Prototype Diamond-like Carbon (DLC) Stripper Foils for NPAs

1. Prototype Diamond-like Carbon (DLC) Stripper Foils for NPAs  Vitaly Liechtenstein RF Progress meeting on 10th ITPA TG on Diagnostics, Kurchatov Inst. Moscow, 10.04.2006

2. Overview  Introduction  The essential features required of a stripper foil for the NPA, why foil of DLC is well suited? Fabrication of prototype DLC stripper foils for NPAs  Irradiation tests of the foils  Summary and outlook

3. Introduction As mentioned in the previous talk, very thin diamond-like carbon (DLC) foils are supposed to be used as advanced strippers for NPA diagnostics at the ITER. A stripper foil is obviously essential for a NPA since it determines the most important parameters of the analyzer. The aim of this talk is to briefly present the main results of the recent prototype DLC stripper R&D

4. The essential features required of a stripper foil for the NPA  Optimum thickness in terms of stripping efficiency, energy straggling and ion transmission through the analyzer  Sufficiently long lifetime under ITER irradiations  High mechanical stability to fit ITER environment conditions and maintenance procedure

5. Why Diamond-like Carbon as a NPA Stripper Material ? Crystalline Diamond is well known as a best target material owing to its exceptionally high irradiation and mechanical hardness. However, it’s obviously impractical to use diamond as a thin stripper foil for NPA Developed in Kurchatov Institute deposition technique allows for fabrication amorphous DLC foils with main physical properties close to those of crystalline diamond. These foils demonstrated the following advantages over ordinary carbon foils in the variety of the comparative tests at different labs: -    much higher mechanical strengthoptimized stripper foils with minimal energy&angle straggling of transmitted particles can be produced -    improved (~ 10 times) ion irradiation lifetimes long –term stable operation in the NPA is expected These promising results as well as reliable long-term operation of DLC strippers in NPAs at TFTR , JET and JT-60 in different periods have governed the proper choice of DLC foils to be used in the NPAs at ITER

6. Strong and homogenous DLC foils in the thickness range of 2 –200nm with the typical size of around 10mm can be produced by this technique Schematic and view of the set-up for sputter DLC films deposition

7. PROTOTYPE DLC STRIPPER FOIL FOR NPAs* Very flat and smooth supporting grid is necessary for the stable performance of a thin stripper foil. To fulfill this requirement, the specific heat treatment technique for perfect stretching of grids over the foil holders has been developed *Patented 5 nm thick DLC foil supported by the copper grid of 50 micronspitch size

8. Irradiation tests of the Prototype DLC Stripper foils BEFORE THE NEUTRON-TEST BEFORE THE D0-TEST UNDER THE He+-TEST

9. Results of the Prototype Stripper Foil Irradiation tests Changes in morphology and thickness of the irradiated foils were verified during the tests * To be updated soon

10. Summary DLC stripper foils have been developed which meet the present requirements of both LENPA and HENPA  The samples of the prototype stripper foils passed the irradiation tests relevant to the ITER plasma conditions  Our next efforts of this year will be aimed at the development of prototype stripper foil for LENPA with enlarged to 20mm effective diameter. Also, we plan to investigate in more detail mechanical and thermal stability of prototype DLC stripper foils intended for NPA s

11. Other coauthors of this work T.M. Ivkova , E.D. Olsahanski, K.Ju. Vukolov (Kurchatov) V.A. Afanasiev, M.P. Petrov (Ioffe) Acknowledgement Collaboration with the teams of the Acceleration Facilities of MPIK, Heidelberg, and VERA-Lab, Vienna on the characterization and comparative tests of the samples of DLC foils is mostly appreciated