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Trend: Ultracold neutral plasmas

S. L. Rolston

Published Jul 14, 2008• 2 citations
OpenAlex

Abstract

Laser-cooled atomic vapors can be photoionized to form plasmas at temperatures as low as 1 K. This may allow the study of very unusual neutral plasmas with liquid and even crystalline properties.

Related papers

Using Laser Cooling to Study Plasma Physics

S. L. Rolston, Robert Samuel Fletcher, Xianli Zhang

Ultracold neutral plasmas are formed by photoionizing laser-cooled atoms. The resulting plasmas are the coldest neutral plasmas ever formed, exhibiting a rich variety of behavior, including Rydberg atom formation, driven expansion, and plasma instabilities.

Frontiers in Optics•Jan 1, 2006•0 citations

Ultracold neutral plasmas

S. L. Rolston

Plasmas are normally thought of as high temperature ionized gases or fluids, such as those in the sun's corona or those found in controlled nuclear fusion experiments.Many interesting plasma phenomena can occur, however, in plasmas at low temperature.With the help of laser trapping and cooling, atoms can be photoionized to form neutral plasmas at extremely low temperatures.These plasmas may exist in the so-called strong coupling regime, where the energy of the Coulomb interactions between particles is larger than their thermal energy.In addition to providing a test bed for studying the strongly coupled plasmas such as those found in Jovian planets and white dwarfs, ultracold plasmas play a critical role in understanding the formation of antihydrogen.

Physics•Jul 14, 2008•35 citations

Ultracold neutral plasmas

Mary Lyon, S. L. Rolston

By photoionizing samples of laser-cooled atoms with laser light tuned just above the ionization limit, plasmas can be created with electron and ion temperatures below 10 K. These ultracold neutral plasmas have extended the temperature bounds of plasma physics by two orders of magnitude. Table-top experiments, using many of the tools from atomic physics, allow for the study of plasma phenomena in this new regime with independent control over the density and temperature of the plasma through the excitation process. Characteristic of these systems is an inhomogeneous density profile, inherited from the density distribution of the laser-cooled neutral atom sample. Most work has dealt with unconfined plasmas in vacuum, which expand outward at velocities of order 100 m/s, governed by electron pressure, and with lifetimes of order 100 μs, limited by stray electric fields. Using detection of charged particles and optical detection techniques, a wide variety of properties and phenomena have been observed, including expansion dynamics, collective excitations in both the electrons and ions, and collisional properties. Through three-body recombination collisions, the plasmas rapidly form Rydberg atoms, and clouds of cold Rydberg atoms have been observed to spontaneously avalanche ionize to form plasmas. Of particular interest is the possibility of the formation of strongly coupled plasmas, where Coulomb forces dominate thermal motion and correlations become important. The strongest impediment to strong coupling is disorder-induced heating, a process in which Coulomb energy from an initially disordered sample is converted into thermal energy. This restricts electrons to a weakly coupled regime and leaves the ions barely within the strongly coupled regime. This review will give an overview of the field of ultracold neutral plasmas, from its inception in 1999 to current work, including efforts to increase strong coupling and effects on plasma properties due to strong coupling.

Reports on Progress in Physics•Nov 17, 2016•77 citations

Ultracold neutral plasmas

T. C. Killian, Ying-Cheng Chen, Priya Gupta +6 more

Ultracold neutral plasmas are formed by photoionizing laser-cooled atoms near the ionization threshold. Through the application of atomic physics techniques and diagnostics, these experiments stretch the boundaries of traditional neutral plasma physics. The electron temperature in these plasmas ranges from 1-1000 K and the ion temperature is around 1 K. The density can approach $10^{11}$ cm$^{-3}$. Fundamental interest stems from the possibility of creating strongly-coupled plasmas, but recombination, collective modes, and thermalization in these systems have also been studied. Optical absorption images of a strontium plasma, using the Sr$^+$ ${^2S_{1/2}} -> {^2P_{1/2}}$ transition at 422 nm, depict the density profile of the plasma, and probe kinetics on a 50 ns time-scale. The Doppler-broadened ion absorption spectrum measures the ion velocity distribution, which gives an accurate measure of the ion dynamics in the first microsecond after photoionization.

