Iwao Kitamura

Purity of nitrogen ion beams produced in a plasma focus

To improve the purity of ion beams produced in a plasma focus (PF), the dependence of the characteristics of the nitrogen ion beams on the shape of the anode was investigated. Two types of anodes, i.e. rod type (type A) and hollow type (type B) were used with a PF pre-filled with nitrogen gas. Thomson parabola spectrometer measurements showed the existence of a large amount of impurity ions, O1–2+, C+, and Cu1–2+, with nitrogen ions (N1–3+) and the percentage of nitrogen ions is only 25% in type A. In contrast, in type B the impurity is extremely reduced and the percentage of nitrogen ions is enhanced to 91%. The maximum energies and power brightnesses of the nitrogen beams were evaluated to be 0.5 MeV and 0.23 GW cm−2 sr in type A and 1 MeV and 1.6 GW cm−2 sr in type B; hence, energy and brightness are also enhanced in type B. From x-ray pinhole images we see that strong electron irradiation occurs on the top of the anode in type A, whereas in type B, electron irradiation is weak and irradiation area is far from the pinch plasma. Hence, the impurity ions observed in type A are considered to be produced in the following process. Due to the strong irradiation of electrons on the anode top, the electrode and the absorbed gas on the electrode are vaporized, mixed with pinch plasma and accelerated with nitrogen ions.

Characteristics of Ion Beams Produced in a Plasma Focus Device

Characteristics of the ion beams produced in a plasma focus device were studied. In the experiment, a Mather type plasma focus device was used and it was pre-filled with 2.3 Torr H2. The plasma focus device capacitor bank of 43.2 µF was charged to 30 kV to get a peak current of 350 kA. Ion spices and their energy spectrums were evaluated using a Thomson parabola spectrometer, and the particle pinhole image was obtained with an aluminum filtered particle pinhole camera. While, the ion current density was measured with a biased ion corrector. The proton beam energy was distributed from 0.15 MeV to 2 MeV. On the other hand, we found singly and multiply ionized ions of C, N,. The particle pinhole image of the proton beam, which has energy more than 1MeV, was spot type. The ion current density of 1200A/cm2 was obtained. The peak power brightness for the proton beams was 18 GW / cm2 / Sr /keV.

Development of bipolar-pulse accelerator for intense pulsed ion beam acceleration

To improve the purity of an intense pulsed ion beams a new type of pulsed ion beam accelerator named ≪bipolar pulse accelerator≫ (BPA) was proposed. To confirm the principle of the accelerator a prototype of the experimental system was developed. The system utilizes By type magnetically insulated acceleration gap and operated with single polar negative pulse. A coaxial gas puff plasma gun was used as an ion source, which was placed inside of the grounded anode. Source plasma (nitrogen) of current density ≈25 A/cm2, duration ≈1.5 μs was injected into the acceleration gap by the plasma gun. The ions are successfully accelerated from the grounded anode to the drift tube by applying negative pulse of voltage 240 kV, duration 100 ns to the drift tube. Pulsed ion beam of current density ≈170 A/cm2, duration ≈50 ns was obtained at 41 mm downstream from the anode surface. To evaluate the irradiation effect of the ion beam to solid material, amorphous silicon thin film of thickness ≈500 nm was used as the target, which was deposited on the glass substrate. The film was found to be poly crystallized after 4- shots of the pulsed nitrogen ion beam irradiation.

Thunderstorm tracking system using neural networks and measured electric fields from few field mills

The paper presents a novel system to asses quickly the direction of thunderstorm by using a few field mills on the ground. As opposed to traditional methods using expensive radar systems to detect thundercloud movement, the presented method simply uses the electric waveforms detected by the field mills and, by using a neural network of suitable complexity, can determine the thunderclouds direction with reasonable accuracy. The neural system is trained with data obtained from the simulation of thundercloud dynamics using parameters observed through experiments. Through extensive testing, it is found that the presented system can reasonably track the direction of the thunderstorm as it propagates while dynamically changing its parameters, and, thus, offers the possibility of creating a practical system. Two types of neural networks are developed and their efficiencies compared.

Characteristics of the nitrogen ion beam produced in a plasma focus device

The characteristics of the nitrogen ion beam produced in a plasma focus device have been studied experimentally to apply the beam to material processing. In this application, the purity of the ion beam is very important. To clarify the mechanism of the production of impurity ions, two types of anode (rod type: type A, hollow type: type B) were used. In the experiment, a Mather type plasma focus device was used with a capacitor bank of 43.2 /spl mu/F. To produce nitrogen ions, the device was pre-filled with N/sub 2/ at 5.5 Pa. Ion species and their energy spectra were evaluated using a Thomson parabola spectrometer. With type B anode, we have obtained a nitrogen ion beam of 90.5%, whereas with type A anode the purity was 26.5% and copper ion was observed as impurity. Next, the device was prefilled with N/sub 2//H/sub 2/ mixture gas at 20/180 Pa. In this experiment, impurity ions were not produced and highly ionized nitrogen ions were produced.

