CHAPTER 1

INTRODUCTION

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1.1 Introduction

1.1.1 Background

1.1.2 Application

1.2 Gyrotron Components and Operating Principle

1.3 Objective and Outline of Thesis

1.3.1 Objective

1.3.2 Outline

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1.1 Introduction
The energy crisis is a foremost problem at present and will be for the future world. Many
research groups are involved to resolve this problem in different ways. A continuous effort is
also going on by the microwave community in the field of microwave devices throughout the
world to enhance the research in the field of energy production [1]. Considering the future
energy crisis, an international activity “International Thermonuclear Experimental Reactor
(ITER)” is started jointly by USA, Russia, European Union, China, Japan, South Korea and India
as global partners, which is based on the electricity production from the fusion power [2].

ITER is an international nuclear fusion research project, which is going on to build up

world's largest and most advanced experimental tokamak nuclear fusion reactor (under
construction) at France (Fig. 1.1) [3]. The ITER fusion reactor is designed to produce 500
megawatts of output power for 50 megawatts of input power. Construction of this facility began
in the year 2007 and the Electron Cyclotron (EC) system is envisioned to generate 8 MW RF
power for the first ITER plasma operation scheduled in November 2019 with the full 24 MW for
the second operating period in late 2021[4]. The plasma is heated to a high temperature by ohmic
heating (running a current through the plasma). Additional plasma heating is created
using neutral beam injection and radio frequency (RF) or microwave heating.

Fig. 1.1: 3D view of International Thermonuclear Experimental Reactor (ITER) [3]

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 For this large activity, a microwave of 110–170 GHz with an RF output power in the
megawatt range is needed. The frequency of 170 GHz with an output power ≥ 1 MW is decided
as the Electron Cyclotron Resonance Heating (ECRH) frequency for the ITER. It is well
established that the gyrotron is capable of producing RF output power upto megawatt level in the
long pulse [5]-[7]. Fig. 1.2 shows the schematic view of ITER EC system with different sub
system [4]. The power supplies, gyrotrons, transmission lines and launchers are included in the
sub system of ITER EC system. Different power supplies such as main power supply, body
power supply, anode power supply, etc. are used in the ITER EC system. The gyrotrons are
designed to generate more than 1MW output power with more than 50% electrical efficiency [4].

Fig. 1.2: Schematic view of ITER EC system with different sub system [4]

Gyrotron oscillators are high-power microwave sources mainly used for Electron
Cyclotron Resonance Heating (ECRH) and plasma stabilization through the localized current
drive in magnetically confined plasmas for controlled thermonuclear fusion experiments. The
device is also called fast wave microwave device, which emits millimeter and sub-millimeter
beams by bunching of the electrons (having velocities required for resonance conditions) with
the cyclotron motion in a strong magnetic field [8]-[10].

In the beginning, the name gyrotron (gyro+ electron) was used by the Russian for a single
cavity oscillator, now often referred to as gyro-monotron. The name now refers to a class of
devices including both oscillators and amplifiers. At the present time, the gyrotron is only the
device which can operate at high frequency range to give high output power. Unlike “slow wave
microwave tubes” (such as magnetron, klystron, etc.) the gyrotron operates in a high order mode

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and thus the dimensions of interaction structure are not limited. Thus there is intense interest in
these devices at the present time [11]-[14].

1.1.1 Background
The first move on the theoretical work on this device was made by Twiss in Australia
[15], J. Schneider in USA [16] and Gapanov in USSR (now Russia) [17] in late 1950’s. The
gyrotron as a device came into picture at Radio-physical Research Institute, Gorki, USSR, which
was developed by Gapanov and Kisel [18]. After this achievement, more experimental work was
prompted on the gyrotron at different power levels at higher harmonics [6].

