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Gekelman, W

Publications and source records attributed to Gekelman, W.

24 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

Structure of an Exploding Laser-Produced Plasma

We describe the first-ever volumetric, time-resolved measurements performed with a moving probe within an expanding dense plasma, embedded in a background magnetized plasma. High-resolution probe measurements of the magnetic field and floating potential in multiple 2D cut planes combined with a 1 Hz laser system reveal complex three-dimensional current systems within the expanding plasma. Static ({omega}{sub real}=0) flutelike density striations are observed at the leading edge of the plasma, which are correlated to variations in the current layer at the edge of the expanding plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Laboratory Measurements of Electrostatic Solitary Structures Generated by Beam Injection

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 ({lambda}{sub De}) enabled the measurement of positive potential pulses with half-widths 4 to 25{lambda}{sub De} 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.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

A new large area lanthanum hexaboride plasma source

A new 18x18 cm{sup 2} active area lanthanum hexaboride (LaB{sub 6}) plasma source for use in a dc discharge has been developed at UCLA. The cathode consists of four tiled LaB{sub 6} pieces indirectly heated to electron emission (1750 deg. C) by a graphite heater. A molybdenum mesh anode 33 cm in front of the LaB{sub 6} accelerates the electrons, ionizing a fill gas to create a 20x20 cm{sup 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{sub e}<30 eV, T{sub i}<16 eV, and n{sub e}<3x10{sup 13} cm{sup -3} in a background field of 100 G<B{sub o}<320 G, giving a magnetized plasma with 0.1<{beta}<1.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Phase-Resolved Measurements of Ion Velocity in a Radio-Frequency Sheath

The time-dependent argon-ion velocity distribution function above and within the plasma sheath of an rf-biased substrate has been measured using laser-induced fluorescence in a commercial plasma processing tool. Discharge parameters were such that the 2.2 MHz rf-bias period was on the order of the ion transit time through the sheath ({tau}{sub ion}/{tau}{sub rf}=0.3). This work embodies the first time-resolved measurement of ion velocity distribution functions within an rf-biased sheath over a large area (30 cm diameter) silicon wafer substrate.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Laboratory Simulation of Arched Magnetic Flux Rope Eruptions in the Solar Atmosphere

Dramatic eruption of an arched magnetic flux rope in a large ambient plasma has been studied in a laboratory experiment that simulates coronal loops. The eruption is initiated by laser generated plasma flows from the footpoints of the rope that significantly modify the magnetic-field topology and link the magnetic-field lines of the rope with the ambient plasma. Following this event, the flux rope erupts by releasing its plasma into the background. The resulting impulse excites intense magnetosonic waves that transfer energy to the ambient plasma and subsequently decay.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