Anode Insert Research Articles

Experimental study on the life and performance of an improved DC arc plasma torch

A novel DC arc plasma torch is designed in this paper in order to reduce the electrode erosion, and a series of experiments are carried out to investigate how to improve the lifetime and performance of the nitrogen DC arc plasma torch. The analysis of voltage characteristics of the plasma torch indicates that the interelectrode insert can increase the average arc voltage and the sudden expansion structure can reduce the voltage fluctuation, which is helpful to improve the working stability to some extent. The spectrum characteristics at the plasma torch outlet and the cold flow simulations show that the dual shielding gas mainly act near the anode and can effectively cover the entire anode wall. Combining the shielding gas distribution with anode heat transfer processes in argon and nitrogen plasma torch, it is inferred that argon shielding gas plays an important role on reducing the anode heat transfer processes in nitrogen plasma torch, which can effectively suppress the anode erosion. The life testing experimental results find that there is no significant erosion of the cathode, anode, and interelectrode insert after cumulative working time exceeding 20 h. The maximum nitrogen plasma jet length can reach ∼35 mm with the outlet jet temperature of about 20 000 K at the current of 100 A and nitrogen gas flow rate of 10 slm. The maximum average specific enthalpy and thermal efficiency are respectively about 14 MJ kg−1 and 75% in the nitrogen plasma torch. Therefore, this newly designed DC arc plasma torch not only can suppress the electrode erosion but also has good working performance, which is expected to have excellent application prospects.

Contribution of Residual Atmosphere Gases to the Flux of Collectively Accelerated Protons in a Luce Diode

The contribution of residual atmosphere gases to the flux of collectively accelerated protons in a Luce diode has been determined by comparing the number of protons generated by anodes made of polyethylene and pyrolytic boron nitride. Radioactivation diagnostics based on the nuclear reactions 10B(p, α)7Be and 12C(p, γ)13N has been used to determine the mean number of protons per pulse and their energy. It has been found that the number of protons accelerated collectively due to adsorption and ionization of water vapor and hydrocarbons from the residual atmosphere of the vacuum chamber on the surface of the dielectric anode insert may be comparable to the number of protons produced directly from the polyethylene dielectric anode insert.

Improvement of the radiographic method for measurement of effective energy of pulsed X-ray emission from a PF device for different anode's insert materials

In this paper, effective energy of pulsed X-Ray emitted from a Mather-type plasma focus device in stored energy of 2.5 kJ with six different anode's insert materials was measured using radiographic method with attenuation filters. Since intensity and energy of X-ray beam were considerably changed with changing the insert material, the method was improved by using different filters simultaneously in all the experiments and selection of the best filter in each experiment according to the appropriate criteria. Effective energy of pulsed X-ray beam was measured 16, 28, 50, 51, 34 and 44 keV when aluminum, copper, zinc, tin, tungsten and lead were used as insert materials, and aluminum, copper, silver, silver, copper and lead were used as filters, respectively.

Effect of inserted metal at anode tip on formation of pulsed X-ray emitting zone of plasma focus device

The effect of the anode's insert material of a plasma focus device on the properties of X-ray emission zone was studied. Inserts were fabricated out of six different materials including aluminum, copper, zinc, tin, tungsten, and lead to cover a wide range of atomic numbers. For each anode's insert material at different gas pressures and different voltages, the shape of X-ray emission zone was recorded by three pinhole cameras, which were installed on sidewall and roof of the chamber of plasma focus device. The results indicated that by changing the gas pressure and the charge voltage of capacitor, the X-ray source of plasma focus emerges with different forms as a concentrated column or conical shape with sharp or cloudy edges. These structures are in the form of a combination of plasma emission and anode-tip emission with different intensities. These observations indicate that the material of the anode-tip especially affects the structure of X-ray emission zone.

Annular structures formed in a beam of ions during their collective acceleration in a system with dielectric anode

We have studied the collective acceleration of protons and deuterons in an electron beam emitted from plasma formed at the surface of a dielectric anode insert. The experiments were performed with a pulsed electron accelerator operating at an accelerating voltage up to 1 MV, current amplitude up to 40 kA, and pulse duration of 50 ns. Reduction of the accelerating voltage pulse front width and optimization of the diode unit and drift region ensured the formation of several annular structures in the electron beam. As a result, up to 50% of the radioactivity induced in a copper target was concentrated in a ring with 4.5-cm diameter and 0.2-cm width. The formation of high energy density in these circular traces and the appearance of an axial component of the self-generated magnetic field of the electron beam are related with the increasing efficiency of acceleration of the most intense group of ions.

