Energetic Particle Experiment Research Articles

Rate coefficients for electron-impact dissociation of O3+ to singly charged fragments

Rate coefficients for electron-impact dissociation of O3 + to the O+ and O2 + fragments are calculated for the new, recommended cross section data set and for various collisional conditions. Two sets of the cross section data, measured recently by different experimental groups, are used. These cross sections differ significantly with each other, but are renormalized and optimized to the coherent data base. Rate coefficients for the ozone cation fragmentation are determined using the Maxwellian and the non-thermal electron energy distribution functions (EEDF). In the case of Maxwellian distribution, mean electron energies cover the range from zero up to 2 keV. Non-thermal electron energy distribution functions are adopted from the recent electron observations by the 3-D plasma and energetic particles experiment on the WIND spacecraft. The non-thermal rates are evaluated for the mean electron energies from 4 to 80 eV. The role of the possible contribution of electron-impact dissociation of O3 + to the ozone layer depletion has been emphasized.

Rate coefficients for electron-impact dissociation of O3+ to singly charged fragments

Rate coefficients for electron-impact dissociation of O3+ to the O+ and O2+ fragments are calculated for the new, recommended cross section data set and for various collisional conditions. Two sets of the cross section data, measured recently by different experimental groups, are used. These cross sections differ significantly with each other, but are renormalized and optimized to the coherent data base. Rate coefficients for the ozone cation fragmentation are determined using the Maxwellian and the non-thermal electron energy distribution functions (EEDF). In the case of Maxwellian distribution, mean electron energies cover the range from zero up to 2 keV. Non-thermal electron energy distribution functions are adopted from the recent electron observations by the 3-D plasma and energetic particles experiment on the WIND spacecraft. The non-thermal rates are evaluated for the mean electron energies from 4 to 80 eV. The role of the possible contribution of electron-impact dissociation of O3+ to the Ozone layer depletion has been emphasized.

Experimental studies of plasma-antenna coupling with the JET Alfvén Eigenmode Active Diagnostic

This paper presents a dedicated study of plasma-antenna (PA) coupling with the Alfvén Eigenmode Active Diagnostic (AEAD) in JET. Stable AEs and their resonant frequencies f, damping rates γ < 0, and toroidal mode numbers n are measured for various PA separations and limiter versus X-point magnetic configurations. Two stable AEs are observed to be resonantly excited at distinct low and high frequencies in limiter plasmas. The values of f and n do not vary with PA separation. However, |γ| increases with PA separation for the low-f, but not high-f, mode, yet this may be due to slightly different edge conditions. The high-f AE is detected throughout the transition from limiter to X-point configuration, though its damping rate increases; the low-f mode, on the other hand, becomes unidentifiable. The linear, resistive MHD code CASTOR is used to simulate the frequency scan of an AEAD-like external antenna. For the limiter pulses, the high-f mode is determined to be an n = 0 GAE, while the low-f mode is likely an n = 2 TAE. During the transition from limiter to X-point configuration, CASTOR indicates that n = 1 and 2 EAEs are excited in the edge gap. These results extend previous experimental studies in JET and Alcator C-Mod; validate the computational work performed by Dvornova et al (2020 Phys. Plasmas 27 012507); and provide guidance for the optimization of PA coupling in upcoming JET energetic particle experiments, for which the AEAD will aim to identify the contribution of alpha particles to AE drive during the DT campaign.

Alfvén eigenmodes and fast ion transport in negative triangularity DIII-D plasmas

The first energetic particle experiments in negative triangularity tokamak plasmas have been carried out on DIII-D. Alfvén eigenmode (AE) activity and associated fast ion transport comparable to that in positive triangularity is observed during the current ramp portion of all plasmas with early beam heating indicating negative triangularity does not confer a special advantage with respect to AE induced transport. In these discharges, a range of mode activity driven by the sub-Alfvénic () 80 kV neutral beams is found including beta induced Alfvén acoustic eigenmodes, beta induced Alfvén eigenmodes, reversed shear Alfvén eigenmodes (RSAEs) and toroidicity induced Alfvén eigenmodes (TAEs). Mode intermittency and possibly chirping appears to be more common than comparable positive triangularity and/or oval discharges but overall, the unstable spectra and mode amplitudes observed on magnetics, CO2 interferometry, and electron cyclotron emission in a set of matched positive and negative triangularity cases at moderate beam power is similar. Large levels of Alfvén eigenmode induced fast ion transport are found in both positive and negative triangularity with up to central fast ion pressure deficits relative to classical predictions early during the current ramp phase for discharges with 3 MW injected 80 kV neutral beam power. The deficit in both cases is reduced toward zero as the current penetrates and eventually reaches classical levels during current flattop with . Fast ion transport in negative triangularity plasmas measured using a beam modulation technique show very similar levels to those measured in oval plasmas over the range of tested beam powers (–7 MW). This similarity is found despite quite different unstable spectra in the highest beam power case where a mixture of coherent and quasi-coherent modes in the TAE frequency range are observed in negative triangularity and a spectrum of more typical narrowband TAEs and RSAEs is observed for the oval plasmas.