Plasma Physics and Controlled Fusion•Apr 20, 2005•5 citations

An Ultracold Neutral Plasma Created by Photoionizing Laser-Cooled Xenon

T. C. Killian, S. A. Kulin, S. L. Rolston

•Jan 1, 2000•0 citations

Ultracold neutral plasmas

T. C. Killian

By photoionizing a sample of laser-cooled xenon atoms, we create ultracold neutral plasmas with initial temperatures of 1–1000 K and densities as high as 1010 cm−3. The plasma is formed by the trapping of electrons by the residual positive charge that is left after some electrons initially leave the sample. We excite plasma oscillations with applied radio frequency fields and use this to monitor the expansion of the unconfined plasma. We have observed significant recombination of the plasma into Rydberg atoms (up to 20%). At these low temperatures, the only traditional form of recombination that could be significant is three-body recombination (TBR), but we see a number of trends in direct contradiction to what one would expect from classical TBR theory.

AIP conference proceedings•Jan 1, 2002•2 citations
Plasmas are normally thought of as high temperature ionized gases or fluids, such as those in the sun's corona or those found in controlled nuclear fusion experiments.Many interesting plasma phenomena can occur, however, in plasmas at low temperature.With the help of laser trapping and cooling, atoms can be photoionized to form neutral plasmas at extremely low temperatures.These plasmas may exist in the so-called strong coupling regime, where the energy of the Coulomb interactions between particles is larger than their thermal energy.In addition to providing a test bed for studying the strongly coupled plasmas such as those found in Jovian planets and white dwarfs, ultracold plasmas play a critical role in understanding the formation of antihydrogen.
By photoionizing samples of laser-cooled atoms with laser light tuned just above the ionization limit, plasmas can be created with electron and ion temperatures below 10 K. These ultracold neutral plasmas have extended the temperature bounds of plasma physics by two orders of magnitude. Table-top experiments, using many of the tools from atomic physics, allow for the study of plasma phenomena in this new regime with independent control over the density and temperature of the plasma through the excitation process. Characteristic of these systems is an inhomogeneous density profile, inherited from the density distribution of the laser-cooled neutral atom sample. Most work has dealt with unconfined plasmas in vacuum, which expand outward at velocities of order 100 m/s, governed by electron pressure, and with lifetimes of order 100 μs, limited by stray electric fields. Using detection of charged particles and optical detection techniques, a wide variety of properties and phenomena have been observed, including expansion dynamics, collective excitations in both the electrons and ions, and collisional properties. Through three-body recombination collisions, the plasmas rapidly form Rydberg atoms, and clouds of cold Rydberg atoms have been observed to spontaneously avalanche ionize to form plasmas. Of particular interest is the possibility of the formation of strongly coupled plasmas, where Coulomb forces dominate thermal motion and correlations become important. The strongest impediment to strong coupling is disorder-induced heating, a process in which Coulomb energy from an initially disordered sample is converted into thermal energy. This restricts electrons to a weakly coupled regime and leaves the ions barely within the strongly coupled regime. This review will give an overview of the field of ultracold neutral plasmas, from its inception in 1999 to current work, including efforts to increase strong coupling and effects on plasma properties due to strong coupling.
Ultracold neutral plasmas are formed by photoionizing laser-cooled atoms near the ionization threshold. Through the application of atomic physics techniques and diagnostics, these experiments stretch the boundaries of traditional neutral plasma physics. The electron temperature in these plasmas ranges from 1-1000 K and the ion temperature is around 1 K. The density can approach 101110^{11}1011 cm−3^{-3}−3. Fundamental interest stems from the possibility of creating strongly-coupled plasmas, but recombination, collective modes, and thermalization in these systems have also been studied. Optical absorption images of a strontium plasma, using the Sr+^++ 2S1/2−>2P1/2{^2S_{1/2}} -> {^2P_{1/2}}2S1/2​−>2P1/2​ transition at 422 nm, depict the density profile of the plasma, and probe kinetics on a 50 ns time-scale. The Doppler-broadened ion absorption spectrum measures the ion velocity distribution, which gives an accurate measure of the ion dynamics in the first microsecond after photoionization.
By photoionizing a sample of laser-cooled xenon atoms, we create ultracold neutral plasmas with initial temperatures of 1–1000 K and densities as high as 1010 cm−3. The plasma is formed by the trapping of electrons by the residual positive charge that is left after some electrons initially leave the sample. We excite plasma oscillations with applied radio frequency fields and use this to monitor the expansion of the unconfined plasma. We have observed significant recombination of the plasma into Rydberg atoms (up to 20%). At these low temperatures, the only traditional form of recombination that could be significant is three-body recombination (TBR), but we see a number of trends in direct contradiction to what one would expect from classical TBR theory.