Laboratory Experiments to Evaluate the Role of Shear Alfvén wave Parametric Instabilities in the Origin and Evolution of the Solar Wind

The physics responsible for the origin and evolution of the solar wind remains an open question. Existing theories rely on magnetic reconnection and/or non-linear Alfvén wave phenomena. The Solar Probe Plus mission to be launched in 2018 will pass within 8.5 solar radii of the sun, providing new in-situ measurements. In preparation for these new observations, it is important to develop a clear idea of signatures that may indicate the presence of various physical processes that may be responsible for the heating and acceleration of the solar wind. Shear Alfvén wave parametric instabilities, in which an unstable large amplitude Alfvén wave non-linearly produces other modes, may be particularly important in the region Solar Probe Plus is expected to study. For instance, the ion acoustic mode produced from parametric delay of a large amplitude Alfvén wave could directly heat ions; thus, this process could help account for unexplained coronal heating. Parametric decay also produces a backward propagating Alfvén wave and thus may help explain why waves propagating in both directions are observed in the solar wind. Parametric instabilities may also serve as an intermediate instability mechanism for the transfer of energy from large to small spacial scales. While there has been an abundance of theoretical work on shear Alfvén wave parametric instabilities, observational evidence is extremely limited. Basic laboratory experiments may play a key role towards validating theoretical models and providing predictions for Solar Probe Plus observations. Central Question: What role do Shear Alfvén wave Parametric Instabilities play in the origin and evolution of the solar wind? Science Questions: 1. Under what sets of plasma parameters are Shear Alfvén wave parametric instabilities observed in the lab? How do these parameters compare to what is expected to be observed by Solar Probe Plus? 2. How do key features of the instability vary with important parameters such as plasma beta and pump wave frequency? How do these features compare to theoretical predictions? 3. Which instability signatures observed in the lab may used to inform future space observations such as Solar Probe Plus? Methodology: Experiments will be conducted at the Large Plasma Device (LAPD) at UCLA, which can produce a 20m long, 60cm diameter plasma column that is ideal for wave studies. The LAPD is equipped with an extensive set of diagnostics and a computer-controlled data acquisition system. Antenna and driver circuits for launching the waves are also available at the facility. The values of various dimensionless parameters (e.g. plasma beta or the ratio between plasma and electron cyclotron frequencies) can span a range of values relevant to the near-Sun solar wind and corona. Relevance: The proposed research is directly relevant to the three Heliophysics Science Goals in the 2014 NASA Science Plan and to the upcoming Solar Probe Plus mission. Specifically: Goal 1) Parametric instabilities represent an important physical process at work in the space environmental. The process may be particularly important close to the sun, where Solar Probe Plus aims to “understand how the Sun's corona is heated and how the solar wind is accelerated.” Parametric instabilities may have a direct impact on coronal heating and the evolution of the solar wind, thus the proposed research is particularly timely and relevant. In particular, the list of observational signatures to be developed will greatly aid the interpretation of future mission data. Goals 2 and 3) The solar wind is an important link between different regions of our Heliopshere. The improved understanding of the corona and near-Earth solar wind gained from the proposed research will advance our understanding of the connections that link the Sun to other regions of our solar system. This improved understanding is also crucial to future predictions of space weather events.

Support NASA's Heliophysics strategic science objectives to understand the Sun and its interactions with Earth and the solar system, including space weather. This will be achieved by developing/demonstrating instrumentation technology necessary to address the following science goals: Explore the physical processes in the space environment from the Sun to the Earth and throughout the solar system; Advance our understanding of the connections that link the Sun, the Earth, planetary space environments, and the outer reaches of our solar system; Develop the knowledge and capability to detect and predict extreme conditions in space to protect life and society and to safeguard human and robotic explorers beyond Earth.

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