Langmuir Probe Measurements in the Gaseous Electronics Conference RF Reference Cell

Numerical profile correction of microwave cavity resonance spectroscopy measurements of the electron density in low-pressure discharges

Low-temperature plasmas are widely studied in laboratory environments and form the backbone of many industrial processes. Highly energized electrons enable processes such as ionization, dissociation, and plasma chemical reactions, while the heavy species, such as neutral gas atoms and molecules, remain near room temperature. Hence, understanding the electron dynamics is crucial to the control and optimization of plasmas and their applications. In this contribution, we investigated the impact of electron density profile correction on microwave cavity resonance spectroscopy (MCRS) as a diagnostic tool for low-pressure discharges. Following standard practice, we first obtained a volume-averaged electron density by assuming a uniform plasma in the interpretation of the MCRS diagnostic technique. Second, we compare the experiments with a numerical model solved using PLASIMO software to evaluate the predictive capabilities. Third, we obtained profile-corrected electron densities by means of incorporating the numerically obtained distribution of the electron density and the numerical solution for the resonant microwave electric field in the interpretation of the experimental data using MCRS. Although the volume-averaged data agree closely with the electron density found from the numerical model, it is shown that implementing the spatial distribution of the electron density and the microwave electric field leads to a significant correction to the experimental data. The developed strategy could easily be implemented in other situations deploying MCRS as a non-invasive technique for measuring the electron density.

Plasma cell adaptation to enhance particle acceleration

A plasma study is performed in order to construct a cell for plasma acceleration purpose. As well, a multicell design is introduced for the injection of beam driver application. The suggested idea is experimentally demonstrated for two plasma cell configuration. The preformed plasma is obtained by a symmetrically driven capacitive audio frequency discharge. It is featured by its moderate pressure of 0.1-0.2 Torr, low consumption power of 130 W maximum, low discharge voltage and frequency up to 950 V and 20 kHz, respectively, and high plasma density from 10(11) to 10(15) cm(-3). The electron temperature obtained by Langmuir double probe varies from 1 up to 16 eV. It is observed that the increases of the discharge voltage and frequency enlarge the plasma parameters to their maximum values. The plasma cell filled with different gases demonstrates that the Ar and He gases manifest the highest ionization efficiency exceeding 100% at 950 V and 20 kHz. The formed plasma is cold; its density is uniform and stable along the positive column for long competitive lifetime. Showing that it follows the conditions to enhance particle acceleration and in conjunction with its periphery devices form a plasma cell that could be extended to serve this purpose. Demonstrating that an injected electron beam into the extended preformed plasma could follow, to long distance, a continuous trajectory of uniform density. Such plasma generated by H(2) or Ar gases is suggested to be used, respectively, for low-density or higher density beam driver.

Retarding field analyzer for ion energy distribution measurements at a radio-frequency biased electrode

A retarding field energy analyzer designed to measure ion energy distributions impacting a radio-frequency biased electrode in a plasma discharge is examined. The analyzer is compact so that the need for differential pumping is avoided. The analyzer is designed to sit on the electrode surface, in place of the substrate, and the signal cables are fed out through the reactor side port. This prevents the need for modifications to the rf electrode--as is normally the case for analyzers built into such electrodes. The capabilities of the analyzer are demonstrated through experiments with various electrode bias conditions in an inductively coupled plasma reactor. The electrode is initially grounded and the measured distributions are validated with the Langmuir probe measurements of the plasma potential. Ion energy distributions are then given for various rf bias voltage levels, discharge pressures, rf bias frequencies--500 kHz to 30 MHz, and rf bias waveforms--sinusoidal, square, and dual frequency.