The scavenger effect – Does it work?

Abstract

The influence of nitrogen injection on the formation of a-C:H films in areas far away from the plasma as well as close to the plasma boundary was studied in the PSI-2 device for collector temperatures between 310 and 350 K. The balance between deposition and erosion determines the net growth rate. Small amounts of nitrogen (Φ(N 2 ) ≈ Φ(CH 4 ) ≈ 2% Φ(H 2 )) strongly reduce the net growth rate in H 2 /CH 4 mixtures. While N 2 injection does not influence erosion far away from the plasma it increases erosion close to the plasma boundary. The experiments show clear evidence for a scavenger effect due to the injected nitrogen. The conversion from N 2 to active species takes place in the hot plasma region.

Suppression of Tritium Retention in Remote Areas of ITER by Nonperturbative Reactive Gas Injection

“…At constant methane concentration in the plasma, the increase of HCN is proportional to the injected ammonia, no matter where the injection is made. All these findings stress the minor role that plasma activation plays in the scavenging efficiency of ammonia, in stark contradiction with the nitrogen behavior [12].…”

“…Recent experiments of nitrogen seeding at the PSI-2 linear plasma device [12] indicate that radical, as opposed to ion, chemistry plays the main role in the scavenger effect. Moreover, a possible direct reaction between ammonia, formed as a chemical product from the recombination of N and H atoms at the walls, and carbon radicals was deduced from mass spectrometric recordings.…”

Suppression of hydrogenated carbon film deposition and hydrogen isotope retention by nitrogen addition into cold remote H/D and CH4 mixture plasmas

“…Nitrogen addition into hydrogen plasmas has been examined as effective methods for suppression of hydrogenated carbon films deposition growth [4,9]. Previous experiments show that nitrogen seeding into H 2 and CH 4 plasmas have a strong scavenger effect on the hydrogenated carbon film deposition, A few percentage of nitrogen addition (N 2 /H 2 $ 2%) into H 2 /CH 4 plasmas led to significant suppression of carbon film deposition and carbon dust formation on silicon targets [5].…”

Effect of nitrogen and ammonia on transfer and deposition of hydrocarbon radicals in different regions of hollow-cathode glow discharge

“…Another approach to resolving this problem can be injection of molecular nitrogen or ammonia [4][5][6][7][8] in a divertor plasma during discharge or during hydrogen conditioning of the device [9].…”