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All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Energetic solar electrons in the interplanetary medium

Results are given of ISEE-3 measurements of energetic solar electrons extending down to 2 keV energy. Such measurements have provided a new perspective on energetic solar electrons in the interplanetary medium. Impulsive solar electron events are observed, on the average, several times a day near solar maximum, with about 40 percent detected only below about 15 keV. The electron energy spectra have a nearly power-law shape extending smoothly down to 2 keV, indicating that the origin of these events is high in the corona. In large solar flares which accelerate electrons and ions to relativistic energies, the electron spectrum appears to be modified by a second acceleration which results in a double power-law shape above about 10 keV with a break near 100 keV and flattening from about 10-100 keV. Solar type-III radio bursts are produced by the escaping 2-100 keV electrons through a beam-plasma instability.

Lin, R. P.↗
NASA NTRS1988

An analysis of whistler mode radiation from the Spacelab 2 electron beam

During the Spacelab 2 mission the plasma diagnostics package (PDP) was released from the Shuttle to free fly. At times during this free flight, when the PDP was magnetically connected to the Shuttle, Stanford's fast-pulsed electron generator, located in the Shuttle cargo bay, ejected a 1-keV 50-mA electron beam. The PDP plasma-wave instrument detected intense whistler-mode radiation during these beam ejections. This paper presents a study of a whistler mode emission detected during one particular continuous electron beam firing. Calculations indicate that the beam radiated approximately 1.6 mW in the whistler mode as the beam traversed the 200 m from the Shuttle to the PDP. The emissivity also decreased by about a factor of 10 over this same distance. The measured wave powers are 10 to the 7th greater than wave powers expected from incoherent Cerenkov radiation, verifying that the radiation is generated by a coherent process. Estimates of the emissivity based on measured electric field intensities in the beam indicate that the whistler-mode noise is produced by radiation from electron bunches created by an electrostatic beam-plasma instability.

Farrell, W. M.↗
NASA NTRS1989

Correlated plasma wave, magnetic field, and energetic ion observations in the ion pickup region of Comet Giacobini-Zinner

Relationships between simultaneous plasma wave, magnetic field, and energetic heavy ion data obtained by the International Cometary Explorer (ICE) spacecraft in the large-scale solar wind particle pickup region surrounding Comet Giacobini-Zinner are examined. In particular, consideration is given to the conditions under which electrostatic emissions at frequencies of a few kilohertz and electromagnetic waves at a few tens of hertz are observed. It is shown that the data are consistent with the view that the kilohertz electrostatic emissions result from a beam-type instability excited by the pickup photoelectron population when the angle alpha between the magnetic field and the plasma velocity vectors is not too large. The data also suggest that the few tens of hertz electromagnetic waves may be excited by a ring-type instability associated with the pickup ion population, which occurs when the magnetic field is near to orthogonality with the flow.

Richardson, I. G.↗
NASA NTRS1992

Electron acceleration by Alfven waves in the magnetosphere

The self-consistent electron kinetics of Alfven waves on the electron inertial scale is studied using a 2D hybrid-kinetic description. The ions follow a fluid description for Alfven waves at frequencies below the ion cyclotron frequency. The parallel electron dynamics is treated kinetically using particle-in-cell techniques. In this model, the electron plasma mode is eliminated, and only the physics of the Alfven waves is retained. At sufficiently large amplitudes, it is found that oblique Alfven waves break due to finite electron inertia in a cold plasma. The consequence of wave breaking is the formation of an electron beam which can be unstable to the beam-plasma instability. The electrons supporting the parallel current thermalize into a non-Maxwellian distribution with an energetic tail up to several keV, assuming a reasonable magnetospheric Alfven speed. In hot plasma simulations, electron trapping is the principal mechanism of electron acceleration. It is proposed that wave breaking or electron trapping of oblique Alfven waves at 1 R(E) can result in electron acceleration and may explain some observed auroral phenomena.

