Thomson scattering on the large plasma device.

We have developed a non-collective Thomson scattering diagnostic for measurements of electron density and temperature on the Large Plasma Device. A triple grating spectrometer with a tunable notch filter is used to discriminate the faint scattering signal from the stray light. In this paper, we describe the diagnostic and its calibration via Raman scattering and present the first measurements performed with the fully commissioned system. Depending on the discharge conditions, the measured densities and temperatures range from 4.0 × 1012 to 2.8 × 1013 cm-3 and from 1.2 to 6.8 eV, respectively. The variation of the measurement error with plasma parameters and discharges averaged is also discussed.

Ferrite based antennae for launching Alfvén waves.

Whistler and Alfvén waves are known to scatter mirror-trapped electrons and protons into the loss cone of the earth's dipole magnetic field. An array of satellites with properly phased antennas can be used to artificially reduce the flux of energetic particles from regions where their flux has been naturally or artificially pumped. In any space based system, the power required to drive antennas is at a premium. We present here experimental evidence that the efficiency of an antenna can be greatly enhanced with the use of ferrite cores with high relative magnetic permeability µ. Ferrite-based antennas were constructed to launch Alfvén waves in a magnetized plasma. The wave magnetic field of shear Alfvén waves launched with a ferrite core was by the magnetization factor µ larger than that of a similar antenna without a ferrite. Combining multiple ferrite antennas allowed control of the injected perpendicular wavelength. This novel technique can be used to efficiently launch low frequency waves with amplitude above the threshold required for nonlinear triggering.

Spiky electric and magnetic field structures in flux rope experiments.

Magnetic flux ropes are structures that are common in the corona of the sun and presumably all stars. They can be thought of as the building blocks of solar structures. They have been observed in Earth's magnetotail and near Mars and Venus. When multiple flux ropes are present magnetic field line reconnection, which converts magnetic energy to other forms, can occur when they collide. The structure of multiple magnetic ropes, the interactions between multiple ropes, and their topological properties such as helicity and writhing have been studied theoretically and in laboratory experiments. Here, we report on spiky potential and magnetic fields associated with the ropes. We show that the potential structures are chaotic for a range of their temporal half-widths and the probability density function (PDF) of their widths resembles the statistical distribution of crumpled paper. The spatial structure of the magnetic spikes is revealed using a correlation counting method. Computer simulation suggests that the potential structures are the nonlinear end result of an instability involving relative drift between ions and electrons.

Experimental Observation of Convective Cell Formation due to a Fast Wave Antenna in the Large Plasma Device.

An experiment in a linear device, the Large Plasma Device, is used to study sheaths caused by an actively powered radio frequency (rf) antenna. The rf antenna used in the experiment consists of a single current strap recessed inside a copper box enclosure without a Faraday screen. A large increase in the plasma potential was observed along magnetic field lines that connect to the antenna limiter. The electric field from the spatial variation of the rectified plasma potential generated E[over →]×B[over →]_{0} flows, often referred to as convective cells. The presence of the flows generated by these potentials is confirmed by Mach probes. The observed convective cell flows are seen to cause the plasma in front of the antenna to flow away and cause a density modification near the antenna edge. These can cause hot spots and damage to the antenna and can result in a decrease in the ion cyclotron range of frequencies antenna coupling.

Erratum: Excitation of Chirping Whistler Waves in a Laboratory Plasma [Phys. Rev. Lett. 114, 245002 (2015)].

This corrects the article DOI: 10.1103/PhysRevLett.114.245002.

A megawatt solid-state modulator for high repetition rate pulse generation.

A novel solid-state modulator capable of generating rapid consecutive power pulses is constructed to facilitate experiments on plasma interaction with high power microwave pulses. The modulator is designed to output a 100 kHz tone burst, which consists of up to 10 pulses, each with 1 µs duration and 1 MW peak power. The pulses are formed by discharging a total of 480 µF capacitors through 24 synchronized MOSFETs and 6 step-up transformers. The highly modular design, as a replacement of an old single-pulse version used in earlier experiments which employs a pulse forming network, brings great flexibility and wide potential to its application. A systematic cost-effectiveness analysis is also presented.

