RF scheme of electron linear
accelerator with energy 200-500 MeV
Levichev A.E
Budker Institute of Nuclear Physics SB RAS
Introduction
Debuncher-monohramator
Accelerating structure
Accelerating structure.
1 – Regular cell, 2 – Wave type transformer, 3 – Connection cell, 4 – Connection
diaphragm, 5 – Structure frame with cooling system.
Accelerating structure
BINP produced accelerating structure.
Accelerating cells and wave type transformers.
Basic parameters of BINP made accelerating structures
2855.5 МHz
Operating frequency f

Operating mode
Unloaded quality factor
Group velocity
Shunt impedance
Unloaded time

Q0
Vgr
Rsh
0 = 2Q0/
1.32104
0.021C
51 МОhм/м
1.47 μs
Attenuation parameter  = 1/(0Vgr)
0.108 1/м
Integrated attenuation parameter L
0.316
Filling time Tf =L/ Vgr
0.465 μs
Period
34.98 мм
Inner diameter of the cell cavity
83.8 мм
Iris aperture diameter
25.9 мм
Iris thickness
6 мм
Overvoltage coefficient
1.7
RF power source
Picture of TH 2100 klystrons
series.
Basic parameters of TH 2128 C/D klystron.
Operating frequency
2856 MHz
Peak output power
45.5 MW
Average power
10 kW
RF pulse duration
4.5 μs
Gain
54 dB
Efficiency
43 %
Maximum input power
200 W
Band width
10 MHz
Cathode voltage
315 kV
Beam current
335 А
Filament heater voltage
30 V
Filament current
24 А
Modulator
Parameters of К2 modulator series (ScandiNova
Systems)
Modulator К2-3
Parameter
Unit
K2-1
K2-2
K2-3
Klystron RF Peak Power
approx
MW
35
40
45
Klystron RF average Power
approx
kW
1,6
1,6
1,6
modulator Peak Power
MW
74,3
91,5
100,5
modulator average Power
kW
4,3
5,0
5,1
Pulse voltage
kV
270
300
314
Pulse current
A
275
305
320
Pulse repetition Frequency
range
Hz
1-10
1-10
1-10
Pulse Length (top)
ìs
4,5
4
3,5
Flatness
%
±1
±1
±1
Repeatability
%
± 0,2
± 0,2
± 0,2
Power compression system
BINP made SLED type power
compression system
Main parameters of BINP made power
compression system.
Cavity diameter
196 мм
D
Cavity height
346.6 мм
H
Operating frequency
2856 МHz
f0
Range of mechanical tuning
f
f/H
Quality factor Q0
Unloaded time
0
Loaded time TC = 0/(1+)
Moment of phase switching
5 МHz
2.75 МHz/мм
95000
11 μs
1 μs
3 μs
RF pulse duration from the klystron
3.5 μs
Power multiplication coefficient К0
7.29
Measured input and reflected power from SLED system cavities
P(t)/Pgen
8
7
Reflected power Pref(t)
6
5
4
Input power Pinp(t)
3
2
1
0
0
1
2
3
t[mcs]
4
5
Bunching system
1 – two sub harmonic cavities, 2-bunching cavity with main
frequency, 3 – parallel coupled accelerating structure
Electric field distribution
along accelerating cavities
Prototype of parallel coupled accelerating structure
Scheme of parallel coupled accelerating
structure
The klystron feeds the cavity 1
based
on
rectangular
waveguide and it excites the
accelerating cavities 2. The
connection between exciting
and accelerating cavities is
performed by magnetic field
with help of slots 3. The copper
reactive posts 4 are needed to
tune the frequency of the
exciting cavity. The magnetic
system based on the solenoids
or permanent magnets can be
placed in the port 5.
