Resistive magnetohydrodynamic simulations are used to evaluate the effects of the aspect ratio A (length to radius ratio) in a spheromak driven by coaxial helicity injection. The simulations are benchmarked against the Sustained Spheromak Physics Experiment (SSPX) [R. D. Wood et al, Nucl. Fusion45, 1582 (2005)]. Amplification of the bias (“gun”) poloidal flux is fitted well by a linear dependence (insensitive to A) on the ratio of gun current and bias flux above a threshold dependent on A. For low flux amplifications in the simulations, the n=1 mode is coherent and the mean-field geometry looks like a tilted spheromak. Because the mode has relatively large amplitude the field lines are open everywhere, allowing helicity penetration. Strongly driven helicity injection at A1.4 in simulations generates reconnection events which generate cathode-voltage spikes, relaxation of the symmetry-breaking modes, and open, stochastic magnetic field lines; this state is characteristic of SSPX. The time sequences of these events suggest that they are representative of a chaotic process. Near the spheromak tilt-mode limit, A1.67 for a cylindrical flux conserver, the tilt approaches 90°; reconnection events are not generated up to the strongest drives simulated. Implications for spheromak experiments are discussed.

1.
T. R.
Jarboe
,
Plasma Phys. Controlled Fusion
36
,
945
(
1994
).
2.
W. C.
Turner
,
G. C.
Goldenbaum
,
E. H.
Granneman
,
J. H.
Hammer
,
C. W.
Hartman
,
D. S.
Prono
, and
J.
Taska
,
Phys. Fluids
26
,
1083
(
1965
).
3.
T. R.
Jarboe
,
F. J.
Wysocki
,
J. C.
Fernández
,
I.
Henins
, and
G. J.
Marklin
,
Phys. Fluids B
2
,
1342
(
1990
).
4.
M.
Nagata
,
T.
Kanki
,
T.
Matsuda
,
S.
Naito
,
H.
Tatsumi
, and
T.
Uyama
,
Phys. Rev. Lett.
71
,
4342
(
1993
).
5.
M. G.
Rusbridge
,
S. J.
Gee
,
P. K.
Browning
,
G.
Cunningham
,
R. C.
Duck
,
A.
al-Karkhy
,
R.
Martin
, and
J. W.
Bradley
,
Plasma Phys. Controlled Fusion
39
,
683
(
1997
).
6.
B.
Hudson
,
R. D.
Wood
,
H. S.
McLean
,
E. B.
Hooper
,
D. N.
Hill
,
J.
Jayakumar
,
J.
Moller
,
D.
Montez
,
C. A.
Romero-Talamás
,
T. A.
Casper
,
J. A.
Johnson
 III
,
L. L.
LoDestro
,
E.
Mezonlin
, and
L. D.
Pearlstein
,
Phys. Plasmas
15
,
056112
(
2008
).
7.
T. R.
Jarboe
, personal communication (
2000
).
8.
E. B.
Hooper
,
D. N.
Hill
,
H. S.
McLean
,
C. A.
Romero-Talamás
, and
R. D.
Wood
,
Nucl. Fusion
47
,
1064
(
2007
).
9.
T. H.
Jensen
and
M. S.
Chu
,
Phys. Fluids
27
,
2881
(
1984
).
10.
E. B.
Hooper
,
T. A.
Kopriva
,
B. I.
Cohen
,
D. N.
Hill
,
H. S.
McLean
,
R. D.
Wood
, and
S.
Woodruff
,
Phys. Plasmas
12
,
092503
(
2005
).
11.
R. L.
Hagenson
and
R. A.
Krakowski
,
Fusion Technol.
8
,
1606
(
1985
).
12.
M. N.
Rosenbluth
and
M. N.
Bussac
,
Nucl. Fusion
19
,
489
(
1979
).
13.
J. M.
Finn
,
W. M.
Manheimer
, and
E.
Ott
,
Phys. Fluids
24
,
1336
(
1981
).
14.
A.
Bondeson
,
G.
Marklin
,
Z. G.
An
,
H. H.
Chen
,
Y. C.
Lee
, and
C. S.
Liu
,
Phys. Fluids
24
,
1682
(
1981
).
15.
C. W.
Barnes
,
T. R.
Jarboe
,
G. J.
Marklin
,
S. O.
Knox
, and
I.
Henins
,
Phys. Fluids B
2
,
1871
(
1990
).
16.
R. D.
Wood
,
D. N.
Hill
,
H. S.
McLean
,
E. B.
Hooper
,
B. F.
Hudson
,
J. M.
Moller
, and
C. A.
Romero-Talamás
,
Nucl. Fusion
49
,
025001
(
2009
).
17.
C. R.
Sovinec
,
J. M.
Finn
, and
D.
del-Castillo-Negrete
,
Phys. Plasmas
8
,
475
(
2001
).
18.
E. B.
Hooper
,
B. I.
Cohen
,
H. S.
Mclean
,
R. D.
Wood
,
C. A.
Romero-Talamás
, and
C. R.
Sovinec
,
Phys. Plasmas
15
,
032502
(
2008
).
19.
M. P.
Bellan
,
Spheromaks
(
Imperial College Press
,
London
,
2000
), p.
131
.
20.
D. A.
Kitson
and
P. K.
Browning
,
Plasma Phys. Controlled Fusion
32
,
1265
(
1990
).
21.
H.
Childs
,
E. S.
Brugger
,
K. S.
Bonnell
,
J. S.
Meredith
,
M.
Miller
,
B. J.
Whitlock
, and
N.
Max
,
IEEE Conf. Proc. Visualization
VIS 05
,
191
(
2005
);
22.
R. C.
Hilborn
,
Chaos and Nonlinear Dynamics
, 2nd ed. (
Oxford
,
New York
,
2000
), Chap. 4.
23.
G. L.
Benettin
,
L.
Galgani
, and
J. M.
Strelcyn
,
Phys. Rev. A
14
,
2338
(
1976
).
24.
J. M.
Finn
,
C. R.
Sovinec
, and
D.
del-Castillo-Negrete
,
Phys. Rev. Lett.
85
,
4538
(
2000
).
25.
A. H.
Boozer
,
Phys. Fluids B
5
,
2271
(
1993
).
26.
R. W.
Moses
,
R. A.
Gerwin
, and
K. F.
Schoenberg
,
Phys. Plasmas
8
,
4839
(
2001
).
27.
R. R.
Mett
and
J. B.
Taylor
,
Phys. Fluids B
4
,
73
(
1992
).
28.
R. C.
Duck
,
P. K.
Browning
,
G.
Cunningham
,
S. J.
Gee
,
A.
al-Karkhy
,
R.
Martin
, and
M. G.
Rusbridge
,
Plasma Phys. Controlled Fusion
39
,
715
(
1997
).
29.
S.
Woodruff
and
M.
Nagata
,
Plasma Phys. Controlled Fusion
44
,
2539
(
2002
).
30.
T. R.
Jarboe
,
F. J.
Wysocki
,
J. C.
Fernández
,
I.
Henins
, and
G. J.
Marklin
,
Phys. Fluids B
2
,
1342
(
1990
).
You do not currently have access to this content.