Plasma Science Enabling Technology, Sustainability, Security, and Exploration (2021) / Chapter Skim
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7 The Cosmic Plasma Frontier
7 The Cosmic Plasma Frontier
Pages 322-380
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From page 322... ...
Space and astrophysical plasmas (SAPs) reach regimes inaccessible to earthbound laboratory experiments, enabling deep insights into fundamental plasma processes that impact observations and understanding of the formation and evolution of the universe.
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(bottom) Beyond lies the exotic plasma physics of galaxies (1018 km across)
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From page 324... ...
To understand and predict how the plasma universe around us operates, the fun damental physical processes responsible for phenomena ranging from electron-scale interactions to galaxy clusters need to be explored. Magnetic fields are paramount in governing the behavior of cosmic plasmas and play a key role in determining the habitability of our planet.
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From page 325... ...
in SAPs varies widely depending on the environment. For example, β is less than 1 in the very local interstellar medium, the solar corona, and the outer regions of molecular clouds, whereas β ≥1 in the solar wind, stellar convective zones, planetary magnetosheaths, and the intracluster medium.
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From page 326... ...
The twin Voyager spacecraft, launched in 1977, have journeyed well past their nominal 5-year missions and are headed into the ISM, revolutionizing our understanding of the interaction of the solar wind with the local interstellar medium (LISM)
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From page 327... ...
Perhaps the most striking growth area in SAP having direct, on-the-ground societal benefit has been the science of space weather -- the causes and consequences of activity generated at the Sun that propagates through the heliosphere toward planetary surfaces, and Earth in particular. Both living organisms and technology can be adversely affected by these solar disturbances that interact with our magnetosphere and ionosphere.
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From page 328... ...
Energetic particles and radiation pose even greater threats to manned space travel and bases on the Moon and planets that lack the natural protection that magnetic fields provide. To understand and ultimately predict space weather events, we must develop deep physical insight into all plasma mechanisms that initiate, transport, and transform these energetic storms.
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From page 329... ...
The highly successful but perpetually underfunded NSF/DOE Partnership in Basic Plasma Science and Engineering has been extensively utilized by members of the space plasma physics and plasma astrophysics communities since 1997, often in collaboration with plasma physicists in different subdisciplines. A significant improvement in interagency collaboration between NASA and NSF, Next Genera tion Software for Data-driven Models of Space Weather with Quantified Uncertain ties (SWQU)
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From page 330... ...
In many astrophysical settings the magnetic field controls the overall dynamics of the plasma, while the dissipation of magnetic energy may power the observed high-energy emission. In the past two decades, magnetars (strongly magnetized neutron stars possessing super-strong magnetic fields)
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From page 331... ...
Simulations of extreme eruptions in such fast-rotator systems, however, found that the tightly wound interplanetary magnetic field complicates and extends the routes taken by the resulting accelerated particles to the exoplanets. Simulations of the possible effect of superflare-produced energetic particles on life-enabling conditions on orbiting planets suggest that the conditions that could foster Earth-like living organisms are quite narrow in terms of radiation dose, atmospheric properties and chemical composition, and presence of liquid water.
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From page 332... ...
Two hours after CME launch, when the CME hit the early Earth's magnetosphere. This study assumed a steady-state paleo-solar wind at 0.7 Gyr with a mass loss rate of 1.7 × 10−12 Msun yr−1.
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From page 333... ...
The dynamo-mediated evolution of solar magnetic fields governs solar irradiance variations and eruption frequency, which affect planetary atmospheres and magnetospheres. A recent breakthrough in dynamo simulations has produced cyclic, solar-like polarity reversals of the large-scale magnetic field.
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From page 334... ...
Lynch, 2016, Magnetic-island contraction and particle acceleration in simulated eruptive solar flares, The Astrophysical Journal 820:60.
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From page 335... ...
. Curved black lines are magnetic field lines originating at the Sun.
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. Recent experiments on Omega and NIF indicate that, in astrophysical environments, strong shocks generate and amplify magnetic fields and accelerate cosmic rays.
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The transport of these energetic particles through the corona and heliosphere with their many shocks remains a difficult problem. Two competing effects influence their propagation: focusing along the IMF due to the decreasing magnetic field strength and pitch-angle scattering by IMF turbulence.
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From page 338... ...
From top to bottom, the panels are the energetic ion counts, the magnetic field strength (|B|) , the elevation and azimuthal angles of the magnetic field direction in the RTN coordinate system, the pitch angle distri bution of 116 eV electrons, proton beta, proton density, proton temperature, solar wind speed, and the total plasma pressure.