Review of the experiments for energetic particle physics on HL-2A

This paper reviews the energetic particle (EP) experiments during electron cyclotron resonance heating (ECRH) and neutral beam injection in the HL-2A tokamak. A number of important results are summarized, which relate to ITER physics, including the behavior of the multi-mode instability, the nonlinear interaction between wave–wave and wave–particles, the losses of EP induced by the instabilities, the effect of the EP instabilities on the thermal plasma confinement and the control of the EP instabilities by means of ECRH. Systematic experiments indicate that when the drive is great enough, the nonlinear effects and the multi-mode coexistence may play an important role, which affect the transport both of the EPs and the background plasma confinement, and these instabilities could be controlled. Some new phenomena about the EP induced instabilities discovered recently on the device, such as high frequency reversed shear Alfvén eigenmodes, Alfvénic ion temperature gradient modes, the geodesic acoustic mode induced by energetic electrons excited by interaction between tearing mode and beta induced Alfvén eigenmode and double e-fishbone in negative magnetic shear discharges etc, have also been presented in the paper.

Oscillations of energetic ions flux near the Earth's bow shock

AbstractA new type of variability in the foreshock and magnetosheath is revealed with the recent energetic particle experiments monitor of electrons and protons (MEP) onboard Spectr‐R spacecraft and solid‐state telescope onboard Time History of Events and Macroscale Interactions during Substorms spacecraft, which have high time resolution. Oscillations of energetic ion fluxes are observed in the broad energy range ∼4–400 keV, with periods 10–30 s, often rather monochromatic waveform and accompanied with magnetic oscillations. Such events are not so rare (∼100 cases are found for 2007–2012) but are associated mostly with high‐speed solar wind.

Energetic particle measurements onboard Spectr-R with MEP-2

The energetic particle experiment MEP-2 onboard the Spectr-R high apogee satellite is briefly described. The instrument measures fluxes and spectra of electrons (30 keV–350 keV) and ions (30 keV–3.2MeV), using two pairs of silicon detectors. The example of first observations upstream from the bow shock illustrates its successful operation in space. Unique observations of ∼30 s strong fluctuations of energetic ions with energies up to two hundred keV are discussed.

ELECTRON ACCELERATION ASSOCIATED WITH SOLAR JETS

This paper investigates the solar source region of supra-thermal (few keV up to the MeV range) electron beams observed near Earth by combining in situ measurements of the three-dimensional Plasma and Energetic Particles experiment on the WIND spacecraft with remote-sensing hard X-ray observations by the Reuven Ramaty High Energy Solar Spectroscopic Imager. The in situ observations are used to identify events, and the hard X-ray observations are then searched for signatures of supra-thermal electrons radiating bremsstrahlung emission in the solar atmosphere. Only prompt events detected above 50 keV with a close temporal correlation between the flare hard X-ray emission and the electrons seen near Earth are selected, limiting the number of events to 16. We show that for 7 of these 16 events, hard X-ray imaging shows three chromospheric sources: two at the footpoints of the post-flare loop and one related to an apparently open field line. The remaining events show two footpoints (seven events, four of which show elongated sources possibly hiding a third source) or are spatially unresolved (two events). Out of the 16 events, 6 have a solar source region within the field of view of the Transition Region and Corona Explorer (TRACE). All events with TRACE data show EUV jets that have the same onset as the hard X-ray emission (within the cadence of tens of seconds). After the hard X-ray burst ends, the jets decay. These results suggest that escaping prompt supra-thermal electron events observed near Earth are accelerated in flares associated with reconnection between open and closed magnetic field lines, the so-called interchange reconnection scenario.

