TY - JOUR
T1 - Experimental evidence of enhanced recombination of a hydrogen plasma induced by nitrogen seeding in linear device Magnum-PSI
AU - Magnum-PSI Team
AU - Perillo, R.
AU - Akkermans, G.R.A.
AU - Classen, I.G.J.
AU - Vijvers, W.A.J.
AU - Chandra, R.
AU - Jesko, K.
AU - Korving, Sven
AU - Vernimmen, J.W.M.
AU - de Baar, M.R.
PY - 2019/5/1
Y1 - 2019/5/1
N2 -
In this work we investigate the effects induced by the presence of nitrogen in a detached-like hydrogen plasmas in linear plasma machine Magnum-PSI. Detachment has been achieved by increasing the background neutral pressure in the target chamber by means of H
2
/N
2
puffing and two cases of study have been set up, i.e. at 2 and 4 Pa. Achieved n
e
are ITER-relevant i.e. above 10
20
m
−3
and electron temperatures are in the range 0.8–2 eV. A scan among five different N
2
/H
2
+N
2
flux ratios seeded have been carried out, at values of 0, 5, 10, 15 and 20%. A n
e
decrease while increasing the fraction of N
2
has been observed for both background pressures, resulting in a plasma pressure drop of ̴ 30%. T
e
remains constant among all scans. The peak intensity of NH*(A
3
∏->X
3
∑
−
, ∆v = 0) at 336 nm measured with optical emission spectroscopy increases linearly with the N
2
content, together with the NH
3
signal in the RGA. A further dedicated experiment has been carried out by puffing separately H
2
/N
2
and H
2
/He mixtures, being helium a poorly-reactive atomic species, hence excluding a priori nitrogen-induced molecular assisted recombination. Interestingly, plasma pressure and heat loads to the surface are enhanced when increasing the content of He in the injected gas mixture. In the case of N
2
, we observe an opposite behavior, indicating that N–H species actively contribute to convert ions to neutrals. Recombination is enhanced by the presence of nitrogen. Numerical simulations with two different codes, a global plasma-chemical model and a spatially-resolved Monte Carlo code, address the role of NH
x
species behaving as electron donor in the ion conversion with H
+
by means of what we define here to be N-MAR i.e. NH
x
+ H
+
→ NH
x
+
+ H, followed by NH
x
+
+ e
−
→ NH
x-
1
+ H. Considering the experimental findings and the qualitative results obtained by modelling, N-MAR process is considered to be a possible plasma-chemical mechanism responsible for the observed plasma pressure drop and heat flux reduction. Further studies with a coupled code B2.5-Eunomia are currently ongoing and may provide quantitative insights on the scenarios examined in this paper.
AB -
In this work we investigate the effects induced by the presence of nitrogen in a detached-like hydrogen plasmas in linear plasma machine Magnum-PSI. Detachment has been achieved by increasing the background neutral pressure in the target chamber by means of H
2
/N
2
puffing and two cases of study have been set up, i.e. at 2 and 4 Pa. Achieved n
e
are ITER-relevant i.e. above 10
20
m
−3
and electron temperatures are in the range 0.8–2 eV. A scan among five different N
2
/H
2
+N
2
flux ratios seeded have been carried out, at values of 0, 5, 10, 15 and 20%. A n
e
decrease while increasing the fraction of N
2
has been observed for both background pressures, resulting in a plasma pressure drop of ̴ 30%. T
e
remains constant among all scans. The peak intensity of NH*(A
3
∏->X
3
∑
−
, ∆v = 0) at 336 nm measured with optical emission spectroscopy increases linearly with the N
2
content, together with the NH
3
signal in the RGA. A further dedicated experiment has been carried out by puffing separately H
2
/N
2
and H
2
/He mixtures, being helium a poorly-reactive atomic species, hence excluding a priori nitrogen-induced molecular assisted recombination. Interestingly, plasma pressure and heat loads to the surface are enhanced when increasing the content of He in the injected gas mixture. In the case of N
2
, we observe an opposite behavior, indicating that N–H species actively contribute to convert ions to neutrals. Recombination is enhanced by the presence of nitrogen. Numerical simulations with two different codes, a global plasma-chemical model and a spatially-resolved Monte Carlo code, address the role of NH
x
species behaving as electron donor in the ion conversion with H
+
by means of what we define here to be N-MAR i.e. NH
x
+ H
+
→ NH
x
+
+ H, followed by NH
x
+
+ e
−
→ NH
x-
1
+ H. Considering the experimental findings and the qualitative results obtained by modelling, N-MAR process is considered to be a possible plasma-chemical mechanism responsible for the observed plasma pressure drop and heat flux reduction. Further studies with a coupled code B2.5-Eunomia are currently ongoing and may provide quantitative insights on the scenarios examined in this paper.
KW - Detachment
KW - Impurity seeding
KW - Linear plasma device
KW - N-MAR
KW - Nitrogen
KW - Plasma chemistry
UR - http://www.scopus.com/inward/record.url?scp=85061902671&partnerID=8YFLogxK
U2 - 10.1016/j.nme.2019.02.018
DO - 10.1016/j.nme.2019.02.018
M3 - Article
AN - SCOPUS:85061902671
SN - 2352-1791
VL - 19
SP - 87
EP - 93
JO - Nuclear Materials and Energy
JF - Nuclear Materials and Energy
ER -