proposal of lhcd & fast electron behaviors study on ht -7 exp2005

HT-7

Proposal of LHCD & fast electron behaviors study on HT -7 Exp2005

ASIPP

PHA team

Email: [email protected]

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HT-7

Motivation

• 低杂波电流驱动（ LHCD ）实验是托卡马克非感应电流驱动的重要手段，也是调节电流密度剖面，实现先进位形（如反剪切）和实现长脉冲稳态运行的重要工具，实验中还发现了其改善约束，抑制sawtooth ， m ＝ 1 模的现象。

• HT － 7 上已经开展了多轮 LHCD 实验，并获得了丰富的物理结果。在 HT － 7 上深入研究 LHCD 下的快电子行为是为 EAST 的稳态先进运行模式打下基础 , 也是 LHCD 反馈控制电流密度和 q profile的基础。

• 低杂波电流驱动的驱动效率，功率沉积剖面，以及快电子与剩余环电压之间的作用有丰富的物理内容，对其进行深入研究有利于我们理解低杂波和等离子体之间的物理过程，以及为 LHCD 反馈控制实验奠定基础。

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Diagnostics and functions

FEB Camera

The energy range of fast electrons build up by the LHW, and DC field

Fast electrons distribution function ， LH wave power deposition profile

Propagation, absorption of the LH waves

Details of momentum dynamics and the relativistic angular anisotropy

slow down ， confinement, relaxation and oscillation behaviors of fast electron

Runaway electron spectrometer

The energy range of runaway electrons ， generation ， evolution

provide confidence for FEB signals

SX_PHA (S.Y.LIN)

Te profile and metallic impurities content

li （ B.Shen, X.Q.Zhang ）

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Lay out of sight lines Improved one-way CdTe detection system

Old detector with T039 house

Upgrade of FEB camera(vertical array)

Vertical 15-channel

Measuring range: + 27 cm

Spatial resolution : 5 cm

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切向硬 X 射线诊断示意图

正向 14 道，分辨率： 5cm

测量范围：－ 25 ～ +30cm

反向 5 道，分辨率： 10cm

测量范围：－ 16 ～ +24cm

电流方向

Upgrade of FEB camera(toroidal array)

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HT － 7 上逃逸电子诊断

NaI 探测器 (40*40), 测量范围： 0.3 ～ 10MeV

正向 2 道，一道正对真空室内壁，一道对等离子体中心反向 1 道，分辨率： 10cm

测量范围：－ 16 ～ +24cm

正向一道 CdTe 探测器 (65mm3)

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1. Fast electron dynamics

Slow down time, confinement time,

Oscillation behavior in sawtooth activity plasma

2. LHCD efficiency with IBW heating plasma

3. Comparison of experimental data in current ramp-up/down with K

arney-Fisch curves

4. Runaway electron dynamics

5. Searching LHEP mode on HT-7

Exp2005 related with FEB

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HT-7

快电子的辐射分布

HT － 7 上低杂波与等离子体作用（ ELD ）产生的快电子能量在 30keV ～ 100keV ，如果存在电场，能量可以达几十 MeV 。高能快电子辐射的硬 X 射线具有空间不均匀性，辐射主要集中于电子运动方向。已有的极向硬 X 射线诊断对环向这种不均匀辐射不敏感，只有沿电子运动方向进行观测才可以得到准确的硬 X 射线能谱。通过 FEB Camera 测量其发射的硬 X射线，我们得到快电子的信息。

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快电子分布模型

• 三温分布模型

三温分布可调节的参数：

T , T//F, T//B,, pc,

分别是垂直光温，前向光温，反向光温，截止动量

对 LHCD ，通常有

T//F>>T//B, T ;T ～ T//B ，

Pc 由低杂波的波谱 n// 决定，但是存在环电压的时候 Pc 可以更高

三温模型一维平行动量分布图

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HT-7FEB sawtooth

Possible explains for FEB inverted sawtooth:1. During internal disruption, runaway electrons travel from q=1 surface to the limiter,

producing thick-target bremsstralung emissions.2. Internal disruption give rise to perturbation, fast electrons were redistributed durin

g internal disruption.3. Resulting from changes in the current profile that shift the drift orbit displacement

of the runaway electrons at the edge of the plasma

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HT-7Relation of current profile with HXR profile

