Investigation of the Synergy of IBW and
LHCD for Integrated High Performance
Operation in the HT-7 Tokamak
Baonian Wan 1), Yuejiang Shi 1), Yanping Zhao 1), Jiafang
Shan 1), Junyu Zhao 1), Yubao Zhu 1), Yinxian Jie 1),
Guosheng Xu 1), Mei Song 1), Jiangang Li 1), Fukun Liu 1),
Bojiang Ding 1), Guangli Kuang 1), Haiqing Liu 1)
1) Institute of Plasma Physics, Chinese Academy of
Sciences, Hefei, China
• Control of the current density profile has been realized with off-axis
current drive by the LHW and its synergetic effect with the IBW in the
HT-7 tokamak. The IBW is explored as a means of improving current
drive efficiency, creating a well-localized fast electron current channel
and extending the high performance volume in LHCD plasmas. High
performance via formation of an ITB-like profile in electron
temperature, which was strongly correlated with the location of the
LHW driven fast electron current, was achieved in the IBW and LHCD
synergetic discharges through moving the IBW resonant layer to
maximize the plasma performance and to avoid MHD activity. A
variety of high performance discharges, indicated by N*H89 = 1–4,
was produced for several tens of energy confinement times. This
operation mode utilizing the synergetic effect of IBW and LHCD
provides a new way to obtain steady-state operation in an advanced
• Steady-state operation of a tokamak plasma is one of the basic requirements
for fusion reactors.
• High performance, as in an advanced tokamak operation scenario, is needed
for the economic use of fusion reactors.
• Control of the current density and electron pressure profiles becomes a crucial
issue in advanced tokamak operation.
• Off-axis LHCD is a powerful tool not only for current sustaining but also for
current density control to achieve an advanced tokamak scenario.
• This means potentials but also difficulties to localize LHW driven current
density actively, if plasma performance and parameters are changed.
• Additional heating and more reliable profile control are needed to improve the
current drive efficiency and to increase the plasma for obtaining high
performance discharges under steady-state condition.
• IBW has good features for heating electrons both locally and globally via
electron Landau damping (ELD), and for controlling the electron pressure
• The parallel wave number n|| of IBW is an oscillating function along the wave
trajectory. This effect on n|| cannot drive net plasma current via ELD.
• But it can enhance the wave damping on electrons, producing a localized
absorption of the coupled RF power around the maximum of n||.
• IBWs can be used in conjunction with LHWs to aid the localization of the
non-inductive current generated in the regime of LHCD.
• A broadening of the electron distribution shape can be produced due to
acceleration by IBW RF field, which results in a localized increase of the
LHCD efficiency and generation of spatially localized current channels.
• Features of off-axis IBW heating can be integrated into LHCD plasma to
extend high performance volume, which is needed for an advanced tokamak
RF Power: 50~350kW
RF Pulse length: 0.5~2s
n||: Peaked at 8 for 27 MHz
Faraday shielding: graphite
• Frequency: 2.45GHz
• Launcher: 316 grill
• Pulse length: CW
• Power: up to 1.2 MW
• N||peak: 1.25~3.45
DF =30 , N// =2.5 0 p
DF=120 , N// =3.1
DF =60 , N// =2.7 50 0 p
DF=150 , N// =3.25
DF =90 , N// =2.9
Power density (a.u.)
50 0 p
DF=180 , N// =3.45
DF =0 , N// =2.35 Power density (a.u) 40 0
DF=270 , N// =1.8
-10 -8 -6 -4 -2 0 2 4 6 8 10 0
-10 -8 -6 -4 -2 0 2 4 6 8 10
• More than 30
most plasma profiles
in one shot or spatial
scanning shot by
shot. Te was
measured by a SX-
PHA shot by shot in
• A CdTe detector
based HX array is
used as main tool in
• Ip was feedback controlled by the poloidal
• Ne was feedback controlled by a pulsed gas
• HT-7 main parameters:
R=1.22m, a=0.27m, Ip = 100 ~ 250 kA,
Bt=1.6 ~ 2 T, n e (0) = 1~ 6.51019/m3,
Te(0) =0.5 ~ 1.5 keV (OH)
In present experiment: N||peak = 2.3 (LHCD),
LHCD+IBW (30 MHZ)
• Ip ~ 150 kA, Bt=2 T, n e (0) ~ 1.51019/m3,
Te(0) ~ 1keV, N||peak = 2.3
Fast electron current density was broadened
• Peak of HXR was shifted outward.
• Simulation can account partially for LHW
• An increase of global HXR imply more
driven fast electrons by LHCD.
• LHW damping enhanced at first IBW n||
maximum is a possible mechanism.
• Increase of HXR was mostly in 0.4~0.8a.
• The first IBW n|| maximum is at ~0.55a
• A broadening of the electron
distribution shape can be
produced by IBW injection,
which results in a localized
increase of the LHCD
efficiency and generation of
spatially localized current
• Asymmetric velocity
distribution produced by
LHCD for IBW to damp
preferentially in one direction.
• Direct IBW driven is small.
similar behavior as in off-axis IBW heating
H ~ 13.5cm
Behavior in a reference off-axis IBW (27MHz)
• Bt=2.03T, H ~ 15.5cm
• Ne increased and broadened
• Te increased and broadened
• Te (13.8) > Te(2) in IBW
• Largest pressure gradient at close to
• High performance volume extended
Strong correlation between Pe(r) and
radial profile of HXR
• Large gradient in Te(r) and Pe(r)
around the IBW resonant layer.
• Peak of HXR located at the
• High performance volume
Shot 46130 Bt=1.9T
Shot 46110 Bt=1.8T
• FP code predict LHW power deposition is more
centered in shot 46130 (Bt=1.9T) than in shot 46130
(Bt=1.9T) . Prediction is not in agreement with
observation from HXR profile.
• The first IBW n|| maximum for 46130 (Bt=1.9T) is at r
~ 0.52a and for 46110 (Bt=1.8T) is at r ~ 0.44a .
• Approximate agreement between observation and
positions of the IBW n|| maxima verifies localized
synergy effect again between LHCD and IBW
• LHCD was used to sustain plasma current and
control current density profile.
• Features of IBW heating was integrated into
• IBW and LHCD synergetic discharges was
optimized through moving the IBW resonant layer
by changing Bt and selecting plasma parameters.
• Strategy was chosen to maximize the plasma
performance and to avoid the MHD activities.
• IBW of 27MHz was selected for extension of high
performance plasma volume.
Integration of performance (high Te)
Ip=215kA, ne0=2.6x1019m-3, BT=2.0T, PLHCD=250kW,
PIBW=130kW, Te =2.9keV, Ti=1.6keV, H89=1.6, tH/tE=53
Integration of high performance
Bt~1.8T, H89*N >3 (4) and H93>1 (1.5) for ~50tE
Integration of high performance
Ip=135kA, ne0=2.2x1019m-3, BT=1.8T, PLHCD=190kW,
PIBW=80kW, Te =1.5keV, Ti=1.1keV, tH/tE=134
• Synergetic interaction between LHW and IBW can
produce a well-localized non-inductive current channel.
Strong synergy effect on driven current profile and
increased driven efficiency was observed.
• The properties of IBWs in controlling Te and Ne profiles
can be integrated into the LHCD plasmas to change local
electron pressure profile and to improve the plasma
• A variety of high performance discharges indicated by
betaN*H89 =1~3 was produced for several tens energy
• The operation mode utilizing synergy effect of IBW and
LHCD provide a new way to obtain steady-state operation
in advanced tokamak scenario.
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