Hui, C.-H.↗
NASA NTRS1992

Prompt ionization in the CRIT II barium releases

Observations of electron and ion distributions inside a fast neutral barium jet in the ionosphere show significant fluxes within 4 km of release, presumably related to beam plasma instability processes involved in the Critical Ionization Velocity (CIV) effect. Electron fluxes exceeding 5 x 10 exp 12/sq cm-str-sec-keV were responsible for ionizing both the streaming barium and ambient oxygen. Resulting ion fluxes seem to be consistent with 1-2 percent ionization of the fast barium, as reported by optical observations, although the extended spatial distribution of the optically observed ions is difficult to reconcile with the in situ observations. When the perpendicular velocity of the neutrals falls below critical values, these processes shut off. Although these observations resemble the earlier Porcupine experimental results (Haerendel, 1982), theoretical understanding of the differences between these data and that of earlier negative experiments is still lacking.

Torbert, R. B.↗
NASA NTRS1993

A new investigation of microbursts at meter-decameter wavelengths

The results of a new investigation of microbursts at meter-decameter wavelengths are reported. Several properties of microbursts reported earlier are confirmed, and some new properties, such as time profile characteristics, flux density, and energy spectra are studied in order to compare the properties of microbursts with those of normal type III bursts. Electron beams of similar characteristics are found to generate both microbursts and type III bursts. Plasma waves generated by the electron beams due to beam-plasma instability are quickly isotropized as they scatter on the density fluctuations in the corona, leading to the low brightness temperature of microbursts. The resulting low levels of plasma waves produce transverse radiation of low brightness temperature. As a result of the isotropization, the second harmonic plasma emission dominates the fundamental, so that microbursts are expected to be primarily a harmonic plasma emission.

Subramanian, K. R.↗
NASA NTRS1994

Studies on equatorial shock formation during plasmaspheric refilling

Investigations based on small-scale simulations of microprocesses occurring when a magnetic flux tube refills with a cold plasma are summarized. Results of these investigations are reported in the following attached papers: (1) 'Numerical Simulation of Filling a Magnetic Flux Tube with a Cold Plasma: The Role of Ion Beam-Driven Instabilities'; and (2) 'Numerical Simulation of Filling a Magnetic Flux Tube with a Cold Plasma: Effects of Magnetically Trapped Hot Plasma'. Other papers included are: 'Interaction of Field-Aligned Cold Plasma Flows with an Equatorially-Trapped Hot Plasma: Electrostatic Shock Formation'; and 'Comparison of Hydrodynamic and Semikinetic Treatments for a Plasma Flow along Closed Field Lines'. A proposal for further research is included.

Singh, N.↗
NASA NTRS1993

Electron generation of electrostatic waves in the plasma sheet boundary layer

Broadband electrostatic noise (BEN) has been shown to occur in conjunction with ion beams; extensive investigations of possible ion beam-related instabilities that could generate the observed wave spectra have been conducted. It has also been demonstrated that unstable electron distribution functions are sometimes measured in the plasma sheet boundary layer. We present simultaneous observations of ion and electron distribution functions and electric field wave spectra measured by ISEE 1 and ISEE 2 in the Earth's magnetotail. As the spacecraft moved from the tail lobe toward the plasma sheet, the fast indication of boundary layer plasma was seen in the electron distributions, followed some minutes later by the detection of boundary layer ions. The onset of large-amplitude electrostatic waves at frequencies up to the electron plasma frequency was coincident with the onset of the boundary layer electrons, suggesting that broadband electrostatic waves may often be generated by unstable electron distributions in the plasma sheet boundary layer, particularly the higher frequency portion of the wave spectrum. The observed changes in the electron distribution functions indicate that the plasma was not heated locally by the waves.