SPECTRA OF SOLAR IMPULSIVE ELECTRON EVENTS OBSERVED NEAR EARTH

A statistical survey of the spectral shapes of 62 solar impulsive electron events detected in the ~ 1 to 300 keV range near Earth by the three-dimensional Plasma and Energetic Particles experiment on the WIND spacecraft is presented. The electron peak flux spectra generally show a broken power-law dependence with a steepening above ~ 60 keV. The break in the spectrum is pronounced with averaged power-law indices below and above the break of δlow = 1.9 ± 0.3 and δhigh = 3.6 ± 0.7, respectively, and an averaged ratio δlow/δhigh of 0.54 with a standard deviation of 0.09. Two correlations are found: (1) δlow and δhigh are linearly correlated (correlation coefficient of 0.61), (2) The peak fluxes around the break energy and δlow are anticorrelated (coefficient 0.74), with larger events having flatter spectra below the break. Whether the observed spectral breaks are direct signatures of the solar acceleration processes or whether they are due to transport effects from the Sun to Earth is currently not understood.

Polar PWI and CEPPAD observations of chorus emissions and radiation belt electron acceleration: Four case studies

We investigated the role of whistler-mode chorus in accelerating outer radiation belt electrons during four moderate geomagnetic storms when data from the Polar Plasma Wave Investigation (PWI) were available. The storm time periods we examined included two storms associated with coronal mass ejections (CMEs), the well-studied January 10–13, 1997 International Solar Terrestrial Physics event and the May 12–15, 1997 event. We compared these two storms with two geomagnetically active periods that were not associated with CMEs. Although strong chorus emissions were observed during all four events, the association of electron acceleration with chorus emissions is not clear. During all four events, the Polar Comprehensive Energetic Particle and Pitch Angle Distribution (CEPPAD) experiment observed increases in the fluxes of energetic electrons (0.8< E<6.4 MeV). The two events associated with CMEs featured a sudden increase in the electron fluxes above 0.8 MeV that may have been related to the impact of the CME shock wave upon the magnetosphere. The other two events featured more gradual increases in the electron fluxes over a period of several days. The data from these events indicate that the role played by resonant interactions with chorus in accelerating electrons may depend on the upstream solar wind conditions driving the storm.

Dynamics of field-aligned currents and energetic particle fluxes in the mid-altitude cusp by INTERBALL-Au, April 1997

In this work, the cases of magnetic field disturbances registered aboard the INTERBALL-Auroral Probe satellite /IMAP Magnetometer in the north mid-altitude cusp have been analyzed. Cusp subregions are investigated by the energetic particle experiments (PROMICS-3 and DOK-2) on the same spacecraft. Images from the DMSP satellite are used for a better definition of the auroral oval. Unusual cases of field-aligned current (FAC) concentration are demonstrated: (1) Strong and highly structured FACs concentrated in the dawn cusp flank; (2) FACs concentrated in a zone of diamagnetic cavity in the dusk flank of the cusp probably related to a cusp energetic particle (CEP) event. The examined cases demonstrate that these regions of concentrations of FACs connect to the outer magnetosphere.

Energetic Particle Experiments in JT-60U and Their Implications for a Fusion Reactor

Energetic particle experiments in JT-60U are summarized, mainly covering ripple loss and Alfvén eigenmodes (AE modes). Significant loss was observed for 85 keV neutral beam injected (NBI) ions and fusion-produced tritons as toroidal field ripple at the plasma surface increased, especially in a reversed shear plasma. Measurement of hot spots on the first wall due to ripple loss confirmed agreement with code predictions, validating the modeling incorporated in an orbit-following Monte Carlo code. A variety of AE modes were destabilized in ion cyclotron range of frequencies (ICRF) minority heating and negative-ion-based NBI (N-NBI) heating. Most of the observed modes are gap modes identified to be toroidicity-induced, ellipticity-induced, and triangularity-induced AE modes. An interesting finding is pulsating modes accompanying frequency sweep, which were destabilized by N-NBI and sometimes induced a beam ion loss of up to 25%. Also presented are energetic particle issues in auxiliary heating with ICRF and N-NBI.