In the whole decades of 1970’s and 1980’s, very progressive work in the theoretical as
well as the experimental area has been carried out on the gyrotron and other gyro-devices like
gyro-klystron, gyro-TWT, etc. The main motive of this work was to improve the efficiency with
high output power. The research work on gyrotron development was also started at Brazil, Korea
and Germany in the late 1980’s and early 1990’s. After then new devices such as co-axial cavity
gyrotrons and terahertz gyrotrons were developed in 1990’s and early 2000’s [19]-[22]. During
1990’s and early 2000’s, the most impressive progress was demonstrated by the gyrotron team of
the FZK, in Germany, where this work was done as an International Thermonuclear
Experimental Reactor (ITER) task in European Fusion Development Agreement (EDFA)
cooperation between FZK Karlsruhe and HUT Helsinki. Work on co-axial gyrotrons also
continued independently in Russia, U.S.A., Brazil, and Japan [23] - [29]. In this way the device
development spans all over the world. At present the progress in gyrotron is remarkable with
almost reaching 1-2 MW power at 140 GHz and 170 GHz, respectively for plasma research and
upto THz with moderate power for nuclear spectroscopy applications [30]–[32] through the
technological breakthroughs and use of new materials. The present status of the gyrotron tube
along with the progress in the development of the tube at the various institutes in the globe with
the detail specifications is described by Manfred Thumm [7], [33]–[34]. Fig. 1.3 shows some
recently developed gyrotrons [35]-[37].

India is working in the field of slow-wave microwave tubes such as magnetron, klystron,
travelling-wave tube, etc. since the last fifty years but the work in the area of fast-wave
microwave tubes, namely, gyrotron and gyro-devices was started mostly in the last decade on
device development level. The extensive work on the design and development of different

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frequency and power levels gyrotrons is started at the CSIR-Central Electronics Engineering
Research Institute (CEERI), Pilani since 2006. A lot of efforts are attempted with an aim to
establish the indigenous design and development technology of gyrotron at CEERI [38]–[47].
The work on gyrotron development at CEERI, Pilani was initiated by its potential use in the
plasma fusion tokamak systems ADITYA and SST-1, ongoing ITER project and upcoming
ITER-India activity.

Presently, two projects are in progress “Design and Development of 200 kW, 42 GHz
CW/Long Pulse Gyrotron” a multi-institutional project, funded by Department of Science and
Technology (DST), New Delhi and “Design and Development of High Frequency, High Power
Gyrotron” funded by Council of Scientific and Industrial Research (CSIR), New Delhi. One
another project “Design and Development of 1MW, 170 GHz gyrotron” is to be soon, funded by
CSIR, New Delhi under network scheme. In India, the research activities around such type of
devices are still limited in few institutes only, namely, CEERI-Pilani, BHU-Varanasi, IPR-
Gandhinagar, IIT-Roorkee, SAMEER-Mumbai, MTRDC-Bangalore and DAV-Indore while the
device is globally getting popularity due to its capability to generate very high power radiation in
millimeter and sub-millimeter wave range.

170 GHz, 2 MW, CW coaxial 140 GHz, 1 MW gyrotron 0.259-THz CW gyrotron for
gyrotron for ITER for WX-7 DNP-NMR spectroscopy
Fig. 1.3: Typical high power gyrotrons [35]-[37]

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1.1.2 Application
The application area of gyrotron oscillators spans a wide range of technologies. These
devices are successfully used for number of applications such as plasma research, energy
generation, medical spectroscopy, material processing, satellite communication, etc. [48]-[50].
The briefs of various applications of the device are as follows:

Plasma fusion: The radio frequency electromagnetic waves are used for plasma heating.
One kind of plasma heating method is Electron Cyclotron Resonance Heating (ECRH) which
requires the sources in the frequency range of 100-200 GHz. At present gyrotron oscillators are
successively used as high power sources for ECRH applications and for plasma diagnosis of
magnetically confined plasmas in controlled thermonuclear fusion research. The latest and very
ambitious international effort in the field of energy production by the controlled nuclear fusion is
started in the form of ITER project with an aim to solve the problem of future energy generation
to a great extent. ITER is the biggest plasma fusion machine under construction. 170 GHz
gyrotron with 1 MW of output power would be used in the ITER for ECRH and ECDD (Electron
Cyclotron Current Drive). High efficiency, high output power and long pulse width are the key
requirements for the development of fusion gyrotrons [48], [51]-[53].

