Plasma Afternoon Session

Plasma Afternoon Session

Plasma Session II

Chair: Joseph Lefkowitz (Technion)



Michael Keidar (GWU)
Keynote Speaker

Adaptive Plasmas for Medical Applications

The uniqueness of plasma is in its ability to change composition in situ [1,2,3]. Plasma self-organization could lead to formation of coherent plasma structures. These coherent structures tend to modulate plasma chemistry and composition, including reactive species, the electric field and charged particles. Formation of coherent plasma structures allows the plasma to adapt to external boundary conditions, such as different cells types and their contextual tissues. In this talk we will explore possibilities and opportunities that the adaptive plasma therapeutic system might offer. We shall define such an adaptive system as a plasma device that is able to adjust the plasma composition to obtain optimal desirable outcomes through its interaction with cells and tissues.
We propose various approaches for plasma therapy based on plasma adaptation to target conditions. This approach is based on the ability of measuring the cellular response to plasma immediately after treatment and modifying the composition and power of plasma via a feedback mechanism. Plasma self-adaptation might be feasible due to self-organization and pattern formation when plasma interacts with targets. Plasma effect on cancer cells is influenced by various factors including the plasma jet discharge voltage, gas composition, humidity and cancer cell type [4]. To address this, we present an optimal feedback control scheme to adjust treatment conditions responsive to the actual cancer cell response [5].

[1] M. Keidar, D. Yan, I.I. Beilis, B. Trink and J. Sherman, Trends in Biotech, 36, 6, p. 586, 2017.
[2] L. Lin, Z. Hou, X. Yao, Y. Liu, J. R. Sirigiri, T. Lee, and M. Keidar, Physics of Plasmas, 27, 063501, 2020. [3] D. Yan, W. Hu, L. Lin, X. Yao, J. Sherman and M. Keidar, Scientific Reports, 2018, 8(1) 15418
[4] L. Lin, Y. Lyu, B. Trink, J. Canady, and M. Keidar, J. Applied Physics, 125, 153301, 2019.
[5] Y. Lyu, L. Lin, E. Gjika, T. Lee, M. Keidar, J. Phys. D: Appl. Phys., 2019, 52, 18520



Eduardo Ahedo (UC3M)
Keynote Speaker

Modeling propulsion plasma physics

Plasma-based thrusters have become the dominant technology for in-space propulsion in near-Earth and inner Solar system missions, ranging from internet-services constellations to geostationary satellites and the planned Lunar orbit station Gateway. Different technologies compete fiercely for this in-expansion market and applications.
This talk will comment some of the main aspects framing that competition, such as the level of complexity of the thruster, the propulsion-related figures and operation envelope, and the technology qualification process for space flight.
Second, we will discuss how the technology competitiveness can be improved through thruster design, experimental characterization, understanding and mastering of discharge physics, and development of predictive simulation tools.
Third, and to illustrate the modeling challenges, we will first discuss the main physical phenomena on Hall-effect thrusters, focusing on turbulent transport and non-Maxwellian features electron velocity distribution function (eVDF). We will present recent eVDF results on a 1D kinetic model, and how they lead to anisotropy and gyroviscosity in the pressure tensor, an unconventional parallel heat flux, and reduced wall losses, three aspects precluding a standard macroscopic characterization. 
Finally, the unconventional heat flux will be found to also appear, together with collisionless cooling, in the kinetic description of a magnetically channeled plasma plume.



Dan Lev (Technion)
Contributed Speaker

Heaterless Cathode Technology for Plasma Propulsion Applications

Hollow cathodes are electron generating devices used to supply a stream of electron necessary for the operation of electric propulsion devices, specifically Hall thrusters or gridded ion engines. The electrons provided by the hollow cathode are used to initiate the thruster discharge, sustain thruster operation and neutralize the ion beam ejected out of the thruster to open space.
Heaterless Hollow Cathodes (HHCs) are a subclass of hollow cathodes that do not require external heating to bring the electron emitter to its operation temperature[1]. Instead of using external heating, as with conventional cathodes [2], HHCs are heated via plasma heating. The plasma, which is generated inside the cathode cavity, exerts the required heat fluxes to heat up the electron emitter. When the electron emitter is sufficiently hot, the HHC may function as any other conventional hollow cathode, under steady state conditions.
The ignition process of HHCs can be divided into three phases[1][3]. In the first phase, gas breakdown is initiated inside the cathode cavity, and between two ignition electrodes – the emitter tube and the keeper. The purpose of this stage is to generate plasma to heat up the electron emitter, or alternatively, to create a burst of electrons able to reach the thruster and initiate the main discharge, a.k.a the anode discharge. In the second phase, the plasma discharge is sustained inside the cathode cavity. During this phase the emitter is heated up gradually until it obtains sufficiently high temperature to emit electrons. In the last stage the main anode discharge is initiated, and the cathode transitions to steady state operation.
Since HHCs do not use external heating for ignition they possess several advantages over heater-utilizing cathodes such as higher reliability, lower design complexity, reduced size and mass and energy-efficient operation.
Despite their advantages HHCs have some drawbacks that make their design challenging such as the requirement to start the cathode under high voltages (>300V), adequate thermal design to allow for efficient plasma heating during the first phases of ignition and the need to develop methods for outgassing the electron emitter before the initial use.
In this presentation we review the operation scheme of conventional hollow cathodes for space propulsion with an emphasis on heaterless hollow cathodes. We also present recent progress in the research and development of HHCs. The presentation will focus on the engineering aspects of HHC design and operation, as well as on the proved performance of these cathodes. We start by introducing the common HHC configurations used today. We then present recent findings regarding the plasma breakdown, heating transient and steady state phases of HHC ignition and operation. Subsequently, we address the destruction mechanisms reported in recent studies. Lastly, we identify some of the current challenges to be solved for further progress of HHC technology.