Development of the hybrid electric field meter for simultaneous measuring of vertical and horizontal electric fields of the thundercloud

This correspondence presents a development of hybrid electric field meter methodology. This particular field meter can simultaneously measure the vertical and horizontal electric fields of the thundercloud. The additional horizontal electric field provides the useful information of the direction of thunderclouds. The capability of the apparatus was experimentally evaluated and has been confirmed that it has the satisfactory sensitivity to both components of electric field. Additionally, an instance of observation results of the cloud-to-ground and ground-to-cloud lightning discharge has been presented.

Generation of an intense pulsed heavy-ion beam by a B y -type, magnetically insulated ion diode with an active ion source

Intense pulsed heavy ion beam (PHIB) of ion current density more than several tens of A/cm2 can be applied to materials processes. To apply PHIB to materials processes purity of the beam is very important. For the purpose a new type of ion beam diode was developed. In the diode a new acceleration gap configuration is used with active ion source of pulsed plasma guns. Two types of plasma guns were developed to generate variety of ion beams, i. e. a gas puff plasma gun and a vacuum arc ion source. With the gas puff plasma gun, source plasma of nitrogen ions was produced. The current density of the plasma was evaluated to be ≈28 A/cm2 at 90 mm downstream from the top of the plasma gun. The plasma was injected into the acceleration gap of the diode and the ion diode was successfully operated at diode voltage ≈200 kV, diode current ≈2.0 kA, pulse duration ~150 ns. Ion beam of ion current density ~13 A/cm2 was obtained at 55 mm downstream from the anode. The energy and species of the beam was evaluated by a Thomson parabola spectrometer and found that N+ and N2+ beam of energy 60-300 keV were accelerated with impurity of protons of energy 60-150 keV. The purity of the beam was estimated to be 87 %. To generate metallic ions vacuum arc plasma gun was developed. The characteristics of the plasma gun were evaluated and source plasma of current density 8 A/cm2, plasma drift velocity 4.7 × 104 m/s was found to be obtained.

Intense pulsed heavy ion beam acceleration using bipolar pulse for implantation to semiconductor

Summary form only given, as follows. Intense pulsed heavy ion beam (HIB) is expected to be applied for pulsed ion implantation to semiconductor since anneal-less process is expected. In the application the purity of the ion beam is very important. However, since the purity of HIB produced in the conventional pulsed power ion diodes are usually very poor and they are not possible to be used in those applications. To improve the purity of the ion beams new type of pulsed power ion accelerator is proposed. The concept of the accelerator is shown in the figure. The accelerator consists of two acceleration gaps (an ion source gap and a post acceleration gap) and a drift tube and a bipolar pulse is used to accelerate the ion beam. In the accelerator purity of the ion beam is expected to be enhanced. As the first step of the development of the accelerator, the characteristics of Br-type magnetically insulated diode was evaluated, which will be used as the 1st gap of the accelerator. An active ion source of carbon plasma gun and a surface flashover ion source were used in the diode. The ion current density, ion species, energy spectrum were evaluated by a Thomson parabola spectrometer, filtered ion pinhole camera, biased ion corrector. In the paper, the result of the experiment is described with the principle and the design concept of the proposed accelerator.

Application of intense pulsed ion beam to materials processes

Intense pulsed ion beams (PIB) are expected to be applied to material processes since they have unique features. To apply the PIB to materials processing two types of beam sources are considered, i.e. plasma focus (PF) and pulsed power ion diode. In the PF experiment Mather type electrode was used with a capacitor bank of 43.2 /spl mu/F. When PF was pre-filled with H/sub 2/ (250 Pa), ion current density (J/sub i/) of 0.65 kA/cm/sub 2/ was obtained at 40 cm downstream from the anode top. From the Thomson parabola spectrometer (TPS) measurement, protons of energy in the range of 0.1-1 MeV were observed. For the case of using mixture of H/sub 2/ (180 Pa) and N/sub 2/ (20 Pa), J/sub i/ was 1.1 kA/cm/sup 2/ and by the TPS protons and variety of nitrogen ions (N/sup (1-5+)/) of energy in the range of 0.4-6 MeV were observed. In the development of pulsed power ion diode, gas puff plasma gun is used as an ion source to produce nitrogen ion beam. In the preliminary experiment Ji of 1 A/cm/sup 2/ was obtained. We are now evaluating the characteristics of the ion diode and the accelerated ion beam. To evaluate the irradiation effect on materials, amorphous silicon films were irradiated by the ion beam produced by PF and we see that amorphous silicon layers are crystallized.

Development of bipolar pulse accelerator for pulsed ion beam implantation to semiconductor

To improve the purity of the ion beams new type of pulsed power ion accelerator named “bipolar pulse accelerator” was proposed. The accelerator consists of two acceleration gaps (an ion source gap and a post acceleration gap) and a drift tube, and a bipolar pulse is applied to the drift tube to accelerate the beam. In the accelerator intended ions are selectively accelerated and the purity of the ion beam is enhanced. As the first step of the development of the accelerator, a Br-type magnetically insulated acceleration gap is developed. The gap has an ion source of coaxial gas puff plasma gun on the grounded anode and a negative pulse is applied to the cathode to accelerate the ion beam. By using the plasma gun, ion source plasma (nitrogen) of current density around 100 A/cm2 is obtained. In the paper, the experimental results of the evaluation of the ion beam and the characteristics of the gap are shown with the principle and the design concept of the proposed accelerator.