Industrial heating: Creation of gyrotrons exposes new possibilities of potential

technologies for industrial material processing [54]. Microwave or millimeter wave heating is a
kind of dielectric heating in which the radiations between the frequencies ranges from 300 MHz
to 300 GHz are used [55]. The utilization of microwave has been taken on in the numerous
industrial heating applications like rubber technology, ceramic sintering, chemical processing,
composite fabrication, food processing, etc. Rather than the heating and sintering of the
ceramics, the millimeter wave heating is also used for surface hardening, drying, removal of the
organic binders and moistures from the surface, growth of nanostructure ceramics, etc [56]-[60].
Mostly the gyrotrons of the frequency range 20 GHz to 35 GHz are used in the millimeter wave
industrial applications [6], [61]. This type of RF heating mechanism directly depends on the
frequency of the radiation. By taking this aspect into consideration, the low frequency gyrotrons
are suitable for heating purpose.

Spectroscopy and medical science: One of the most important properties of THz
radiation also called submillimeter wave radiation (300 GHz to 3 THz) is its penetration through

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the several kinds of non-conducting and non polar materials like cloth, papers, wood, etc. and
can be used for the security systems [6], [62]-[64]. The THz frequency fall in the spectral range
of subatomic particle (like electron spin system) and useful to characterize the materials via
subatomic particles resonance [65]-[67]. It is non-ionizing radiation (due to small energy of
photon) and does not damage the tissues and DNA unlike X-ray. THz radiation shows unique
spectral properties for several materials and used in the form of time domain spectroscopy [63].
In the medical science and structural biology, a THz radiation source emerged as a key
component in the form of DNP/NMR/ESR spectroscopy [63], [68]-[69]. The major areas of
applications of THz gyrotrons are ESR and solid state NMR spectroscopy [70]. People are also
working on other potential areas of applications of gyrotron as a THz source like radioactive
material detection, security, etc [63], [65], [71]-[74].
Security and atmospheric science: The Active Denial System (ADS) developed by
Raytheon for the US Air Force Research Labs is a non lethal, counter-personnel, directed energy
weapon system which can be used against human targets at a distance beyond the effective range
of small arms. ADS launches a focused millimeter wave energy beam which induces intolerable
heating sensation on an adversary's skin so that individual might be repelled without injury [63]
[71], [75]. 95 GHz millimeter wave radiation is used in the ADS because of the natural
atmospheric window at this frequency [76], [77]. This system can focus the 95 GHz millimeter
wave effectively upto few kilometers. Another advantage of 95 GHz frequency is its small skin
depth compared to the other commercial microwave frequencies like 2.45 GHz or 915 MHz [71].
The radiation can reach upto 1/64th inch in the human skin and create burning sensation. The
blood vessels and nerve system are located beneath this skin depth and thus the radiation is not
harmful. The 95 GHz gyrotron with the output power of 100 kW or more is an effective source
of millimeter wave for ADS system [78]. The gyrotron operates at second or higher harmonic, so
that the permanent magnet can be used in place of the bulky superconducting magnets. The high
power millimeter wave sources open the technological possibilities for the various kinds of
atmospheric diagnosis such as cloud monitoring, measurement of humidity, turbulence structure
determination, etc. 94 GHz radar system is used in the atmospheric diagnosis because of the
natural atmospheric propagation window at this frequency. Rather than the cloud monitoring, the
millimeter wave technology can be used for the various other atmospheric diagnosis like
detection of turbulence structure, relative humidity, etc [79]

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 Communication: A narrow frequency band around 35 GHz and 95 GHz show natural
atmospheric window and thus can be used in the communication and the detection applications
[48], [68], [76]. The THz radiation can be used in satellite to satellite communication in space
and in short distance communication which is very useful for the military applications [80].

