Progress of RF system development for LHFW Heating and Current Drive on VEST 2016 Korea-Japan Workshop 16 th . Dec. 2016 S. H. Kim a , B. K. Jung a , S. H. Jeong a , H. W. Lee b , B. J. Lee b , J. G. Jo c , H. Y. Lee c , and Y. S. Hwang c a Korea Atomic Energy Research Institute b Kwangwoon University c Seoul National University
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Progress of RF system development for LHFW Heating and Current Drive on VEST
2016 Korea-Japan Workshop
16th. Dec. 2016
S. H. Kima, B. K. Junga, S. H. Jeonga, H. W. Leeb, B. J. Leeb, J. G. Joc, H. Y. Leec, and Y. S. Hwangc
aKorea Atomic Energy Research InstitutebKwangwoon University
cSeoul National University
2
Contents
Introduction to LHFW (Lower Hybrid Fast Wave)
- LHFW on CMA / Dispersion relation / Propagation Boundary
- Advantages & Disadvantages
Status of RF system development for LHFW experiment on VEST
- Klystron
- RF components
- Antenna
- Safety & Diagnostics
Summary
3
Introduction to LHFW(0)
The continuous current drive is one of the key issues toward steady-state
operation of tokamak fusion reactors.
Though the current drive by using bootstrap is the main strategy in tokamak,
the external current drive is still required to control pressure profile and fill the
gap between the bootstrap and target current.
Most efficient current drive ever is the LHCD which is a scheme by using slow
wave in lower hybrid resonance frequency range.
There, however, is density limit and it is hard to propagate into the central
region in high temperature plasmas due to highly damping.
Therefore, alternatives are required.
LHFW could be an alternative.
4
Introduction to LHFW(1)Lower Hybrid Fast Wave(LHFW) on CMA diagram
<H2 plasmas>
LHFW is a fast wave
between lower hybrid
resonance frequency
and electron cyclotron
resonance frequency.
2 lh ceω ω ω< <<
5
Dispersion Relation1/ 22
||
1/ 22 2|| ||
2||
( )
( )( )( )
⊥
− − ≅ − −− −
r
P N SSlow Wave
SN
N R N LFast Wave
N S
Introduction to LHFW(2)Dispersion & Propagation Boundary
Propagation Boundary
The perpendicular wave number of LHFW is less than
that of slow wave in this frequency range(LHSW).
1/ 2 3 2,
1/ 2 3 2
, 2 2||
2
exp( )
exp( )
1
r SW
i r FWce
pe
N LHSW
N N LHFWN
π η η
π η ηωω
⊥
⊥ ⊥
− −≅ −
The imaginary wave number of LHFW becomes
higher as the density increases.
6
Advantage of LHFW(1)Parallel electric field Ez to B
<Polarization of FW and SW on CMA>
It has favorable polarization for current drive compared to FWs in other frequency range.
|| ||
22
0 ||2||0|| /
12
ps sLD z
v k
FP v v dv Evk
ω
ω ωε ω πω
∞
⊥ ⊥
=
∂≅ − ∂
∫
7
It has deep penetration property in high density.
<Angle of Group Velocity Vg to magnetic field of LHFW and LHSW>
Advantage of LHFW(2)More perpendicular Vg to B
B
Vg
8
Launching condition
Accessibility condition.
( )
202
20||2 1
e
launche
ce
m LHSWen
m N LHFWe
ε ω
ε ωω
≅ −
2 20||2
14
econfluence ce
mn Neε ω≅
Disadvantage of LHFWCoupling Issue
< Propagation Boundary >
* High density is required to launch
LHFW compared to LHSW.
☞ Coupling Problem
* The same accessibility condition as LHSW
should be satisfied.
* The confluence density condition above is a more generalized accessibility condition.
2||~ ce Nω
ω
LHFW launching
LHSW launching
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RAY tracing simulation on VEST (GENRAY)
Comparison between LHFW and LHSW launching (0.2T/ 500 MHz / 3x1018 #/m3/ 3 keV/ N||=4)
LHFW can propagate into more central region. In addition, the current drive is comparable to
LHSW.
LHFWlaunching
LHSWlaunching
100 kA / 10kW125 kA / 10kW
Normalized radius
10
RF System for LHFW experiment on VEST
Schematic of LHFW RF System
- Frequency : UHF
- Power : 10 kW(Klystron)
- Antenna : Comb-line antenna
Klystron (UHF)
- Old klystron system for UHF broadcasting has been refurbished.
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Klystron (1)
VarianFrequency 470~700 MHzOutput 37.5 kWDrive Power 600 mWGain 48 dBBeam voltage 19.5 kVBeam current 5.4 AElectrode voltage 19.5 kVHeater voltage 7 VHeater current 17 ABody current 50 mAMagnet Voltage 145 VMagnet Current 32 AMagnet Cooling Water(2.0 gal/min)Cooling(Collector) Water 1.5 gal/minCooling(Body) Water 2.0 gal/min
Cooling(Gun/Heater) Forced Air 50 ft3/min
Harris transmitter frame(SNU)
Varian Tube (SNU/KAPRA)
NEC Beam P/S(KAPRA) Harris UHF transmitter Specification
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Klystron (2)
Front control panel
Controlpanel
High VTR
IVRTR
RectifierDiode
Rectifiercapacitor
RectifierInductor
ModulatingAnode
Surgeprotector
Front view of Inside
Refurbished klystron beam power supply : NEC (15kV-6A)
Rear view of Inside
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Klystron (3)
Test of beam power supply : NEC (15kV-6A)
DC beam P/S (15kV-6A)
Air cooled resistor assembly : 3.58 kOhm
Test of the vacuum degree
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Circuit for Vacuum test
- Normal conditionGas current(Digital volt meter) < 0.5uA(5V)