The upgraded Large Plasma Device, a machine for studying frontier basic plasma physics.

In 1991 a manuscript describing an instrument for studying magnetized plasmas was published in this journal. The Large Plasma Device (LAPD) was upgraded in 2001 and has become a national user facility for the study of basic plasma physics. The upgrade as well as diagnostics introduced since then has significantly changed the capabilities of the device. All references to the machine still quote the original RSI paper, which at this time is not appropriate. In this work, the properties of the updated LAPD are presented. The strategy of the machine construction, the available diagnostics, the parameters available for experiments, as well as illustrations of several experiments are presented here.

Excitation of Chirping Whistler Waves in a Laboratory Plasma.

Whistler mode chorus emissions with a characteristic frequency chirp are important magnetospheric waves, responsible for the acceleration of outer radiation belt electrons to relativistic energies and also for the scattering loss of these electrons into the atmosphere. Here, we report on the first laboratory experiment where whistler waves exhibiting fast frequency chirping have been artificially produced using a beam of energetic electrons launched into a cold plasma. Frequency chirps are only observed for a narrow range of plasma and beam parameters, and show a strong dependence on beam density, plasma density, and magnetic field gradient. Broadband whistler waves similar to magnetospheric hiss are also observed, and the parameter ranges for each emission are quantified.

A resistively heated CeB6 emissive probe.

The plasma potential, V(p), is a key quantity in experimental plasma physics. Its spatial gradients directly yield the electrostatic field present. Emissive probes operating under space-charge limited emission conditions float close to V(p) even under time-varying conditions. Throughout their long history in plasma physics, they have mostly been constructed with resistively heated tungsten wire filaments. In high density plasmas (>10(12) cm(-3)), hexaboride emitters are required because tungsten filaments cannot be heated to sufficient emission without component failure. A resistively heated emissive probe with a cerium hexaboride, CeB6, emitter has been developed to work in plasma densities up to 10(13) cm(-3). To show functionality, three spatial profiles of V(p) are compared using the emissive probe, a cold floating probe, and a swept probe inside a plasma containing regions with and without current. The swept probe and emissive probe agree well across the profile while the floating cold probe fails in the current carrying region.

Excitation of shear Alfvén waves by a spiraling ion beam in a large magnetoplasma.

Generation of shear Alfvén waves by the Doppler-shifted ion-cyclotron-resonance (DICR) of a spiraling H(+) ion beam with magnetic fluctuations in a dual-species magnetized plasma with He(+) and H(+) ions has been investigated on the Large Plasma Device. The ambient plasma density and electron temperature were significantly enhanced by the beam. The Alfvén waves were left-handed polarized and traveled in the direction opposite to the ion beam. This is the first experimental demonstration of the DICR excitation of traveling shear Alfvén waves in a laboratory magnetoplasma.

Direct detection of resonant electron pitch angle scattering by whistler waves in a laboratory plasma.

Resonant interactions between energetic electrons and whistler mode waves are an essential ingredient in the space environment, and in particular in controlling the dynamic variability of Earth's natural radiation belts, which is a topic of extreme interest at the moment. Although the theory describing resonant wave-particle interaction has been present for several decades, it has not been hitherto tested in a controlled laboratory setting. In the present Letter we report on the first laboratory experiment to directly detect resonant pitch angle scattering of energetic (∼keV) electrons due to whistler mode waves. We show that the whistler mode wave deflects energetic electrons at precisely the predicted resonant energy, and that varying both the maximum beam energy, and the wave frequency, alters the energetic electron beam very close to the resonant energy.

Hard x-ray tomographic studies of the destruction of an energetic electron ring.