Study of the electrode material and insulator length effect on high-energy X-rays emitted by a 4-kJ plasma focus device

In this paper, behavior of hard X-ray (HXR) anisotropy and its intensity along the anode bar of the APF plasma focus device (16 kV, 36 μF, 115 nH) with different anode tip materials is studied. The signals obtained by scintillation detectors by a special arrangement at each angular position show that the employment of higher Z anode insert materials not only increases the intensity of HXR signal, but also results in the high degree of HXR emission isotropy. The highest HXR intensity was observed with a conic W anode insert and the lowest, with a flat Al anode insert. The side-on emitted intensity along the anode bar has been studied by moving the scintillation detector in the direction of the central electrode axis. For Pyrex and quartz insulators, the lengths of 40 and 50 mm, respectively, would seem optimal to produce the maximum HXR intensity. Also the Pyrex insulator would cause a higher HXR intensity than the quartz insulator.

Anisotropic Investigation of Hard X-ray Emission with Flat Anode Tips in APF Plasma Focus Device

In this paper behavior of hard X-ray (HXR) anisotropy and its intensity along the anode bar from APF plasma focus facility (16 kV, 36 μf, and 115 nH) with different anode tip materials investigated experimentally. Magnetic probe signals registered to choose only discharges with high degree of current sheath symmetry. The signals obtained by scintillation detectors by a special arrangement at each angular position show that the employment of higher Z anode insert materials not only increase the intensity of HXR signal, but also result to high degree isotropic emission of HXR. The side on emitted intensity along the anode bar has been studied by moving the detector in the direction of central electrode axis. The results confirm the importance of anode tip material on HXR signal intensity.

Experimental Study of Hard X-ray Emission with Different Anode Tips in APF Plasma Focus Device

To investigate the effect of different anode tips on the hard X-ray (HXR) emission from APF plasma focus device (16 kV, 36 μf, and 115 nH) we considered two shapes of anode tips, i.e., flat or conic, with Cu, Al and W anode tip materials. The highest HXR intensity was observed with conic W anode insert and the lowest with flat Al anode insert. In comparison with the hollow anode tube the HXR signals obtained from flat and especially conic W inserts nearly tending to have the same intensity along the axis of the device. Therefore the shape and the material of the anode tip has significant effect on the production of HXR emissions. This study show that the employment of a convenient shape of anode tip results to more isotropic emission of HXR.

Investigation of Plasma Facing Components in Plasma Focus Operation

Both aspects of the plasma–wall interactions, counter effect of plasma and materials, have been considered in our experiments. The AEOI plasma focus, Dena, has Filippov-type electrodes. The experimental results verify that neutron production increases using tungsten as an anode insert material, compared to the copper one. The experiments show decrement of the hardness of Aluminum targets outward the sides, from 135 to 78 in Vickers scale. The sputtering yield is about 0.0065 for deuteron energy of 50 keV.

Effect of Impurities on the Exclusive Parameters of Plasma-Focus Dena

Fusion performance of a plasma-focus is negatively affected by the presence of impurities that originated from the countereffect of the current sheath and the electrodes, which lower the plasma temperature and dilute the reacting deuterons. The experimental results of the Filippov-type plasma-focus Dena (90 kJ, 25 kV, and 288 muF) demonstrate the profound influence of anode insert materials on the exclusive parameters of the device. The spike depth, the average of the second derivative of current Vimp, and the hot spots are the parameters that clearly display the effect of impurities on the pinch structure and consequently the radiations emitted from the compressed region

Transport of plasma through the tubular anode and discharge stability in a vacuum arc plasma source

The influence of the magnetic field geometry and an anode insert on the ion current output, efficiency and discharge stability of a vacuum-arc plasma source were studied. Truncated cone cathodes made of either titanium or graphite were investigated. Magnetic coils produced a stabilizing field near the cathode and a focusing field with an annular magnetic cusp in the anode. The arc current I arc was adjusted in the range of 100–110 A. The ion current I i was measured by a flat collector. It was found, that the grid anode insert allowed the Ti cathode to be operated with magnetic field intensities in the anode up to a level sufficient for coupling with the magnetic filter field (∼ 20 mT). The maximal value of the system efficiency ratio I i / I arc reached 8%. Using the cusped focusing magnetic field (without the insert), I i / I arc = 7%. Influence of the insert in the form of a diaphragm, positions of a magnetic cusp in the anode and intensity of the longitudinal component of the focusing magnetic field on the transport efficiency of carbon plasma and on the level of ion current deviation were studied using the graphite cathode source. Optimizing the above mentioned factors provided I i / I arc = 8% and decreased the deviation of the ion current from ∼ 50% down to 10%.