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From page 339... ...
Ionosphere, thermosphere, and mesosphere (ITM) plasma physics has made substantial progress on several fronts.
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From page 340... ...
The related plasma processes exhibit a large variety of visual forms, which collec tively span the full range of altitudes between the tropopause and the ionosphere. The luminous optical manifestations of these observed events roughly distinguish among the various distinctive classes: sprites, elves, and blue jets (see Figure 7.9)
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From page 341... ...
For example, PSP magnetic-field and plasma measurements during the first solar encounter at 35.7 Rsun identified a slow Alfvénic solar wind emerging from a small equatorial coronal hole, apparently escaping from above low-lying, complex magnetic structures, which exhibited a highly dynamic magnetic field with polarity reversals on timescales from seconds to hours. These varying field structures were associated with clustered radial plasma jets with enhanced energy flux and turbulence.
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From page 342... ...
Voyager 1 revealed that the very local interstellar medium (VLISM) is very much influenced by the solar wind.
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From page 343... ...
Zhang, 2015, The heliotail, The Astrophysical Journal Letters 812:L6, © 2015 The American Astronomical Society, all rights reserved. supersonic solar wind, are transmitted across the heliospheric termination shock, propagate through the heliosheath, and are then partially transmitted into the VLISM at the heliopause.
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From page 344... ...
Ambient turbulence and its transport and coupling to large-scale flows govern the scattering and transport of energetic charged particles, while coherent structures such as flux ropes can scatter, trap and accelerate particles. Our current inability to predict magnetic fields and particle distributions at specific locations in the heliosphere, as well as uncertainties in space weather prediction, largely stem from our inability to accurately measure or model local turbulent properties.
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From page 345... ...
Geomagnetic storms also cause energetic particles to be ejected from the radiation belts surrounding Earth, potentially damaging spacecraft in low Earth and geostationary orbits. The entire causal chain, from solar eruptions to the impact on the magnetosphere to the space weather effects on our technology, corresponds to a chain of intimately coupled plasma processes.
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From page 346... ...
In the United States, agencies such as Department of Homeland Security and the Federal Energy Regulatory Commission began to consider the societal and technological impacts of space weather events, and to include them in disaster planning. Electric power companies, space plasma scientists, and gov ernment representatives collectively developed and adopted new reliability stan dards to mitigate the impacts of geomagnetic disturbances.
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From page 347... ...
Examples include the linear and nonlinear physics of plasma waves (e.g., Alfvén waves) , collisionless shocks, magnetic reconnection, interaction between energetic particles and waves, and turbulence and transport, over a wide plasma-β range.
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From page 348... ...
SPSC provides a platform to collaboratively investigate the underlying physics of space plasmas under con trolled, reproducible, scaled laboratory conditions, particularly those representative of the near-Earth space plasma environment, and a realistic testbed for the develop ment and preflight testing of space diagnostics and hardware. The device is used for the study of ionospheric, magnetospheric, and solar wind plasma phenomena; testing/calibration of space-qualified diagnostic instruments for missions; space craft charging; large-volume plasma generation; and other investigations requiring a low-pressure environment.
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From page 349... ...
aimed at understanding the Sun and its influence on Earth and near-Earth space environment. EOVSA focuses on studying the magnetic structure of the solar corona, transient phenomena resulting from magnetic interactions (e.g., solar flares and associated particle acceleration and heating)
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From page 350... ...
codes offer opportunities to understand how exotic/relativistic pair plasma is produced, and how coherent radio and high-energy emissions are generated. These developments are enabling, for the first time, truly ab-initio studies of important phenomena such as Crab Nebula γ-ray flares, pulsed high-energy emission from pulsar magnetospheres, the coronae of accreting BHs, and pair-production cascades in pulsar and BH magnetospheres, as well as basic processes such as magnetic reconnection and particle acceleration in astrophysical plasmas.
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From page 351... ...
Developing time-dependent simulations with evolving boundary conditions derived from observations is essential to improving the predictive capability of space-weather modeling. For example, AFRL's ADAPT code prepares a time series of magnetograms of the solar photosphere to drive the bottom boundary of coronal and solar wind models.
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From page 352... ...
will address major challenges in several subareas of plasma astrophysics: • Extreme plasma physics of multimessenger cosmic plasmas • Physics of extremely rarefied/weakly collisional plasmas • Plasma physics of the early solar system evolution, exoplanets, and the origin of life • Plasma physics of the interstellar medium Multimessenger astrophysics combines information from multiple extrasolar electromagnetic radiation, gravitational waves, neutrinos, and cosmic ray obser vations. Exploiting these four "messengers" is transforming plasma astrophysics by opening new windows on the universe.
