Scoperto il "motore" del vento solare. Forse può aiutarci ad avere energia da fusione.

Questa è bellissima. Una sonda NASA, Wind, lanciata nel lontano 1994 e dotata di una strumentazione i cui dati vengono registrati su nastro per essere ogni volta riprodotti e trasmessi a terra, contiene forse i dati che spiegano perché il vento solare soffi tanto veloce e tanto caldo. Un perché che i ricercatori della fusione nucleare sono molto interessati a capire, perché da questa spiegazione possono a loro volta ricavare un metodo che renderà più efficienti i futuri reattori a fusione.

Il sole è un po' come una pentola che bolle, rilasciando in tutte le direzione un "vapore" costituito da un gas magnetico ricco di particelle. Al contrario della pentola, però, questo vapore non diventa più freddo e lento man mano che si allontana dal sole. Al contrario: il vento solare accelera fortemente e si riscalda attraversando l'atmosfera solare, la corona. Secondo gli scienziati alle origini del fenomeno ci sarebbero le onde di ciclotrone ionico (ione cyclotrone waves), un effetto di risonanza che coinvolge gli ioni pesanti del plasma solare e li accelera come una fionda, conservandone l'energia e quindi il calore. Forse sfruttando questo stesso meccanismo, si potrebbero intercettare e eliminare gli ioni pesanti che staccandosi dalle pareti delle camere di reazione di fusione emettono calore togliendolo alla reazione stessa, e causandone l'interruzione.

Solar Wind Energy Source Discovered

March 8, 2013: Using data from an aging NASA spacecraft, researchers have found signs of an energy source in the solar wind that has caught the attention of fusion researchers. NASA will be able to test the theory later this decade when it sends a new probe into the sun for a closer look.

The discovery was made by a group of astronomers trying to solve a decades-old mystery: What heats and accelerates the solar wind?

The solar wind is a hot and fast flow of magnetized gas that streams away from the sun's upper atmosphere.  It is made of hydrogen and helium ions with a sprinkling of heavier elements.  Researchers liken it to the steam from a pot of water boiling on a stove; the sun is literally boiling itself away.

“But,” says Adam Szabo of the NASA Goddard Space Flight Center, “solar wind does something that steam in your kitchen never does.  As steam rises from a pot, it slows and cools.  As solar wind leaves the sun, it accelerates, tripling in speed as it passes through the corona. Furthermore, something inside the solar wind continues to add heat even as it blows into the cold of space."

Finding that "something" has been a goal of researchers for decades.  In the 1970s and 80s, observations by two German/US Helios spacecraft set the stage for early theories, which usually included some mixture of plasma instabilities, magnetohydrodynamic waves, and turbulent heating.  Narrowing down the possibilities was a challenge. The answer, it turns out, has been hiding in a dataset from one of NASA's oldest active spacecraft, a solar probe named Wind.

Launched in 1994, Wind is so old that it uses magnetic tapes similar to old-fashioned 8-track tapes to record and play back its data.  Equipped with heavy shielding and double-redundant systems to safeguard against failure, the spacecraft was built to last; at least one researcher at NASA calls it the "Battlestar Gallactica" of the heliophysics fleet. Wind has survived almost two complete solar cycles and innumerable solar flares.

"After all these years, Wind is still sending us excellent data," says Szabo, the mission’s project scientist, “and it still has 60 years' worth of fuel left in its tanks.”

Using Wind to unravel the mystery was, to Justin Kasper of the Harvard-Smithsonian Center for Astrophysics, a "no brainer." He and his team processed the spacecraft's entire 19-year record of solar wind temperatures, magnetic field and energy readings and ...

(continua)