Arrival times of Flare/Halo CME associated shocks at the Earth: comparison of the predictions of three numerical models with these observations

Abstract. The arrival times at L1 of eleven travelling shocks associated both with X-ray flaring and with halo CMEs recorded aboard SOHO/LASCO have been considered. Close to the Sun the velocities of these events were estimated using either Type II radio records or CME speeds. Close to the Earth the shocks were detected in the data of various solar wind plasma, interplanetary magnetic field (IMF) and energetic particle experiments aboard SOHO, ACE, WIND, INTERBALL-1 and IMP-8. The real-time shock arrival predictions of three numerical models, namely the Shock Time of Arrival Model (STOA), the Interplanetary Shock Propagation Model (ISPM) and the Hakamada-Akasofu-Fry Solar Wind Model (HAFv.2) were tested against these observations. This is the first time that energetic protons (tens of keV to a few MeV) have been used to complement plasma and IMF data in validating shock propagation models. The models were all generally successful in predicting shock arrivals. STOA provided the smallest values of the "predicted minus measured" arrival times and displayed a typical predictive precision better than about 8 h. The ratio of the calculated standard deviation of the transit times to Earth to the standard deviation of the measurements was estimated for each model (treating interacting events as composite shocks) and these ratios turned out to be 0.60, 1.15 and 1.02 for STOA, ISPM and HAFv.2, respectively. If an event in the sample for which the shock velocity was not well known is omitted from consideration, these ratios become 0.36, 0.76 and 0.81, respectively. Larger statistical samples should now be tested. The ratio of the in situ shock velocity and the "Sun to L1" transit velocity (Vsh /Vtr) was in the range of 0.7–0.9 for individual, non-interacting, shock events. HAFv.2 uniquely provided information on those changes in the COBpoint (the moving Connection point on the shock along the IMF to the OBserver) which directly influenced energetic particle rise times. This model also illustrated the non-uniform upstream conditions through which the various shocks propagated; furthermore it simulated shock deformation on a scale of fractions of an AU. On the spatial scale (300 RE ), where near-Earth spacecraft are located, the passing shocks, in conformity with the models, were found to be locally planar. The shocks also showed tilting relative to the Sun-Earth line, probably reflecting the inherent directionality associated with their solar origin. Key words. Interplanetary physics (energetic particles; interplanetary shocks; solar wind plasma)

The Coronal Mass Ejection of 1998 April 20: Direct Imaging at Radio Wavelengths

We observed the fast coronal mass ejection (CME) of 1998 April 20 with the radioheliograph at Nancay, France, between 164 and 432 MHz. Spectroscopic data were obtained between 40 and 800 MHz by the spectrometer at Tremsdorf, Germany, and between 20 kHz and 14 MHz with the WAVES instrument on board the Wind spacecraft. Energetic particle data were obtained from the Wind 3D Plasma and Energetic Particle experiment. The was observed in white light by the Large-Angle Spectrometric COronagraph experiment on board the Solar and Heliospheric Observatory spacecraft. For the first time, the expanding loops are imaged directly at wavelengths. We show that the radio-emitting loops are the result of nonthermal synchrotron emission from electrons with energies of ~0.5-5 MeV interacting with magnetic fields of ~0.1 to a few gauss. They appear nearly simultaneously with the onset of an associated type II burst, shock-accelerated type III bursts, and the initiation of a solar energetic particle event. We suggest possible sources of the energetic electrons responsible for this radio CME and point out diagnostic uses for synchrotron emission from loops.

A relation between dynamics of coronal mass ejections and production of solar energetic particles

During January 1997-June 1998, the Large Angle Spectroscopic Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory spacecraft (SOHO) registered 670 coronal mass ejections (CMEs). We compare two groups of the 300-800 km s-1 CMEs: (i) (very) gradually accelerating CMEs with acceleration below , and (ii) impulsively accelerating CMEs with acceleration near the Sun, continuing then with the constant speed across the LASCO field of view. An association of those CMEs with solar energetic particle (SEP) events is studied using the data of the energetic particle experiment ERNE also aboard SOHO. There were no SEP events registered in association with the first group CMEs, whereas about 8% of the second group CMEs produced an enhancement in the ~10 MeV proton flux at SOHO. This result along with a number of additional tests supports an idea that production of SEPs by the moderate speed CMEs depends not only on the final speed but also on the magnitude of acceleration that CME experiences during its liftoff. The SEP-producing CMEs are typified by impulsively accelerating CMEs accompanied by soft X-ray flares and coronal shocks.