1.2 Gyrotron Components and Operating Principle

Fig. 1.4: 3D view of the major components of a gyrotron [81]

Fig. 1.4 shows the 3D view of the major components of a gyrotron [81]. The gyrotron
shown in Fig. 1.4 is also called a quasi-optical gyrotron with radial output, where RF window is
perpendicular to the gyrotron axis for RF output. The other type of gyrotron built today is an
axial output gyrotron, where RF window is put along with the gyrotron axis and joined after
collector for RF output [41], [68]. In gyrotron oscillator an annular electron beam is produced by
the electron gun also known as magnetron injection gun (MIG) [82]. This is a very important
component of gyrotron or any other vacuum device. The electron gun is used to generate an
electron beam with the beam properties (beam diameter, beam density etc.) required at
interaction structure for its interaction with the RF wave. The high power gyrotron typically uses
the thermionic magnetron injection gun (MIG), which produces large annular electron beams
with the electron beams with the electrons executing small cyclotron orbits as required for the
cyclotron resonance interaction [83]. Fig. 1.5 shows the schematic view of a triode type
magnetron injection gun with electron beam profile [83], [84]. Another type of MIG is diode-

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type MIG, where only one anode is used [84]. In MIG, the electron beam is emitted from the
conical shaped cathode working on the principle of thermionic emission, which is based on the
heating of an emitting surface to allow electrons to overcome the work function and escape upto
the surface [85]. The external magnetic field produced by a superconducting magnet located at
the center of the cavity causes the electrons to gyrate. This gyrating electron beam is transported
to the interaction region through beam tunnel [85], [86].

Fig 1.5: Schematic view of magnetron injection gun with electron beam profile [83].

The beam tunnel provides the path for the gyrating electron beam from the magnetron
injection gun (MIG) to the interaction cavity. The magnetic field is strongly inhomogeneous in
the beam tunnel so that the gyrating electron beams are compressed sufficiently to achieve the
required beam parameters for the interaction in the cavity. Approximately 3% to 5% of generated
RF power in cavity can reach the MIG. This amount of RF power is sufficient to degrade the
beam quality and even can damage the MIG cathode. The beam tunnel is mainly used to prevent
the propagation of generated RF power from the cavity to the MIG. In the pure metallic beam
tunnel, the gyrating electron beam may excite the parasitic modes which degrade the electron
beam quality. Lossy ceramics are used in the beam tunnel to absorb the RF power and to avoid
the excitation of the parasitic modes. An absorbing beam tunnel of alternate rings of oxygen free
high conductive (OFHC) copper and lossy dielectric material is widely used in the gyrotron [87],
[88]. The grounded conductor rings are placed between lossy ceramic rings to remove the charge
accumulated on the surface of the lossy ceramic rings during the absorption of RF power. Fig.
1.6 shows the schematic view of gyrotron beam tunnel [89].

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 Ceramic
rings

Grounded OFHC
copper rings

Fig. 1.6: Schematic view of gyrotron beam tunnel [89]

After crossing the beam tunnel, this gyrating electron beam is transported to the
interaction region (also called cavity) where due to beam-wave interaction; a fraction of electron
beam power is converted into RF power. In conventional gyrotron, the cavity is usually a three-
section smooth wall cylindrical structure as shown in Fig. 1.7 [90]. The input taper is a cut-off
section, which prevents the back propagation of RF power to the electron gun. The beam wave
interaction takes place mainly in the uniform middle section where the RF field reaches peak
values. The up taper connects the cavity with the output wave-guide. This circuit can support
many different electromagnetic modes.
pa ra bolic smoothing
4 mm

