Beyond Maxwell-Boltzmann electrons for RF microscale sheath modeling

Radio frequency (RF) sheaths are of fundamental importance in understanding boundary ICRF interactions in fusion devices. A microscale (Debye scale) RF sheath model, considered here, provides an RF sheath admittance boundary condition for global wave codes, and the sheath potential for sputtering calculations. The commonly employed Maxwell-Boltzmann (MB) electron model can be invalid at high RF frequencies relative to the electron sheath transit time, and the RF-induced jitter motion of bulk electrons in the sheath can cause direct wall impact. In this work a 1D RF sheath microscale model that generalizes the MB model for electrons is presented using a fluid framework, taking into account the electron current lost to the wall from both electron thermal and RF jitter motion. MB electrons are recovered in an appropriate limit. Challenges and progress in numerical implementation will be discussed.