RF POWER SUPPLY SYSTEM FOR CW PROTON LINEAR
ACCELERATORS FOR THE ENERGY OF 1 GEV AND CURRENTS UP
TO 30 mA AND 300 mA
B.P.Murin, Yu.D.Ivanov, N.I.Uksusov, I.V.Shumakov
Moscow Radiotechnical Institute, Russian Academy of Sciences,
132, Warshavskoe Shosse, Moscow, 113519, Russia
In the report the problems of RF power supply systems design of a high-energy part of
CW proton linear accelerators for the energy of the order 1 GeV and currents up to 30 mA and
300 mA for an electronuclear power engineering are considered. Reaching high efficiency and
reliability of operation are considered as main problems. Two versions of RF systems design
are presented: for accelerators with superconducting resonators and for accelerators with
"warm" resonators and focussing by superconducting solenoidal magnets.
At present time MRTI develops two types of proton and H- linear accelerators with
output energy of about 1-1,5 GeV in CW mode. The first type is superconlucting linac with
proton (ion) current up to 30 mA. It is dedicated for application in installations for weapon
plutonium conversion and in of "energy amplifier". The second type is linac with current of
250-300 mA with application of superconducting focusing solenoids and new high-power RF
regotron-type amplifiers. It is dedicated for application in installation for transmutation of
long-living radioactive wastes of nuclear stations.
Main part of superconducting linac  with acceleration rate of 15 MeV/m contains 84
nine-cell axially symmetric cavities with elliptical shaped cells excited at the frequency of
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The main part of linac with "warm" resonators and superconducting focusing solenoids,
dedicated for application new high-power RF regotron-type amplifiers with output power of
5,5 MW contains 65 resonators . Alternatively, the version with each resonator excitation
from the group of 6-8 klystrons with output power of 1.2 MW is considered as well. The
reserve of total RF power allows supporting a level of accelerating field at emergency in one-
two klystron amplifiers.
Problem of Reliability and Efficiency of RF Power Supply System
At installation of proton linear accelerator for ADS (Accelerator Driven Power
System) main problems are maintenance of a high reliability and efficiency it of systems. It is
supposed , that a factor of idle time of the linear accelerator there should not be more than
3 % from an operating time of the ADS installation. Accordingly, the factor of idle time of RF
system of linac high-energy part, one of the complicated systems of the accelerator, should not
exceed 0,5-0,8 %. For maintenance of these rigid requirements on a reliability and the reaching
of RF system effective operation it is necessary to reduced channels number, applying in them
super-power RF generating devices with high efficiency. The parameters some super-power
RF generators intended for use in accelerating technique are listed in Table 1.
Parameters of super-power generating devices
1 Klystron K3513 CW 352 MHz 1300 kW 41dB 65 % EEV
2 Klystron K3510 CW 700 MHz 1000 kW 41dB 65 % EEV
3 Klystron YK125 CW 1000 MHz 400 kW 43db 60 % PHILIPS
4 Klystron - CW 1249 MHz 1200 kW 50db 65 % PNC (JAPAN)
5 Regotron CW 1050 MHz 5500 kW - 70 % MRTI
All four types of klystrons have beam voltage of 90 kV and modulating anod. In PNC
klystron (Power Reactor and Nuclear Fuel Development Corporation, Japan) beryllia pill - box
window  is applied. The average life-time of these high power klistrons is expected to be
18000 hours .
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In the regotron project (MRTI)  8 outputs of energy with beryllia pill-box window
For determination of conditions, at which the requirements on a reliability RF system
can be achieved, we shall take equation for calculation of system idle time coefficient "κ". Thus
we shall recognize that a system consists from "n" identical devices (channels) and the failure
results anyone from them to interruption of beam acceleration.
where: T0 – mean time between failure of amplification channel, Tb - time of recovery of
Time of recovery accelerator operation Tb is a result of tree components: time of repair
of amplification channel, time of obtaining of a nominal field in a resonator of the accelerator
(after actuation of the repaired channel) and time necessary for recovery of a nominal mode of
Results of an evaluation of idle time factor "κ" of RF system depending on number of
channels for four values of T0/Tb: 2500, 5000, 7500 and 10000 are presented at Fig.1.