• , If collisional slowing down time prevails on radial diffusion, transport

of parallel momentum across field lines is small, and the radial LH current profile

matches that of the LH power deposition, with a possible minor broadening due to

radial transport. And fast electron confinement time is approximately given by a

verage of over the plasma volume, . Or else, the HXR profile cann’t

be used to estimated the current profile.

• , parallel momentum is transported radially before its destruction be Cou

lomb collisions, leading to a decoupling between the power deposition and LH curre

nt profile. , and the CD efficiency value is smaller than theory prediction.

dds

dsd

dsf f

sd

df

It is important to determine the LHW power deposition profile in HT-7. Last experiment on this point has failed due to the generated runaway electrons in LHW turn off phase. Slow down time and power profile.

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FEB spectrum

• Fast electron dynamics during OH free

• Fast electron dynamics with partial current drive by LHW( different loop voltage)

• Fast electron dynamics during pellet injection

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arney-Fisch curves




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LHCD 实验结果

快电子的约束与能量损失 JT-60

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CD efficiency with non-zero loop voltage (v) can be well derived when the 0 and 1 have been obtained.

rf

erf

P

RnIv )(

normnorm PP

1

10

1)(

norm

norm

P

P

1

10

OH 1

)(

V

V

Ip=126kAne=1.45*1019m-3

)]1

1()[(

OHOH V

V

V

V

norm

norm

P

P

1

10

OH 1

)(

V

V'

OHspLHsp RR )/()(

Hot conductivity theory

E1RFOHtot J JJ

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Dependence of the current drive efficiency

with plasma density. LH wave with phase

of 0º, there exist a density range for higher

current drive efficiency

Dependence of the current

drive efficiency on LH wave n//

Parameter dependence of CD efficiency

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The fast electron hot conductivity can be determined as a by-product f

rom the 1. From the defining of , the hot conductivity can be deter

mined: psnormP /11 1

This need the Rsp to be determined accurately. One of ways to determine it is to obtain the current decay time, D

spD RL /

测量方法：当电流到达平顶端时，关断 OH 场，让电流自由衰减，其复合指数函数衰减，根据衰减时间，和等离子体电感，我们可以得到等离子体电阻，大约是几个微欧。

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Synergy effect of LHCD and IBW has been observed in HT-7. Such

as high performance, H mode…

Global CD efficiency may be improved in combination of LHCD with

IBW heating. Local CD efficiency has be improved combination of

IBW heating.

HT-7 data

Investigating the CD efficiency

with IBW heating plasma,

which may give valuable

information on the volume

averaged temperature

dependence for HT-7 plasma

Scan IBW Power(kW):

100, 200, 300, 400 …

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1. Fast electron distribution function(Three temperature model)



arney-Fisch curves




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Power flow in LHCD experiments

Model (2) － K-F curve

These inefficiency arise for some reasons: a fraction for the rf energy may be launched in the wrong direction, may be scattered off various plasma inhomogeneity, or for other reasons, may not be absorbed by the intended electrons

u

uG

P

P

abs

el /

Karney-Fisch curve

Pel=VloopIrf , Pabs=Pinjected , nabs=n//0 VR is the run away velocity

abs

el

P

P

RabsR Vn

c

V

Vu vs

Fisch’s theory:

Hot electron

Prf (1- )Prf

Bulk LI2/2V2/Rsp

PelPH

Pabs=Prf

Pext

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HT-7

HT-7 data with various values of density, current, LH phase velocity, and LH power, were plotted in terms of Pel/Pabs and Vph/VR in Karney-Fisch Curve.

