study of beam dynamics of electron beam in a...

Electron Beam

Energy (Peak current) 5 MeV (0.5 A)

Emittance < 5 mm mrad

Energy spread ~ 0.4%

Undulator (Helical)

Type hybrid EM

Period (Number of periods) 25 mm (28)

Peak magnetic induction (K-value) 4 – 7 kG (1 – 1.8)

Waveguide mode (Radius) TE11 (2 mm)

High power table-top THz FEL

Microtron is the device that accelerates the electrons with circular orbit. Electrons in a microtron are accelerated by an alternating electric and a uniform magnetic field in a RF resonator. The electrons

must have exactly same phase of acceleration electric field which is supplied from a magnetron to gain the certain energy at each passage through the RF resonator. Korea Atomic Energy Research Institute

has operated microtron with thermionic cathode for the THz Free Electron Laser (FEL) generation and has a future plan of photocathode microtron for compact FEL. We will present the studying on the

dynamics of electrons in a microtron with thermionic cathode and measure the current and the energy of each orbit in using PIC code.

Basic concept of Microtron

Study of beam dynamics of electron beam in a microtron for KAERI THz FEL

Sunjeong Park1,2 , Eun-San Kim2, Nikolay Vinokurov1, Sergey Miginsky1, Young Uk Jeong1, Seong Hee Park1, Kyu Ha Jang1

1Center for Quantum Beam Based Radiation Research, Korea Atomic Energy Research Institute, Korea2Department of Physics, Kyungpook National University, Korea

Study of beam dynamics of electron beam in a microtron for KAERI THz FEL

Sunjeong Park1,2 , Eun-San Kim2, Nikolay Vinokurov1, Sergey Miginsky1, Young Uk Jeong1, Seong Hee Park1, Kyu Ha Jang1

1Center for Quantum Beam Based Radiation Research, Korea Atomic Energy Research Institute, Korea2Department of Physics, Kyungpook National University, Korea

THz beam

Wavelength (frequency) 200 – 500 m (0.5 – 1.5 THz)

Average power ~ 1 W

Micropulse

Pulse duration 20 – 30 ps

Power 20 – 30 kW

Repetition rate 2.8 GHz

MacropulsePulse duration 4 s

Repetition rate 200 Hz

Main parameters

Abstract

THz FEL2.7 x 5.3 m2

Variable-period Helical undulator

Mirror control& Beam Dump

Microtron (dia. 65 cm)

45 Dipole

THz FEL

45 Dipole

1.7 x 2.7 m2

MagnetronFaradayRotator

Compact size

The existing system

Simulation Result of Microtron

E

RF

net

RF cavity

magneticshield

ronce

B

evBr

vm

20

Bec

E

eB

mT e

20 222

nn eB

mT 02

gnn eB

mTTT

0

1

2

Synchronicity condition (energy gain per turn)

RFg f

l

eB

mT 02

(l, l': integer, l < l' )

RFf

l

eB

mT

1

01

2

Orbit period

Circular motion

Energy at nth orbit

Period at nth orbit and time duration between orbits

0m

eB

r

v

ecB

E

eB

cmr e

0

; First turn

gn n 11

At RF cavity

s

Emax

Ef < 0EEmaxcoss

i < 0 Emaxcoss)/

f = i for

Ef = - iEmaxsin(s) + Ei

At microtron magnet

B

reference particle

Ei > 0f < 0

Ef = Ei

EE

l

sif

cos

2

max

fer matrix at microtron

Phase stability

1sin

01

10cos

21

maxmax

6665

5655

ssRFBMM

EE

lRR

RR

RRR

1tan

2tan21

1sin

cos

2tan21

max

max

s

s

s

s

sM

EE

ll

EE

ll

R

nMRR

Criteria for longitudinal stability : -2 < Tr(RM) < 2

For l = 1 : - 32.5 < s < 0

For l = 2 : - 17.7 < s < 0Choose the fundamental mode (l=1)because of lager range of stability.

k γinj γg V [keV] BΔ [T] E1 [MeV] d1 [mm] n En [MeV] dn [mm]

1.09 0.099 1.099 561.538 0.110 1.123 60.718 12 7.300 442.115

1.125 0.143 1.143 584.000 0.115 1.168 61.313 11 7.008 408.021

1.126 0.144 1.144 584.668 0.115 1.169 61.330 11 7.016 408.023

1.5 1.000 2.000 1022.0 0.200 2.044 66.020 6 7.154 238.038

At 2.8 GHz, l′ = 2 and l = 1, B = 0.09 ~ 0.12 T & phase stable region ~ 90 to 122.5

The relation of initial injection energy(k), acceleration energy and strength of the magnetic field to get about 7.01MeV

i

i

E

f

f

ERzz

1tan

01

sRF E

R

10

21

E

lRBM

Transfer matrix at microtron

Design of Microtron

microtron for high frequency Waveguide

Module

Maximum RF Power 50 MW

Wave-guide sizes 72 mm34 mm430 mm

Material of the RF flanges Stainless steel covered by copper with high vacuum, high temp. diffusion process

Operating vacuum pressure 10-9 Torr

Cathode filament bias voltage up to 2.0 kV

Cathode filament feeding current up to 40 A

Water-cooling pipes internal dia. 4 mm

Water-cooling connector size M10

Trial produced microtron RF cavity Produced microtron

RF port 전자석용전선

650 mm

external inside

coil

Shim

RF port Wire for electromagnet

Water cooling

port

650 mm

Magnet & EM wave input

B field direction

Dynamics of Electron beam

Emission current Driver voltage Electron acceleration voltage(center of resonator)

Loss of the resonator

Properties of RF

properties of Electron beam after 11th orbit

Average current of electron beam Average voltage of electron beam Average power of electron beam

ConclusionRecently, high power femtosecond THz FEL is under development for pump-probe applications at KAERI, using photocathode. In thermionic emission, the several bunches of electrons with different radius are

accelerated at the same time, while only one bunch with high peak current is accelerated in photocathode emission. Unlike to thermionic cathode, high peak current may degrade the beam quality due to RF instabilit

To upgrade thermionic cathode to photocathode, We has simulated the microtron with photocathode code.

World Class Institute

Center for Quantum‐Beam‐based Radiation Research