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1
Development of Frequency-Tunable
Terahertz Radiation Sources
Tsun-Hsu Chang 張存續
Department of Physics, National Tsing Hua University,
Taiwan
2008 FISFES WorkshopNovember 6 – 8, NCKU, Tainan, Taiwan
2
Introduction:
3
Objective: Filling the Terahertz Gap
R. Kleiner, “Filling the terahertz gap”, Science 318, 1254 (2007).
Science, 23 November 2007
4
Terahertz Research
THz photonics THz spectroscopy THz plasmonics Plasma diagnostics
Fusion ESR DNP NMR Material processing
Number of publications in Physical Review Letters.
2 0 0 0 2 0 0 1 2 0 0 2 2 0 0 3 2 0 0 4 2 0 0 5 2 0 0 6 2 0 0 7 2 0 0 8
Y e ar
0
2 0
4 0
6 0
8 0
Num
ber
of p
ubli
catio
n fo recas t
Search title/abstract using the key word--- “terahertz”.
5
Applications: high power
ESR
DNPNMR
6
How to Generate Terahertz Radiations
Photonics: (low power, non-coherent)
Josephson effect
Quantum cascade laser
Far infrared laser
Femtosecond laser
Electronics: (high power, coherent)
Free electron laser
Electron cyclotron maser - gyrotron
Backward-Wave Oscillator
Generate THz radiations:
7
Terahertz vacuum electron devices
Terahertz FEL
Generate THz radiations: high power
FEL
gyrotron
BWO
8
高頻電磁實驗室High Frequency Electrodynamics Laboratory
指導教授 : 朱國瑞老師 , 張存續老師
博士後 : 邱陳琦 , 姜惟元
博士班 : 高士翔 , 戴玲潔 , 吳家勳 , 吳光磊 , 陳乃慶 , 袁景濱
碩士班 : 林冠男 , 林柏年 , 康迺豪 , 劉煜 , 林柏宏 ,
姚仁傑 , 吳智遠 , 徐複樺 , 吳俊潭 , 姚欣佑
學士班:姜博瀚 , 郭彥廷 , 任德育 , 李育浚
校外合作 : 工研院材化所 , 中科院 , 同步輻射 , 高速電腦
國際合作 :UC-Davis, USA, Fukui Univ., Japan
Terahertz gyrotron term
9
Toward Bridging the Terahertz Gap
one photon multiple-photon multiple photon per excitation, per electron, per electron,
large interaction large interaction interaction space space space ~ wavelength
Frontier in science and technology.
Terahertz gap
10
ECM based Devices --- gyrotrons
gyro-monotronhigh average power
gyro-BWO continuous frequency tunability
(relatively unexploited)
The gyrotron is a coherent radiation source based on the electron cyclotron maser (ECM) interaction
11
Difficulties for Terahertz gyro-BWO
12
Difficulties: Underlying Physics
• 2000 Nonlinear field contraction
• 2001 Nonstationary and chaotic behavior
• 2002 Linear and time-dependent behavior of gyro-BWO
• 2005 Dynamics of mode competition
All published in PRL.
13
The high efficiency gyro-BWO
1 3 .5 1 4 1 4 .5 1 5 1 5 .5 1 6B o (k G )
3 2 .5
3 3
3 3 .5
3 4
3 4 .5
3 5
Fre
quen
cy (
GH
z)
0
5
1 0
1 5
2 0
2 5
3 0
Eff
icie
ncy
(%)
0
2 5
5 0
7 5
1 0 0
1 2 5
1 5 0
Pow
er (
kW)
ex p erim en t
sim u la tio n
ex p erim en t
sim u la tio n
5 0 6 0 7 0 8 0 9 0 1 0 0 11 0V b (k V )
3 2 .5
3 3
3 3 .5
3 4
3 4 .5
3 5
Fre
quen
cy (
GH
z)
0
5
1 0
1 5
2 0
2 5
3 0
Eff
icie
ncy
(%)
ex p erim en t
sim u la tio n
ex p erim en t
sim u la tio n
T. H. Chang, C. T. Fan, K. F. Pao, K. R. Chu, and S. H. Chen, “Stability and tunability of Gyrotron Backward-Wave Oscillator”, Appl. Phys. Lett. 90, 191501 (2007).
