Theoretic And Experimental Investigation Into Gas-Puff Load For Z-Pinch

The configuration and line mass-density of gas puff load used in Z-pinch areinvestigated theoretically and experimentally in this paper. The experiments ofArgon gas-puff Z-pinch are finished using new and old nozzle respectively in"Yang" accelerator. The results show that the load structure, configuration and linemass-density are optimized and energy coupling efficiency between load and pulsedpower device and X-ray are improved using new nozzle. The energy of soft X-ray is1.7 kJ, power is 22 GW, pulse width (FWHM) is 16 ns. Numeric simulation aboutgas-puff load is carried out by three steps: Firstly, planar Laval nozzle is designedusing engineering method. Secondly, the flow process that gas flow moves from gasstoring chamber to the exit of nozzle is simulated by Navier—Stokes equation.Thirdly, expanding process of supersonic velocity gas flow from the exit to vacuumarea is simulated using DSMC method. The configuration and line mass density ofgas puff load are obtained by the method above.A high sensitive He-Ne laser interferometer that is able to check 0.2°phase shift is built using the method of heterodyne and tracking phase. The measurementof line mass-density of gas puff z-pinch load is carried out. The interruption ofmachine vibration to interference signal is eliminated by means of putting theinterferometer into vacuum chamber and setting laser and vacuum chamber andoptical elements on the full gas optical platform. The time-dependent curve ofaverage line mass-density of Argon in inner single Laval structure nozzle is obtained.It can be used to optimize the design of Laval nozzle. The forming time of gas flowstation is helpfully to adjust the synchronization between the opening time ofelectric-magnetic valve and the driving current pulse in order to match the timebetween load and driving device in Z-pinch experiment. The Argon Z-pinchexperiments are carried out using new and old nozzle respectively in Yangaccelerator. The picture of plasma forming at different time are obtained by means ofvisible light multi-frame camera and X-ray multi-frame camera and laser differenceinterferometer. The experimental results show that the distribution of gas flow andpinch effect of new nozzle is better than the old nozzle obviously. In addition, thehigh sensitive laser interferometer is also applied to measure the electronics densityof cable plasma gun used in plasma opening switch (POS). With this interferometer,the characteristics of plasma generated by a cable, plasma gun have been investigatedsystematically. The reproducibility, spatial and temporal distributions, and theaverage injection velocity of the plasma is presented. The main research taskscompleted are as follows:1. Through a lot of researching on Z-pinch studying, a total review is given.2. The fast electric-magnetic valve is designed and manufactured. It is 12.4 cm highand 1 kg weight. It consists of electric-magnetic wire, stainless steel chamber, valve,soft iron hammer and spring. It is connected with a group of capacitors by siliconcontrolling rectifier. In the coiling process, fiberglass is added into the inner of wireto improve intensity. The fast electric-magnetic valve is made of titanium metal thatis less weight and higher intensity. Soft iron hammer is composed of high resistancerate silicon steel piece. Insulated material is filled into each piece and repeating slotis parallel to magnetic induction line. The piping length between valve and throat of nozzle is optimized in designing to improve oscillation frequency of gas flow. It ishelpful to form new stay condition quickly in order to obtain stabilization gas puffload in short time. The process of opening valve is screened using high speedcamera and laser. The result shows that the uplifting time is 2.0 ms and averagespeed is 12 m/s. The airproof capability of valve is better and steady in dynamicprocess. The jitter is less then 20μs, as is satisfied the experimental requirement.3. Three different configurations Laval nozzles (single introflexion shape, outersingle shape and dual-shape) are designed and manufactured by engineering method.The exit of nozzle is circularity. The gas flow is parallel to the axial direction. It isof high mach numbers in the exit. This design reduces the diffuse of gas flow inradial direction. It ensures gas flow to arrive towards electrode in shorter time. Theslide effect is reduced. The nozzle may be affected by many factors such as openingspeed of nozzle, closing time, geometry form of vacuum tube, pressure of gasstoring chamber, dimension of throat and exit, shape and average radius et al.4. Tile flowing process that gas flows