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Objective: Pituitary adenomas are common neoplasms and represent between 10 and 20% of all primary brain tumors. Historically, the treatment armamentarium for pituitary adenomas included medical management, microsurgery, and fractionated radiotherapy. More recently, radiosurgery has emerged as the adjuvant treatment of choice. This review is intended to assess the efficacy, safety, and role of radiosurgery...
Operation and characterization of the CubeSat Ambipolar Thruster (CAT), a miniature helicon electric propulsion device, is presented. Its small plasma volume (∼10 cm3) and low power requirements (<100 W) make it ideal for propelling nanosatellites (<10 kg). Permanent magnets generated a magnetic nozzle with a maximum field strength of 600 G. This field decreased to 0.5 G, the strength of earth's...
A mechanism for ambipolar ion acceleration in a magnetic nozzle is proposed. The plasma is adiabatic in the diverging section of a magnetic nozzle so any energy lost by the electrons must be transferred to the ions via the electric field. Fluid theory indicates that the change in average electron energy equals the change in plasma potential. These predictions were compared to measurements in the VX-200...
A new design for a permanent magnet helicon thruster is presented. Its small plasma volume (∼10 cm3) and low power requirements (<100 W) make it ideal for propelling nanosatellites (<10 kg). The magnetic field reached a maximum of 600 G in the throat of a converging-diverging nozzle and decreased to 0.5 G, the strength of earth's magnetic field, within 50 cm allowing the entire exhaust plume...
The potential of a sheath surrounding a planar, electron emitting cathode was measured in the afterglow of a capacitively coupled RF plasma. Using Langmuir and emissive probes, the electron temperature and plasma potential were measured as a function of time. The inflection point in the limit of zero emission, a highly accurate emissive probe technique to measure the plasma potential, was used to...
A new design for a permanent magnet helicon thruster is presented. Its small plasma volume (∼10 cm3) and low power requirements (<100 W) make it ideal for propelling nanosatellites (<10 kg). The magnetic field reached a maximum of 500 G in the throat of a converging-diverging nozzle and decreased to 0.5 G, the strength of earth's magnetic field, within 50 cm allowing the entire exhaust plume...
An observed 50 eV argon ion energy is attributed to a measured axial plasma potential profile within the expanding magnetic nozzle region of a 35 kW helicon plasma source. The ion acceleration mechanism is identified as an ambipolar flow caused by expanding plasma that follows the fluid equations using the adiabatic definition of pressure, resulting in a maximum ion energy of several kTe. The helicon...
Negative plasma potentials with respect to a grounded wall that was coated with a dielectric have been achieved in an electropositive plasma confined by a multidipole device. A Langmuir probe was used to measure the density and temperature of the electrons and an emissive probe was used to measure the plasma potential profile near the plasma boundary. For many discharge parameters, the potential profile...
It has long been known that electron emission from a surface significantly affects the sheath at that surface.1 Typical fluid theory of a planar sheath with emitted electrons assumes that the plasma electrons follow the Boltzmann relation and the emitted electrons are emitted with zero energy and predicts a potential drop of 1.03Te across the sheath at a floating boundary. By removing the assumption...
The plasma-surface interaction in the presence of strong thermionic or secondary electron emission has been studied theoretically and experimentally both as a basic phenomenon and in relation to numerous plasma applications such as, for example, cathodes, emissive probes, divertor plasma, surface discharges, dusty plasmas, plasma thrusters and plasma processing. In a typical low-pressure gas discharge,...
Accurate measurements of the plasma potential is a critical challenge especially for complex plasmas such as magnetized and flowing. We compare various emissive probe techniques for measurements of the plasma potential. The measurements were conducted in a low-pressure magnetized discharge of the Hall thruster. The thruster was operated with xenon gas in subkilowatt power range and the discharge voltage...
Summary Background. Disorders of fluid and sodium regulation, often termed “diabetes insipidus,” are a frequent occurrence following surgery for pituitary adenomas. The present study was undertaken to identify the incidence of diabetes insipidus after pituitary surgery and its associated factors. Methods. A retrospective review of the medical records 300 patients who underwent transsphenoidal surgery...
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