Gyrotron vs. Magnetron vs. Orbitron vs. Peniotron vs. Ubitron: A Comparison

This page compares Gyrotron, Magnetron, Orbitron, Peniotron, and Ubitron, highlighting the key differences between them.

Gyrotron

• Gyrotrons typically operate in the millimeter-wave frequency band, ranging from 30 GHz to 300 GHz.
• They exhibit narrower bandwidths compared to some other microwave tubes.
• Gyrotrons are capable of continuous wave (CW) operation at very high power levels. Pulsed powers exceeding 7 GWatt have been achieved.
• They are driven by high-energy electron beams, similar to linear beam tubes, requiring a mono-energetic beam of high quality.
• High operating frequencies necessitate the use of strong magnetic fields.
• Gyrotrons can theoretically achieve efficiencies in the range of 70% to 90%.

Microwave frequencies interact with the helical beam in the waveguide.

As shown in the figure above, microwave frequencies in the waveguide interact with a helical beam. In this single-coil tube design, the helical beam is generated into the TE10 mode waveguide, which has a rectangular shape. Microwaves travel from right to left, while the helical beam travels from left to right. When the microwave frequency, magnetic flux density, and acceleration voltage are properly adjusted, the device functions as a backward-wave amplifier.

Electrons within the tube interact with transverse microwave electric fields, which are velocity-modulated on the left side of the waveguide as the beam enters. The gyrotron is formed when the electron gun is modified to incorporate a side-emitting cathode, and the waveguide is changed to provide the TE11 mode in an oversized circular waveguide. Both ends of the waveguide are open, resulting in sufficient reflections for positive feedback. This characteristic leads to the gyrotron being classified as a forward-wave oscillator.

single coil gyrotron

There are two main types of gyrotrons: single-coil and double-coil. The single-coil helical beam gyrotron is illustrated in the figure above.

Magnetron

magnetron

The magnetron differs significantly from a normal vacuum tube. Here, an external magnetic field forces the electron beam to follow a spiral path from the cathode to the anode.

Orbitron Microwave Maser

The Orbitron is also utilized as a high-power microwave source. This device produces power at millimeter and sub-millimeter wave frequencies, typically radiating at 1 Watt power levels. Orbitrons serve as a bridge between microwave tubes and lasers.

Advantages of Orbitrons:

• They do not require strong magnetic fields.
• They do not require relativistic electrons.

Peniotron

If the microwave input and output ports are interchanged in the “Helical Beam Tube Structure” figure shown for Gyrotron above, the resulting system is known as a forward-wave amplifier. This type of forward-wave amplifier is called a peniotron.

Ubitron

In gyrotrons, when electrons are accelerated by extremely high voltages, they become relativistic. This means that the electron’s mass becomes a function of its velocity, as expressed by the following equation:

m = m0 / ( (1-(c/v) 2 ) 0.5 )

Where:

• m = relativistic mass of electron
• m0 = static mass of electron
• c = speed of light in vacuum
• v = speed of electron in question

Sets of quantum numbers specify the energy states of electrons. Transitions between these energy states will occur. Specifically, sets of quantum numbers will define the low-energy and high-energy orbits of the electron.

This principle is used in the Ubitron, also known as a free-electron laser. Ubitrons operate at frequencies in the millimeter or sub-millimeter wave range and typically function at high power levels.

Ubitron structure

The figure depicts a schematic diagram of a Ubitron. As shown, a high-speed electron beam is emitted from an electron gun and focused using an applied DC magnetic flux density (B). It is periodically deflected using magnetic means. These repetitive deflections create high and low energy states for the electrons.

When electrons in a high-energy state are stimulated by the resonance frequency of a waveguide resonator, a downward transition occurs. The emission at microwave frequency results from these energy transitions at the stimulation frequency.