma only scarcely in its motion along the filed lines themselves (Lorenz force along the magneitc field lines vanishes identically). So, people decided to develop configurationswith magnetic field with closed field lines. Among these configurations, just a few are stable. Stable configurations may either be entirely ruled by external coils (i.e., absolutely no current across the plasma) or induce a current across the plasma to sustain the field. Today, the former case corresponds to stellarators, which are well known although of almost unbearable engineering complexity; the latter case corresponds to reversed field pinches and tokamaks, which differ from each other according to the stabilization mechanism (a delicate interplay of plasma turbulence and external coils in reversed field pinch, a huge magnetic field superimposed by the external world in tokamas, where the plasma carries just the current which is responsible for heating and the confinining magnetic field). Reversed field pinch have laughable confinement properties (to date, at least). Tokamaks perform much better, but at the price of enormous magnetic energy and related stresses. Do rule-of-thumb rules exist? Sure thing, but quite pessimistic indeed: older estimates predicted that the power losses away from the plasma decrease with the square of the magnetic field intensity, recent (and more realistic) scaling laws predict that power losses decrease just with the first power of the magnetic field intensity. As a result, look at ITER: the plasma is so huge just to make the travel of the pwer from the core towards the walls a bit onger, as the field is barely enough to stabilize it.

Analysis shows that plasma in technical devices can exist for a long time only at continuous supply of energy to it. In this case, recombination is balanced by ionization. In nature, a rare cosmic plasma stably exists - because of the low density, there is not a particle of another sort for recombination next to it.

Millions of years exists a stars and tens of minutes exists a ball lightning -  structures like the electrical domain of a spherical shape. Stability conditions are given in my article:  “An investigation of the generation and properties of laboratory-produced ball lightning” Journal of Plasma Physics,  Cambridge,

2015. Continuous existence of a ball lightning takes place when the following conditions are satisfied:

1. The ball lightning kernel is located in the area with the minimum of induction of the poloidal magnetic field which creates a circular current existing in the external spherical layer. The charged particles of the kernel cannot move in the direction of increasing the magnetic field induction;

2. The excess charge of one sort and the lack of charge of other sort in the kernel or in the external spherical layer significantly reduces the possibility of an electron capture by the nearest ion, therefore the recombination processes in a ball lightning becomes difficult;

3. The inequality of positive and negative charges in the elements of ball lightning also significantly reduces the losses of charged plasma due to bremsstrahlung;

4. The resultant of all forces, including the force of electrostatic interaction between the elements of a ball lightning, the force of Lorentz, the force of gas-kinetic pressure and the force caused by the centripetal acceleration should be equal to zero in the equatorial plane;

5. It is possible that a reaction of nuclear fusion takes place due to the existence of strong fields in the ball lightning and the presence of deuterium in a water vapor in the atmosphere.

The splashs of neutron generation during the passage of ball lightning in the laboratory were obtained a month ago and results were reported on ICPIG2017 in Estoril. Ball lightning with a diameter of 0.94 meters was obtained earlier and published in the materials of the Zvenigorod conference on plasma physics and contolled fusion (available on the website).

I have no desire and time to participate further in this discussion due to lack of prospects of magnetic insulation to solve the energy problem. Nature does not tolerate violence!

Fusion is the process of fusing two isotopes of Hydrogen namely Tritium  and Deuterium to produce Helium. To achieve this requires tremendous heat (about a million degrees Celsius) and tremendous pressure. To achieve this, the hydrogen is made into a plasma through rarefaction so it becomes susceptible to magnetic fields. Electro-Magnets surround the chamber/reactor and are pulsed adiabatically (as in a bicycle pump) and the gas becomes extremely hot that may melt the surroundings. The fusion process releases large amounts of very high speed neutrons which impinge against an absorbent wall heating it up. Behind the wall  are a series of circulating water pipes, where the water turns to steam, then the steam turns a turbine attached to a generator to produce electricity. In a nutshell.

