Large-scale sources for negative hydrogen ions, capable of delivering an extracted ion current of several ten amperes, are a key component of the neutral beam injection system of the upcoming ITER fusion device. Since the created heat load of the inevitably co-extracted electrons after magnetic separation from the extracted beam limits their tolerable amount, special care must be taken for the reduction of co-extracted electrons—in particular, in deuterium operation, where the larger amount of co-extracted electrons often limits the source performance. By biasing the plasma grid (PG, first grid of the extraction system) positively with respect to the source body, the plasma sheath in front of the PG can be changed from an electron repelling towards an electron attracting sheath. In this way, the flux of charged particles onto the PG can be varied, thus changing the bias current and inverse to it the amount of co-extracted electrons. The PG bias affects also the flux of surface-produced H towards the plasma volume as well as the plasma symmetry in front of the plasma grid, strongly influenced by an E × B drift. The influence of varying PG sheath potential profile on the plasma drift, the negative hydrogen ion density, and the source performance at the prototype H source is presented, comparing hydrogen and deuterium operation. The transition in the PG sheath profile takes place in both isotopes, with a minimum of co-extracted electrons formed in case of the electron attracting PG sheath. The co-extracted electron density in deuterium operation is higher than in hydrogen operation, which is accompanied by an increased plasma density in deuterium.

1.
R.
Hemsworth
,
H.
Decamps
,
J.
Graceffa
,
B.
Schunke
,
M.
Tanaka
,
M.
Dremel
,
A.
Tanga
,
H. D.
Esch
,
F.
Geli
,
J.
Milnes
,
T.
Inoue
,
D.
Marcuzzi
,
P.
Sonato
, and
P.
Zaccaria
,
Nucl. Fusion
49
,
045006
(
2009
).
2.
B.
Schunke
,
D.
Bora
,
R.
Hemsworth
, and
A.
Tanga
,
AIP Conf. Proc.
1097
,
480
490
(
2009
).
3.
A.
Masiello
,
G.
Agarici
,
T.
Bonicelli
,
M.
Simon
,
J.
Alonso
,
M.
Bigi
,
D.
Boilson
,
G.
Chitarin
,
C.
Day
,
P.
Franzen
,
S.
Hanke
,
B.
Heinemann
,
R.
Hemsworth
,
A.
Luchetta
,
D.
Marcuzzi
,
J.
Milnes
,
T.
Minea
,
R.
Pasqualotto
,
N.
Pomaro
,
G.
Serianni
,
W.
Rigato
,
P.
Sonato
,
V.
Toigo
,
F.
Villecroze
,
C.
Waldon
, and
P.
Zaccaria
,
Fusion Eng. Des.
86
,
860
863
(
2011
).
4.
R. S.
Hemsworth
,
A.
Tanga
, and
V.
Antoni
,
Rev. Sci. Instrum.
79
,
02C109
(
2008
).
5.
M.
Bacal
and
M.
Wada
,
Appl. Phys. Rev.
2
,
021305
(
2015
).
6.
E.
Speth
,
H.
Falter
,
P.
Franzen
,
U.
Fantz
,
M.
Bandyopadhyay
,
S.
Christ
,
A.
Encheva
,
M.
Fröschle
,
D.
Holtum
,
B.
Heinemann
,
W.
Kraus
,
A.
Lorenz
,
C.
Martens
,
P.
McNeely
,
S.
Obermayer
,
R.
Riedl
,
R.
Süss
,
A.
Tanga
,
R.
Wilhelm
, and
D.
Wünderlich
,
Nucl. Fusion
46
,
S220
(
2006
).
7.
W.
Kraus
,
U.
Fantz
,
P.
Franzen
,
M.
Fröschle
,
B.
Heinemann
,
R.
Riedl
, and
D.
Wünderlich
,
Rev. Sci. Instrum.
83
,
02B104
(
2012
).
8.
U.
Fantz
,
L.
Schiesko
, and
D.
Wünderlich
,
Plasma Sources Sci. Technol.
23
,
044002
(
2014
).
9.
A. J. T.
Holmes
,
Rev. Sci. Instrum.
53
,
1517
1522
(
1982
).
10.
K. N.
Leung
,
K. W.
Ehlers
, and
M.
Bacal
,
Rev. Sci. Instrum.
54
,
56
61
(
1983
).
11.
