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

RF Progress meeting on 10th ITPA TG on Diagnostics, Kurchatov Inst. Moscow, 10.04.2006

 Vitaly Liechtenstein

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

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

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

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

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

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 holdershas been developed

*Patented

PROTOTYPE DLC STRIPPER FOIL FOR NPAs *

5 nm thick DLC foil supported by the copper grid of 50 microns pitch size

Irradiation tests of the Prototype DLC Stripper foils

BEFORE THE NEUTRON-TEST BEFORE THE D0-TEST

UNDER THE He+-TEST

Results of the Prototype Stripper Foil Irradiation tests

* To be updated soon

Type of the radiation

Test facility Exposure(fluence)

Neutrons, ~ 0.1 MeV

IR-8, Kurchatov 10^16 cm-2

He+, 3 MeV MPIK, Heidelberg 8x 10^18 cm-2

D0, 1 kev ACL, Ioffe 4x 10^16 cm-2 *

Changes in morphology and thickness of the irradiated foils were verified during the tests

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

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