Action of Runaway Electron Preionized Diffuse Discharges on Steel： Composition, Structure, and Properties

In the work, we studied the effect of the plasma of a runaway electron preionized （REP） diffuse discharge （DD） on the composition, structure, and properties of ST3PS steel surface layers. Voltage pulses with an incident wave amplitude of up to 30 kV, FWHM of around 4 ns, and rise time of around 2.5 ns were applied to the gap in an inhomogeneous electric field. The ST3PS steel specimens exposed to this type of discharge revealed changes in their defect subsystem, suggesting that the runaway electron preionized diffuse discharge provides surface hardening of the steel.

Atmospheric Pressure Cold Argon/Oxygen Plasma Jet Assisted by Preionization of Syringe Needle Electrode

An atmospheric pressure nonequilibrium argon/oxygen plasma jet assisted by the preionization of syringe needle electrode discharge is reported. With the syringe needle plasma as its pre-ionization source, the hybrid barrier-jet was shown to generate uniform discharge with a lower breakdown voltage and a relatively low gas temperature varying from 390 K to 440 K, even when the vol.% oxygen in argon was up to 6%. Utilizing the actinometry method, the concentration of atomic oxygen was estimated to be about in an orders of magnitude of 10^17 cm^-3. The argon/oxygen plasma jet was then employed to clean out heat transfer oil, with a maximum cleaning rate of 0.1 mm/s achieved.

Microwave preionization and electron cyclotron resonance plasma current startup in the EXL-50 spherical tokamak

Preionization has been widely employed to create initial plasma and help the toroidal plasma current formation.This research focuses on implementing a simple,economical and practical electron cyclotron resonance(ECR)preionization technique on the newly constructed EXL-50 spherical tokamak,and evaluating the effectiveness on improving the plasma current startup.Two types ECR microwave preionization experiments for the plasma initialization without the central solenoid are reported:(1)2.45 GHz microwave preionization and current startup with2.45 GHz ECR source;(2)2.45 GHz microwave preionization and current startup with 28 GHz ECR source.Application of the 2.45 GHz ECR microwave preionization to the experiments has contributed to(1)getting rid of the plasma breakdown delay;(2)the significant improvement of the discharge quality:the discharge is much longer and more stable while the driven plasma current is larger,compared to the discharge without preionization.

Preliminary Experiment of Non-Inductive Plasma Current Startup in SUNIST Spherical Tokamak

The non-inductive plasma current startup is an important motivation in SUNIST spherical tokamak. In the recent experiment, the magnetron microwave system of 100 kW and 2.45 GHz has been used to the ECR plasma current startup. Besides the toroidal field, a vertical field was applied to generate preliminary toroidal plasma current without the action of the central solenoid. As the evidence of plasma current startup with the effect of vertical field drift, the direction of plasma current is changed when the direction of vertical field changes during the ECR plasma current startup discharge. We also observed a maximum plasma current by scanning vertical field in both directions. Additionally, we used electrode discharge to assist the ECR plasma current startup.

Improvement of the Uniformity of Surface Barrier Discharge in Atmospheric Nitrogen by Spark Discharge

A spark generator was employed to assist surface barrier discharge （SBD） in nitrogen at atmospheric pressure. The influence of spark discharge on the SBD electrical behavior is investigated by means of volt-ampere characteristics. Also, the electron density of plasma in the filament of each SBD arrangement is determined by plasma radiation method. It is found that the filaments in spark-assistant SBD are much stronger, while the corresponding mean electron density is much lower. Results show that the spark generator can improve the uniformity of SBD in atmospheric nitrogen in a particular range of applied frequency.