M.
Bacal
,
J.
Bruneteau
, and
P.
Devynck
,
Rev. Sci. Instrum.
59
,
2152
2157
(
1988
).
12.
F. E.
Balghiti-Sube
,
F. G.
Baksht
, and
M.
Bacal
,
Rev. Sci. Instrum.
67
,
2221
2227
(
1996
).
13.
Y.
Takeiri
,
Y.
Oka
,
M.
Osakabe
,
K.
Tsumori
,
O.
Kaneko
,
T.
Takanashi
,
E.
Asano
,
T.
Kawamoto
,
R.
Akiyama
, and
T.
Kuroda
,
Rev. Sci. Instrum.
68
,
2003
2011
(
1997
).
14.
P.
McNeely
,
M.
Bandyopadhyay
,
P.
Franzen
,
B.
Heinemann
,
C.
Hu
,
W.
Kraus
,
R.
Riedl
,
E.
Speth
, and
R.
Wilhelm
,
AIP Conf. Proc.
639
,
90
111
(
2002
).
15.
S.
Lishev
,
L.
Schiesko
,
D.
Wünderlich
, and
U.
Fantz
,
AIP Conf. Proc.
1655
,
040010
(
2015
).
16.
J. P.
Boeuf
,
J.
Claustre
,
B.
Chaudhury
, and
G.
Fubiani
,
Phys. Plasmas
19
,
113510
(
2012
).
17.
C.
Wimmer
,
U.
Fantz
, and
NNBI-Team
,
AIP Conf. Proc.
1515
,
246
254
(
2013
).
18.
R.
McAdams
,
A. J. T.
Holmes
,
D. B.
King
, and
E.
Surrey
,
Plasma Sources Sci. Technol.
20
,
035023
(
2011
).
19.
D.
Wünderlich
,
R.
Gutser
, and
U.
Fantz
,
Plasma Sources Sci. Technol.
18
,
045031
(
2009
).
20.
P.
Franzen
,
L.
Schiesko
,
M.
Fröschle
,
D.
Wünderlich
,
U.
Fantz
, and
NNBI Team
,
Plasma Phys. Controlled Fusion
53
,
115006
(
2011
).
21.
M.
Berger
,
U.
Fantz
,
S.
Christ-Koch
, and
NNBI Team
,
Plasma Sources Sci. Technol.
18
,
025004
(
2009
).
22.
P.
McNeely
,
S. V.
Dudin
,
S.
Christ-Koch
,
U.
Fantz
, and
NNBI Team
,
Plasma Sources Sci. Technol.
18
,
014011
(
2009
).
23.
F. F.
Chen
,
Plasma Sources Sci. Technol.
18
,
035012
(
2009
).
24.
J. P.
Sheehan
,
Y.
Raitses
,
N.
Hershkowitz
,
I.
Kaganovich
, and
N. J.
Fisch
,
Phys. Plasmas
18
,
073501
(
2011
).
25.
S.
Christ-Koch
,
U.
Fantz
,
M.
Berger
, and
NNBI Team
,
Plasma Sources Sci. Technol.
18
,
025003
(
2009
).
26.
P.
McNeely
and
L.
Schiesko
,
Rev. Sci. Instrum.
81
,
02B111
(
2010
).
27.
D.
Wünderlich
,
S.
Mochalskyy
,
U.
Fantz
,
P.
Franzen
, and
NNBI-Team
,
Plasma Sources Sci. Technol.
23
,
015008
(
2014
).
28.
P.
Franzen
,
H.
Falter
,
U.
Fantz
,
W.
Kraus
,
M.
Berger
,
S.
Christ-Koch
,
M.
Fröschle
,
R.
Gutser
,
B.
Heinemann
,
S.
Hilbert
,
S.
Leyer
,
C.
Martens
,
P.
McNeely
,
R.
Riedl
,
E.
Speth
, and
D.
Wünderlich
,
Nucl. Fusion
47
,
264
(
2007
).
29.
U.
Fantz
,
L.
Schiesko
,
D.
Wünderlich
, and
NNBI Team
,
AIP Conf. Proc.
1515
,
187
196
(
2013
).
30.
R.
Gutser
,
D.
Wünderlich
,
U.
Fantz
, and
NNBI-Team
,
Plasma Phys. Controlled Fusion
51
,
045005
(
2009
).
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