The WAKEfield Advanced Experiment (AWAKE) is a large experiment conducted at CERN to investigate Wakefield acceleration in plasma. It is the first research effort in this field that uses a relativistic proton beam as a driver of plasma fields to accelerate witness electrons to high energies.
Use proton Several advantages set for plasma acceleration experiments. Notably, it allows researchers to maintain a large accelerating gradient over long distances, without having to split the accelerator into several different sections.
The AWAKE Collaboration, a group of researchers involved in the AWAKE Experiment, includes more than 100 engineers and physicists from 23 different institutes around the world. In a recent research paper published in physical review messagesthis large team of scientists demonstrates that self-modulation of the proton beam can be controlled by implanting instability.
“The available proton beams are much longer than the normal wavelength of plasma,” Livio Vera, one of the researchers who conducted the study, told Phys.org. “To drive large-amplitude Wakefield fields, we rely on the instability of the beam self-modulation in plasma. This process turns the long cluster into a series of small clusters, spaced apart by the period of the Wakefields, which drives the large-amplitude wakefield fields.”
To ensure that the proton array self-modulation process is repeatable and controllable with high levels of precision, the beam instability needs to be “seeded”. In their previous studies, the researchers achieved this by running plasma inside a proton beam with a laser pulse.
Despite their promising results, they found that this method has significant limitations to modifying only a small portion of the proton beam.
“In our new research paper, we show that self-modulation can be implanted using Wakefield fields that are driven by a previous electron array,” Vera explained. “In this case, the entire proton assembly self-modifies in a controlled and reproducible manner, and this is an important milestone for the future of the experiment.”
In the context of Wake field accelerators for proton-driven plasmas, the process of self-modulation is essentially a state of instability, as the amplitude of protective fields in plasma grows along the proton array and along the plasma. The growth of this self-modulation is determined by two main parameters, the capacity of the seed fields, which determines the initial value of the fields, and growth ratewhich determines how fast the instability grows.
“By sowing the self-modification with the previous set of electrons, we separate these two parameters, which other seeding methods are always related to,” Vera said. “This means that the parameters of the seed electron group determine the amplitude of the seed fields, and the parameters of the proton beam determine the growth rate of the instability.”
Using the approach presented in their paper, Vera and colleagues were able to independently control the growth of the self-modulating proton beam in the CERN plasma particle accelerator using two distinct “knobs”. These are basically the two main parameters that determine self-modifying growth.
Recent work by this team of researchers shows that the entire proton array in their plasma particle accelerator is self-adjusting in a reproducible manner. This crucial discovery could pave the way for a new proton-driven experimental design plasma wakefield accelerationwhich are based on separate plasmas.
One of these plasmas will be particularly involved in the process of self-modification, while the other will be involved in electron acceleration. These two plasmas will be separated by a gap region, where the injection of the witness electron group takes place.
“Since the second plasma will be preformed, the entire proton beam needs to be self-priming,” Vera said. “Moreover, demonstrating the control of instability is an important stand-alone finding in physics, which could extend to certain other topics in plasma physics.”
Since the beginning of 2022, the AWAKE collaboration has conducted several studies focusing on scattering self-modulation instability in plasmas using an electronic array. Currently, they are specifically exploring variations of their method in terms of spatial and temporal alignment between beams.
“The questions we are trying to address are: How far apart from each other in the transverse mode can electron and proton beams be injected, without causing destructive instabilities?” Vera added. “And: How far should the electron array be injected with respect to the proton beam for effective seeding? In 2023-2024, we will study the effect of the plasma density step on self-modulation and on wakefields amplitude, after which we will modify the experiment to fit the second plasma To experience acceleration. “
The team’s ultimate goal will be to deliver high-quality, high-energy electron beams within particle physics experiments. Their next studies will take further steps in this direction.
Controlled growth of self-formation of the relativistic proton beam in plasma. physical review messages(2022). DOI: 10.1103/ PhysRevLett.129.024802.
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