Gyrotron - microwave tube capable of
delivering very high microwave power in the long-pulse and CW
operation at millimeter and submillimeter wavelengths.
Gyrotron is the most practically attractive
variety of cyclotron resonance maser (CRM). In CRM the
relativistic dependence of cyclotron frequency of electron on
their energy lead to coherent radiation of fast waves by the
electrons rotating in the external homogeneous magnetic field.
This effect (under certain conditions) may be very important even
for subrelativistic beams with 20-100 keV energy electrons.
CRM-monotron
with specific (described below) electron-optical and
electrodynamic systems was called a gyrotron (see Fig.). A
magnetron-type electron gun which forms an annular electron beam
was suggested as the basic element of the electron-optical
system. In such a system electrons are emitted from the cathode
under the action of the electric field produced by the voltage
applied between the cathode and the anode and move in the
gradually increasing magnetic field towards the interaction
space. In this motion the electron beam is adiabatically
compressed; part of energy of the electron motion along the lines
of magnetic force is transformed into the energy gyration which
grows according to the adiabatic invariant (pgyro)2
/ B = const (pgyro
is the orbital momentum of particles). As a result, a substantial
part of the kinetic energy of the electron beam at the input to
the interaction space placed in the region of a strong magnetic
field is related to the gyration of the particles and under
appropriate conditions can be consumed by the RF field. The
electrons leaving the interaction space move in the decelerating
magnetic field, which leads to their decompression and reduces
the heat problems on a collector.
The electrodynamic system of a gyrotron is
an open resonator with diffraction radiation output. Such a
resonator is formed by a regular section of a slightly irregular
waveguide. The system has a cutoff narrowing at the cathode end,
which prevents the penetration of the waves into the near-cathode
region. At the output cross section, the part of the waveguide
where the interaction with the electron beam takes place is
coupled to the tapered waveguide through which the radiation
output from the interaction space occurs. Such a system has no
small-scale elements which provoke microwave breakdown at high
microwave power levels. Besides, cyclotron resonance interaction
of electrons with fast waves makes it possible to use space
extended system, which mitigates specific heat loads caused by
the ohmic losses of microwave power and, hence, the problem of
heat transfer from the resonator at CW and long-pulse operation.
In the region of millimeter wave (frequency
range - 30...300 GHz) gyrotron tubes can generate microwave
radiation with high output powers (a few kW up to some MW). The
applications of such millimeter wave powers are mainly heating of
nuclear fusion plasmas and thermal treatment of materials, e.g.
sintering of low loss ceramics or tempering of semiconductors.
GYROTRON in INTERNET
ATRI 2000 High Performance Gyroklystron Amplifier
Gyrotron Project of School of Physics, Sydney University
Gyrotron Research in MIT Plasma Science and Fusion Center
Gyrotrons of Insight Product Company
About Gyrotron at CRPP (Ecole Polytechnique Federale de Lausanne)
High Power Millimeter Waves Research in IHE of Universitat Karlsruhe