Onsager, T. G.↗
DOE OSTI2023

Recent Beam Stability Analysis for the EIC

This document summarizes work done in WBS 6.02.02 during FY23. Additional details can be found in the EIC overview paper presented at IPAC’23 [1], and the references therein. Progress has been made in the ESR and HSR lattice design, dynamic aperture optimization, and the RCS lattice design. The impedance and Collective effects are progressing and include the impedance optimization process of the vacuum systems for RCS, HSR, and ESR; collective effects studies; collective effects and beam-beam interaction; coupled bunch instabilities and the crab cavities; low-level RF feedback system design and beam-ion instability. The reversed phasing RF system has been numerically studied for the ESR to mitigate Robinson instability and demonstrate reliable stable beam operation. Various codes, including C++, SPACE [2], ELEGANT [3], and Mbtrack2 [4] have been employed to benchmark the results. The simulation of HSR bunch splitting with beam loading has been performed at 275 GeV energy. The evaluation of Beam Position Monitors aimed to validate their expected performance, with the primary objective being to verify their accuracy. Calculations of Electron Polarization in the ESR, RCS, and HSR are showing good progress. In the RCS, preliminary studies indicate excellent polarization transmission over intrinsic spin resonances, achieving over 90% transmission with improved performance compared to the previous lattice. Preliminary simulations in the ESR indicate encouraging results in minimizing depolarization and improving equilibrium polarization.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Stopping-power enhancement from discrete particle-wake correlations in high-energy-density plasmas

Three-dimensional (3D) simulations of electron beams propagating in high-energy-density plasmas using the quasistatic Particle-in-Cell (PIC) code QuickPIC demonstrate a significant increase in stopping power when beam electrons mutually interact via their wakes. Each beam electron excites a plasma wave wake of wavelength ~ 2 π c / ω p e , where c is the speed of light and ω p e is the background plasma frequency. Here we show that a discrete collection of electrons undergoes a beam-plasma-like instability caused by mutual particle-wake interactions that causes electrons to bunch in the beam, even for beam densities n b for which fluid theory breaks down. This bunching enhances the beam's stopping power, which we call “correlated stopping,” and the effect increases with the “correlation number” N b ≡ n b ( c / ω p e ) 3 . For example, a beam of monoenergetic 9.7 MeV electrons with N b = 1 / 8 , in a cold background plasma with n e = 10 26 cm – 3 (450 g cm – 3 DT), has a stopping power of 2.28 ± 0.04 times the single-electron value, which increases to 1220 ± 5 for N b = 64 . The beam also experiences transverse filamentation, which eventually limits the stopping enhancement.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Brief Overview of the ASD Integrated Test Stand, Activities and Hazards

The ITS venue provides the first opportunity to fully assemble and test the performance of the injector; integrate, assemble and test four modules; measure the severity of the Beam Break-Up instability and perform the first set of beam measurements. Figure 1 shows a high level configuration of the ITS without the system of overhead cable management trays. The final configuration will integrate the injector, 4 modules (12 accelerator cells), 264 SSPP Line Replaceable Units (LRUs), global controls, data acquisition, and a subset of the downstream transport, Table 1. This was chosen because it provides the minimum accelerator cells required to measure the Beam Break-Up (BBU) instability and perform measurements required to validate the ASD beam transport computer models, which are priority measurements for commissioning.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

First experimental report of nonlinear collimator in the SuperKEKB

SuperKEKB collimator system protects the superconducting final focusing magnets (QC1 and QC2) from quenching caused by beam halo particles. For effective shielding, the minimum aperture of vertical collimators is set smaller than the physical aperture of QC1. However, such collimators become dominant sources of beam coupling impedance, which can limit the maximum beam current due to impedance-driven instabilities. To address this issue, a nonlinear collimator (NLC) was introduced in February 2024. NLC is designed to reduce both beam backgrounds and collimator impedance, thereby suppressing beam instabilities caused by short-range wakefields. In this paper, we describe the results on impedance effects, beam background reduction, and beam lifetime when the nonlinear collimation system is turned on and off. These results validate the NLC concept and offer a promising approach for future high-luminosity colliders.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1990