φup

φdown
Rcav

L down L cav L up
Fig.1.7: Interaction structure with gradually tapered cylindrical wave-guide [90]

The magnetic field causes the electron beam to begin to gyrate as the Lorentz force
contains the cross product of electric and magnetic fields. Due to rapidly increasing magnetic
field, the electron beam is also compressed. The electron beam starts gyrating with the angular
frequency ( ω c ) given as [90]-[92]:

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 e Bo
ωc = (1.1)
mo γ o

where γ o e , mo are the relativistic factor at cavity entrance, the electron charge and the rest
mass of electron, respectively. The beam wave interaction produces angular velocity modulation,
which in turn produces a modulation of electron energy. This can produce electron bunching of
the beam. To achieve such a mechanism, a resonance condition must be satisfied between the
periodic motion of electrons and the electromagnetic wave in the interaction region represented
as [90]-[92]:
ω − k z vz = s ωc . (1.2)

Here, ω is the wave RF angular frequency, k z is the characteristic axial wave number, v z is the

axial velocity of gyrating electron, s is the harmonic number, ωc is the electron cyclotron

frequency. In case of gyrotron v z is always kept below v⊥ (transverse velocity of electrons) and
thus the Doppler shift term becomes very small and thus (1.2) becomes:
ω ≈ sωc . (1.3)

The helical beam produced by the magnetron injection gun interacts with the
electromagnetic field (in TEm,n mode) of the same frequency as of the cyclotron frequency, when
the electron beam passes through the interaction region. This causes bunching of the electron
beam. The dispersion diagram ( ω versus k z plot) indicates a resonance of the beam with the

cavity mode as an intersection of the waveguide mode dispersion curve (hyperbola) which may
be obtained through the expression expressed as [90]-[92]:

ω 2 = k z2 c 2 + k ⊥2 c 2 . (1.4)

While, the beam-wave resonance line (straight line) is given by (1.2). Here, k⊥ is the
characteristic transverse wave number and c is velocity of light in free space. In case of a device
with cylindrical resonator, the transverse wave number may be defined as:

k ⊥ = χ m′ , n / Rc (1.5)

where χ m′ , n is the mth root of corresponding Bessel function (TMm,n) or derivative (TEm,n) and Rc

is the waveguide radius. Phase velocity synchronism of the two waves is desired in the
intersection region.

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 Fig. 1.8: Dispersion diagram for the gyrotron interaction for different harmonics [93].

The dispersion diagram for the gyrotron interaction structure can be represented as shown
in Fig. 1.8. The straight lines in the Fig. 1.8 show the electron cyclotron harmonic modes (for
s=1, 2, 3 and 4) obtained from (1.2) and the parabolic curve indicates the waveguide mode
obtained from (1.4). The matching point of the electron cyclotron harmonic mode and waveguide
mode is the resonance point between the electron beam and the RF. In order to understand the
process of bunching, assume a small group of electrons orbiting about the same guiding center.
Considering that initially ω is slightly greater than ωc . In the presence of transverse electric
field (E), the electrons experience an additional force eE which cause some electrons to
accelerate and others to decelerate depending on the relative phase of the electric field [93]. Due
to this mechanism, the electrons ultimately form a bunch as shown in Fig. 1.9 (cross-sectional
view) [93].

Fig. 1.9: Front view of one orbit before and after electron bunching [93].

