Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Expansion of an ultracold Rydberg plasma   We report a systematic experimental and numerical study of the expansion of
ultra-cold Rydberg plasmas. Specifically, we have measured the asymptotic
expansion velocities, $v_0$, of ultra-cold neutral plasmas (UNPs) which evolve
from cold, dense samples of Rydberg rubidium atoms using ion time-of-flight
spectroscopy. From this, we have obtained values for the effective initial
plasma electron temperature, $T_{e,0} = m_{ion} v_0^2/k_B$ (where $m_{ion}$ is
the Rb$^+$ ion mass), as a function of the original Rydberg atom density and
binding energy, $E_{b,i}$. We have also simulated numerically the interaction
of UNPs with a large reservoir of Rydberg atoms to obtain data to compare with
our experimental results. We find that for Rydberg atom densities in the range
$10^7 - 10^9$ cm$^{-3}$, for states with principal quantum number $n > 40$,
$T_{e,0}$ is insensitive to the initial ionization mechanism which seeds the
plasma. In addition, the quantity $k_B \, T_{e,0}$ is strongly correlated with
the fraction of atoms which ionize, and is in the range $0.6 \times |E_{b,i}|
\lesssim k_BT_{e,0} \lesssim 2.5 \times |E_{b,i}|$. On the other hand, plasmas
from Rydberg samples with $n \lesssim 40$ evolve with no significant additional
ionization of the remaining atoms once a threshold number of ions has been
established. The dominant interaction between the plasma electrons and the
Rydberg atoms is one in which the atoms are deexcited, a heating process for
electrons that competes with adiabatic cooling to establish an equilibrium
where $T_{e,0}$ is determined by their Coulomb coupling parameter, $\Gamma_e
\sim 0.01$.

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The categories of this paper are: hep-ph
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
9
The categories of this paper are: nlin
33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
26
The categories of this paper are: bayes-an
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The categories of this paper are: math
4
The categories of this paper are: cond-mat
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
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The categories of this paper are: hep-ex
19
The categories of this paper are: eess