Strong drive compression of a gas-cooled positron plasma

Cassidy, D. B.; Greaves, R. G.; Meligne, V. E.; Mills, A. P.

doi:10.1063/1.3354005

Cited by 9 publications

(19 citation statements)

References 20 publications

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“…Unfortunately this only occurs up to some maximum drive frequency value, which for us is ~ 12 MHz [51], although higher values (up to 50 MHz) have been observed in a similar system [52]. The reasons why compression fails above a certain frequency are not presently known.…”

Section: A Positron Accumulatormentioning

confidence: 99%

“…However, the implantation of positrons will also generate some e-h pairs, and if the positron beam density is high enough, e-h pair production by one positron may increase the probability that another positron is emitted as a Ps atom, leading to a linear relationship between f RW and f d , which we indeed observe in Fig 4 (c). This figure shows the Ps yield as a as a function of the RW drive frequency as well as a linear fit, excluding the 8.1 MHz point, which is due to a zero-frequency mode (ZFM) plasma resonance that causes a loss of plasma density [49,51]. The reason why the maximum yield in Fig 4 (a) is larger than that of Fig 4 (b) is that the higher magnetic field that is required for attaining a high positron density leads to magnetic quenching of positronium [68].…”

Section: B Ps Yieldmentioning

confidence: 99%

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Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

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Recent experiments combining lifetime and laser spectroscopy of positronium (Ps) show that these atoms are emitted from p-Si(100) at a rate that depends on the sample temperature, suggesting a thermal activation process, but with an energy that does not, precluding direct thermal activation as the emission mechanism. Moreover, the amount of Ps emitted is substantially increased if the target is irradiated with 532 nm laser light just prior to the implantation of the positrons. Our interpretation of these data was that the Ps was emitted via an exciton-like positron-electron surface state, not dissimilar to an electronic surface exciton observed on Si in two-photon photoemission measurements. The hypothesis that this state may be populated by electrons from one of the occupied electronic surface states, either thermally or by laser excitation, is consistent with our observations and suggests that one should expect a high Ps yield at room temperature from an n-doped Si(100) sample, since in this case the same surface states will already be occupied. Here we present data obtained with an n-Si(100) target that supports our model, and also reveals the unexpected result that the kinetic energy of Ps emitted from this material actually decreases when it is heated, an effect we attribute to shifts in the surface energy levels due to the presence of a high density of thermally generated electrons. We show data obtained with a Ge(100) sample that corroborate the idea that the effects we observe are related to surface electron states, and hence should occur for any indirect band gap semiconductor with dangling bond states. Our model is further confirmed by the observation that the Ps yield from p-Si depends linearly on the surface density of the implanted positrons due to the effects of electron-hole pairs created as the positrons slow down.

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Section: A Positron Accumulatormentioning

confidence: 99%

Section: B Ps Yieldmentioning

confidence: 99%

Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

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“…These modes have also been shown to limit strong-drive compression in experiments with positron plasmas at low magnetic fields and using buffer gas cooling [see Fig. 25 and Cassidy et al (2010b)]. …”

Section: Strong Drive Regimementioning

confidence: 99%

Plasma and trap-based techniques for science with positrons

Danielson¹,

Dubin²,

Greaves³

et al. 2015

Rev. Mod. Phys.

233

222

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In recent years, there has been a wealth of new science involving low-energy antimatter (i.e., positrons and antiprotons) at energies ranging from 10 2 to less than 10 −3 eV. Much of this progress has been driven by the development of new plasma-based techniques to accumulate, manipulate and deliver antiparticles for specific applications. This article focuses on the advances made in this area using positrons. However many of the resulting techniques are relevant to antiprotons as well. An overview is presented of relevant theory of single-component plasmas in electromagnetic traps. Methods are described to produce intense sources of positrons and to efficiently slow the typically energetic particles thus produced. Techniques are described to trap positrons efficiently and to cool and compress the resulting positron gases and plasmas. Finally, the procedures developed to deliver tailored pulses and beams (e.g., in intense, short bursts, or as quasi-monoenergetic continuous beams) for specific applications are reviewed. The status of development in specific application areas is also reviewed. One example is the formation of antihydrogen atoms for fundamental physics [e.g., tests of invariance under charge conjugation, parity inversion and time reversal (the CPT theorem), and studies of the interaction of gravity with antimatter]. Other applications discussed include atomic and materials physics studies and study of the electron-positron many-body system, including both classical electron-positron plasmas and the complementary quantum system in the form of Bose-condensed gases of positronium atoms. Areas of future promise are also discussed. The review concludes with a brief summary and a list of outstanding challenges.

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“…In one experiment a porous silica target was utilized, as shown in Figure 39, and in the other Ps 2 was generated on an Al(1 1 1) surface, as indicated in Figure 40. In both cases a high-density positron pulse was obtained using a pulsed 2.3 T magnetic field [356] and plasma manipulation techniques [593]. The positron beam densities required to obtain Ps densities sufficient to observe Ps-Ps interactions (and thus also Ps 2 formation) can be estimated from calculated Ps-Ps scattering cross sections σ Ps = 1 × 10 −15 cm −2 [589].…”

Section: Ps 2 Spectroscopymentioning

confidence: 99%

“…In previous experiments [356] this was done by stacking positrons in an accumulator and using plasma compression methods (i.e., strong drive rotating wall techniques [353][354][355]593]) to increase the beam density. This beam was then further compressed with a pulsed magnetic field.…”

Section: Bose-einstein Condensationmentioning

confidence: 99%

Experimental progress in positronium laser physics

2018

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Abstract. The field of experimental positronium physics has advanced significantly in the last few decades, with new areas of research driven by the development of techniques for trapping and manipulating positrons using Surko-type buffer gas traps. Large numbers of positrons (typically ≥10 6 ) accumulated in such a device may be ejected all at once, so as to generate an intense pulse. Standard bunching techniques can produce pulses with ns (mm) temporal (spatial) beam profiles. These pulses can be converted into a dilute Ps gas in vacuum with densities on the order of 10 7 cm −3 which can be probed by standard ns pulsed laser systems. This allows for the efficient production of excited Ps states, including long-lived Rydberg states, which in turn facilitates numerous experimental programs, such as precision optical and microwave spectroscopy of Ps, the application of Stark deceleration methods to guide, decelerate and focus Rydberg Ps beams, and studies of the interactions of such beams with other atomic and molecular species. These methods are also applicable to antihydrogen production and spectroscopic studies of energy levels and resonances in positronium ions and molecules. A summary of recent progress in this area will be given, with the objective of providing an overview of the field as it currently exists, and a brief discussion of some future directions.

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Strong drive compression of a gas-cooled positron plasma

Cited by 9 publications

References 20 publications

Positronium formation via excitonlike states on Si and Ge surfaces

Positronium formation via excitonlike states on Si and Ge surfaces

Plasma and trap-based techniques for science with positrons

Experimental progress in positronium laser physics

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