Generation of a focused proton beam with a self-magnetically BΘ-insulated ion diode

A self-magnetically BΘ -insulated ion diode was investigated and optimized at the pulsed power line KALIF (2 MV, 50 ns, 2 Ω) to produce a focused and pulsed high-intensity proton beam for generation of high-power density in matter. This diode is characterized by an azimuthal insulating magnetic field that is generated by the diode current. The beam is neutralized by electrons from the cathode vanes, so that neither a gas filled drift space nor foils are needed. The beam therefore propagates in vacuum and repeated shots are possible without changing parts. The protons had energies up to 1.8 MeV and the proton content in the ion beam was about 50%. The maximum total diode current was about 800 kA and its efficiency was as high as 70%. The beam microdivergence was determined to be 1.1°. The radial dependence of the proton current density was measured and is proportional to r−1.74. This result was confirmed by 2D quasistatic particle-in-cell simulations. The focus was optimized by adjusting the anode shape and the gap geometry and by decreasing the beam divergence. The FWHM diameter of the focus at a distance of 300 mm was about 10 mm and the resulting focused power density was 0.13 TW/cm2. The effect of the gap distance on focusing and impedance was investigated and it was found necessary to adjust the gap to better than 0.1 mm over the total 30-cm-diam anode to obtain the best performance. The electron loss and the corresponding erosion at the posts that hold the anode was reduced. The lifetime is now limited by the plastic anode insert to 10–15 pulses. Based on these results a ‘‘small BΘ diode’’ is suggested for which a power density increase of a factor of 3 is estimated.

Gas discharge ion source. I. Duoplasmatron

The effects of the plasma expansion cup on the operation of a duoplasmatron ion source have been investigated by measuring the total ion current and the distributions of the ion energy, mass, and current density. A copper expansion cup did not affect the magnetic field near the anode of the ion source and consequently the ion current density distribution was sharply peaked near the center of the cup. Ion energy distributions were approximately symmetrical about anode potential. The dominant ionic species were D(+) (3) and D(+) at low and high arc currents, respectively. Changes in the electrical potential of the copper cup with respect to the anode produced negligible changes in the above data. A mild steel plasma expansion cup caused the magnetic field to diverge and intercept the cup walls, resulting in ion current density distributions that were flatter and more amenable to focusing than the ones with the copper cup. With the steel cup at anode potential, the ion mass distribution was similar to that from the copper cup; however, the ion energy distribution was asymmetrical about the anode potential with a peak about 10-20 V above anode potential. The total ion current from this mode of operation was about one-third the value from the copper cup. If the steel cup assumed floating potential, about 50 V below anode potential, the total current increased to the level observed from the copper cup and the ion energy distribution was similar to that observed with the copper cup but the current density distribution was much flatter than that of the copper cup. The ion mass distribution was 60%-70% atomic ions over the entire arc current range investigated. Based on these data, a modified plasma expansion cup was designed with tapered steel walls lined with a boron nitride insert. The overall performance of the duoplasmatron ion source with this cup was superior to any of the previous three modes of operation. The improved design uses a molybdenum anode insert which is far superior to copper in regard to erosion over extended operating times. A total beam current of 200 mA was produced at an arc current of 24 A.

Operation of a plasma-focus device with D2 and He3

Two plasma-focus devices at the Lawrence Livermore Laboratory, the B Division device (BDPF), with a stored energy of 73 kJ at 18 kV, and the Physics Department device (PDPF), with a stored energy of 67 kJ at 20 kV, were operated with various mixtures of D2 and He3. The purpose of the experiments was to evaluate the D-D/D-He3 yield ratio as a diagnostic tool for determining the plasma ion temperature. Measurements were made in the high-pressure mode (total pressure of 4.0 Torr for the BDPF, 7.5 Torr for the PDPF), where previous measurements using carbon activation showed no significant ion acceleration to energies above the 330-keV carbon (d,n) reaction threshold. The yield from the D(d,n)He3 reaction was determined from measurements of the total neutron yield using the standard silver-activation technique. The yield from the He3(d,p) He4 reaction was determined by measuring the reaction-product protons by copper activation. The Cu anode insert from the center electrode was analyzed for γ activity following each series of shots to measure the presence of Zn63 from the 4.21-MeV-threshold Cu63(p,n)Zn63 reaction. The thick-target yield for this reaction at the proton energy of 14.6 MeV was calculated from cross-section data, giving a value of 7.5×10−4 Zn63 atoms per incident proton. In operation with 50/50 atomic or molecular mixtures of D2 and He3, the D-D/D-He3 yield ratio varied from a minimum of 13.6 to a maximum of 60.5. This corresponds to a plasma temperature range from 4.0 to 6.5 keV, or if a beam-target model is assumed, to a deuteron beam ranging in energy from 28 to 47 keV incident upon stationary He3 ions. Operating with fractions of He3 ranging from 0.053 to 1.0 at a total pressure of 4 Torr, the D-D neutron yield showed the expected dependence on the square of the deuterium fraction [f (D)].

