RF scheme of electron linear RF scheme of electron linear accelerator with energy 200-500 MeVaccelerator with energy 200-500 MeV

Levichev A.EBudker Institute of Nuclear Physics SB RAS

IntroductionIntroduction

Debuncher-monohramatorDebuncher-monohramator

Accelerating structureAccelerating structure

Accelerating structure.1 – Regular cell, 2 – Wave type transformer, 3 – Connection cell, 4 – Connection

diaphragm, 5 – Structure frame with cooling system.

Accelerating structureAccelerating structure

BINP produced accelerating structure.

Accelerating cells and wave type transformers.

Operating frequency f 2855.5 МHz

Operating mode

Unloaded quality factor Q0 1.32104

Group velocity Vgr 0.021C

Shunt impedance Rsh 51 МОhм/м

Unloaded time 0 = 2Q0/ 1.47 μs

Attenuation parameter = 1/(0Vgr) 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

Basic parameters of BINP made accelerating structuresBasic parameters of BINP made accelerating structures

RF power sourceRF power source

Picture of TH 2100 klystrons series.

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

Basic parameters of TH 2128 C/D klystron.

ModulatorModulator

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

Parameters of К2 modulator series (ScandiNova Systems)

Modulator К2-3

Power compression systemPower compression system

Cavity diameter D 196 мм

Cavity height H 346.6 мм

Operating frequency f0 2856 МHz

Range of mechanical tuning f 5 МHz

f/H 2.75 МHz/мм

Quality factor Q0 95000

Unloaded time 0 11 μs

Loaded time TC = 0/(1+) 1 μs

Moment of phase switching 3 μs

RF pulse duration from the klystron 3.5 μs

Power multiplication coefficient К0 7.29

Main parameters of BINP made power compression system.

BINP made SLED type power compression system

0 1 2 3 4 50

1

2

3

4

5

6

7

8

Reflected power Pref

(t)

Input power Pinp

(t)

P(t)/Pgen

t[mcs]

Measured input and reflected power from SLED system cavitiesMeasured input and reflected power from SLED system cavities

1 – two sub harmonic cavities, 2-bunching cavity with main frequency, 3 – parallel coupled accelerating structure

Bunching systemBunching system

Electric field distribution along accelerating cavities

Prototype of parallel coupled accelerating structure with electron

beam energy of 4 MeV and frequency of 2450 MHz

Prototype of parallel coupled accelerating structurePrototype 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.

Scheme of parallel coupled accelerating structure

Results of beam dynamics calculation in the bunchig system: L(z) Results of beam dynamics calculation in the bunchig system: L(z) – beam length, Wav(z) – average beam energy– beam length, Wav(z) – average beam energy

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

Initial and final beam parameters in the bunching systemInitial and final beam parameters in the bunching system

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

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 linacBeam dynamics in the main linac

-12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 20,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

N(W)/N0, [%]

W/Wav

, [%]

Beam energy spread in the end of accelerator with bunching and preaccelerating

-50 -40 -30 -20 -10 0 100

1

2

3

4

5

6

7

8

9

10

N(W)/N0, [%]

W/Wav

, [%]

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.

Beam dynamics in the main linacBeam dynamics in the main linac

0 10 20 30 40 500

10

20

30

40

50

60

70

80

90

100N(W)/N

0, [%]

W/Wav

, [%]

1 2

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

Compare energy spreadCompare energy spread

Beam dynamics with bunching and preaccelerating systemBeam dynamics with bunching and preaccelerating system

Beam dynamics with bunching and without preaccelerating Beam dynamics with bunching and without preaccelerating systemsystem

Beam dynamics in the debuncher monochromatorBeam dynamics in the debuncher monochromator

Longitudinal distribution for 97% of particles after debuncher-monochromator system

-2,0 -1,8 -1,6 -1,4 -1,2 -1,0 -0,8 -0,6 -0,4 -0,2 0,0 0,2 0,40,0

0,5

1,0

1,5

2,0

2,5

N(W)/N0, [%]

W/Wav

, [%]

Beam energy spread after debuncher-monochromator system

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,40

10

20

30

40

50

60

70

80

90

100

W/Wav

, [%]

N(W)/N0, [%]

Integral of particles number depending on beam energy spread in the end of debuncher-monochromatir system

ConclusionConclusion

• 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.