We measured the velocity distribution of ions in the ultracold neutral plasma (UNP) during its early evolution by the technique of velocity map imaging. The ion temperature during the phase of ion equilibrium was obtained experimentally through this method. The Coulomb coupling parameter of ions in the UNP after disorder-induced heating was also determined to be 2.1, which agreed well with the prediction from a charged particle tracing simulation. In addition, the ion expansion during the ion equilibration phase was observed. Notably, the experimentally observed expansion speed is larger than the value obtained from the self-similar expansion model, indicating the involvement of additional mechanisms, besides the electron thermal pressure, in driving the ion expansion. We have also discussed the contributions of ion–ion correlations and charge imbalance to the plasma expansion.

1.
T. C.
Killian
,
S.
Kulin
,
S. D.
Bergeson
,
L. A.
Orozco
,
C.
Orzel
, and
S. L.
Rolston
,
Phys. Rev. Lett.
83
(
23
),
4776
(
1999
).
2.
S.
Ichimaru
,
Rev. Mod. Phys.
54
(
4
),
1017
(
1982
).
3.
R. S.
Fletcher
,
X. L.
Zhang
, and
S. L.
Rolston
,
Phys. Rev. Lett.
96
(
10
),
105003
(
2006
).
4.
J.
Castro
,
P.
McQuillen
, and
T. C.
Killian
,
Phys. Rev. Lett.
105
(
6
),
065004
(
2010
).
5.
K. A.
Twedt
and
S. L.
Rolston
,
Phys. Rev. Lett.
108
(
6
),
065003
(
2012
).
6.
X. L.
Zhang
,
R. S.
Fletcher
, and
S. L.
Rolston
,
Phys. Rev. Lett.
101
(
19
),
195002
(
2008
).
7.
M. S.
Murillo
,
Phys. Rev. Lett.
87
(
11
),
115003
(
2001
).
8.
T.
Pohl
,
T.
Pattard
, and
J. M.
Rost
,
Phys. Rev. Lett.
94
(
20
),
205003
(
2005
).
9.
C. E.
Simien
,
Y. C.
Chen
,
P.
Gupta
,
S.
Laha
,
Y. N.
Martinez
,
P. G.
Mickelson
,
S. B.
Nagel
, and
T. C.
Killian
,
Phys. Rev. Lett.
92
(
14
),
143001
(
2004
).
10.
S. D.
Bergeson
,
S. D.
Baalrud
,
C. L.
Ellison
,
E.
Grant
,
F. R.
Graziani
,
T. C.
Killian
,
M. S.
Murillo
,
J. L.
Roberts
, and
L. G.
Stanton
,
Phys. Plasmas
26
(
10
),
100501
(
2019
).
11.
A.
Burrows
and
J.
Liebert
,
Rev. Mod. Phys.
65
(
2
),
301
(
1993
).
12.
B. A.
Remington
,
R. P.
Drake
, and
D. D.
Ryutov
,
Rev. Mod. Phys.
78
(
3
),
755
(
2006
).
13.
E. A.
Cummings
,
J. E.
Daily
,
D. S.
Durfee
, and
S. D.
Bergeson
,
Phys. Rev. Lett.
95
(
23
),
235001
(
2005
).
14.
E. A.
Cummings
,
J. E.
Daily
,
D. S.
Durfee
, and
S. D.
Bergeson
,
Phys. Plasmas
12
(
12
),
123501
(
2005
).
15.
S.
Laha
,
P.
Gupta
,
C. E.
Simien
,
H.
Gao
,
J.
Castro
,
T.
Pohl
, and
T. C.
Killian
,
Phys. Rev. Lett.
99
(
15
),
155001
(
2007
).
16.
A. T. J. B.
Eppink
and
D. H.
Parker
,
Rev. Sci. Instrum.
68
(
9
),
3477
3484
(
1997
).
17.
A. G.
Suits
,
Rev. Sci. Instrum.
89
(
11
),
111101
(
2018
).
18.
T. C.
Killian
,
T.
Pattard
,
T.
Pohl
, and
J. M.
Rost
,
Phys. Rep.
449
(
4
),
77
130
(
2007
).
19.
20.
V. F.
Kovalev
and
V. Y.
Bychenkov
,
Phys. Rev. Lett.
90
(
18
),
185004
(
2003
).
21.
S.