14
Outer electrodeElectron emitter
AnodeVacuum container
Center electrode(Cathode nose)
14
W-band TE01 gyro-BWO
40 50 60 70 80 90 100 11 0 120V 0 (k V )
0
30
60
90
120
Pou
t (kW
)
95
96
97
98
99
Fre
q. (
GH
z)
39 40 41 42 43 44B 0 (k G )
0
30
60
90
120
Pou
t (kW
)
95
96
97
98
Fre
q. (
GH
z)
Vb=100 kV , B0=40.4 kG , =1.0, rc /rw =0.466-0.4763, rw =0.189-0.193 cm TE01 S1
Ib= 5 A
4 A3 A
Ib= 5 A4 A3 A
(a )
(b )
@ 3-5 A, 100 kV
@ 3-5 A, 40.4 kG
Difficulty #1: 110 GHz PNA
Difficult #3: Electron gun
Difficulty #4: Magnet
Difficulty #2: THz mode converter
40 50 60 70 80 90 100 11 0 120V 0 (k V )
0
30
60
90
120
Pou
t (kW
)
95
96
97
98
99
Fre
q. (
GH
z)
39 40 41 42 43 44B 0 (k G )
0
30
60
90
120
Pou
t (kW
)
95
96
97
98
Fre
q. (
GH
z)
Vb=100 kV , B0=40.4 kG , =1.0, rc /rw =0.466-0.4763, rw =0.189-0.193 cm TE01 S1
Ib= 5 A
4 A3 A
Ib= 5 A4 A3 A
(a )
(b )
T. H. Chang, et al., “W-band TE01 gyrotron backward-wave oscillator with distributed loss”, Phys. Plasmas 15, 073105 (2008).
1515
First difficulty: Basic diagnostic system
2006: vector network analyzer E8363B 2,800,000 NTD.
2007: test set controller N5260A 2,400,000 NTD.
2008: Millimeter wave head module N5260AW10 2,600,000 NTD.
Solved
16
Second difficulty: TE01 mode converter
85 90 95 100 105 110Frequency (G H z)
-6
-5
-4
-3
-2
-1
0
Tra
nsm
issi
on
(dB
)Exp.
Th.
22 GHz
Solved
17
Second difficulty a main vantage
T. H. Chang, C. H. Li, C. N. Wu, and C. F. Yu, “Exciting circular TEmn modes at low terahertz region”, Appl. Phys. Lett. 93, 111503 (2008).
18
Terahertz Devices Using LIGA
Require high precision machining (<2 um) LIGA technique
1. irradiation (mask)
2. development (SU-8)
3. electroforming
200 GHz TE02 mode converter (for Fukui University, Japan) 400 GHz TE41 mode converter (Fourth harmonic gyrotron)
4. cold test
1919
Scaled experiment: Ka-band TE01 gyro-BWO
1 3 1 4 1 5 1 6 1 7 1 8 1 9
B z (k G )
0
10
20
30
5
15
25
effi
cien
cy (
%)
3 0
3 2
3 4
3 6
3 8
freq
(G
Hz)
dotted line - experim ent broken line - sim ulation
1 3 1 4 1 5 1 6 1 7 1 8 1 9
B 0 (k G )
0.6
0.8
1
1.2
1.4
0
0.04
0.08
0.12
0.160.2
vz/v
z0
0 2 4 6 8 10 12 14 16Z (c m )
0.50.520.540.560.58
0.6
r w (
cm)
A quadaqC oating
(a ) 4-P in Interface
6-P inInterface
(c)
(b )
v z/v z 0
Distributed loss suppresses the axial-mode competition. Mode-selective circuit suppresses the transverse-mode competition.
Tuning range: 15.8%Peak efficiency: 23.7%
20
Problem for gyro-BWO
Old design(for gyro-TWT)
Third difficulty: Electron gun
1 3 1 3 . 5 1 4 1 4 . 5 1 5 1 5 . 5 1 6 (k G )
6 0
7 0
8 0
9 0
1 0 0
1 1 0
(
kV)
bV
B0
Magnetron Injection Gun (MIG) for W-band gyro-BWO. CUSP gun for high harmonic gyro-BWO.
