高参数下 LHCD 与 IBW 协同改善约束的实验研究

丁伯江 赵燕平 单家方 匡光力

HT-7

Proposal for HT-7 2004 spring experiment

Outline

Motivation

Possibility

Synergetic mechanism of LHCD and IBW

Obtained results on HT-7 tokamak

Experiment arrangement

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MotivationTo extend HT-7 high performance with

LHCD&IBW

利用 LHCD & IBW 协同优化等离子体密度、温度、电流密度等参数的分布，以形成 ITB( 增加等离子体体积） , 实现尽可能高的等离子体约束运行 ( 能量约束和粒子约束 ) 。为此，我们有目的地改变低杂波功率谱，使得低杂波的功率尽可能沉积在 IBW 的共振层附近，这样就可以在该区域驱动更大的等离子体电流，有可能形成中空的电流分布，即通常所说的反剪切位形，改善等离子体约束。

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Possibility

低杂波的驱动效率直接依赖与等离子体的温度， IBW 可以加热局部的等离子体温度（ 27MHz, 4200A 时， IBW 共振层对应在 13cm 左右），而低杂波的功率谱在一定范围内可以调节，完全有可能使低杂波的功率沉积在 IBW 共振层附近，从而有可能负剪切位形，改善等离子体约束。

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IBW 对低杂波功率沉积分布的影响

0 5 10 15 20 250.0

0.5

1.0

1.5

2.0

2.5

Ip=200kABt=2.0TNe(0)=2.25Te(0)=1.5keV

Po

we

r d

en

sit

y (

wc

m-3)

Minor radius (cm)

with IBW N=2.35 N=2.9 N=3.1 N=3.25 N=3.45

N=2.35 without IBW

 

HT-7tokamak 不同纵场(A) 、频率 (MHz) 时的2D 共振层位置 (cm)

It(A)

 fIBW

3600 3800 4000 4200

30 -18 -12.5 -6.7 -0.9

27 -6.7 -0.3 6.1 12.5

24 7.7 15 22.1 29.3

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Synergetic mechanism of LHCD and IBW

IBW can modify the distribution function of the electrons by extracting the thermal electrons from the bulk distribution and accelerate them to contribution to the LHCD

IBW can sustain driven current, dissipating its energy on the parallel velocity of the asymmetric electron tail

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Obtained results on HT-7 tokamak ---electron heating by IBW

 

 

Global electron heating (left, f=27MHz, Bt=1.85T, r~3.4cm) and local electron heating (right, f=27MHz, Bt=2.0T, r~15.8cm) by IBW

 

Revolution of oscillating IBW n// during the wave propagation along the trajectory

IBW off-axis heating can modify the electron pressure profile

B.N. Wan et al., Nucl. Fusion 43(2003)1279

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Obtained results on HT-7 tokamak---synergy of IBW and LHCD

 

 

f=27MHz, Bt=2.0T (Global IBW electron heating ), N//peak=2.35

B.N. Wan et al., Nucl. Fusion 43(2003)1279

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Experiment arrangement

实验方法：改变纵场、 IBW 频率，移动 IBW 共振层的位置；改变低杂波波谱，优化低杂波功率沉积分布。

实验条件及参数 :

Ip~200kA, Ne~1.5, Te(0)~1.5keV

PIBW~300-400kW, PLHW~300-400kW

fIBW=27MHz, 30MHz, 24MHz

It~3600,3800, 4000, 4200A

低杂波功率谱 (N//peak)=0 (2.35), 30(2.5),60(2.7),90 (2.9), 120 （ 3.1),150 (3.2

5) ,180 (3.45)

希望需要配合的诊断：Te(r,t), Ti(r,t), Ne(r,t), HX(r,t), SX(r,t), W(t), li(t), Ha, AXUV(r,t), LP

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等离子体形状对低杂波耦合的影响

Effect of plasma shape on wave-plasma coupling

丁伯江 揭银先 高翔 张晓东 单家方

Proposal for HT-7 2004 spring experiment

HT-7

OUTLINE

实验目的

实验背景

实验方法

预期结果

• To investigate the effect of mismatch of plasma shape and LHW antenna on lower hybrid wave coupling

