Modern switches for pulse-power technology have special requirements such as long lifetime, reliability in a wide pressure and voltage range, as well as small delay time. In order to meet these requirements, two trigger methods were developed and examined. These two different trigger methods based on a flashover were tested for the emission behavior by variation of different parameters. The first configuration is a semiconductor surface flashover trigger, where electron emission is based on a surface flashover between the contact area of a copper spring and a carbide cylinder. The second trigger concept is the high-dielectric trigger, where electrons are released by the field emission effect at the transition between metal-vacuum and dielectric. For this system, high dielectric materials with dielectric constants in the order of 2000 are available. The electrical and optical measurements of both trigger systems were done in a modular structured vacuum chamber. For lower pressure, the high-dielectric trigger shows better performances and higher emitted charge of the electron emission within all adjusted parameters like gas pressure, applied voltage, and different wirings. In addition to the higher emitted charge, the emitted electrons from the high-dielectric material have higher energies. For the lifetime characteristic, the high-dielectric trigger shows lifetimes much higher than 100 million discharges.
"The ignition of the discharge during the trigger phase occurs over the long distances of the cathode back space . As a trigger we already used for single LDS a semiconductor surface trigger . After the ignition of the main discharge between the coaxial electrode system and due to the interaction of the induced radial magnetic field with the plasma, the gas discharge will be accelerated to the open end of the coaxial electrode system. "
[Show abstract][Hide abstract] ABSTRACT: The planed Facility for Antiproton and Ion Research (FAIR) is a new international accelerator laboratory at the GSI in Darmstadt, Germany. One research topic at this facility is aimed to protons and anti protons colliding experiments. After generation of these antiprotons strong magnetic fields are necessary to focus the antiprotons. To achieve this high magnetic fields a magnetic horn will be used. To generate for this application the necessary high magnetic field the designed stripline of the pulse forming network (PFN) has to handle a peak current of 400kA with a pulse length of 20μs. Currently the only possibility to handle this high current is the use of mercury filled Ignitrons. The plasma physics working group at the University of Frankfurt develops a mercury free switch, which is able to replace the Ignitrons in the PFN of the magnetic horn. This contribution shall give an overview about the development of a gas discharge switch with minimized local electrode erosion. The experimental setup of the switch consists of coaxial electrodes, similar to the geometry used for plasma focus devices. The main discharge between the coaxial electrode system will be initiated by a trigger predischarge. After the ignition of the main discharge between the coaxial electrode system and due to the interaction of the induced radial magnetic field with the plasma, the gas discharge will be accelerated to the open end of the coaxial electrode system1. This acceleration of the plasma sheet is due to the Lorentz force, which interacts with the discharge. Therefore the switch will be called a Lorentz Drift Switch (LDS). For the special application of the magnetic horn to provide enough charged particles several of these coaxial devices will be stacked together in a parallel.
Plasma Science (ICOPS), 2013 Abstracts IEEE International Conference on; 06/2013
[Show abstract][Hide abstract] ABSTRACT: The study put forth demonstrates that the seed electrons average kinetic energy influences the discharge characteristics making it possible to maximize the rate of development of the virtual anode in a pseudospark, with a suitable choice of the neutral gas pressure as determined by the seed's average injection speed. This investigation also brings to light two distinct operating regimes; (1) mid-energy, where electron-impact ionization energy losses result in a decrease in the cross-section as the electrons travel downstream and (2) high-energy, where, in contrast, the ionization cross-section increases. In the latter case, both the fastest delay time and the neutral gas pressure producing this value have linear dependencies on the seed electrons energy resulting in a constant value of their product over the different injection speeds. The discharge is seeded by injecting a current pulse for a period of one nanosecond along the axis from the hollow cathode cavity back wall over a range of mean speeds corresponding to 100 to 900 V accelerations; the initial electric field is insufficient to enhance ionization throughout most of the hollow cathode backspace. Data is obtained through computer simulation using the two-dimensional kinetic plasma code OOPIC Pro. 51.50.+v, 52.75.Kq, 52.80.Tn.
The Open Plasma Physics Journal 02/2010; 3(1):20-27. DOI:10.2174/1876534301003010020
[Show abstract][Hide abstract] ABSTRACT: Evolution maps of the sputtered copper vapor in the hollow cathode and the main gap areas of two experimental pseudospark switches operating with several buffer gases are obtained with laser-induced fluorescence. The measurements aim to understand the pseudospark breakdown formation and are deliberately made at low charging voltages (1 kV) at which the interval between the trigger pulse and the pseudospark breakdown is characterized with a low current (~10 A) and a long (1-5 mus) randomly variable shot-to-shot duration. Reported are the results for prebreakdown intervals with different lengths. On the other hand, the unfavorable statistical behavior is utilized with the method of the Laue diagrams, which allow phenomenological investigation of the breakdown. In addition, spectrally integrated plasma-emission images taken with an intensified charge-coupled-device camera are represented
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