Kulin
,
T. C.
Killian
,
S. D.
Bergeson
, and
S. L.
Rolston
,
Phys. Rev. Lett.
85
(
2
),
318
(
2000
).
22.
T. K.
Langin
,
G. M.
Gorman
, and
T. C.
Killian
,
Science
363
(
6422
),
61
(
2019
).
23.
G. M.
Gorman
,
M. K.
Warrens
,
S. J.
Bradshaw
, and
T. C.
Killian
,
Phys. Rev. Lett.
126
(
8
),
085002
(
2021
).
24.
T.
Pohl
,
T.
Pattard
, and
J. M.
Rost
,
Phys. Rev. A
70
(
3
),
033416
(
2004
).
25.
C.
Witte
and
J. L.
Roberts
,
Phys. Plasmas
21
(
10
),
103513
(
2014
).
26.
F.
Fang
,
W.
Zhou
,
Y.
Li
,
D.
Qian
,
C.
Luo
,
D.
Zhao
,
X.
Ma
, and
J.
Yang
,
Rev. Sci. Instrum.
92
(
4
),
043103
(
2021
).
27.
R. N.
Strickland
and
D. W.
Chandler
,
Appl. Opt.
30
(
14
),
1811
1819
(
1991
).
28.
C. J.
Dasch
,
Appl. Opt.
31
(
8
),
1146
1152
(
1992
).
29.
M. J. J.
Vrakking
,
Rev. Sci. Instrum.
72
(
11
),
4084
4089
(
2001
).
30.
V.
Dribinski
,
A.
Ossadtchi
,
V. A.
Mandelshtam
, and
H.
Reisler
,
Rev. Sci. Instrum.
73
(
7
),
2634
2642
(
2002
).
31.
A. T. J. B.
Eppink
,
S.-M.
Wu
, and
B. J.
Whitaker
, in
Imaging in Molecular Dynamics: Technology and Applications
, edited by
B. J.
Whitaker
(
Cambridge University Press
,
Cambridge
,
2003
), pp.
65
112
.
32.
G. A.
Garcia
,
L.
Nahon
, and
I.
Powis
,
Rev. Sci. Instrum.
75
(
11
),
4989
4996
(
2004
).
33.
B.
Dick
,
Phys. Chem. Chem. Phys.
16
(
2
),
570
580
(
2014
).
34.
S. D.
Bergeson
,
A.
Denning
,
M.
Lyon
, and
F.
Robicheaux
,
Phys. Rev. A
83
(
2
),
023409
(
2011
).
35.
M. P.
Reijnders
,
P. A.
van Kruisbergen
,
G.
Taban
,
S. B.
van der Geer
,
P. H. A.
Mutsaers
,
E. J. D.
Vredenbregt
, and
O. J.
Luiten
,
Phys. Rev. Lett.
102
(
3
),
034802
(
2009
).
36.
G.
ten Haaf
,
S. H. W.
Wouters
,
S. B.
van der Geer
,
E. J. D.
Vredenbregt
, and
P. H. A.
Mutsaers
,
J. Appl. Phys.
116
(
24
),
244301
(
2014
).
37.
D.
Murphy
,
R. W.
Speirs
,
D. V.
Sheludko
,
C. T.
Putkunz
,
A. J.
McCulloch
,
B. M.
Sparkes
, and
R. E.
Scholten
,
Nat. Commun.
5
(
1
),
4489
(
2014
).
38.
T.
Kroker
,
M.
Großmann
,
K.
Sengstock
,
M.
Drescher
,
P.
Wessels-Staarmann
, and
J.
Simonet
,
Nat. Commun.
12
(
1
),
596
(
2021
).
39.
R. T.
Farouki
and
S.
Hamaguchi
,
J. Chem. Phys.
101
(
11
),
9885
9893
(
1994
).
40.
S.
Hamaguchi
,
R. T.
Farouki
, and
D. H. E.
Dubin
,
J. Chem. Phys.
105
(
17
),
7641
7647
(
1996
).
41.
S.
Hamaguchi
,
R. T.
Farouki
, and
D. H. E.
Dubin
,
Phys. Rev. E
56
(
4
),
4671
4682
(
1997
).
42.
P.
McQuillen
,
T.
Strickler
,
T.
Langin
, and
T. C.
Killian
,
Phys. Plasmas
22
(
3
),
033513
(
2015
).
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