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From page 353... ...
Although these plasmas are dominated by thermal rather than magnetic pressure, even weak magnetic fields change the overall dynamics as well as dissipative and transport properties. The dynamics of such plasmas are governed by large-scale bulk motions and complex, multiscale interactions between kinetic phenomena under conditions not in local thermodynamic equilibrium.
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From page 354... ...
The LTP com munity has long addressed partially ionized, chemically reactive, and multiphase plasmas, offering possible strategic opportunities for the SAP and LTP communities to collaborate on low-ionization astrophysical plasmas. Heliophysics Space weather is recognized nationally and internationally as a potential threat to our technology-dependent society and to our space programs, includ ing human-flight to the Moon, Mars, and beyond.
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From page 355... ...
Currently, many global-scale geospace models treat the ionosphere simply as an input boundary condition. This problem is often exacerbated by actual physical gaps between the computational domains being coupled, complicating realistic simulation of the transfer of plasma, electromagnetic energy, and energetic particles between domains.
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From page 356... ...
To date, all in situ observations of solar wind plasmas have been single point measurements or have focused on a narrow range of scales through the use of carefully controlled formations of a few spacecraft. Unfortunately, the dynamics of turbulence depends critically on the orientation of the magnetic and plasma fluctuations relative to the mean magnetic field -- a 3D quantity that no single spacecraft can measure.
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From page 357... ...
Voyager and IBEX observations have challenged and transformed our earlier concepts about the global structure and energetics of the heliosphere, and of the plasma processes acting at its boundary. IMAP, and eventually an Interstellar Probe, will be critical to unraveling the multiple challenges listed above in understanding the interaction of the solar wind with the LISM.
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From page 358... ...
The committee anticipate that future MMS studies will analyze electromagnetic waves upstream of and at/within the shock front; examine the evolution of ion and electron distributions from upstream through the shock ramp and into the downstream region; discover PI signatures at the shock; and investigate periodic nonlinear structures, such as double layers and electron holes downstream of collisionless shocks. Whistler waves are very low frequency electromagnetic waves that can be generated in geospace and other planetary magnetospheres during particle injec tion events associated with lightning and geomagnetic storms and substorms.
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From page 359... ...
Similarly, although plasma processes and instabilities that can create magnetic fields have been identified, most saturate with weak, tangled fields, and it is unclear whether such fields seeded those observed today. This major gap in basic plasma physics theory simultaneously
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in a longitudinal plane, magnetic field lines (thin gold lines) , the radiative core (inner yellow)
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From page 361... ...
Although the high Reynolds number, high-β regime is difficult to produce in the laboratory, there is a large payoff for success. Understanding how stars cyclically generate and reverse their magnetic fields will not only shed light on our own Sun, but is profoundly important for studies of heliospheric structure and evolution, exoplanets and habitability in other stellar systems, and the generation of magnetic fields in more extreme environments.
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From page 362... ...
as an important agent in achieving magnetic self-organization on large spatial scales, while other research indicates that stars without tachoclines can have strong magnetic fields. What is the role of the tachocline in the dynamo process, and in determining its cyclic nature?
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From page 363... ...
Collisionless shocks can now be generated in the laboratory, positioning us to answer a multitude of basic questions about these important phenomena in the next decade. • What are the dominant plasma instabilities that mediate the stagnation of the flow in collisionless shocks, and how is the magnetic field amplified?
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From page 364... ...
Energy and radiative input to their atmospheres can be im mense, particularly in EUV and X-ray wavelengths, and frequent stellar eruptions can produce a lethal mix of energetic particles, high-energy photons, and magnetic interactions with the planet's magnetic field (if it has one)
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From page 365... ...
Over the next decade, unprecedented remote-sensing observations from missions such as SDO, IRIS, and Fermi, as well as exquisite in situ data from missions such as MMS, PSP, Solar Orbiter, and BepiColombo, will deliver a wealth of critical new insights on magnetic reconnection. An encouraging development is the new NSF/NASA collaborative program, Next Generation Software for Data-driven Models of Space Weather with Quantified Uncertainties (SWQU)
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From page 366... ...
Choosing the appropriate subgrid model is a difficult decision for simulating other turbulent plasmas in their large-scale envi ronments, including the solar wind, astrophysical jets, and the ICM. Consequently, progress in this area will benefit a wide range of SAP investigations.
