Magnetic shielding of Hall thrusters has been shown to reduce erosion of the channel walls by at least a few orders of magnitude, thereby enabling the use of these devices in deep space missions. Wear tests of magnetically shielded thrusters, such as the H6 and HERMeS, have revealed that some sputtering occurs at the surface of the inner pole, a phenomenon not observed in unshielded thrusters. Even though the sputtering rates measured at the inner pole during ground testing are typically an order of magnitude lower than those found in the acceleration channel of unshielded thrusters, it is critical to understand how the source(s) of this erosion may change with operating conditions during flight. Hall2De is a 2-D axisymmetric code that makes use of a hydrodynamics formulation for both electrons and ions and assumes a quasi-neutral plasma. Since its computational domain is large enough to account for the discharge channel, poles, cathode, and plume regions, Hall2De can be used to investigate the physical mechanisms that produce the erosion of the poles. The simulation results are compared with experimental laser-induced fluorescence measurements of the ion velocity along the discharge channel of the H6 thruster. We find that the erosion of the poles in the magnetically shielded H6 is a result of the acceleration region moving outside of the discharge channel, which in turn is a consequence of a shift in the location of the maximum magnetic field along the channel centerline that occurs when magnetic shielding is implemented. When the acceleration region moves downstream, the plasma potential contours at the edges of the beam allow for high energy ions to be accelerated radially toward the pole surfaces.

1.
I. G.
Mikellides
,
I.
Katz
,
R. R.
Hofer
,
D. M.
Goebel
,
K. H.
de Grys
, and
A.
Mathers
, “
Magnetic shielding of the channel walls in a hall plasma accelerator
,”
Phys. Plasmas
18
(
3
),
033501
(
2011
).
2.
I. G.
Mikellides
and
I.
Katz
, “
Numerical simulations of hall-effect plasma accelerators on a magnetic-field-aligned mesh
,”
Phys. Rev. E
86
,
046703
(
2012
).
3.
K.
De Grys
,
A.
Mathers
, and
B.
Welander
, “Demonstration of 10,400 hours of operation on a 4.5kW qualification model Hall thruster,” in Proceedings of the 46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Nashville, TN, AIAA Paper 2010-6698, 2010.
4.
I. G.
Mikellides
,
I.
Katz
,
R. R.
Hofer
, and
D. M.
Goebel
, “
Magnetic shielding of a laboratory hall thruster. I. Theory and validation
,”
J. Appl. Phys.
115
,
043303
(
2014
).
5.
R. R.
Hofer
,
D. M.
Goebel
,
I. G.
Mikellides
, and
I.
Katz
, “
Magnetic shielding of a laboratory Hall thruster. II. Experiments
,”
J. Appl. Phys.
115
,
043304
(
2014
).
6.
J. M.
Haas
,
R. R.
Hofer
,
D. L.
Brown
,
B. M.
Reid
, and
A. D.
Gallimore
, “Design of a 6-kW Hall thruster for high thrust/power investigation,” in 54th JANNAF Propulsion Meeting, Denver, Colorado, 2007.
7.
R. R.
Hofer
,
B. A.
Jorns
,
J. E.
Polk
,
I. G.
Mikellides
, and
J. S.
Snyder
, “Wear test of a magnetically shielded Hall thruster at 3000 seconds specific impulse,” in Proceedings of the 33rd International Electric Propulsion Conference, Washington, DC, IEPC Paper No. 2013-033, 2013.
8.
J. M.
Sekerak
,
R. R.
Hofer
,
J. E.
Polk
,
B. A.
Jorns
, and
I. G.
Mikellides
, “Wear testing of a magnetically shielded Hall thruster at 2000-s specific impulse,” IEPC 2015-155, 2015.
9.
I. G.
Mikellides
,
R. R.
Hofer
,
I.
Katz
, and
D. M.
Goebel
, “
Magnetic shielding of Hall thrusters at high discharge voltages
,”
J. Appl. Phys.
116
,
054402
(
2014
).
10.
I. G.
Mikellides
and
A.
Lopez Ortega
, “Assessment of pole erosion in a magnetically shielded Hall thruster,” AIAA Paper 2014-3897, 2014
11.
A.
Lopez Ortega
,
I. G.
Mikellides
, and
I.
Katz
, “Hall2De numerical simulations for the assessment of pole erosion in a magnetically shielded Hall thruster,” IEPC 2015-249, 2015.
12.
I. G.
Mikellides
,
I.
Katz
,
D. M.
Goebel
,
J. E.
Polk
, and
K. K.
Jameson
, “
Evidence of non-classical plasma transport in hollow cathodes for electric propulsion
,”
J. Appl. Phys.
101
(
6
),
063301
(
2007
).
13.
B. A.
Jorns
,
I. G.
Mikellides
, and
D. M.
Goebel
, “
Ion acoustic turbulence in a 100-A LaB6 hollow cathode
,”
Phys. Rev. E
90
,
063106
(
2014
).
14.
E. K.
Zavoiskii
and
L. I.
Rudakov
, “
Turbulent heating of plasma
,”
Sov. J. Atomic Energy
23
,
417
431
(
1967
).
15.
E. D.
Volkov
,
N. F.
Perepelkin
, and
V. A.
Suprunenko
,
Collective Phenomena in Current-Carrying Plasma
(
Naukova Dumka
,
Kiev
,
1979
), p.
86
.
