1

Primary Research of Massive Gas Injection for Disruptions Mitigation

on HT-7

H.D. Zhuang X.D. Zhang Y.Zhang

Institute of Plasma Physics. CAS

2011.7.20

ASIPP

2

Outline• 1 、 Background and motivation

• 2 、 Design of fast valve on HT-7

• 3 、 Experimental arrangement and results

• 4 、 Summary

• 5 、 Reference

ASIPP

3

Outline• 1 、 Background and motivation

• 2 、 Design of fast valve on HT-7

• 3 、 Experimental arrangement and results

• 4 、 Summary

• 5 、 Reference

ASIPP

4

• Disruption is a threat to Tokamak[1](1)the sudden deposit of the plasma stored energy on the

divertor plates

(2)the halo and eddy currents induced in all the structures;

(3)the multi-MeV runaway electrons accelerated and lost on the first wall

ASIPP

The threat will become worse with the increase of the device size and plasma parameters.

5

One method of disruption mitigation[2,3,4,5,6,7]

(1)Large increase of plasma density during disruption can lower the plasmas temperature and thus mitigate effects of thermal damage.

(2)Particles must penetrate into the current channel during the current quench to prevent runaway electron formation

(3)Methods to increase the density are: ---Gas injection: large burst of gas from a fast valve --- Pallet injection: solid pellets accelerated by gas

ASIPP

6

ASIPPReview of massive gas injection experiments

Different kind and quantity of noble gas to the influence of the mitigation effect

7

• The requirements of disruption mitigation for fast valve

1 ， Short response time!(several ms)

2 、 large throughput!(different tokamka and parameters have different requirements ) for the purpose of inhibit the generation of runaway electrons

ASIPP

Must establish warning system of disruption ------it’s a hard work, Warning time is very short

8

Outline• 1 、 Background and motivation

• 2 、 Design of fast valve on HT-7

• 3 、 Experimental arrangement and results

• 4 、 Summary

• 5 、 Reference

ASIPP

9

• 1 、 The principle of the fast valve ASIPP

The valve is a fast valve.When the current like below was through into the pancake coil ,the piston will suffer strong electromagnetic force, the valve will be opened, after the force disappear, the piston will come back, then the valve was closed.

“V”-workingchamber;“b”-theBack chamber;“P”-the aluminium piston;“C”-the pancake coil;

10

• 2 、 The structure and the power supply system of the fast valve

ASIPP

11

• The primary testing data of the fast valve

ASIPP

Different color line represent different pressure

The relationship between aeration amount

and voltage

12

• 3 、 The character of the fast valve (1) It is drive by eddy current, which will open in less tha

n 2 milliseconds

(2) The number of the injection gas could be changed

easily,which could meet the requirement of the

disruption mitigation

(3) It will work in high state magnetic field ,because the

piston does not exploit any ferromagnetic materials

ASIPP

13

• The position of the valve on HT-7 It was installed near the west manhole.the length and th

e diameter of the connection pipe respectively is 750mm and 16mm

ASIPP

14

Outline• 1 、 Background and motivation

• 2 、 Design of fast valve on HT-7

• 3 、 Experimental arrangement and results

• 4 、 Summary

• 5 、 Reference

ASIPP

15

• 1 、 Experimental arrangement

platform: ohmic discharge

IP:130KA, ne:1.4E+19/m3.

the type of injection gas: He

The pressure of the injection gas is 2bar

ASIPP

16

• 2.1、experimental results

ASIPP

In limiter configuration, In order to reduce the eddy current ,so reduce the electromagnetic force,it should make the current decay slowly.

Expression of current quench:

17

• 2.2 、 experimental results

After trigger, several millisecond later, the boundary temperature droped, after a period of time ,the central temperature droped, and the boundary density began to increase. And the ratiation intensity increase

ASIPP

18

• 2.3 、 experimental results(decrease the quantity of the injection gas)

ASIPP

When we decrease the amonut of the injection gas , we found that ,the curent quench time is become longger.from the figure ,we can get that, after trigger, 3.6 millisecond later, the boundary temperature droped, after 10.5ms later ,the central temperature droped, and the boundary density began to increase. And the ratiation intensity increase

19

ASIPP

2.4 、 The comparision of plasma density and current decay after MGI

The bule shot has less quantity than the gray one, the accurate injection quantity of the fast valve is in calibrating

20

ASIPP

by reduce the quantity of the injection gas, the current decay rate is changed from 14.4MA/S to 2.8MA/S. so the electromagnetic force could be reduced.

21

Outline• 1 、 Background and motivation

• 2 、 Design of fast valve on HT-7

• 3 、 Experimental arrangement and results

• 4 、 Summary

• 5 、 Reference

ASIPP

22

summary

• 1 、 After trigger signal ,the gas will enter the boundary of the plasma within about 3.6 ms,the valve is fast enough for the requirement of the disruption mitigation.

• 2 、 the rate of current quench could be reduce by change the quantity of the injection gas.so the electromagnetic force will be reduced

• 3 、 lack of effective diagnosis ， so we can't estimate the electromagnetic force

ASIPP

23

Outline• 1 、 Background and motivation

• 2 、 Design of fast valve on HT-7

• 3 、 Experimental arrangement and results

• 4 、 Summary

• 5 、 Reference

ASIPP

24

reference[1] ITER Physics Basis 1999 Nucl.Fusion 39 2251[2]FinkenK.H.,MankG.,etal.,Mitigation of Disruptions by Fast Helium Gas Puffs,N

uclearFusion,vol.41(2001),pp.1651-1661[3]SavchkovA.,Mitigation of Disruptions in a Tokamak by Means of Large Gas Inje

ction[4]BakhtiariM ,KawanoY,etal,Fast Plasma Shutdown Scenarios in the JT-60U To

kamak Using Intense Mixed Gas Puffing ,Nuclear Fusion, vol. 42(2002),pp.1197-1204

[5]BakhtiariM.,TamaiH.,etal.,Study of Plasma Termination Using High-Z Noble Gas Puffing in the JT-60U Tokamak,Nuclear Fusion 45 (2005),pp.318-325

[6]TaylorP.L.,KellmanA.G.,etal.,Experimental Measurements of the Current,Temperature,and Density Profile Changes during a Disruption in the DIII-D Tokamak,Physical Review Letters,76(1996),pp.916-919

[7]IzzoV.A.,ANumerical Investifation of the Effects of Impurity Penetration Depth on Disruption Mitigation by Massive High-pressure Gas Jet,NuclearFusion,vol.46(2006),pp.541-547

ASIPP

25

Thanks f

or your attention!

ASIPP