For Vph/VR>0, it corresponds to current ramp-up,

or OH transformer recharging, RF power flows int

o the field energy.

For Vph/VR<0, it indicates that RF power is insuffi

cient to sustain the constant current and the power

flows from the poloidal field energy into the kinetic

energy of resonant electrons.

For Vph/VR=0, it corresponds full driven current o

peration.

The two free parameters and are related through the wave damping mechanism.

=0.75, =1.9, 1.7, 1.5, 2.6 for LH phase velocity 0, 90, 180, 270 respectively are choose to fit

the experiment data well. It correspond to the absorbed n// at the value of about 5.

The efficiency of recharging OH transformer during LHCD is about 7%

Experiment results from 2004Exp (1)

HT-7 data with 180shots

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CD efficiency can be well determined according the theory form:

2//

2)5(ln

1240

NZeffcd

Upshift of LH waves n// in plasma

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Runaway probability R(u)

The remarkable fitting results for the experiment dat

a to theory curves provide us a guidance to achieve high

conversion efficiency in current ramp up experiments.

It seems that large u is in favor of high efficiency, but

this depends on the role of runaway electrons. Since the

theory curves have ignored the role of runaway electron

s, if the number of runaway electrons is not negligible, o

r the runaway electrons are confined well, the theory wi

ll not hold. Runaways are very important in the convers

ion efficiency because runaways gain energy at the expe

nse of the poloidal magnetic field. For u>2, almost all re

sonant electrons will run away. Unless they are not conf

ined, even a small number of runaway electrons can gre

atly reduce the efficiency.

Optimizing Current ramp-up region

For HT-7 machine, the highest ramp-up efficiency may be achieved by operating ramp-up experiments in the region of 1.5<u<2.

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Ramp-up experimentAim at:1. High ramp-up efficiency2. Fast ramp-up3. Reverse shear physics4. Effect of runaway electron on ramp-up experiment5. Maximum ramp-up velocity6. No transformer ramp-up

我们用 2 倍的全波驱动功率进行 ramp-up 实验 , 期望其在优化的区域运行

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2. CD efficiency with different volume averaged temperature

3. Comparison of experimental data in current ramp-up with Karne

y-Fisch curves




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For fast electrons, them endure both the electric filed force due to the residual loop voltage and the damp force due to collisions.

The critical kinetic energy of fast electron to be runaways is

=2.21*(2+Zeff)*ne/E (keV)

E

ZneW effecrit 2

0

3

8

)2(ln

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Runaway electron dynamics Aim at:OH pulse, MHD activity, disruption

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2. CD efficiency with different volume averaged temperature

3. Comparison of experimental data in current ramp-up with Karne

y-Fisch curves




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HT-7

Searching LHEP mode on HT-7(1)

LHEP － LH enhanced performance

Suppress sawtooth and the m=1mode by high power LHW, may be 500kW LHW is enough for HT-7 plasma.

The suppress effect is related with the peaked n//

ASDEX

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HT-7

Searching LHEP mode on HT-7(2)

LH enhanced performance during OH free

pulse. The current will be ramp-up again if

the LHEP mode is triggered.

Ip

LH

Traim-1M

OH free

LHEP phase

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Synergy effect with LHW+IBW

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LHW power deposition on axis during IBW heating

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HT-7 实现长脉冲的可选方案：低杂波引起的杂质，以及限制器温度上升在长脉冲放电中影响较大。由于等离子体的电流的衰减时间在几百毫秒左右，我们可以采取低杂波调制运行方式，

Ip

PLH

Ip=50~60kA

Long pulse operation alternation LHW power

300kW, 5~10Hz

>10 minutes ?

OH free

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Thank you for your attention!

proposal of lhcd & fast electron behaviors study on ht -7 exp2005

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