0 40 80 120 160 200
RF system idle time coefficient κ vs. channel number n for 4 values of T0/Tb:
1 – 2500, 2 – 5000, 3 – 7500, 4 – 10000
From them follows, that for "κ" = 0,5-0,8 the channels numbers should be within the
limits of 30-50, and T0/Tb more than 5000. We shall assume, that the mean time between
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failure of the channel is equal to klystron service life-time (30000 h estimated). Then with
n = 40 and κ = 0.5% the time of recovery of accelerator operation Tb is about 4 hours. This
time can appear unacceptable with a point of view of exploitation of the ADS installation. To
reduce non-operation time of accelerator because of failure in RF system it is possible by
several paths. One of them consists of application of RF channels reservation, which has
justified on the linear accelerator of the Moscow Meson Factory . The reservation
eliminates time of repair of a channel. The additional reduction of time losses can be achieved
by application of the scheme ensuring stability of a thermal mode of accelerator resonators (it
is ensure for SC resonators). The reduction of failures number of RF system will be promoted
by application of the functional control behind a klystron condition and channel apparatuses,
that will allow to make klystron replacement before origin of emergency.
The high efficiency of RF system is determined by use of amplifying devices with
efficiency more than 65%. Such efficiency klystrons provide at nominal power. With decrease
of consumed load power efficiency is decreased (fig.2).
0 20 40 60 80 100
% of Max Pow e r
Efficiency η for a klystron vs. % of maximum output power
It is necessary to remember it, when association of resonators in one group for is made
for excitation of one RF channel. The problem becomes complicated by that RF power
consumption for beam acceleration with preservation of accelerating rate increase in
accordance with increase of beam energy.
RF Supply System of a main part of superconducting accelerator.
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The RF supply system of a main part of the accelerator provides excitation of 84 SC
resonators  at frequency of 1056 MHz. RF power required for excitation of one resonator
varies in accordance with increase of beam energy from 159 kW (first resonator) up to
435,6 kW (last resonator). Thus the difference in RF power between adjacent resonators at the
beginning of a main part is 5-6 %, and at the end - 0,2%. Total RF power required for
excitation of all resonators is equal to 28,5 MW. As RF amplifiers in channels are supposed to
be used klystrons with parameters of PNC klystron at operating frequency of 1050 MHz. Thus
at the beginning of a high-energy (main) part of the accelerator from one klystron 5 resonators
are exciting having regard to reserve on RF power on compensation of losses in elements of
waveguide and reserve of RF power on automatic control of RF field amplitude in resonators.
Further number of resonators in group decreases and at the end of the accelerator from one
klystron 2 resonators are excited.
Block diagram of RF power supply of SC resonator group from one klystron is shown
in Fig.3. Here the schemes automatic control of frequency (ACF), automatic control of
amplitude (ACA) and phase (ACP) which are conventional for proton linear accelerators are
shown. RF power on resonators inputs from output of klystron amplifying channel feeds
through waveguide distribution system. The RF power distribution system is derived by a
excitation line EL-M with directional coupler DC and bridge device BS. In each output branch
of a system the circulators C and phase-shifter ϕ are placed. If two resonators are excited from
one amplification channel, the distribution of RF power is accomplished through one bridge
device. In the case of an amplification channel failure instead of it to a distribution system with
the help of switches S the reserve channel can be connected. The reserve amplification channel
can be connected also instead of an amplification channel of the consequent group of SC
resonators. It is supposed, that all there will be 35 active channels. The number of reserve
channels of RF system of a main accelerator part is determined at final development of the
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Block diagram of RF supply system of resonator group of main part of SC accelerator
EL-A – exiting line of accelerator, EL-M - exiting line of cavity, DC – directional coupler, BD – bridge
device, S – switcher, ϕ - phase shifter, C – circulator, R – load, AFC – automatic system of frequency control,
AAC - automatic system of amplitude control, APC - automatic system of phase control, KA – klystron
RF power supply scheme of long "warm" resonators of the accelerator with SC focusing
In a main part of the proton linear accelerator with a focussing by superconducting
solenoids are used "long" (up to 15 m) accelerating resonators with disk and washers (D&W
structure) without division on separate section . The D&W structure has a high coupling
coefficient (40-50%) and low sensitivity to deviations of the sizes at manufacturing. As a result
main part of “warm” accelerator can be partition on identical on RF power consumed
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accelerating modules. In the case of regotrons use with output power of 5,5 MW the number
of accelerating modules will be 65.
