Pan Dong

Note: A pulsed laser ion source for linear induction accelerators

We have developed a high-current laser ion source for induction accelerators. A copper target was irradiated by a frequency-quadrupled Nd:YAG laser (266 nm) with relatively low intensities of 10(8) W/cm(2). The laser-produced plasma supplied a large number of Cu(+) ions (∼10(12) ions/pulse) during several microseconds. Emission spectra of the plasma were observed and the calculated electron temperature was about 1 eV. An induction voltage adder extracted high-current ion beams over 0.5 A/cm(2) from a plasma-prefilled gap. The normalized beam emittance measured by a pepper-pot method was smaller than 1 π mm mrad.

Electrical shielding box measurement of the negative hydrogen beam from Penning ion gauge ion source.

The cold-cathode Penning ion gauge (PIG) type ion source has been used for generation of negative hydrogen (H(-)) ions as the internal ion source of a compact cyclotron. A novel method called electrical shielding box dc beam measurement is described in this paper, and the beam intensity was measured under dc extraction inside an electrical shielding box. The results of the trajectory simulation and dc H(-) beam extraction measurement were presented. The effect of gas flow rate, magnetic field strength, arc current, and extraction voltage were also discussed. In conclusion, the dc H(-) beam current of about 4 mA from the PIG ion source with the puller voltage of 40 kV and arc current of 1.31 A was extrapolated from the measurement at low extraction dc voltages.

Note: Self-biased voltage to suppress secondary electrons by a ZnO varistor in a compact pulsed neutron generator

A large amount of back streaming electrons will bring about a part of current drain on power supply, cause sparking or high-voltage breakdowns, and affect the neutron yield and waveform for a compact sealed-tube pulsed neutron generator. A novel idea which uses a ZnO varistor to provide a constant self-biased voltage to suppress the secondary electrons is introduced. The I-V curve for the ZnO varistor was measured in the experiment. The effects of suppressing the secondary electrons were investigated using a ZnO varistor, linear resistors, and an independent power supply, respectively. The results show that the secondary electrons are suppressed effectively by the compact ZnO varistor, while not increasing the size and the component of the device. It is a promising design for compact sealed-tube neutron generators.

Note: Triggering behavior of a vacuum arc plasma source

Axial symmetry of discharge is very important for application of vacuum arc plasma. It is discovered that the triggering method is a significant factor that would influence the symmetry of arc discharge at the final stable stage. Using high-speed multiframe photography, the transition processes from cathode-trigger discharge to cathode-anode discharge were observed. It is shown that the performances of the two triggering methods investigated are quite different. Arc discharge triggered by independent electric source can be stabilized at the center of anode grid, but it is difficult to achieve such good symmetry through resistance triggering. It is also found that the triggering process is highly correlated to the behavior of emitted electrons.

Three-dimension numerical simulation of a large-scale rectangular surface wave plasma source

Summary form only given. Surface wave plasma (SWP) source can generate large-scale, high-density and uniform plasma without the use of electrodes and external magnet field. Due to the complex coupling mechanisms between antenna array, surface wave and plasma in the SWP source, it urgently needs computer numerical simulation to study relevant physical mechanisms as well as to optimize the design of device. In this paper, the propagation of plasma surface wave excited by slot antenna and the spontaneous outspread of plasma under the “push” of surface wave are simulated by using a quasi-steady-state time-stepping plasma fluid model coupled with the Maxwells equations. The temporal evolutions of electron density and temperature in three dimensions are presented. The impacts of different antenna arrays, microwave input power and gas pressure on the spontaneous outspread of plasma are analyzed.

