Marcus Iberler

Experimental characterization of a coaxial plasma accelerator for a colliding plasma experiment

We report experimental results of a single coaxial plasma accelerator in preparation for a colliding plasma experiment. The utilized device consisted of a coaxial pair of electrodes, accelerating the plasma due to J×B forces. A pulse forming network, composed of three capacitors connected in parallel, with a total capacitance of 27 μF was set up. A thyratron allowed to switch the maximum applied voltage of 9 kV. Under these conditions, the pulsed currents reached peak values of about 103 kA. The measurements were performed in a small vacuum chamber with a neutral-gas prefill at gas pressures between 10 Pa and 14 000 Pa. A gas mixture of ArH2 with 2.8% H2 served as the discharge medium. H2 was chosen in order to observe the broadening of the Hβ emission line and thus estimate the electron density. The electron density for a single plasma accelerator reached peak values on the order of 1016 cm−3. Electrical parameters, inter alia inductance and resistance, were determined for the LCR circuit during the plas...

Excimer Emission from Pulsed Tandem Microhollow Cathode Discharges in Xenon

This paper describes an extension of a basic single microhollow cathode discharge (MHCD) to a tandem MHCD, i.e., two discharges in series from an anode–cathode–anode configuration. When a high-voltage pulse is superimposed with a direct current (DC) tandem MHCD, an intense excimer emission along the discharge axis in a high pressure xenon gas is generated which is two orders of magnitude higher than that of the DC tandem MHCD. In addition, the emission intensity increases to almost twice by increasing cathode thickness from 250 to 1000 µm. The emission is further enhanced by increasing the gas pressure from 400 to 800 mbar.

Xenon excimer emission from multicapillary discharges in direct current mode

Microdischarges in xenon have been generated in a pressure range of 400–1013 mbar with a fixed flow rate of 100 sccm. These microdischarges are obtained from three metallic capillary tubes in series for excimer emission. Total discharge voltage is thrice as large as that of a single capillary discharge tube at current levels of up to 12 mA. Total spectral irradiance of vacuum ultraviolet (VUV) emission also increases significantly compared to that of the single capillary discharge. Further, the irradiance of the VUV emission is strongly dependent on pressure as well as the discharge current.

Density enhancement of an RF plasma in a magnetic quadrupole

A new method for the effective confinement of a low pressure gas discharge has been proposed by Christiansen and Jacoby. The principal component is a magnetic quadrupole superimposed upon an RF-driven gas discharge plasma. It has been suggested to use the device as an ion source for accelerator applications and as a plasma target to investigate the interaction of heavy ion beams with a magnetically confined plasma. A complete experiment including a capacitively coupled radio frequency (CCRF) discharge and an electric quadrupole magnet was set up and investigated by applying spectroscopic diagnostic methods. The plasma parameters for the magnetically confined CCRF discharge were measured using a Ar : He gas mixture. The electron temperature and the electron density as a function of the gas pressure and the magnetic field could be determined. A maximum of the mean electron temperature was identified as due to collisionless heating. Further, an ion beam was extracted and the mean electron density derived. The confinement of the plasma at low pressures between 0.4 and 1 Pa has also been obtained with an electron density of 3 × 1017 m−3.

Electron density and plasma dynamics of a colliding plasma experiment

We present experimental results of two head-on colliding plasma sheaths accelerated by pulsed-power-driven coaxial plasma accelerators. The measurements have been performed in a small vacuum chamber with a neutral-gas prefill of ArH2 at gas pressures between 17 Pa and 400 Pa and load voltages between 4 kV and 9 kV. As the plasma sheaths collide, the electron density is significantly increased. The electron density reaches maximum values of ≈8 ⋅ 1015 cm−3 for a single accelerated plasma and a maximum value of ≈2.6 ⋅ 1016 cm−3 for the plasma collision. Overall a raise of the plasma density by a factor of 1.3 to 3.8 has been achieved. A scaling behavior has been derived from the values of the electron density which shows a disproportionately high increase of the electron density of the collisional case for higher applied voltages in comparison to a single accelerated plasma. Sequences of the plasma collision have been taken, using a fast framing camera to study the plasma dynamics. These sequences indicate a maximum collision velocity of 34 km/s.