16.
C. T.
Dum
,
R.
Chodura
, and
D.
Biskamp
, “
Turbulent heating and quenching of the ion sound instability
,”
Phys. Rev. Lett.
32
(
22
),
1231
1234
(
1974
).
17.
E. K.
Zavoiskii
,
S. L.
Nedoseev
, and
L. I.
Rudakov
, “
Ion heating in a turbulent plasma
,”
JETP Lett.
6
,
367
369
(
1967
).
18.
T.
Honzawa
and
Y.
Kawai
, “
Ion heating caused by ion acoustic waves in an ion-streaming plasma
,”
Plasma Phys.
14
,
27
36
.
19.
B. A.
Jorns
,
C. A.
Dodson
,
R. A.
Anderson
,
D. M.
Goebel
,
R. R.
Hofer
,
J. M.
Sekerak
,
A.
Lopez Ortega
, and
I. G.
Mikellides
, “Mechanisms for pole piece erosion in a 6-kW magnetically shielded Hall thruster,” AIAA Paper 2016-4839, 2016.
20.
R. J.
Cedolin
,
W. A.
Hargus
,
P. V.
Storm
,
R. K.
Hanson
, and
M. A.
Cappelli
, “
Laser-induced fluorescence study of a xenon hall thruster
,”
Appl. Phys. B
65
(
4–5
),
459
469
(
1997
).
21.
W. A.
Hargus
and
M. A.
Cappelli
, “
Laser-induced fluorescence measurements of velocity within a hall discharge
,”
Appl. Phys. B
72
(
8
),
961
969
(
2001
).
22.
A.
Lopez Ortega
and
I. G.
Mikellides
, “
The importance of the cathode plume and its interactions with the ion beam in numerical simulations of hall thrusters
,”
Phys. Plasmas
23
,
043515
(
2016
).
23.
I.
Katz
and
I. G.
Mikellides
, “
Neutral gas free molecular flow algorithm including ionization and walls for use in plasma simulations
,”
J. Comput. Phys.
230
,
1454
1464
(
2011
).
24.
G. D.
Hobbs
and
J. A.
Wesson
, “
Heat flow through a Langmuir sheath in presence of electron emission
,”
Plasma Phys.
9
(
1
),
85
87
(
1967
).
25.
I. G.
Mikellides
and
I.
Katz
, “
Wear mechanisms in electron sources for ion propulsion I: Neutralizer hollow cathode
,”
J. Propulsion Power
24
(
4
),
855
865
(
2008
).
26.
I. G.
Mikellides
,
I.
Katz
,
D. M.
Goebel
,
K. K.
Jameson
, and
J. E.
Polk
, “
Wear mechanisms in electron sources for ion propulsion II: Discharge hollow cathodes
,”
J. Propulsion Power
24
(
4
),
866
879
(
2008
).
27.
I. G.
Mikellides
,
I.
Katz
,
K. K.
Jameson
, and
D. M.
Goebel
, “Numerical simulations of a Hall thruster hollow cathode plasma,” in Proceedings of the 30th International Electric Propulsion Conference, Florence, Italy, IEPC-2015-018, 2007.
28.
R. P.
Doerner
,
D. G.
Whyte
, and
D. M.
Goebel
, “
Sputtering yield measurements during low energy xenon plasma bombardment
,”
J. Appl. Phys.
93
(
9
),
5816
(
2003
).
29.
D.
Rosenberg
and
G. K.
Wehner
, “
Sputterin yields for low energy He+-, Kr+-, and Xe+-ion bombardment
,”
J. Appl. Phys.
33
,
1842
(
1962
).
30.
R. D.
Kolasinski
,
J. E.
Polk
,
D. M.
Goebel
, and
L. K.
Johnson
, “
Carbon sputtering yield measurements at grazing incidence
,”
Appl. Surf. Sci.
254
(
8
),
2506
2515
(
2007
).
31.
J.
Bohdansky
,
J.
Roth
, and
H. L.
Bay
, “
An analytical formula and important parameters for low-energy ion sputtering
,”
J. Appl. Phys.
51
,
2861
(
1980
).
32.
Y.
Garnier
,
V.
Viel
,
J. F.
Roussel
, and
J.
Bernard
, “
Low-energy xenon ion sputtering of ceramics investigated for stationary plasma thrusters
,”
J. Vac. Sci. Technol. A
17
,
3246
3254
(
1999
).
33.
Y.
Yamamura
and
S.
Shindo
, “
An empirical formula for angular dependence of sputtering yields
,”
Radiat. Eff.
80
,
52
72
(
1984
).
34.
A.
Lopez Ortega
,
I.
Katz
, and
V. H.
Chaplin
, “A first-principles model based on saturation of the electron cyclotron drift instability for electron transport in hydrodynamics simulations of Hall thruster plasmas,” IEPC Paper No. 2017-178, 2017.
35.
A.
Lopez Ortega
,
I.
Katz
, and
V. H.
Chaplin
, “Application of a first-principles anomalous transport model for electrons to multiple Hall thrusters and operating conditions,” in Propulsion and Energy 2018, Cincinnati, OH, AIAA Paper 2018-4903, 2018.
36.
I. G.
Mikellides
and
A.
Lopez Ortega
, “
Challenges in the development and verification of first-principles models of the anomalous transport in hall-effect thrusters
,”
Plasma Sources Sci. Technol.
(published online).
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