1. 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. 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. 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. 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. 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. 6 Review of massive gas injection experiments Different kind and quantity of noble gas to the influence of the mitigation effect

7. 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 ----- -its a hard work, Warning time is very short

8. 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. 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 -the Back chamber; P -the aluminium piston; C -the pancake coil;

10. 10 2 The structure and the power supply system of the fast valve ASIPP

11. 11 The primary testing data of the fast valve ASIPP Different color line represent different pressure The relationship between aeration amount and voltage

12. 12 3 The character of the fast valve (1) It is drive by eddy current, which will open in less than 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. 13 The position of the valve on HT-7 It was installed near the west manhole.the length and the diameter of the connection pipe respectively is 750mm and 16mm ASIPP

14. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 24 reference [1] ITER Physics Basis 1999 Nucl.Fusion 39 2251 [2]FinkenK.H.,MankG.,etal.,Mitigation of Disruptions by Fast Helium Gas Puffs,NuclearFusion,vol.41(2001),pp.1651-1661 [3]SavchkovA.,Mitigation of Disruptions in a Tokamak by Means of Large Gas Injection [4]BakhtiariM,KawanoY,etal,Fast Plasma Shutdown Scenarios in the JT-60U Tokamak Using Intense Mixed Gas Puf ng,Nuclear Fusion, vol. 42(2002),pp.1197-1204 [5]BakhtiariM.,TamaiH.,etal.,Study of Plasma Termination Using High-Z Noble Gas Puf ng 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 Pro le 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. 25 Thanks for your attention! ASIPP