Abstract
Electron beam polarization in the bubble regime of the interaction between a high-intensity laser and a longitudinally pre-polarized plasma is investigated by means of the ...Thomas–Bargmann–Michel–Telegdi equation. Using a test-particle model, the dependence of the accelerated electron polarization on the bubble geometry is analysed in detail. Tracking the polarization dynamics of individual electrons reveals that although the spin direction changes during both the self-injection process and acceleration phase, the former has the biggest impact. For nearly spherical bubbles, the polarization of electron beam persists after capture and acceleration in the bubble. By contrast, for aspherical bubble shapes, the electron beam becomes rapidly depolarized, and the net polarization direction can even reverse in the case of a oblate spheroidal bubble. These findings are confirmed via particle-in-cell simulations.
Abstract
Current laser-plasma based accelerators are promising options with respect to the acceleration of spin-polarized particle beams. We give an overview over the effects relevant during the ...acceleration process and more specifically discuss the acceleration of protons via Magnetic Vortex Acceleration (MVA). With the aid of particle-in-cell simulations we show that the length of the density down-ramp at the end of the plasma target affects the final beam quality regarding its collimation. The average spin-polarization of the obtained bunch remains largely robust at about 80% and only decreases for significantly longer ramps.
Circularly polarized (CP) extreme ultraviolet- and x-ray radiation is an essential tool for analyzing the magnetic properties of materials. Elliptically polarized high harmonic generation (HHG) has ...been demonstrated by focusing bi-chromatic (800 + 400 nm wavelengths), counter-rotating CP laser pulses into gas targets (Fleischer et al 2014 Nat. Photonics 8 543). More recent theoretical studies indicate that a bi-circular laser driver can also work in both under- and overdense plasmas with analogous selection rules to those in gases: for example, every third harmonic is suppressed and adjacent harmonics have opposite helicity for counter-polarized CP ω0 and 2ω0 pumps. In this work, an analytical theory of bi-circular HHG from underdense plasmas is formulated which provides quantitative predictions of harmonic efficiency scaling, selectivity and helicity for both co- and counter-polarized drivers of arbitrary frequency ratio. This is compared to a fully non-linear, one-dimensional fluid model and particle-in-cell simulations, showing good agreement with both.
Polarized atomic beam sources have been in operation for many years to produce either nuclear polarized atomic hydrogen or deuterium beams. In recent experiments, such a source was used to polarize ...both isotopes independently at the same time. By recombination of the atoms, hydrogen-deuterium molecules with all possible nuclear spin combinations can be created. Those spin isomers are useful for further applications, like precision spectroscopy, as polarized targets for laser-particle acceleration, polarized fuel for fusion reactors, or as an option for future measurements of electric dipole moments.
Plasma-based particle sources Fuchs, M.; Andonian, G.; Apsimon, O. ...
Journal of instrumentation,
01/2024, Letnik:
19, Številka:
1
Journal Article
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Abstract
High-brightness particle beams generated by advanced
accelerator concepts have the potential to become an essential part
of future accelerator technology. In particular, high-gradient
...accelerators can generate and rapidly accelerate particle beams to
relativistic energies. The rapid acceleration and strong confining
fields can minimize irreversible detrimental effects to the beam
brightness that occur at low beam energies, such as emittance growth
or pulse elongation caused by space charge forces. Due to the high
accelerating gradients, these novel accelerators are also
significantly more compact than conventional technology. Advanced
accelerators can be extremely variable and are capable of generating
particle beams with vastly different properties using the same
driver and setup with only modest changes to the interaction
parameters. So far, efforts have mainly been focused on the
generation of electron beams, but there are concepts to extend the
sources to generate spin-polarized electron beams or positron beams.
The beam parameters of these particle sources are largely determined
by the injection and subsequent acceleration processes. Although,
over the last decade there has been significant progress, the
sources are still lacking a sufficiently high 6-dimensional (D)
phase-space density that includes small transverse emittance, small
energy spread and high charge, and operation at high repetition
rate. This is required for future particle colliders with a
sufficiently high luminosity or for more near-term applications,
such as enabling the operation of free-electron lasers (FELs) in the
X-ray regime. Major research and development efforts are required
to address these limitations in order to realize these approaches
for a front-end injector for a future collider or next-generation
light sources. In particular, this includes methods to control and
manipulate the phase-space and spin degrees-of-freedom of ultrashort
plasma-based electron bunches with high accuracy, and methods that
increase efficiency and repetition rate. These efforts also include
the development of high-resolution diagnostics, such as full 6D
phase-space measurements, beam polarimetry and high-fidelity
simulation tools.
A further increase in beam luminosity can be achieve through
emittance damping. Emittance cooling via the emission of synchrotron
radiation using current technology requires kilometer-scale damping
rings. For future colliders, the damping rings might be replaced by
a substantially more compact plasma-based approach. Here, plasma
wigglers with significantly stronger magnetic fields are used
instead of permanent-magnet based wigglers to achieve similar
damping performance but over a two orders of magnitude reduced
length.
A number of laser facilities coming online all over the world promise the capability of high-power laser experiments with shot repetition rates between 1 and 10 Hz. Target availability and technical ...issues related to the interaction environment could become a bottleneck for the exploitation of such facilities. In this paper, we report on target needs for three different classes of experiments: dynamic compression physics, electron transport and isochoric heating, and laser-driven particle and radiation sources. We also review some of the most challenging issues in target fabrication and high repetition rate operation. Finally, we discuss current target supply strategies and future perspectives to establish a sustainable target provision infrastructure for advanced laser facilities.
The use of spin polarized fuel could increase the deuterium-tritium (D-T) fusion cross section by a factor of 1.5 and, owing to alpha heating, increase the fusion power by an even larger factor. ...Issues associated with the use of polarized fuel in a reactor are identified. Theoretically, nuclei remain polarized in a hot fusion plasma. The similarity between the Lorentz force law and the Bloch equations suggests polarization can be preserved despite the rich electromagnetic spectrum present in a magnetic fusion device. The most important depolarization mechanisms can be tested in existing devices. The use of polarized deuterium and 3 He in an experiment avoids the complexities of handling tritium, while encompassing the same nuclear reaction spin-physics, making it a useful proxy to study issues associated with full D-T implementation. 3 He fuel with 65% polarization can be prepared by permeating optically-pumped 3 He into a shell pellet. Dynamically polarized 7 Li-D pellets can achieve 70% vector polarization for the deuterium. Cryogenically-frozen pellets can be injected into fusion facilities by special injectors that minimize depolarizing field gradients. Alternatively, polarized nuclei could be injected as a neutral beam. Once injected, the lifetime of the polarized fuel is monitored through measurements of escaping charged fusion products. Multiple experimental scenarios to measure the polarization lifetime in the DIII-D tokamak and other magnetic-confinement facilities are discussed, followed by outstanding issues that warrant further study.
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