Time-Resolved Measurements Of Laser Far-Field Patterns

Computer-controlled scanning photometric instrumentation system measures intensity pattern in far field of pulsed laser as function of time during each pulse (provided that pulse is at least 1 ns long). Such measurements important in studying dynamics of laser operation: they reveal such previously unobservable phenomena as oscillations of undesired spatial modes of radiation pattern during pulse, steering of beam during pulse, and instability of intensity of laser beam. Principal advantages of system are its relatively low cost and its ability to function under normal lighting conditions without incurring damage.

Forrest, Kathrine↗
NASA NTRS1995

Electromagnetic Components of Auroral Hiss and Lower Hybrid Waves in the Polar Magnetosphere

DE-1 has frequently observed waves in the whistler and lower hybrid frequencies range. Besides the electrostatic components, these waves also exhibit electromagnetic components. It is generally believed that these waves are excited by the electron acoustic instability and the electron-beam-driven lower hybrid instability. Because the electron acoustic and the lower hybrid waves are predominately electrostatic waves, they cannot account for the observed electromagnetic components. In this work, it is suggested that these electromagnetic components can be explained by waves that are generated near the resonance cone and that propagate away from the source. The role that these electromagnetic waves can play in particle acceleration processes at low altitude is discussed.

Wong, H. K.↗
NASA NTRS1995

Linear and nonlinear properties of the ULF waves driven by ring-beam distribution functions

The problem of the exitation of obliquely propagating magnetosonic waves which can steepen up (also known as shocklets) is considered. Shocklets have been observed upstream of the Earth's bow shock and at comets Giacobini-Zinner and Grigg-Skjellerup. Linear theory as well as two-dimensional (2-D) hybrid (fluid electrons, particle ions) simulations are used to determine the properties of waves generated by ring-beam velocity distributions in great detail. The effects of both proton and oxygen ring-beams are considered. The study of instabilities excited by a proton ring-beam is relevant to the region upstream of the Earth's bow shock, whereas the oxygen ring-beam corresponds to cometary ions picked up by the solar wind. Linear theory has shown that for a ring-beam, four instabilities are found, one on the nonresonant mode, one on the Alfven mode, and two along the magnetosonic/whistler branch. The relative growth rate of these instabilities is a sensitive function of parameters. Although one of the magnetosonic instabilities has maximum growth along the magnetic field, the other has maximum growth in oblique directions. We have studied the competition of these instabilities in the nonlinear regime using 2-D simulations. As in the linear limit, the nonlinear results are a function of beam density and distribution function. By performing the simulations as both initial value and driven systems, we have found that the outcome of the simulations can vary, suggesting that the latter type simulations is needed to address the observations. A general conclusion of the simulation results is that field-aligned beams do not result in the formation of shocklets, whereas ring-beam distributions can.

Killen, K.↗
NASA NTRS1985

Instabilities excited by an energetic ion beam and electron temperature anisotropy in tandem mirrors

Tandem mirrors are magnetic confinement devices, which have the objective to prevent a leaking out of ions in a central (solenoidal) cell at the end. This is accomplished by making use of an electrostatic potential, which is maintained by a denser plasma in mirror end cells. In the Tandem Mirror Experiment (TMX), Correll et al. (1982) have successfully verified the basic concepts involved in the design of the considered device. However, it was also found that the simple tandem mirror could not be easily scaled to a reactor-size device. Approaches for solving the arising problems were studied, taking into account also the utilization of a thermal barrier. In this connection, Winske et al. (1985) studied the nonlinear development of the instability in a finite beta plasma with isotropic electrons. The present investigation is concerned with an extension of the calculations conducted by Winske et al., giving attention to the parameter regime of the TMX. It is found that three instabilities can occur.

Da Jornada, E. H.↗