Hence, the electromagnets are to keep the plasma afloat without touching any surroundings, and to pump the hydrogen to heat it up. there are other methods of achieving the required high temperatures; but that is another story !!  

 Thank you Prof Nicholas Sion  for sharing valuable information

 Thank you prof. Florian Glodeanu  for sharing valuable information.

Thank you prof. Alexander Oreshko for sharing valuable information

 Thank you prof. Andrea Di Vita for sharing valuable information

For the fusion of nuclei, very high density and temperature are required i.e. fusion triple product should meet some criteria. To achieve that plasma species have to be confined in small space that can be done with strong magnetic field as magnetic field has force that cause charged particle to around it. 

In short one can say that magnetic field is necessary to confine the plasma and its energy. Once the confinement is perfect plasma as well as its temperature will lost for a longer time that is useful for fusion reactor. In realty both the fusion mechanism that is magnetic fusion as well as Inertial confinement fusion are still suffering from perfect confinement problem. Once it is solved, fusion reactor will be a reality for power production.

I have responded earlier (above) on the operation and principles of fusion reactors. It is imperative that the plasma is stable else fusion is not likely to occur. This is where current research is on-going. I am listing some published papers on stability issues in the plasma

1- Fusion Energy --- Status and Radiological Feasibility.

Author Nicholas Sion; presented at the CRPA conference, April 2018 in Quebec City, Canada

2- Magneto hydrodynamic Equilibrium and Stability of Plasma, Lino Salamon; Advisor Prof. Dr. Toma Gyergyek, Lubljana, June 2015.

3- A General Comparison Between Tokamak and Stellarator Plasmas. Author panel by Yuhong Xu

https://doi.org/10.1016/j.mre.2016.07.001, Open Access funded by Science and Technology Information Center, China Academy of Engineering Physics

Dear Awani Bhushan ,

I know your question is an old one, but I thought you should contribute.

I can talk about Tokamaks.

In a Tokamak machine, there are basically composition of two magnetic fields, poloidal and toroidal.

These fields are responsible for confining plasma column inside Tokamak vacuum chamber. The composition of poloidal magnetic field and toroidal magnetic field form helical magnetic field. It is this field that allows existence and formation of plasma confined to a Tokamak.

In small and medium sized machines they can obtain energy for these fields via batteries or capacitors. On larger machines and energy is extracted directly from electrical network.

Here are some papers to help.

Article PROJETO E ANÁLISE DOS CIRCUITOS DE PRODUÇÃO DE CAMPO MAGNÉTI...

Conference Paper THE ETE SPHERICAL TOKAMAK - PRESENT STATUS CONSTRUCTION

Article SISTEMA ELÉTRICO PULSADO COM CONTROLE DIGITAL DO TOKAMAK ETE...

Conference Paper STATUS OF CONSTRUCTION OF THE ETE SPHERICAL TOKAMAK

Conference Paper THE ETE SPHERICAL TOKAMAK PROJECT

Article Pulsed electric system for production and confinement of pla...

Conference Paper OVERVIEW AND INITIAL RESULTS OF THE ETE SPHERICAL TOKAMAK

Article CONCEPTUAL PROJECT AND PRESENT STATUS OF THE ETE CONTROL AND...

Conference Paper OVERVIEW OF THE ETE SPHERICAL TOKAMAK EXPERIMENT

Presentation Progress on the ETE Spherical Tokamak (Experimento Tokamak Esférico)

Article SPHERICAL TOKAMAK DEVELOPMENT IN BRAZIL

Poster INTELLIGENT CONTROL BASED ON NEURAL CONTROLLER FOR APPLICATI...

Regards,

Wiltgen

Magnetic field in nuclear reactor

https://www.researchgate.net/project/Research-topic-map-analysis-review/update/62515897ce371e48825685a0

Nuclear Science, Physics and Technology

https://www.researchgate.net/project/Research-topic-map-analysis-review/update/625303ec19eb97629d42261c