Excimer emission from pulsed microhollow cathode discharges in xenon

Direct current (dc) microhollow cathode discharge (MHCD) is an intense source for excimer radiation in vacuum ultraviolet at a wavelength of 172 nm in a high pressure xenon (Xe) gas. The concentration of precursors for the excimer formation, i.e., excited and ionized gas atoms, increases significantly by applying high voltage pulse onto the dc MHCD over the pulse duration range from 20 to 100 ns. The intensity of the excimer emission for the voltage pulse of 20 ns duration exceeds that of the emission intensity obtained from the same MHCD operated only in the dc mode, by one order of magnitude. In addition, the emission intensity increases by one order of magnitude over the pulse duration range from 20 to 100 ns. It can be assumed that the emission intensity of the MHCD source increases as long as the duration of the high voltage pulse is shorter than the electron relaxation time. For the high voltage pulse of 100 ns duration, the emission intensity has been found to be further enhanced by a factor of thr...

Review of the State-of-the-Art Development of the Spherical Theta Pinch Plasma Source

After the spherical theta pinch had been developed at the Institute of Applied Physics in Frankfurt, considerable progress in creating high efficiency and long lifetime plasma sources had been made. Several devices have been built to study the characteristics of the spherically confined plasma. Scaling rules and investigated setups are presented, showing devices with electron densities of up to some 1023 m-3, electron temperatures of several eV and confinement times of ~10 μs. Typical dimensions are: discharge vessel radius R = 10 cm, radius of the pinched plasma r = 2 cm, initial gas pressures of 1-200 Pa at currents of up to 35 kA and resonance frequencies of 10-40 kHz. During the harmonic discharge of the stored energy, the plasma periodically pinches and expands again as long as the current rise rate creates sufficient electrical field strengths for ionization, which allows for pinching sequences in the millisecond range. The principles, improvements, theoretical approaches, and applications including pulsed ion source, plasma ion stripping, and vacuum ultraviolet flash lighting are discussed.

Optical and electrical investigations of a high power Lorentz Drift based gas discharge switch

Summary form only given. For switching high current and high voltage there are two completely different physical principles. One method is based on the use of semiconductors but limited in voltage, where as the other is based on a triggered breakdown in gases or in vacuum. Now this contribution gives an introduction in a new kind of a triggered gas discharge switch. This new switch consists of a coaxial electrode geometry. At the initial state the inner electrode acts as high voltage anode whereas the outer coaxial electrode as cathode. Similar to the plasma accelerator the self induced magnetic field will force the discharge to the open end of the coaxial electrode system. The nomenclature is based by its underlying effect to Lorentz drift switch (LDS). The main advantages of the system are the low inductive set up of the coaxial electrode configuration and the loval erosion rate during operation. The Lorentz drift discharge is a low pressure gas discharge which is positioned on the left branch of a breakdown voltage curve, similarly to the Paschen curve. One important feature of a high voltage and high current switch is the reliability for triggering. A surface flashover trigger was mounted outside the coaxial electrode system. With this external trigger system a gas breakdown is initiated and forms a conductive plasma sheath and penetrates through bore holes into the main gap and closes the switch. For first investigations voltage- and current measurements were preformed. For a voltage lower than 2.5 kV current chopping was observed. For time resolved investigation of the cathode spots and propagation of the moving arc a fast shutter camera will be used. Further, the speed of the moving arc was detected by a fast photodiode and was determined to a maximum speed of almost 60 km/s.

Radio frequency quadrupole confined noble gas discharge laser

A typical multiple wavelength noble gas laser, like an argon ion laser, consists of a capacitively coupled high current density glow discharge in the presence of a magnetic field. The output power of a noble gas ion laser is extremely dependent on the current density of the discharge. Typical conditions of such a plasma are current densities (J) between 100 and 1000 A/cm2. The upper laser level population N2 varies as N2~J2. Recently, a new kind of plasma source for a noble ion gas laser was proposed by J. Christiansen and J. Jacoby. With this new configuration, high power radio frequency is inductively coupled via a coil into the plasma. To achieve a high current density the plasma was focused by a quadrupole magnetic field. The main advantages of this system are the electrodeless configuration to avoid impurities, and the high temperature and particle density in the centre of the discharge

Construction, characterization and optimization of a plasma window based on a cascade arc design for FAIR at the GSI Hemholtz Center

Summary form only given. High intensity ion beams are important tools to investigate the interaction of ions with matter. Especially at GSI and for the new FAIR project it is important, to transport the ion beam from the UHV-accelerator into a gas filled target chamber. This is relevant for experiments concerning the generation of matter at high energy density matter. This is true also for gas stripper systems, where the pressure inside the stripper is significantly higher than inside the accelerator.