Magnetic Field Amplification by a Plasma Cavitation Instability in Relativistic Shock Precursors

Plasma streaming instabilities play an important role in magnetic field amplification and particle acceleration in relativistic shocks and their environments. However, in the far shock precursor region where accelerated particles constitute a highly relativistic and dilute beam, streaming instabilities typically become inefficient and operate at very small scales when compared to the gyroradii of the beam particles. We report on a plasma cavitation instability that is driven by dilute relativistic beams and can increase both the magnetic field strength and coherence scale by orders of magnitude to reach near-equipartition values with the beam energy density. This instability grows after the development of the Weibel instability and is associated with the asymmetric response of background leptons and ions to the beam current. The resulting net inductive electric field drives a strong energy asymmetry between positively and negatively charged beam species. Large-scale particle-in-cell simulations are used to verify analytical predictions for the growth and saturation level of the instability and indicate that it is robust over a wide range of conditions, including those associated with pair-loaded plasmas. These results can have important implications for the magnetization and structure of shocks in gamma-ray bursts, and more generally for magnetic field amplification and asymmetric scattering of relativistic charged particles in plasma astrophysical environments.

Magnetic field amplification driven by the gyro motion of charged particles

Spontaneous magnetic field generation plays important role in laser-plasma interactions. Strong quasi-static magnetic fields affect the thermal conductivity and the plasma dynamics, particularly in the case of ultra intense laser where the magnetic part of Lorentz force becomes as significant as the electric part. Kinetic simulations of giga-gauss magnetic field amplification via a laser irradiated microtube structure reveal the dynamics of charged particle implosions and the mechanism of magnetic field growth. A giga-gauss magnetic field is generated and amplified with the opposite polarity to the seed magnetic field. The spot size of the field is comparable to the laser wavelength, and the lifetime is hundreds of femtoseconds. An analytical model is presented to explain the underlying physics. This study should aid in designing future experiments.

RBIO-06. MECHANISM OF ACTION AND ASSOCIATED EFFECTS OF TUMOR TREATING FIELDS (TTFIELDS) ON LIVING CELLS USING SIMULATIONS

Following FDA approval, TTFields treatment has become a commonly used modality for treating patients with Glioblastoma (GBM) and Mesothelioma. From the early 2000’s, extensive research has been performed in in-vitro systems for studying the effects of TTFields on living cells. These studies have shown that multiple cellular functions are affected by TTFields. However, the physical mechanism by which the fields exert effects on cells are not well understood. We propose an analytical model for predicting the geometric and electrical parameters enabling amplification of the electric field in the living cells. This amplification favors the emergence of local heating, dielectrophoretic (DEP) force, or electrostatic pressure at TTFields frequencies. This model is supported by simulations of cells in different configurations. Computational studies were performed with Comsol Multiphysics software. Cell models were constituted of cytoplasm, membrane and extracellular matrix. A field of 1V/cm was generated at different frequencies between 10kHz and 1GHz. Maximal field amplification of X20 of the applied field (@200 kHz) was observed in a model of confluent cells with 5nm intercellular distance. Such field amplification could create electrostatic pressure on the membrane potentially leading to its deformation and to stress on the cytoskeleton. Analytical calculations show the field gradient could result in DEP forces of ~10pN on the membrane. Such force could potentially disrupt the membrane or junctions. Results show that a 10nm pore in membrane would lead to a 450 times amplification in the pore’s vicinity, potentially resulting in forces of between 0.1pN and 100pN on intracellular structures. Those forces are sufficient for disrupting microtubules. Specific Absorption Rates of up to 106 W/kg were observed in the vicinity of the pore, suggesting that strong thermal effects may also explain the effect of TTFields on cells. Our generic analytical model predicts the conditions for field amplification at TTFields frequencies.

Self-consistent Monte Carlo model of particle acceleration by relativistic shocks

We present a self-consistent Monte Carlo model of particle acceleration by relativistic shock waves. The model includes the magnetic field amplification in the shock upstream by cosmic ray driven plasma instabilities. The parameters of the Monte Carlo model are obtained based on PIC calculations. We present the spectra of accelerated particles simulated in the frame of the model.

Magnetic Field Amplification Driven by the Gyro Motion of Charged Particles

Spontaneous magnetic field generation plays important role in laser-plasma interactions. Strong quasi-static magnetic fields affect the thermal conductivity and the plasma dynamics, particularly in the case of ultra intense laser where the magnetic part of Lorentz force becomes as significant as the electric part. Kinetic simulations of giga-gauss magnetic field amplification via a laser irradiated microtube structure reveal the dynamics of charged particle implosions and the mechanism of magnetic field growth. A giga-gauss magnetic field is generated and amplified with the opposite polarity to the seed magnetic field. The spot size of the field is comparable to the laser wavelength, and the lifetime is hundreds of femtoseconds. An analytical model is presented to explain the underlying physics. This study should aid in designing future experiments.

Low-Power OR Logic Ferroelectric In Situ Transistor Based on a CuInP2S6/MoS2 Van Der Waals Heterojunction

Due to the limitations of thermodynamics, the Boltzmann distribution of electrons hinders the further reduction of the power consumption of field-effect transistors. However, with the emergence of ferroelectric materials, this problem is expected to be solved. Herein, we demonstrate an OR logic ferroelectric in-situ transistor based on a CIPS/MoS2 Van der Waals heterojunction. Utilizing the electric field amplification of ferroelectric materials, the CIPS/MoS2 vdW ferroelectric transistor offers an average subthreshold swing (SS) of 52 mV/dec over three orders of magnitude, and a minimum SS of 40 mV/dec, which breaks the Boltzmann limit at room temperature. The dual-gated ferroelectric in-situ transistor exhibits excellent OR logic operation with a supply voltage of less than 1 V. The results indicate that the CIPS/MoS2 vdW ferroelectric transistor has great potential in ultra-low-power applications due to its in-situ construction, steep-slope subthreshold swing and low supply voltage.