• Try to solve this problem by gas puffing near the LHW antenna

• To analyze the plasma behavior under these two conditions

NOTE THAT this experiment is a pre-performance for EAST

MOTIVATION HT-7

可耦合条件•LH 波的可耦合条件：

在天线发射面处应满足： p≥0

for f0=2.45GHz

要求： ne≥7.44x1010cm-3

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实验背景

r (cm) 28.0 27.0 26.0 25.0 24.0 23.0 22.0

d (cm)

2.0 2.046 2.094 2.146 2.202 2.226 2.328

)exp(,,SOL

LCMSegrille

dnn

2/1)/( sCSOL cLD

实验背景 HT-7

理论研究表明天线端口附近的等离子体密度及其梯度是影响耦合效率的决定性因素。如果等离子体形状（最外层封闭磁面）与低杂波天线端口的形状基本吻合（即具有同样的曲率半径），则整个低杂波天线端口处于同一个磁面上，各处的密度相等，即反射系数基本差不多。在偏滤器位形等离子体（ EAST ）放电时，很难等离子体形状会经常发生变化，以致于等离子体形状很难与低杂波天线的曲率半径保持一致。等离子体形状的改变，导致等离子体的曲率半径亦发生变化，使得不同位置的磁力线长度不同，导致天线端口密度的不均匀性，使得各子波导的反射系数不一样。这种不平衡的反射使得低杂波在天线端口形成多次反射，影响波与等离子体的耦合。况且，距离太大，可能会导致天线端口的密度低于截止密度，增加低杂波的反射。

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实验背景 ---JET

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实验背景 ---JET

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实验背景 -Tore Supra

1.1x1013cm-3, 105KA, 135KW,// 扫描

等离子体位置扫描对耦合稍有影响（反射系数由 4%增加到 6.5% ） , 但全程仍处于良好耦合之下

实验背景 ---HT-7

解决途径 HT-7

为了解决由于曲率半径不匹配而引起的多次反射，在低杂波天线端口处充入可电离的气体，尽可能在天线端口

处得到尽可能均匀的等离子体密度，且使其满足 ne,grill, >

ne,cut-off, 以提高波与等离子体的耦合效率。

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实验方法 :

（ 1）通过移动极向活动石墨限制器来改变等离子体半径，然后改变等离子体水平位置保持等离子体和低杂波天线在赤道水平面上的距离 dcp 不变；

（ 2）观察改变等离子体半径时上、中、下三排的反射系数；

（ 3）通过喷气结构对天线周围喷射（ gas puffing ） CD4 气体，再重复（ 1）、（ 2）的实验 .

希望需要配合的诊断：Te(r,t), Ti(r,t), Ne(r,t), HX(r,t), SX(r,t), W(t), li(t), AXUV(r,t), Ha ,LP

HT-7 实验预期结果

通过对天线周围喷射 CD4 气体来改善天线附近的等离子体密度，从而改善等离子体形状与低杂波天线不匹配时波与等离子体耦合状况；

可能得到 LHCD 情形下改善等离子体约束的一种新的途径；

有望为解决将来偏滤器位形的 EAST 因改变等离子体形状而引起的波与等离子体耦合问题进行探索和积累经验。

LHCD 实现 H-mode 等离子体的实验研究

丁伯江 单家方 匡光力

ASIPPASIPP

HT-7

Proposal for HT-7 2004 spring experiment

OutlineOutline

Motivation Improved confinement by LHCDImproved confinement by LHCD a. Improved core plasma with an ITB b. Improved edge plasmaWhat is elicited from the resultsExperiments arrangement

ASIPPASIPP

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Motivation在 HT-7 上实现 LHCD作用下的 H-mode 等离子体，分析形

成 H-mode等离子体的功率阈值。

HT-7实验结果 (#46693)表明在 LHCD 的作用下，在等离子体芯部形

成了 ITB ，能量约束时间从 14.6ms （ OH phase ）增加到 24.5ms （ LHCD phase ），相应的能量约束改善因子由 0.78 增加到 1.42 。在同样参数的情况下， Langmuir探针的测量结果也表明边缘等离子体约束得到了一定程度的改善， LHCD 使得边缘的径向电场发生了变化。以上这些结果表明在 HT-7 上似乎有形成了 H-mode 、甚至 Double Transport Barrier 的迹象。但是，证据还不充分，尤其是缺乏边缘区域的等离子体参数。因此，进一步完善该部分工作是十分必要的。

ASIPPASIPP

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A typical waveform of LHCD experiments (#46693) ne=1.51019m-3 , Ip=220kA, BT=2.0T, , N//

peak=2.9 ,PLH =240kW.