0 10 20 30 40 50
Z (cm )
0
2
4
6
8
10
12
r (c
m)
0
10000
20000
30000
40000
Bz
(G)
StructureM agnetic fie ldEqual-potentia l lineElectron tra jectory
5 A m p s 7 0 k V
v z/v z = 2 .3 %v /v = 5 .4 %r g = 0 .9 5 9 m mr L = 0 .1 9 9 m m
3 8 k G
New design(for gyro-BWO)
W-band MIG gun is ready for fabrication.
CUSP gun simulation
21
Fourth difficulty: Magnet
Superconducting magnet (8 Tesla, 6,000,000 NTD)
Pulsed magnet (40 Tesla, 3,000,000 NTD)
Our old magnet is agingand has hysteresis effect.2 Tesla is barely okay.
Magnet is the biggest problem to us. Sufficient research funding can solve the problem.
2222
Reducing the Magnetic Field Requirement Second harmonic slotted gyro-BWO:
6 6.4 6.8 7.2 7.6 8
B z (k G )
0
4
8
12
16
20
24
effi
cien
cy (
%)
3 1
3 2
3 3
3 4
3 5
3 6
freq
(G
Hz)
I b= 5 (A )I b= 4 (A )I b= 3 (A )
p z/p z 0= 0.0 5
- 8 - 4 0 4 8
k z ( c m -1)
0
20
40
60
80
f (G
Hz)
b o rken l in e : sm o o th -b ore w aveg u ideso l id l in e : s lo t ted -b o re w a vegu id e (b /a = 1 .5 )
B z= 6 .8 k G
m o d e (T E 2 1)
/2 m o d e (T E 1 1)
2 m o d e (T E 0 1)
/2 m o d e ()
s= 1
s= 2
s= 3
a
b
N. C. Chen, C. F. Yu, and T. H. Chang, “A TE21 second-harmonic gyrotron backward-wave oscillator with slotted structure”, Phys. Plasmas, 14, 123105 (2007).
23
Gyrotrons at Fukui FIR Center
0.4 THz, 1.5 kW1 THz 0.25 kW
A series of LHe free superconducting magnets:
8T, 12 T, 17 T, and 21 T.
2424
International Cooperation: 394 GHz Frequency tunable gyrotron
7 .15 7 .20 7 .25 7 .30 7 .35 7 .40 7 .45B o (T )
1 0 -2
1 0 -1
1 0 0
1 0 1
I st (A
)Vb=13.7 kV , =1.6, rc /rw =0.16 rw =0.2372 cm
TE06 S2 starting currentw ith s lightly W G taper 02 lossless
2 .5 o
3 .0 om ild ly tap e red
0 .3 5 A
l =1 2 3
4 5
u n ifo rm
0 .4 cm 2 .0 cm 0 .5 cm
0 .4 cmr w = 0 .2 3 7 2 cm
(a )
(b )
7 .20 7 .25 7 .30 7 .35 7 .40 7 .45B o (T )
0
5 0
1 0 0
1 5 0
2 0 0
Pou
t (W
)
394
395
396
397
398
399
Fre
q (G
Hz)
l =1
l = 2
l = 3
l = 4
l = 5
pumping port
pumping port
collector
water jacket
super conductingmagnet
interaction section
output window
MIG gun
gun coils
2525
International Cooperation: 203 GHz TE02 gyro-BWO
Novel TE02 mode converter using LIGA technique.
Novel mode-selective circuit
7 2 7 6 8 0 8 4 8 8 9 2
B 0 (k G )
0
10
20
30
effi
cien
cy (
%)
190
200
210
220
230
freq
(G
Hz)
v z/v z 0= 5 %Ib= 0 .7 A
Ib= 0 .5 A
Ib= 0 .4 A
203 G H z
26
Conclusion and Foresight
Terahertz gap
NTHU Terahertz Research Center