A self-magnetic field penning-like vacuum arc ion source design

Summary form only given. Occluded hydrogen vacuum arc ion source can be used as pulsed proton source. Increase the proton percent is one of the design goal. Improved on traditional two washers source, the new design adopts two cathodes and one anode. The main cathode is titanium hydride washer adjacent anode. The arc occurs between these two electrodes. Downstream of the plasma jet, in the plasma expansion zone, a molybdenum mesh is used as anticathode. A solenoid is set co-axially outside the electrode washers, which could produce several hundred gauss magnetic field. The coil current is supplied by the arc current. This design absorbed the conception of penning gauge. By applying magnetic field and potential well to constrain the electrons, the ionization rate could be increased. The experiment shows proton ratio of the extracted ion current could reach 30% on the condition of 80A discharge current, which is an ordinary value as the conventional source. More works are planned to optimize this design.

Non-thermal plasma excited by compact nanosecond solid-state pulse forming line in atmospheric air

Summary form only given. Non-thermal plasma is a promising technology for the generation of ozone and removal of exhausted fuel gases. Energy efficiencies become more and more important in many industry applications. Discharge excited by nanosecond pulsed power is said to be one of the most efficient method1,2. In this study, a compact 4 stages stacked blumlein pulse forming line based power source will be introduced to generate pulsed plasma. Photoconductive semiconductors witches has been used as the main switch of the compact pulsed source. These switches were driven by laser diodes for its compact size and low jitter3. This compact source could achieve over 50kV with 10ns pulse width and 3ns pulse rising time4. A concentric coaxial cylindrical reactor was employed to generate a pulsed streamer discharge driven by the nanosecond pulsed source in atmospheric air. Some parameters of the streamer such as discharge voltage and current have been taken measured in this study. And some of the plasma parameters will be given by diagnosing the emission spectrum of the plasma. Experiments of high speed photography with the exposure time of 2ns has been used to observe the evolution process, the results will also be mentioned in the report.

Primary experiment on high current hollow cathode ion source

Hollow cathode ion source has many advantages such as long lifetime, high density due to the hollow cathode effect, so it is used widely in spacecraft, accelerator, gas switch and sputter. A high current cathode ion source is studied in our lab. The reaction gas is hydrogen. Its pressure is between 1 Pa and 10 Pa. The current could be changed from 40 A to 120 A and the arc voltage is about 90 V. The typical V-I characteristics are measured under different pressures. The photograph of discharge is taken by a CCD camera. It shows that the discharge is uniformity. And the temporal photographs of discharge are taken by an ICCD camera. They show that at the beginning the discharge focuses on a spot, then grow to a uniformity circle, and finally extinguish. The higher the pressure is, the better the stability and uniformity are. The micrographs of cathode electrode are taken by a microscope, which confirm the discharge is in the cavity of cathode.

Treatment of polytetrafluoroethylene films by atmospheric AR three-dielectric layers barrier discharge plasma

Atmospheric pressure dielectric barrier discharge(DBD) plasma surface treatment is a useful means to modify the properties of polytetrafluoroethylene(PTFE) films, such as hydrophily, adhensive ability. A generator with more dielectric layers will affect the plasma characteristics, and then affects the treatment effects on PTFE films. To investigate this influence, some experiments were carried out with a three-dielectric-layer generator induced by a sub-microsecond pulsed power, whose amplitude is about 120kV, pulse width 230ns, rise time 120ns and frequency 130Hz~1kHz. And The plasma was obtained in atmospheric pressure Argon gas. The Surface properties are investigated by different conditions, including the applied voltage, current and frequency and compared to the results from two-dielectric-layer discharge plasma. The surface water contact angle changed from 118 degree to about 85 degree on more strict conditions. The most important is that the treatment surface area is increased one time. It indicates that this means is effective and potential.

Spectrum diagnoses of laser ion source at IFP

Laser ion source is a key component of induction accelerators for heavy ion fusion, and such a source is under research at institute of fluid physics (IFP). In this paper, optical emission spectroscopy is used to diagnose the Cu plasma irradiated by a quadruplicated frequency Nd: YAG laser (266 nm). The spectra show that there are no highly charged ions. The results show that the electron temperature is about 1 eV and the electron density is 4.4×1016 cm-3. And the temporal spectra are measured, which indicate that the lifetime of excited state particles is over 3 μs. The temporal electron temperature is calculated, which stays the same in the most of the time during plasma expansion.