92 unifying physics of accelerators, lasers and plasma
A schematic design of a klystron is shown in Fig.5.27.
Klystrons are similar to small linear accelerators, and operate as follows. First, electrons are emitted from a round
cathode, which has a large surface area. Electrons are then
accelerated by a voltage of a few tens of kV. A round beam is
formed with a current from a few amperes to tens of amperes.
The beam is focused by near-cathode electrodes and is further
Permanent magnet focusing focused by the solenoid field (which is essential to ensuring
has been used in klystrons effective beam transportation). The particles leaving the cathwith the intention to increase ode pass through an input cavity operating at TM 011 mode,
their wall-plug efficiency.
which is fed from an external pre-amplifier.
The klystron output power is given by
P klystron = ηU 0 I beam
(5.27)
where U 0 is the klystron supply voltage (e.g., 350 kV), I beam is
the electron beam current (e.g., 420 A) and η is the klystron
efficiency (e.g., 45%). The numbers given above as examples
correspond to the SLAC 5054 klystron running at 2.856 GHz.
The klystron efficiency (which typically ranges from 45% to
65%) is one of the most important parameters and is the subject of continuous innovations.
IOTs, klystrons and similar RF power generators — while
still extremely popular — are gradually being replaced by
solid-state devices, for frequencies lower than 1 GHz in parThe trend of RF power sources ticular. The solid-state RF power systems have the advantechnology development is a tage of compactness, higher efficiency and also reliability. The
good illustration of TRIZ modular design of solid-state RF power sources, when each
conclusions about the evolu- module contributes only a small fraction of the total power,
tion of technical systems.
makes it possible to significantly increase the reliability of
the entire system.
5.4.3 Magnetron
Magnetron is an RF power source popular in particular for
CW applications. In a magnetron the cylindrical cathode is
located in the center and magnetic field is applied along
the axis of the device. When the electrons are moving from
the cathode to the anode, the magnetic field turns them and
makes them move on spiral trajectories, creating azimuthal
variations of the electron trajectories.
At certain parameters (of the voltage and magnetic field)
the azimuthal variations of the electron trajectories will
match the azimuthal spacing of the cavities arranged around
the perimeter on the anode body, exciting fields in the cavities. The exited fields in their turn will enhance the velocity
modulation and thus the spatial density modulation of the
electron beam. Increased modulations will further increase
the fields generated in the cavities. The magnetron amplitude
will grow until saturation (due to effects related to the electron beam space charge) and remain constant.
A schematic design of a klystron is shown in Fig.5.27.
Klystrons are similar to small linear accelerators, and operate as follows. First, electrons are emitted from a round
cathode, which has a large surface area. Electrons are then
accelerated by a voltage of a few tens of kV. A round beam is
formed with a current from a few amperes to tens of amperes.
The beam is focused by near-cathode electrodes and is further
Permanent magnet focusing focused by the solenoid field (which is essential to ensuring
has been used in klystrons effective beam transportation). The particles leaving the cathwith the intention to increase ode pass through an input cavity operating at TM 011 mode,
their wall-plug efficiency.
which is fed from an external pre-amplifier.
The klystron output power is given by
P klystron = ηU 0 I beam
(5.27)
where U 0 is the klystron supply voltage (e.g., 350 kV), I beam is
the electron beam current (e.g., 420 A) and η is the klystron
efficiency (e.g., 45%). The numbers given above as examples
correspond to the SLAC 5054 klystron running at 2.856 GHz.
The klystron efficiency (which typically ranges from 45% to
65%) is one of the most important parameters and is the subject of continuous innovations.
IOTs, klystrons and similar RF power generators — while
still extremely popular — are gradually being replaced by
solid-state devices, for frequencies lower than 1 GHz in parThe trend of RF power sources ticular. The solid-state RF power systems have the advantechnology development is a tage of compactness, higher efficiency and also reliability. The
good illustration of TRIZ modular design of solid-state RF power sources, when each
conclusions about the evolu- module contributes only a small fraction of the total power,
tion of technical systems.
makes it possible to significantly increase the reliability of
the entire system.
5.4.3 Magnetron
Magnetron is an RF power source popular in particular for
CW applications. In a magnetron the cylindrical cathode is
located in the center and magnetic field is applied along
the axis of the device. When the electrons are moving from
the cathode to the anode, the magnetic field turns them and
makes them move on spiral trajectories, creating azimuthal
variations of the electron trajectories.
At certain parameters (of the voltage and magnetic field)
the azimuthal variations of the electron trajectories will
match the azimuthal spacing of the cavities arranged around
the perimeter on the anode body, exciting fields in the cavities. The exited fields in their turn will enhance the velocity
modulation and thus the spatial density modulation of the
electron beam. Increased modulations will further increase
the fields generated in the cavities. The magnetron amplitude
will grow until saturation (due to effects related to the electron beam space charge) and remain constant.