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Only very recently have laboratory experiments been able to reproduce plasma conditions in the solar convective envelope and approaching the radiative zone. Dedicated DOE and NSF programs are urgently sought to support the nextgeneration experimental facilities and diagnostic instrumentation in concert with SAP observations.
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Recently, a national space weather plan has been formulated that involves all agencies whose purview includes space weather. New opportunities for basic and applied space weather research are being created in partnership with the scientific and end-user communities.
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From page 369... ...
Using adaptive optics technology, DKIST's 4.2-m primary mirror and five major instruments will provide the sharpest views ever taken of the solar surface, with the spatial, temporal, and spectral resolution and dynamic range needed to measure elemental magnetic structures at and above the photosphere. When DKIST is fully operational, there will be unprecedented data revealing the roles played by magnetic fields and the embedding plasma in generating and transporting solar activity.
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From page 370... ...
By making global measurements of the solar wind properties, turbulence, and transients with radio propagation diagnostics, the ngVLA would be highly complementary to in situ measurements made by pro posed next-generation heliospheric missions such as Helioswarm. For the ISM, the ngVLA will characterize interstellar turbulence, with the same instrument using the same technique (angular broadening)
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Solar Orbiter will address the following fundamental questions: • How and where do the solar wind plasma and magnetic field originate in the corona? • How does solar activity drive heliospheric variability?
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From page 372... ...
IMAP addresses two critical problems in SAP physics: the acceleration of energetic particles in interplanetary space and the interaction of the solar wind with the local interstellar medium. IMAP's science objectives are to: • Improve understanding of the composition and properties of the LISM; • Advance understanding of the temporal and spatial evolution of the dynamic boundary between the solar wind and the ISM; • Identify and advance understanding of processes governing the interactions between the magnetic field of the Sun and the LISM; and • Identify and advance understanding of particle injection and acceleration processes near the Sun, in the distant heliosphere, and in the heliosheath.
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From page 373... ...
spacecraft are to find and map all massive galaxy clusters in the observable universe at X-ray wavelengths, and to search for other cosmic X-ray sources, including active galactic nuclei, star formation regions, and stellar activity. Several astrophysical satellites that probe hot cosmic plasmas with high-energy emissions are planned: for example, the Athena X-ray observatory, the Hard X-ray Modulation Telescope, the Imaging X-ray Polarimetry Explorer, and the X-ray Imaging and Spectroscopy Mission.
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and corona (visible and near-infrared light) ; study the solar particle flux, reach the L1 orbit, and measure magnetic field strength variation around L1.
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Most successful international programs have been enabled by professional organizations such as the United Nations, the International Council of Scientific Unions, and the International Astronomical Union, often without commensurate funding. One recent example is the International Space Weather Action Teams (ISWAT)
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From page 376... ...
Finding: Unfortunately, the level of funding for the highly successful NSF/DOE Partnership in Basic Plasma Science and Engineering has lagged that recom mended by the 2000 Plasma Decadal Review, despite its very central role in discovery plasma science and its capacity to create effective multidisciplinary bridges within plasma science. The recent NSF/NASA Next Generation Software for Data-driven Models of Space Weather with Quantified Uncertainties is an example of a focused SAP-oriented collaboration.
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From page 377... ...
to develop a collaborative program that enables space and astrophysical plasma scientists to collaborate with laboratory plasma experimentalists and advance both fields by leveraging their different needs and knowledge bases. As noted by the 2016 National Academies report Achieving Science with CubeSats,3 CubeSats and smallsats offer novel and transformational opportunities to explore geospace and the heliosphere with unprecedented spatial and temporal coverage, as needed to resolve fundamental plasma physics problems requiring multipoint observations -- for example, solar wind turbulence and magnetosphereionosphere coupling.
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From page 378... ...
The committee lauds this level of collaboration in a program that effectively combines workforce development and exciting plasma research. Recommendation: With NASA and NSF as lead agencies, NASA, NSF, and DoD, as the primary sources of space missions, should explore avenues, including rideshares, international partners, and partnering with com mercial launch providers, for reducing costs, lowering barriers, enabling higher-risk missions, and boosting launch opportunities for these pioneer ing investigations using CubeSats, smallsats, and clusters of these satellites.
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From page 379... ...
Hiring plasma-knowledgeable scientists within universities, national laboratories, and other institutions is critical to the long-term health of SAP and the development of the future STEM workforce. Traditionally, university physics and astronomy departments have rarely hired faculty in plasma heliophysics and plasma astrophysics, despite the highly interdisciplinary and fundamental nature of the discipline.
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