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 Since the cyclotron frequency is inversely proportional to relativistic mass factor (see,
(1.1)), the frequency will decrease for the accelerated electrons and increase for the decelerated
electrons. After few cycles, the electrons that gaine energy lag in phase and the electrons those
loose energy advance in phase, resulting in phase bunching. If the electric field frequency is
exactly equal to the electron cyclotron frequency, this bunching process will continue until the
entire beamlet is bunched at a zero-field phase point. In order to extract power, the bunch must
be formed at a field maximum. This is accomplished by a slight tuning of the axial magnetic
field so that the cyclotron frequency is slightly lower than the RF frequency. When this condition
is achieved, then bunches will orbit in phase with the electric field and give up rotational energy
to the TE mode of RF field [93], [94]-[96]. After the electron-cyclotron-interaction in the cavity,
the generated RF field and the electron beam propagate within a hollow waveguide towards the
so-called quasi-optical output system. Fig. 1.10 shows the schematic view of quasi-optical
output system [97]. In the quasi-optical output system, several methods, which can be described
equivalent to quasi-optical phenomena, are utilized to transform the generated high-order cavity
mode into one or more beams. The quasi-optical output system has two main functions. The
spent electron beam and the generated RF-power have to be separated. In addition, the high order
cavity mode has to be converted to one or more linearly polarized paraxial beams, which can exit
the tube radially through one or more output windows[97]-[100].

Fig. 1.10: Schematic view of mode Launcher [97].

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 The gyrotron window acts as an outlet for the RF output power and it is also used as a
vacuum seal for the tube (Fig. 1.11) [90]. It must be fabricated from a low-loss material, which is
also suitable for ultra high vacuum application. The conditions for oscillations in the interaction
cavity especially the mode competition problems are dependent on the reflections from the
window. Because of the high power, the thermal management of the output window becomes an
important aspect. The design as well as the choice of the working temperature of the window has
to be carefully chosen. Edge cooling does not seem to be sufficient even for medium power
gyrotron at room temperature. Face cooling is much more efficient, but it requires a double disc
window. For high power gyrotron a temperature of 77˚K or lower is necessary to minimize the
reflection [90], [101]-[103].

Fig. 1.11: Schematic view of single disk edge cool window [90]

To collect the spent electron beam another component called collector is used. Fig. 1.12
shows the schematic view of gyrotron collector [90]. In gyrotron and similar devices, the energy
of electrons after participating in the interaction process is dissipated on the walls of the
collecting surface. Collector is one of the major components of gyrotron to collect the spent
electron beam and dissipate heat efficiently. If there is no collector in the tube then after passing
through the interaction region and transferring energy to the output RF beam there is no region
for collecting spent beam, so efficiency decreases. To increase the efficiency of gyrotron we
need an energy recovery system known as collector. In collector the kinetic energy remaining in
the spent beam is converted into electrical energy [104]-[107].

In collector, the kinetic energy remaining in the spent beam after participating in the
interaction process is converted into electrical energy. The energy of the beam is distributed upto

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certain region instead of collecting at one portion in order to avoid melting of the collector
surface. The wall loading for collector surface should not be more than 2.0 kW/cm2. Collectors
are of two types, namely (i) undepressed and (ii) depressed collectors, respectively. The
depressed collector helps to increase the overall efficiency of the gyrotron tube in comparison to
undepressed collector as the electron beam lands at lower potential in depressed collector. To
increase the efficiency one should design and build gyrotron with a suitable energy recovery
system, namely, depressed collectors [108]-[111].

Fig. 1.12: Schematic view of gyrotron collector [90].

1.3 Objective and Outline of Thesis

1.3.1 Objective
A powerful 24 MW Electron Cyclotron System with operating frequency 170 GHz
having pulse width upto 3600s is planned to be installed for ITER Tokamak system which will
be used for central heating and current derive applications. For this purpose 26 gyrotrons will be
used along with other sub-systems. The responsibility of the development of these gyrotrons is
on the various countries, namely, Europe, Russia, Japan and India. Considering this ongoing
ITER project and upcoming ITER-India activity, the extensive work on the design and
development of 170 GHz, 1 MW gyrotron is started at the Central Electronics Engineering
Research Institute (CEERI), Pilani and lot of efforts are attempted with an aim to establish the
indigenous design and development technology of gyrotron at CEERI. For India, it is a rare
opportunity to work in this field and whatever knowledge grown in this new type of microwave
tubes would directly help the country in the self reliance in the design and development of these
device for the present gyrotron developed at this stage and to be developed in future as per
requirement.