In a Fig.4 the block diagram of an accelerating module is shown. On the scheme RF
excitation of resonators is accomplished through 8 power input, which are located from each
other on distance of 1/8 lengths of a resonator and on distance 1/16 from face walls. To avoid
instability in regotron operation on an accelerating resonator, before each power input in RF
feeder ferrite circulator C is placed. With the help of phase-shifter ϕ the RF signals phasing at
regotron outputs is implemented. The regulation of a level of regotron RF power output is
made by control of injector I current.
Block diagram of RF supply system
of “warm” accelerator main part (accelerating module) from regotron
R – regotron, EL-A – exiting line of accelerator, C – circulator, ϕ - phase shifter, APC - automatic system of
phase control, AFC – automatic system of frequency control, AAC - automatic system of amplitude control, I
– injector, B – buncher, E - exciter
Systems of RF field phase control and resonator tuning are traditional ones.
In a Fig.5 the block diagram of an accelerating module with excitation of a resonator by
group of 8 regotrons is presented. It is supposed, that amplitude and phase everyone klystron
amplifier are stabilized with the help of internal systems of automatic control. On a fig.5 RF
voltage from a accelerator reference line EL-A amplifies by the preliminary amplifier CA-D and
feed to reference line of an accelerating module EL-K. RF power from amplifiers outputs KA
through switches "S" and ferrite circulators "C" feeds to RF power resonator input. In case of
emergency in anyone from amplifiers, last one with the help of switches S can be switched to
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an load equivalent R. For preservation of a RF field level in a resonator total RF power of
remaining amplifiers should be increased by the value of ∆P. The value ∆P takes into account
RF power of disconnected klystron and shunting of a resonator by output impedance of a
circulator. Thus, the given scheme of resonator excitation has the increased reliability, as the
time of accelerator operation recovery here can be reduced to about several minutes. For an
accelerating module with a resonator consuming 5,5 MW will be enough 6 klystrons with
output power of 1,2 MW (PNC klystron).
Block scheme of RF power supply system of “warm” accelerator main part
from klystron group.
EL-A – exiting line of accelerator, EL-K - exiting line of klystron, C – circulator, R – load, AFC – automatic
system of frequency control, AAC - automatic system of amplitude control, APC - automatic system of phase
control, S – switcher, KA – klystron amplifier, CA-D - exciter
The schemes RF systems design of two types of CW proton linear accelerators are
considered: the linear accelerator with superconducting resonators and linear accelerator with
long "warm" resonators with a focussing by superconducting solenoids. It is possible to make a
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conclusion about suitability of the offered schemes from the point of view of maintenance of
demanded efficiency and safety of operation in conditions of linear accelerators use in ADS
1. B.Murin, G.Batskikh, V.Belugin, B.Bondarev, A.Durkin, Y.Ivanov, A.Fedotov,
I.Shumakov, N.Uksusov. Designing problems of superconducting proton linac with output
energy of 1 GeV and CW current of 30 mA. This conference.
2. B.P.Murin, G.I.Batskih, V.M.Belugin, B.I.Bondarev, A.P.Durkin, A.P.Fedotov,
Yu.D.Ivanov, V.A.Konovalov, I.V.Shumakov, N.I.Uksusov (MRTI), A.A.Vasiljev (Minatom
RF). Superconducting devices use in high current linear proton accelerators for energy
purposes. The Second International Conference on Accelerator-Driven Transmutation
Technologies and applications, Kalmar, Sweden, June 3-7, 1996, v.2, p.p. 1047-1053.
3. C.Rubbia et al., Conceptual Design of a Fast Neutron Operated High Power Energy
Amplifier ", CERN Report, CERN/AT/95-44 (ET), Geneva, 29th September, 1995.
4. S.Toyama et al., High Power CW Linac in PNC, Proceedings of the 1993 Particle
Accelerator Conference, Washington, 17-20 May. v.1, p.546-548.
5. D.Boussard and E.Chiaveri. The LEP Superconducting RF System: Characteristics
and Operational Experience, NEA Workshop on Utilization and Reliability of High Power
Accelerators, 13-15 October 1998, Mito, Japan.
6. B.P.Murin, B.I.Bondarev, A.P.Durkin, I.V.Shumakov, Regotron as CW High-
Power Source for Ion Linac. Proceedings of the XVIII International Linear Accelerator
Conference, 26-30 August 1996, Geneva, Switzerland, CERN 96-07, v.2, pp.758-760.
7. “Linear accelerators of ions”, Volume 2. "Basic systems", Edited by B.P.Murin, M.,
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