A tomography system was designed and built at the Large Plasma Device to measure the spatial distribution of hard x-ray (100 KeV-3 MeV) emissivity. The x-rays were generated when a hot electron ring was significantly disrupted by a shear Alfvén wave. The plasma is pulsed at 1 Hz (1 shot/s). A lead shielded scintillator detector with an acceptance angle defined by a lead pinhole is mounted on a rotary gimbal and used to detect the x-rays. The system measures one chord per plasma shot using only one detector. A data plane usually consists of several hundred chords. A novel Dot by Dot Reconstruction (DDR) method is introduced to calculate the emissivity profile from the line integrated data. In the experiments, there are often physical obstructions, which make measurements at certain angles impossible. The DDR method works well even in this situation. The method was tested with simulated data, and was found to be more effective than previously published methods for the specific geometry of this experiment. The reconstructed x-ray emissivity from experimental data by this method is shown.

Flow cytometry for the development of biotechnological processes with microalgae.

The current interest in microalgae as a sustainable source of next generation biofuels and other valuable substances is driving exploration of their use as unique biotechnological production systems. To design and optimise appropriate production strategies, the behaviour of particular microalgal species should be well characterised under different culture conditions. Thus, flow cytometric (FCM) methods, which are already well established in environmental and toxicological studies of microalgae, are also useful for analysing the physiological state of microalgae, and have the potential to contribute to the rapid development of feasible bioprocesses. These methods are commonly based on the examination of intrinsic features of individual cells within a population (such as autofluorescence or size). Cells possessing the desired physiological or morphological features, which are detectable with or without fluorescent staining, are counted or isolated (sorted) using an FCM device. The options for implementation of FCM in the development of biotechnological processes detailed in this review are (i) analysing the chemical composition of biomass, (ii) monitoring cellular enzyme activity and cell viability, and (iii) sorting cells to isolate those overproducing the target compound or for the preparation of axenic cultures.

Development of a radio-frequency ion beam source for fast-ion studies on the large plasma device.

A helium ion beam source (23 kV/2.0 A) has been constructed for studying fast-ion physics in the cylindrical magnetized plasma of the large plasma device (LAPD). An inductive RF source produces a 10(19) m(-3) density plasma in a ceramic dome. A multi-aperture, rectangular (8 cm × 8 cm) three-grid system extracts the ion beam from the RF plasma. The ion beam is injected at a variety of pitch angles with Alfvénic speeds in the LAPD. The beam current is intense enough to excite magnetic perturbations in the ambient plasma. Measurements of the ion beam profile were made to achieve an optimum beam performance and a reliable source operation was demonstrated on the LAPD.

A new large area lanthanum hexaboride plasma source.

A new 18x18 cm(2) active area lanthanum hexaboride (LaB(6)) plasma source for use in a dc discharge has been developed at UCLA. The cathode consists of four tiled LaB(6) pieces indirectly heated to electron emission (1750 degrees C) by a graphite heater. A molybdenum mesh anode 33 cm in front of the LaB(6) accelerates the electrons, ionizing a fill gas to create a 20x20 cm(2) nearly square plasma. The source is run in pulsed operation with the anode biased up to +400 V dc with respect to the cathode for up to 100 ms at a 1 Hz repetition rate. Both the cathode and anode "float" electrically with respect to the chamber walls. The source is placed in a toroidal chamber 2 m wide and 3 m tall with a major radius of 5 m. Toroidal and vertical magnetic fields confine the current-free plasma which follows the field in a helix. The plasma starts on the bottom of the machine and spirals around it up to four times (120 m) and can be configured to terminate either on the top wall or on the neutral gas itself. The source typically operates with a discharge current up to 250 A in helium making plasmas with T(e)<30 eV, T(i)<16 eV, and n(e)<3x10(13) cm(-3) in a background field of 100 G

Trachydiscus minutus, a new biotechnological source of eicosapentaenoic acid.