ASIPPASIPP

050

100150200250

0.0

0.5

1.0

1.5

2.0

-0.50.00.51.01.52.02.53.0

-0.5

0.0

0.5

1.0

0.0 0.3 0.6 0.9 1.20

50100150200250300

0.0 0.3 0.6 0.9 1.2-0.50.00.51.01.52.0

Phase II(LHCD Phase)

Phase I(OH Phase)

Phase I(OH Phase)

Phase II(LHCD Phase)

I p(k

A)

ne(

101

9 m-3)

Vp(V

)

Inte

nsit

y o

f

so

ft x

-ray (

a.u

.)

LH

W p

ow

er

(kW

)

Time (s)

D(

a.u

.)

Time (s)

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An ITB seems visible in the region around r/a ~ 0.55An ITB seems visible in the region around r/a ~ 0.55

Electron temperature profiles Ion temperature profiles

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0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00.0

0.2

0.4

0.6

0.8

1.0

1.2 ITB

OH phase LHCD phase

Ion

tem

pera

ture

(keV

)r / a

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2 ITB

OH phase LHCD phase

Ele

ctro

n t

emp

erat

ure

(ke

V)

r / a

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Plasma density profile measured by the HCN laserThe electron density increases from 1.5 to 2.01019m-3 because of LHCD near the

region of r/a~0.5. Also, the density profile broadens and the gradient becomes steeper in the outer region.

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-1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.000.0

0.4

0.8

1.2

1.6

2.0

OH phase LHCD phase

Pla

sm

a d

en

sit

y (

10

19 m

-3)

r / a

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Energy confinement time and H factor are improved by LHCDEnergy confinement time and H factor are improved by LHCD ne=1.51019m-3 , Ip=220kA, BT=2.0T, N//

peak=2.9 ,PLH =240kW

phase I : E 14.6ms, EITER89P =18.7ms

phase II : E 24.5ms,EITER89P =17.2ms, E

ITER93ELM free=27ms The experimental energy confinement times during OH phase and during LHCD phase coincide

with those predicated by EITER89P and E

ITER93ELM free, respectively.

0.0 0.3 0.6 0.9 1.20

100

200

0

1

2

1

2

3

0100200300

I p(kA

)n

e(101

9 m-3)

Current

Electron density

Loop voltage

Vp(V

)

Shot 46693

Phase I Phase IILHW

Time (sec)

PL

H (k

W)

Phase I:

H = 0.78

Phase II:

H = 1.42

(H = E / EITER89P )

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0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.0

0.1

0.2

0.3

0.4

De

po

sit

ed

po

we

r d

en

sit

y (

Wc

m-3)

r / a

0.0 0.2 0.4 0.6 0.8 1.00

100

200

300

400

500

600

700

before LHCD (OH phase) after LHCD (LHCD phase)

Cur

rent

den

sity

(Acm

-2)

r / a

Power deposition and current density profile

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The magnetic shear modified by LHCD is thought to be an possible causality of confinement improvement

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0.0 0.2 0.4 0.6 0.8 1.00.0

0.5

1.0

1.5

2.0

2.5

3.0

q

r / a

after LHCD (LHCD phase) before LHCD (OH phase)

a low magnetic shear is possibly formed because of the hollow current profile inside the surface of q=2

(r/a~0.8). Experiments described in

early references show that a low magnetic shear inside the

q=2 surface is favorable condition to form an ITB

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Signals of Langmuir probes Signals of Langmuir probes (LCMS)(LCMS) before/after the onset of LHCDbefore/after the onset of LHCD

Shot 46283 r = 27 cm Ne = 1.5 PLHCD= 240 kW ASIPPASIPP

0 200 400 600 800 1000-120

-600

60120

-120-60

060

-120-60

060

120

0

60

120

floating potential measured by another poloidal probe

LHCD

Vf2 (

a.u

.)