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 This Thesis presents the design of 170 GHz, 1 MW gyrotron for ITER application. The
objective of the study for Ph.D. thesis is to design the gyrotron which produces high output
power with high efficiency and to contribute some knowledge in the real scenario of design and
development of gyrotron in India. The RF powers at different frequencies are supplied by
different gyrotron oscillators. This makes the whole RF system more complicated as the separate
power supplies, magnet system, transmission line system, etc., are required for each gyrotron,
which enhances the overall cost of ECRH system. The ECRH RF system can be simplified if the
single gyrotron device delivers MW power at two or more frequencies (also called multi
frequency gyrotron). Therefore, the author has also attempted the design of multi-frequency
gyrotron.

1.3.2 Outline
This thesis basically covers the design methodology developed for the design of 170
GHz, 1 MW gyrotron. The study of multi-frequency gyrotron is also accomplished. The thesis
work carried out is presented in seven chapters as briefly discussed in the following paragraphs.

In Chapter 1, which is an introduction to the thesis, the general introduction of gyrotron is

presented. The historical background, application and current status of gyrotron are presented.
The gyrotron consists of several components like electron gun, interaction structure, collector,
RF window, magnet system, etc. All the components have their discrete roles in the function of
the device. In this respect, it is important to study the operating principle of gyrotron and the
various components of gyrotron and thus presented in Chapter 1.
Chapter 2 presents the synthesis of RF interaction structure for 170 GHz, 1 MW Gyrotron
and triple frequency gyrotron (TFG), respectively. In this Chapter 2, the generalized nonlinear
theory of gyrotron, design parameter and technical constraint are discussed. The chapter also
includes the operating mode selections and cold cavity analyses for both types of gyrotrons.

In Chapter 3, the beam-wave interaction analyses are carried out for 170 GHz, 1 MW
Gyrotron using commercial available code for the estimation of actual power growth, efficiency,
output signal frequency, etc. The thermal and structural analyses of the interaction cavity are
important for the operation of the gyrotron cavity and thus also presented in this Chapter 3. The
beam-wave interaction for triple frequency gyrotron is also attempted and discussed in this

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Chapter. The optimized cavity and beam parameters of 170 GHz, 1 MW gyrotron and TFG are
used in the MIG design.

The electron beam analysis related to the electron beam emission and transmission is
significant for design of the magnetron injection gun. The analysis finally leads to the
optimization of MIG for beam performance through the sensitivity analysis. Chapter 4 covers the
designs of MIG’s for 170 GHz, 1 MW gyrotron and triple frequency gyrotron, respectively. The
design involves the steps starting from the preliminary design, the electron beam analysis, the
sensitivity study and finally the thermal analysis. The preliminary design of the electron gun is
performed by using some trade off equations. The electron beam analysis is carried out by using
the commercially available codes. The sensitivity study has been carried out by changing the
different gun parameters to decide the fabrication tolerance.

Chapter 5 presents the design of single disk edge cool RF window and the Brewster
window for 170 GHz, 1 MW Gyrotron and triple frequency gyrotron, respectively. The chapter
covers the electrical as well as mechanical design of RF window.

The designs of electron beam collector for 170 GHz, 1 MW gyrotron and triple frequency
gyrotron are studied and presented in Chapter 6. The design covers the initial design, the
trajectory analysis, the thermal analysis and the structural analysis of electron beam collector.

It is always of interest to summarize and conclude the work and results presented in the
thesis for the sake of concise awareness. Chapter 7 is devoted for this purpose highlighting the
role of the thesis work in formulating a general indigenous design base for design of 1 MW, 170
GHz gyrotron under present activity at CEERI. The limitations of the work and the scope for
further work are also discussed.

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