Two Classes of Solar Proton Events Derived from Onset Time Analysis

We analyze onset times for 26 solar energetic (from 30 keV to 6 MeV) proton events that exhibit clear velocity dispersion, as observed by the three-dimensional Plasma and Energetic Particles experiment on the Wind spacecraft. Assuming that the particles are injected simultaneously at all energies and travel the same path length, we find two classes of proton events: (1) for the 18 class 1 events, the derived path lengths are between 1.1 and 1.3 AU, indicating that the first arriving protons travel essentially scatter-free; and (2) the eight class 2 events show longer path lengths around 2 AU. For all proton events, the observed temporally related electron events all have electron path lengths around 1.1-1.3 AU. Relative to the electron injection time at the Sun, the protons of the first class are injected ~0.5-2 hr later. Assuming these particles are accelerated by the associated coronal mass ejection (CME) shock, the protons at all energies between 0.03 and 6 MeV appear to be accelerated (or released) simultaneously high in the corona, roughly ~1-10 R☉ above the electrons. The pitch-angle distributions are observed to be similar for both classes of events, making it unlikely that propagation effects are responsible for the longer path length of class 2 events. The late proton onset times at 1 AU of class 2 are therefore more likely explained by a successively later solar release (or escape) of protons at successive lower energies. Assuming again acceleration at the CME shock, the release (or escape) of the protons of class 2 events appears to depend on energy and occur at a higher altitude for lower energies, with the most energetic protons possibly released simultaneously with the electrons.

A gyrophase‐bunched electron signature upstream of the Earth's bow shock

A possible sustained signature of a gyrophase‐bunched electron distribution just upstream of the Earth's bow shock is presented. The data, obtained by the ISTP WIND 3‐D Plasma and Energetic Particle Experiment, show several clear examples of a non‐gyrotropic, energetic electron distribution moving into the upstream. The signature is probably that of a locally phase‐trapped electron distribution.

Hot plasma pressure variations on the geostationary orbit on the base of Gorizont satellite data

Plasma and energetic particles pressure distribution is studied using data from the plasma and energetic particle experiment (0.1 – 133 keV) onboard the Gorizont-35 geostationary satellite for the period from 11 to 25 March 1992. The analysed period consists of relatively quiet time, small geomagnetic storms, SC and the time of the northern orientation of the IMF. The calculations show that the basic contribution to the total particle pressure was made by ions at the energy from 0.1 to 12.4 keV. The derived average value of the calculated pressure (∼1 nPa) points to the important role of the geostationary orbit plasma population in the formation of the magnetosphere pressure balance and of the near-Earth magnetic field distortion.

Geostationary orbit plasma pressure variations according to gorizont satellite data

Plasma and energetic particles pressure distribution is studied using data from the plasma and energetic particle experiment (0.1 –133 keV) onboard the Gorizont-35 geostationary satellite for the period from 11 to 25 March 1992. The analysed period consists of relatively quiet time, small geomagnetic storms, SC and the time of the northern orientation of the IMF. The calculations show that the basic contribution to the total particle pressure was made by ions at the energy from 0.1 to 12.4 keV. The derived average value of the calculated pressure (≈1 nPa) points to the important role of the geostationary orbit plasma population in the formation of the magnetopause pressure balance and of the near-Earth magnetic field distortion.

Observations of near plasma sheet, ring current and energetic electrc radiation belt under northward IMF condition

The dynamics of different plasma domains is studied using data from the plasma (Ei,e=0.1–12.4 keV) and energetic particle (Ei=41–133 keV, Ee=97–1010 keV) experiments onboard the geostationary satellites “Gorizont-34” and “Gorizont-35” for the period from 11 to 25 March 1992. The analysed period consists of relatively quiet time, small geomagnetic storms, SC and the long time (>4 days) of the northward interplanetary magnetic field.The observed features of the energetic particle flux distributions were “untypical” for the geostationary orbit region: the decrease of the electron fluxes by about a factor of ten; the decrease of the ion fluxes in the energy range from about 100 eV to 400 eV by about a factor of 5–10 and the formation of the intensive fluxes of ions at the energy ∼5–12.4 keV. The obtained results consist qualitatively with the conception of a closed topology of the magnetosphere for the steady northward interplanetary magnetic field condition and point to the dependence of the magnetospheric mechanism of the charged particle acceleration on the interplanetary magnetic field parameters.