[1]. D. Lev and L. Appel. "Heaterless Hollow Cathode Technology - A Critical Review". The 5th Space Propulsion Conference (SPC), 2-6 May, 2016, Rome, Italy, SP2016_3125366.
[2]. D.M. Goebel and I. Katz, Fundamentals of Electric Propulsion: Ion and Hall Thrusters, John Wiley & Sons, NJ, USA 2008.
[3]. Vekselman, V., et al. “Characterization of a Heaterless Hollow Cathode.” Journal of Propulsion and Power, vol. 29, no. 2, 2013, pp. 475–486., doi:10.2514/1.b34628.



Omri Hamo (Technion)
Contributed Speaker

Optical Emission Spectroscopy Measurements of the Narrow Channel Hall Thruster Plume

A non-intrusive optical emission spectroscopy technique for studying Xenon plasma was used for studying a low power Hall effect thruster, known as the Narrow Channel Hall Thruster (NCHT). The relevant optical setup was assembled and calibrated. A Xenon collisional radiative model, crucial for extracting the plasma properties from the measurements, was implemented. Electron temperature measurements were obtained in the plume region of the NCHT. The preliminary results show similar qualitative behaviour to conventional measurements techniques and simulation results.



Amnon Fruchtman (H.I.T)
Contributed Speaker

Plasma-based mass separation by waves and space-charge fields

Standing or evanescent electromagnetic waves can accelerate charged particles by the ponderomotive force. The direction of acceleration is mass dependent, depending on whether the cyclotron frequency of the particle in the steady magnetic field is larger or smaller than the wave frequency. Schemes for mass separation can be proposed based on the different dynamics of particles of different mass. For a significant yield, the space-charge fields of the plasma have to be considered. A configuration for mass separation for industrial needs is considered, where one particle is resonant and other particles are pushed by space-charge electric fields.



Asher Yahalom (Ariel U.)
Contributed Speaker

A Three Function Variational Principle for Stationary Non-Barotropic Magnetohydrodynamics

Variational principles for magnetohydrodynamics were introduced by previous authors both in Lagrangian and Eulerian form. In this paper we introduce simpler Eulerian variational principles from which all the relevant equations of non-barotropic stationary magnetohydrodynamics can be derived for surface covering field topologies. This is thus a generalization of a similar variational principle for stationary barotropic magnetohydrodynamics which was previously introduced. The variational principle is given in terms of only three independent functions for stationary non-barotropic flows. This is a smaller number of variables than the eight variables which appear in the standard equations of non-barotropic magnetohydrodynamics which are the magnetic field B the velocity field v, the specific entropy s and the density ρ. The three functions are two surfaces χ and η the intersection of which are the magnetic field lines. And an additional function which varies along the magnetic field lines the magnetohydrodynamic metage μ (however, its surfaces are generally not orthogonal to the field lines).  We further investigate the case in which the flow along magnetic lines is not ideal, and we transport phenomena along the temperature gradients.



Amir Weinberg (Ariel U.)
Contributed Speaker

Dogleg design for an MeV Ultra-fast electron Diffraction beamline for the hybrid Photo-emitted RF GUN at Ariel University

A secondary parallel beamline is proposed for the construction of a Mega electron Volt Ultrafast electron Diffraction (Mev UED) facility, based on the novel hybrid 6 MeV RF-GUN in the Schlesinger center for compact accelerators in Ariel University. The Addition of a second beamline requires kicking the beam sideways and back, using a dogleg section. In order to change the trajectory of the beam, while preserving as much as possible the quality of the relativistic electron beam, requires a careful design and simulation process. Start-to-end comprehensive simulations of the dogleg design were performed using GPT (General Particle Tracer) software followed by analysis and optimization for the simulations in order to achieve optimal beam parameters in the second beamline. We present the results of the dogleg design and optimization.



Roundtable Discussion

Moderator: Igal Kronhaus
Panel members: Aduardo Ahedo, Michael Keidar, Amnon Fruchtman, Dav Lev


Space Plasma Propulsion

One of the most successful examples of industrial application of plasma technology is in space propulsion. More than one thousand plasma thrusters are currently in space aboard various spacecraft: from miniature satellites, no larger than a shoebox, to large multi-ton communication satellites, up to manned orbital stations. In this panel we will discuss current and near-future developments in plasma thruster science and technology. The panel will host top scientists in the field of electric propulsion.


Our Sponsors


IVS-IPSTA 2021 - 39th Annual Conference
November 17, 2021 | ONLINE

Conference Organizing Team

Gilbert Daniel Nessim (IVS President, BIU) | Ilya Grinberg (BIU) | Haim Barak (BIU)

Tatyana Bendikov (WIS) | Elad Koren (Technion) | Muhammad Bashouti (BGU) 
Noa Lachman-Senesh (TAU) | Igal Kronhaus (Technion)
Sharon Waichman (NRCN, Rotem Industries)