Electrostatic solitary structures are generated by injection of a suprathermal electron beam parallel to the magnetic field in a laboratory plasma. Electric microprobes with tips smaller than the Debye length (λDe) enabled the measurement of positive potential pulses with half-widths 4 to 25λDe and velocities 1 to 3 times the background electron thermal speed. Nonlinear wave packets of similar velocities and scales are also observed, indicating that the two descend from the same mode which is consistent with the electrostatic whistler mode and result from an instability likely to be driven by field-aligned currents. [4,5]. Electron holes were also recently detected in a laboratory magnetic reconnection experiment [6]. Electron holes can be generated by energetic streaming electrons and are thought to play an important role in scattering these electrons. However, although these small-scale (one to tens of Debye lengths, λ De ) solitary structures seem ubiquitous in key regions of space their exact origin often remains unclear. In the laboratory, experiments dedicated to electron holes were carried out in a strongly magnetized Q-machine [7]. These holes were generated by a voltage pulse and had sizes comparable to the plasma column radius, making comparison with holes observed in space difficult.This Letter reports measurements of electrostatic solitary waves generated by an electron beam injected into a magnetized low-β plasma column much larger than the structure scales (Fig. 1). The experiment was conducted at the upgraded Large Plasma Device (LAPD) [8] at the University of California, Los Angeles. The helium plasma column has a 60 cm diameter, is 17.1 m long and pulsed at 1 Hz with pulses lasting several milliseconds (Fig. 1a) An electron beam 0.4 to 1 cm in diameter is injected from a 3 mm diameter LaB6 crystal source for about 140 µs along the axis of the column in the afterglow phase, between 50 and 150 ms after the end of the discharge pulse. The beam density 5 cm from the source is approximately 25% of the background electron density. The magnetic field strength, plasma density and beam voltage can be changed from experiment to experiment. The range of the main plasma parameters is summarized in

Microelectromechanical systems ͑MEMS͒ have led to the development of a host of tiny machines and sensors over the past decade. Plasma physics is in great need of small detectors for several reasons. First of all, very small detectors do not disturb a plasma, and secondly some detectors can only work because they are very small. We report on the first of a series of small ͑sub-Debye length͒ probes for laboratory plasmas undertaken at the basic Plasma Science Facility at UCLA. The goal of the work is to develop robust and sensitive diagnostic probes that can survive in a plasma. The probes must have electronics packages in close proximity. We report on the construction and testing of probes that measure the electric field.

Abstract-As conventional sensors are scaled down in size for proper usage in high-density laboratory plasmas, they become harder to construct reliably by hand. Devices fabricated utilizing microelectromechanical systems (MEMS) techniques are superior to hand-made devices in terms of size scale, process control, and precision. Microprobes give experimentalists the ability to take direct measurements under controlled conditions. This paper discusses flexible MEMS multiaxis probes that have been developed for use in the Large Plasma Device, a cathode-discharge plasma, at UCLA. The probes are custom built and tailored to fit the unique specifications of individual experiments. Postfabrication assembly also allows for simultaneous sensing in multiple axis. MEMS electric-field probes have been successfully used to detect electron solitary structures in a high-density plasma that are predicted in theory but never seen before except in low-density space plasmas.Index Terms-B-dot microcoil, electric-field (E-field) measurements, microelectromechanical systems (MEMS) devices, plasma diagnostics.

No abstract

No abstract