from storing chamber to exit of nozzle issimulated by solving Navier—Stokes equation. As the flowing process is verycomplex during the process that valve is opened and closed. It just only is solved byapproximate method. In order to simplify the calculation, suppose the valve isopened and closed suddenly. The delay time between opening and closing isestimated by experimental results. Before opening, the left of the valve is filled withhigh pressure gas and the right is vacuum area. When the valve is opened suddenlythe high pressure gas will move from left to right quickly and than forms non-stationary flow. This is a typical shock wave tube problem. When the valve isclosed suddenly, the gas in the right side will continue moving toward front asinertia and different pressure in the two sides. As the throat of nozzle is very narrow,the gas can not go through quickly. The shock wave and exploring wave shall reflectbetween the throat and the valve repeatedly than a uniform standing gas is formed.In the calculation, the condition of gas storing chamber is as beginning condition ofLaval nozzle and steady flowfield mode is used to calculate, the calculation result is10 times of experimental result. It does not satisfy the designing requirement. When unsteady flowfield mode is used to calculate, the result is near to the experimentalresult.5. The distension process that the gas expands toward vacuum area is simulatedusing direct emulation Monte-Carlo method. The line mass-density andconfiguration of gas puff load are obtained. The line mass -density and shape of gasare calculated for three different shape nozzles under different pressure and underdifferent size throat.6. The cylinder vacuum chamber is made of stainless steel. The diameter and high is580mm and 300mm respectively. It is enough large for setting interferometer intovacuum chamber. The vacuum rate is 1×10^-3Pa.7. A high sensitive He-Ne laser interferometer that is of checking 0.2°phase shift isset up using heterodyne technology and tracking phase. In this system theinterruption of machine vibration from molecule pump and machine pump tointerference signal is eliminated through putting the interferometer into vacuumchamber and setting laser and vacuum chamber and optical elements on the full gasoptical platform.Ï€/2 phase locking method is set up using a oscillograph firstly. Itis easy thatÏ€/2 phase is set as initialized phase point using this method. The mostsensitive interference point is gained in phase measurement.8. The measurement of line mass-density of gas puff z-pinch load using singleintroflexion shape nozzle was carried out using the high sensitive interferometer.The time-dependent curve of average line mass-density of Argon gas is obtained bythe Laval nozzle of inner single structure. The result shows that the gas flow arrivesat the 10mm place far away the exit of nozzle at 1.6ms after the current ofelectric-magnetic valve. 0.3ms late the gas flow forms steady station and the keepingtime is up to 0.4 ms.9. The Argon Z-pinch experiments are carried out using new and old nozzlerespectively in "Yang" accelerator. The picture of plasma forming at different timeare obtained by means of visible light multi-frame camera and X-ray multi-framecamera and laser difference interferometer. The experimental results show that thedistribution of gas flow and pinch effect of new nozzle is better than the old nozzle obviously. The energy of X-ray is 1.7 kJ, the power is GW, the width of pulse is(FWHM) 16 ns.10. The time-resolved sensitive He-Ne laser interferometer is used to measure tolow-density plasma. The measurement of electronics density is completed aboutcable plasma gun used in plasma opening switch. The precision of the phasemeasurement about 0.2°that equals to line-integrated plasma density as low as8.3×10¹³ cm^-2 was reached. With this interferometer, the characteristics of plasmagenerated by a cable plasma gun were investigated systematically. Thereproducibility, spatial and temporal distributions, and the average injection velocityof the plasma are presented. In addition, the interaction of plasma flow with a metalconductor was studied by placing a metal plate in downstream of the cable gun.11. Experimental scheme of one dimension array measurement is designed. Thepoint laser beam is transformed into piece laser beam using extending lens andcylinder lens. The density of different place is noted using one dimension array fiberand PIN diodes. One dimension distribution of gas density in X direction can beobtained in one shot experiment. Two dimensions distribution of gas density can beobtained by moving device or laser beam in Y direction. This method suits densitymeasurement in fast plasma.