The yellow-green alga Trachydiscus minutus (class Xanthophyta) was cultivated in a standard medium and in media without sulfur and nitrogen. Its yield after a 16-d cultivation reached 13 g dry mass per 1 L medium. The content of oligoenoic ('polyenoic') fatty acid (PUFA), i.e. eicosapentaenoic (EPA), was in excess of 35 % of total fatty acids; the productivity was thus 88 mg/L per d. This result makes the alga a very prospective organism that may serve as a new biotechnological source of single cell oil.

Design, construction, and calibration of a three-axis, high-frequency magnetic probe (B-dot probe) as a diagnostic for exploding plasmas.

A three-axis, 2.5 mm overall diameter differential magnetic probe (also known as B-dot probe) is discussed in detail from its design and construction to its calibration and use as diagnostic of fast transient effects in exploding plasmas. A design and construction method is presented as a means to reduce stray pickup, eliminate electrostatic pickup, reduce physical size, and increase magnetic signals while maintaining a high bandwidth. The probe's frequency response is measured in detail from 10 kHz to 50 MHz using the presented calibration method and compared to theory. The effect of the probe's self-induction as a first order correction in frequency, O(omega), on experimental signals and magnetic field calculations is discussed. The probe's viability as a diagnostic is demonstrated by measuring the magnetic field compression and diamagnetism of a sub-Alfvenic (approximately 500 km/s, M(A) approximately 0.36) flow created from the explosion of a high-density energetic laser plasma through a cooler, low-density, magnetized ambient plasma.

Correlation analysis of waves above a capacitive plasma applicator.

Capacitively coupled plasma glow discharges have been extensively used for materials processing in numerous industrial applications. Considerable research has been performed on plasma sheaths and standing waves over a capacitive applicator, which typically holds the processed substrate (e.g., a semiconductor wafer). In this work, we demonstrate for the first time the existence of normal modes in electric potential analogous to the vibrational modes in circular membranes and plates. These modes are exhibited through cross spectral analysis of the plasma potential measured with an emissive probe at 208 spatial positions and sampled at 1 GHz. These modes exist at several frequencies and are described by a series of Bessel functions. The data further suggests a nonlinear interaction between modes of different frequencies.

The effect of light color on the nucleocytoplasmic and chloroplast cycle of the green chlorococcal alga Scenedesmus obliquus.

The color of light (white, red, blue, and green) had a significant effect on the growth and reproductive processes (both in the nucleocytoplasmic and chloroplast compartment of the cells) in synchronous cultures of Scenedesmus obliquus. This effect decreased in the order red > white > blue > green. In the same order, the light phase of the cell cycle (time when first autospores started to be released) was prolonged. The length of dark phase (time when 100 % of daughters were allowed to release from mothers) was not influenced and was the same for all colors. Critical cell size for cell division in green light was shifted to a smaller size (compared with cells grown in other lights) and so was the size of released daughters. The nuclear cycle was slowed in blue and even in green light, contrary to cells grown in red and white light. At the beginning of the cell cycle, one-nucleus daughters possess approximately 10 nucleoids; during the cell cycle their number doubled in all variants before the division of nuclei. Both events were delayed in cultures grown more slowly most markedly in green light. Smaller daughters in the green variant possessed a lower number of nucleoids. Motile cells released in continuous green or blue lights but not in red one were rarely observed.

Comparative study of zooid and non-zooid forming strains of Scenedesmus obliquus. Physiology and cytomorphology.

Two zooid forming strains and four non-zooid strains of the green chlorococcal alga Scenedesmus obliquus were compared in terms of growth, morphological and physiological characteristics. Large differences were observed among the strains grown under various growth conditions (light and temperature). The assumption that the zooid forming strains may be similar was not confirmed. Since they considerably differed in daughter cells morphology, photosynthesis, growth rate in batch culture or commitment to cellular division. Molecular-genetic comparison of 18S RNA/DNA might distinguish zooid forming strains from non-zooid ones.