Ion Cyclotron Resonance Heating
A little more power!!
Today we are briefly touching upon the basic principles of external plasma heating within a tokamak, in particular ion cyclotron heating.
Basics: This is a machine that pumps microwaves into a tokamak, much like when you put food in your microwave but much more powerful!
The Ion and electron cyclotron heating approach utilises the properties of electromagnetic radiation (radio waves) modulating them at different frequencies, this heats the electromagnetically contained plasma to even higher temperatures. This energy is transferred to the ions within the plasma by this intense beam of electromagnetic radiation.
Lets investigate this further!
Within magnetically confined plasmas (like inside of a tokamak), the particles such as electrons are rotating around the magnetic field line, and the frequency of rotation is determined by three things:
3. Magnetic field strength
However density and temperature have no effect at cyclotron’ frequency, this means that when electromagnetic wave at cyclotron resonant frequency is driven into the plasma, the particles with mass and charge are now being heated by this added frequency. However this will only work if the magnetic field around the plasma is running at the same frequency as the cyclotron resonance frequency being injected.
The tokamaks magnetic field will decrease as the distance increases from the tokamaks major axis. By forcing this it allocates a small region where the beam can be injected giving us a simple control over deposition of the cyclotron resonant wave. To meet the complicated wave system propagation guidelines, multiples of the base cyclotron frequency, called ‘higher harmonics’ are mostly injected into the tokomak.
By injecting higher harmonic resonance, it heavily relies on space variations in the wave intensity (much like a duty cycle and amplitude of a sign wave). This means that the higher harmonic resonance frequency reacts stronger for particles with larger orbits.
Pictures below of this system
How an ion reacts when inside of a magnetic field
Ion Cyclotron resonance Heating Unit
Ion Cyclotron resonance Heating Unit Schematic upon tokamak
The video below shows Fourier Transform Ion Cyclotron Resonance Mass Spectrometry – Identifying some underlying principles of Ion Cyclotron Resonance heating