Characterization of inductively coupled plasma generated by a quadruple antenna

Abstract

The results of the characterization of large-scale RF plasma for studying nonlinear interaction with a high-power (∼400 MW) short duration (∼0.8 ns) microwave (∼10 GHz) beam are presented. The plasma was generated inside a Pyrex tube 80 cm in length and 25 cm in diameter filled by either Ar or He gas at a pressure in the range 1.3-13 Pa using a 2 MHz RF generator with a matching system and a quadruple antenna. Good matching was obtained between the plasma parameters, which were determined using different methods including a movable Langmuir probe, microwave cut-off, interferometry, and optical emission spectroscopy. It was shown that, depending on the gas pressure and RF power delivered to the antenna, the plasma density and electron temperature can be controlled in the range 1×10 10 -5×10 12 cm −3 and 1-3.5 eV, respectively. The plasma density was found to be uniform in terms of axial (∼60 cm) and radial (∼10 cm) dimensions. Further, it was also shown that the application of the quadruple antenna, with resonating capacitors inserted in its arms, decreases the capacitive coupling of the antenna and the plasma as well as the RF power loss along the antenna. These features make this plasma source suitable for microwave plasma wake field experiments.

Experiments Designed to Study the Non-Linear Transition of High-Power Microwaves through Plasmas and Gases

“…This reflects the good axial alignment of the system axis and the magnetic field axis. The operation of the two SR-BWO systems was tested by MAGIC-PIC [40] simulations and the resulting HPM pulse shape and power were close to that obtained experimentally [40,41]. The X-SR-BWO produces ~500 MW whereas the Ka-SR-BWO, ~1.2 GW peak power in a ~0.4 ns long pulse.…”

“…A set of diagnostic tools, receiving antennas to measure microwave transmission, a fast frame camera to visualize the plasma in time and space, a spectrometer to study the plasma parameters and scintillators attached to photomultipliers to measure electron energies, are placed around this experimental chamber as seen in Figure 1. A matrix of Neon lamps placed on plane perpendicular to the microwave beam axis inside or outside the chamber, is also used to produce a The operation of the two SR-BWO systems was tested by MAGIC-PIC [40] simulations and the resulting HPM pulse shape and power were close to that obtained experimentally [40,41]. The X-SR-BWO produces~500 MW whereas the Ka-SR-BWO,~1.2 GW peak power in a~0.4 ns long pulse.…”

“…The TM 01 mode electromagnetic wave produced by the X-SR-BWO is transmitted through a mode-converter which transforms it to TE 11 , followed by an appropriate antenna which radiates the power towards a hyperbolic dielectric lens (34 cm diameter) which focuses the power~8 cm from its tip inside a Pyrex tube (see Figure 1). This tube may be filled with gas to controllable pressures, with RF plasma produced by a set of quadrupole antennas placed near its walls [41], or pumped to near vacuum. A set of diagnostic tools, receiving antennas to measure microwave transmission, a fast frame camera to visualize the plasma in time and space, a spectrometer to study the plasma parameters and scintillators attached to photomultipliers to measure electron energies, are placed around this experimental chamber as seen in Figure 1.…”

Self-channeling of a powerful microwave beam in a preliminarily formed plasma

“…A preliminary plasma was generated inside the Pyrex tube by a 2 MHz inductively coupled $300 ms long rf discharge, induced by a quadruple antenna in either He or Ar within a range of 5-130 Pa gas pressure. The parameters of the rf plasma were studied earlier 15 without the presence of the Ultem lens inside the Pyrex tube. In the present work, we used microwave interferometry and visible spectroscopy to determine the plasma parameters along a line extending from the tip of the lens and averaged along 240 mm in the radial direction.…”

“…In the absence of the Ultem lens, the axial and radial distributions of the plasma density was found to be close to uniform. 15 The lens can change these distributions at the distances comparable with the lens radius because of the change of rf field configuration and absorption/desorption processes at the lens surface. With the lens, the radially averaged density measured by microwave interferometry, increases gradually along the axis, as it is shown in Fig.…”