![]() ![]() In a plasma, a similar field can arise when a “driver,” such as a laser pulse, separates negatively charged electrons from positively charged ions. What is a plasma wakefield? A helpful analogy is a capacitor, where two oppositely charged parallel plates generate an electric field that can accelerate particles from one plate to the other. These are both key achievements, but the goal of having wakefield accelerators will have to wait until researchers gain more control over the output beams. A different approach, with proton beams as drivers, is not far behind, with recent experiments demonstrating its ability to accelerate electrons up to 2 GeV. One method using laser-driven wakefields has generated 8-GeV electrons, a new energy record that doubles the previous record. There exist different methods for generating wakefields, and now researchers are reporting significant progress for two of these techniques. ![]() The implication is that wakefield acceleration has the potential to work over much smaller lengths, which would allow a reduction in the size (and cost) of accelerator facilities. The amplitude of this accelerating field is not limited, as it is in conventional acceleration techniques that use radio frequency pulses. This method, which was first proposed in 1979, creates a collective motion of plasma particles, generating an accelerating field in its wake. The field of plasma wakefield acceleration is picking up speed. The resulting microbunches can accelerate electrons injected into the stream. A relatively weak laser pulse ionizes the gas at the mid-point of the bunch, leading to a modulation of the bunch's tail. In the proton-driven scenario (bottom), a high-energy proton bunch is sent into a gas. The pulse induces charge separation in the plasma, and the electric field from this charge configuration can accelerate trapped electrons. In the laser-driven case (top), a strong laser pulse is fired into a preformed plasma. APS/ Alan Stonebraker Figure 1: Wakefield acceleration can use different drivers.
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