Time (ms)

floating potential measured by one poloidal probe

Vf1 (

a.u

.)

positive biased potential

(d)

(c)

(b)

Vp (

a.u

.)

saturated ion current (a)#46283

I s (a

.u.)

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Edge fluctuations are suppressed by LHCD Edge fluctuations are suppressed by LHCD

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400 500 600 700

1x1032x1033x1034x103

5

10

151x1017

2x1017

3x1017

5.0x10-3

1.0x10-2

1.5x10-2

Er

ms

Time (ms)

Te

rms

I srm

sne

rms

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Edge fluctuations in the whole frequency Edge fluctuations in the whole frequency region are suppressed by LHCD region are suppressed by LHCD

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0 100 200 300 400 50005

10

-101

0.00.51.0

0123024

cos

n

Frequency (kHz)

OH(t=400ms) LHCD(t=600ms)

(e)

En

PE

(a.u

.)

(c)

(d)

(b)

Pn(

a.u.

)

(a)

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Particle and Heat Loss are greatly reduced after Particle and Heat Loss are greatly reduced after the onset of LHWthe onset of LHW

Er and Vph are modified by LHCDEr and Vph are modified by LHCD

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400 450 500 550 600 650 7000

1

2

3

a

Qe

( W

m-2 )

e (

102

0 m-2s-1

)

400 450 500 550 600 650 700

-2

-1

0

1

2

3

c

Vph

( k

m/s

)

400 450 500 550 600 650 700

0

1000

2000

3000

4000

5000

6000

7000

8000

b

conv. loss cond. loss total loss

#46283LCFSr = 27 cm

Times (ms)

400 450 500 550 600 650 700-12

-10

-8

-6

-4

-2

0

2

LHCD LHCD

d

Er

( kV

/m )

Times (ms)

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Possible candidate for the improved edge plasma

All of the above data indicate that turbulence and transport of edge plasma were suppressed, which suggests that edge plasma was i

mproved due to LHW. WHY?Since the change of the poloidal propagation of the turbulence is nearly simultaneous with the evolution of the radial electric field, it may be regarded that the change of poloidal phase velocity of the turbulence is mainly resulted from the effect of ErxB.The electric radial electric is changed by LHW because of the energetic electrons loss. Due to the change of radial electric field, it is possible to form a sheared flow in the edge region. Therefore, the transport of the edge plasma might be reduced and the plasma confinement might be improved because of the poloidal sheared flow resulted from the varied radial electric field.

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What is elicited from the results

已有的实验数据表明： 由于 LHCD 的作用，很有可能在等离子体边缘存在 pedestal 结构 , 即通常所说的 H-mode. 甚至，可能存在 Double-Transport Barrier （ ITB and ETB) 。但是，我们还缺乏足够的证据。

为此，我们打算测量 LHCD情形下的边界等离子体参数的分布，包括温度分布、密度分布、和径向电场的分布等。

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Experiment arrangement

参照以前的放电条件（ #46693, #46283 ），改变低杂波功率，观察边界等离子体参数分布的变化，以及等离子体芯部密度、温度分布的变化（ ITB强度的变化）；

改变低杂波功率谱，让低杂波主要沉积在边缘；同时改变功率，观察 ITB 位置和边界等离子体参数分布的变化

分析不同功率大小、不同功率谱时的 ITB的情形以及形成H-mode等离子体的功率阈值

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Experiment condition and expected results

实验条件：Ip~220kA, Bt=2.0T, Ne~1.5,Te(0)~1.5keV,

Plhw~150~400kW低杂波功率谱 (N//

peak)=60(2.7),90 (2.9), 120 （ 3.1),150 (3.25)

预期结果： 在 HT-7 上实现 LHCD作用下的 H-mode 等离子体，得到形成 H-mode等离子体的功率阈值。

• 希望需要配合的诊断：• Te(r,t), Ti(r,t), Ne(r,t), HX(r,t), SX(r,t), W(t), li(t), Ha, AXUV(r,t), LP

ASIPPASIPP

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