Prototype of parallel coupled
accelerating structure with electron
beam energy of 4 MeV and
frequency of 2450 MHz
Results of beam dynamics calculation in the bunchig system: L(z)
– beam length, Wav(z) – average beam energy
Initial and final beam parameters in the bunching system
Initial beam parameters are
following:
•
•
•
•
•
energy is 200 keV,
particles number is 2×1010,
current length is 2 ns,
beam radius is 5 mm,
uniform
longitudinal
and
transverse beam distribution
Beam parameters in the end
of bunching system are
following:
•beam capture is 100%
•average beam energy is 6.1
MeV
•normalized transverse and
longitudinal beam emittances
are 55 mm∙mrad
•r.m.s. energy spread is 0.25
MeV
•beam radius less then 5 mm
•equivalent beam with normal
distribution will have σz=1.7
mm
Longitudinal distribution for 100% of particles in the end of bunching system: 1 – result of
beam dynamics calculation, 2 – equivalent normal distribution with σz=1.7 mm
Beam dynamics in the main linac
Longitudinal distribution for 100%
of particles in the end of
accelerator with bunching and
preaccelerating: 1 – result of
beam dynamics calculation, 2 –
equivalent normal distribution with
σz=1.7 mm
Longitudinal distribution for 100% of
particles in the end of the second
accelerating structure with bunching and
without preaccelerating : 1 – result of beam
dynamics calculation, 2 – equivalent
normal distribution with σz=1.0 mm.
Beam dynamics in the main linac
N(W)/N0, [%]
N(W)/N0, [%]
10
5,0
9
4,5
8
4,0
7
3,5
-12 -11 -10
-9
-8
-7
-6
-5
-4
-3
-2
3,0
6
2,5
5
2,0
4
1,5
3
1,0
2
0,5
1
0,0
-1
0
0
1
W/W av, [%]
Beam energy spread in the end
of accelerator with bunching and
preaccelerating
2
-50
-40
-30
-20
W/W av, [%]
-10
0
Beam energy spread in the end of
the second accelerating structure
with
bunching
and
without
preaccelerating. In compare with
preaccelerating system average
energy less in 1.5 times.
10
Compare energy spread
N(W)/N0, [%]
100
1
2
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
W/W av, [%]
1- in the end of linac with bunching and preaccelerating system; 2 – in the end
of the second accelerating structure with bunching and without preaccelerating
system
Beam dynamics with bunching and preaccelerating system
Beam dynamics with bunching and without preaccelerating
system
Beam dynamics in the debuncher monochromator
N(W)/N0, [%]
2,5
Longitudinal distribution for
97% of particles after
debuncher-monochromator
system
2,0
Beam energy spread
after
debunchermonochromator
system
1,5
1,0
0,5
0,0
-2,0 -1,8 -1,6 -1,4 -1,2 -1,0 -0,8 -0,6 -0,4 -0,2 0,0
0,2
0,4
W/W av, [%]
100
N(W)/N0, [%]
90
80
Integral of particles
number depending
on beam energy
spread in the end of
debunchermonochromatir
system
70
60
50
40
30
20
10
0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
2,2
2,4
W/W av, [%]
Conclusion
•
•
•
•
•
•
•
•
•
•
bunching system with parallel coupled accelerating structure
regular accelerating structure of main linac is disk-loaded waveguide with traveling wave
power compression system SLED-type feeds two accelerating structures
beam number in the end of main linac is about 2×1010
accelerating gradient 20 MeV/m
total average energy is 200-500 MeV
number of accelerating structures is 9, SLED system is 5
drift space with quadrupole lenses and diagnostic system between structures is 1 м
total length of main linac is 35 m
transverse beam emitances in the end of the linac are εx,y=0.3 mm∙mrad and εx,y=0.055
mm∙mrad for energy 200 and 500 MeV correspondingly
• beam energy spread is ΔW/Wav ≈ 10% for 100% particles, ΔW/Wav ≈ 1% for 60%
particles
• schemes of linac feeding are following: for energy of 500 MeV every accelerating
structures have input power of 80 MW, for energy of 200 MeV the last two klystrons
have half of the maximum power and phase shifting of 1800
One of the key element of the accelerator is bunching system. If the bunched beam is not
relativistic the first and the second regular accelerating structure must have individual
operating regime: phases of accelerating fields, focusing system based on long solenoid
and etc. To decrease the energy spread in beam it is need to sacrifice average beam
energy accelerating it in not maximum of electric field. In this case the capture of particles
can be differing from 100%. All of talk above complicates the accelerator construction and
the next tuning.