Mo layer thickness requirement on the ion source back plate for the HNB and DNB ion sources in ITER
- ITER Organisation, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance (France)
All the inner surfaces of the ion sources and the upstream surface of the plasma grid of the ITER neutral beam ion sources are proposed to be coated with molybdenum. This is done to avoid sputtering of the base material (Cu or CuCrZr) by the ions in the source plasma (D{sup +}, D{sub 2}{sup +}, D{sub 3}{sup +} or H{sup +}, H{sub 2}{sup +}, H{sub 3}{sup +}). The sputtering of Mo by the ions in the source plasma is low compared to that from Cu, and the threshold energy for sputtering ∼80 eV) is high compared to the energy of the ions in the source. However the D{sub 2}{sup +}, H{sub 2}{sup +} and D{sup +}, H{sup +} ions backstreaming from the accelerators will have energies that substantially exceed that threshold and it is important that the Mo layer is not eroded such that the base material is exposed to the source plasma. In the case of the HNB, the backstreaming ion power is calculated to be in the order of ∼1 MW, and the average energy of the backstreaming ions is calculated to be ∼300 keV. The ion sources in the HNB beam lines, 40 A 1 MeV D and 46 A 870 keV H beams, are supposed to operate for a period of 2 x 10{sup 7} s. For the DNB, 60 A 100 keV H beams, the corresponding number is 1.4 × 10{sup 6} s considering a beam duty cycle of 3s ON/20s OFF with 5 Hz modulation. The Mo layer on the ion source back plate should be thick enough to survive this operational time. Thickness estimation has been carried out taking into account the sputtering yields (atoms/ion), the energy spectrum of the backstreaming ions and the estimated profiles on the ion source back plate.
- OSTI ID:
- 22391430
- Journal Information:
- AIP Conference Proceedings, Vol. 1655, Issue 1; Conference: NIBS 2014: 4. International Symposium on Negative Ions, Beams and Sources, Garching (Germany), 6-10 Oct 2014; Other Information: (c) 2015 U.S. Government; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
- Country of Publication:
- United States
- Language:
- English
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