Influence of Cooling Conditions on Anode Behavior in a Nitrogen Plasma Jet Design

AbstractSome characteristic data are recorded for a nitrogen plasma jet design of the wall stabilized type incorporating a strongly and a poorly cooled tungsten hollow anode insert for currents between 133 and 175 A and mass flow rates between 0.94 and 1.54 g/s N2.From the characteristic data, conclusions are drawn relative to the anode behavior in dependence from the cooling conditions.The results especially of the calorimetric measurements and of the survey spectrum photographs indicate that the anode root area is greater in the case of the poorly cooled anode with the higher mean working temperature, and that in this case more heat at a lower level of heat flow density is transferred from the plasma to the anode body. The voltage oscillogramms indicate that even in the case of the poorly cooled anode the anode root is of the moving spot type, and that a transformation into the spotless immovable anode root has not yet been arrived. This will be attributed to the relative low level of the mean anode temperature even in the case of the poorly cooled anode for which estimations give values of below 2000 K.

X-Ray Analysis for Electron Beam Enhancement in the Plasma Focus Device*

AbstractThe plasma focus device, a form of linear pinch discharge, produces an intense x-ray and neutron (D2) burst from a magnetically heated dense plasma. Rapidly changing magnetic fields at pinch time generate large axial electric fields which accelerate electrons and ions. In the experiments reported here the x-ray production during the plasma pinch of a 96 kilojoule (at 20 kV) plasma focus device was measured.The purpose of these experiments was to evaluate the energy in accelerated electrons in the plasma focus device and to learn how to enhance these electron hursts. Well focused, megampere electron beams at a few hundred kilovolts, lasting less than 10 nanoseconds have applications in fusionable pellet heating experiments. (1) X-rays were monitored to evaluate these electron bursts using a defocusing bent crystal spectrometer, doubly diffused silicon (PIN) detectors, with Ross filters, thermoluminescent dosimeters (TLDs) with filters, and x-ray pinhole photography.Thermoluminescent dosimeters indicated maximum x-ray yields of 140 joules above 3 keV at 57.3 kilojoules stored energy (16 kV) for a conversion efficiency to x-rays of 0.2%. 40 joules are above 60 keV and 15 joules above 80 keV. The hard x-ray pulse typically rises in 3 ns and frequently has a pulse width less than 10 ns. The low energy x-ray spectrum consists almost entirely of lines from the high Z anode insert, and the high energy spectrum is characteristic of a nonthermal power law distribution with an exponent of 2.2 ± 0.8. Peak hard x-ray production is obtained at 1 torr deuterium in contrast to peak neutron production (3 x 1010) at 5 torr. The addition of argon reduces total x-ray yield and increases the relative fraction of soft x-rays.These measurements suggest that the plasma focus produces 1200 joules of electrons with an average energy of 150 keV, in 10 nanoseconds with a stored energy of 57.3 kilojoules. This is a power of 1.2 × 1011 watts and power density of 1.5 × 1013 watts cm−2.

A Study of a Duoplasmatron Ion Source with an Expansion Cup

This work describes a study of the Duoplasmatron ion source for the purpose of investigating the conditions necessary to improve its performance. First a general review is made of theoretical considerations involved in the source's plasma mechanism and the geometry of the extraction system. Then the experimental work deals with the arc discharge characteristics as well as the source's performance when the beam is extracted with a simple Pierce extracting electrode. Through an invar anode insert a 70 mA was obtained at 35 kV. The main improvement was then due to beam extraction from an expansion cup which rendered a 300 mA beam at a lower voltage of 18 kV. The use of different anode materials has indicated the influence of magnetic field penetration on plasma focusing within the expansion cup. A beam current reaching 1 ampere was noticed when a non-magnetic anode was used.