Discharge initiation by ICRF antenna in IShTAR

IShTAR is a linear magnetized plasma test facility dedicated to the investigation of RF wave/plasma interaction. The IShTAR ICRF system consists of a single strap RF antenna. When using the antenna for plasma production without an external plasma source, it is shown that the plasma is either produced in front of the antenna strap or inside the antenna box depending on the antenna parameters. Here, we present experimental and numerical investigation of the plasma initiation parametric dependencies. Detailed pressure and RF power scans were performed in helium at f = 5.22 MHz and f = 42.06 MHz. The experiment shows the parameter ranges for which the plasma is produced in front of the strap, or inside the antenna box. These ranges are validated by simulations with the RFdinity model, and by theoretical predictions

Advanced ponderomotive description of electron acceleration in ICRF discharge initiation

This contribution proposes a new approach for the ponderomotive description of electron acceleration in ICRF discharge initiation. The motion of electrons in the parallel electric field Ez is separated into a fast oscillation and a slower drift around the oscillation centre. Three terms are maintained in the Taylor expansion of the electric field (0th , 1st and 2nd order). The efficiency for electron acceleration by Ez (z, t) is then assessed by comparing the values of these terms at the slow varying coordinate z0 . When (i) the 0th order term is not significantly larger than 1st order term at the reflection point, or when (ii) the 2nd order term is negative and not sufficiently small compared to the 1st order term at the reflection point, then the electron will gain energy in the reflection. An example for plasma production by the TOMAS ICRF system is given. Following the described conditions it can be derived that plasma production is (i) most efficient close to the antenna straps (few cm's) where the field gradient and amplitude are large, and (ii) that the lower frequency field accelerates electrons more easily for a given antenna voltage

Advanced ponderomotive description of electron acceleration in ICRF discharge initiation

This contribution proposes a new approach for the ponderomotive description of electron acceleration in ICRF discharge initiation. The motion of electrons in the parallel electric field Ez is separated into a fast oscillation and a slower drift around the oscillation centre. Three terms are maintained in the Taylor expansion of the electric field (0th , 1st and 2nd order). The efficiency for electron acceleration by Ez (z, t) is then assessed by comparing the values of these terms at the slow varying coordinate z0 . When (i) the 0th order term is not significantly larger than 1st order term at the reflection point, or when (ii) the 2nd order term is negative and not sufficiently small compared to the 1st order term at the reflection point, then the electron will gain energy in the reflection. An example for plasma production by the TOMAS ICRF system is given. Following the described conditions it can be derived that plasma production is (i) most efficient close to the antenna straps (few cm's) where the field gradient and amplitude are large, and (ii) that the lower frequency field accelerates electrons more easily for a given antenna voltage

Discharge initiation by ICRF antenna in IShTAR

IShTAR is a linear magnetized plasma test facility dedicated to the investigation of RF wave/plasma interaction. The IShTAR ICRF system consists of a single strap RF antenna. When using the antenna for plasma production without an external plasma source, it is shown that the plasma is either produced in front of the antenna strap or inside the antenna box depending on the antenna parameters. Here, we present experimental and numerical investigation of the plasma initiation parametric dependencies. Detailed pressure and RF power scans were performed in helium at f = 5.22 MHz and f = 42.06 MHz. The experiment shows the parameter ranges for which the plasma is produced in front of the strap, or inside the antenna box. These ranges are validated by simulations with the RFdinity model, and by theoretical predictions