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Setup for large area low-fluence irradiations with quasi-monoenergetic 0.1−5 MeV light ions

Setup for large area low-fluence irradiations with quasi-monoenergetic 0.1−5 MeV light ions. M. Laitinen 1 , T. Sajavaara 1 , M. Santala 2 and Harry J. Whitlow 1. 1 Department of Physics, P.O.B 35, FIN-40014 University of Jyväskylä, Finland

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Setup for large area low-fluence irradiations with quasi-monoenergetic 0.1−5 MeV light ions

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  1. Setup for large arealow-fluence irradiations withquasi-monoenergetic 0.1−5 MeVlight ions M. Laitinen1, T. Sajavaara1, M. Santala2 and Harry J. Whitlow1 1 Department of Physics, P.O.B 35, FIN-40014 University of Jyväskylä, Finland 2 Laboratory of Advanced Energy Systems, P.O.B 4100, FIN-02015 HUT, Finland email: mikko.i.laitinen@jyu.fi

  2. Motivation for the setup • Particle response of prototype detectors, requirements for testing facility: • Large area for testingmultiple detectors at thesame time • Up to 10 cm x 10 cm • Low fluence • Well known uniform distribution needed • Flux lower than 1 particle s-1 mm-2 • Monoenergetic beam • Energy distribution of the flux below 10 keV (FWHM), from 100 keV to 5 MeV • Quick change of beam energy From JET collaboration web-page

  3. Methods for low fluence large area irradiations • How to irradiate ? • Radioactive sources • Limited energy (~3-6 MeV) range • Limited ion range (only 4He ions) • Implanters/ion sources • High flux • Energy range limited to < 1 MeV(normally < 100 keV)

  4. Methods for low fluence large area irradiations • RADEF (JYFL cyclotron, with direct beam) • Minimum energy ~5 MeV • Small accelerators (with direct beam) • Scatterers/wobblers needed → energy spread • Small fluxes difficult • Large homogenous areas difficult

  5. The idea of the setup • Not using the primary beam but instead the secondary beam of the small linear accelerator in JYFL • Secondary beam from particles that have undergone backscattering is used in detector testing with well known properties • Target is made of thin self-supporting carbon foil (10 mg cm-2 ~50nm) where thin layer (2-25 nm) of single isotope element (Au, Rh, Nb, Co, Al eg.) has been deposited • Most of the primary beam goes through the target and hits the targetholder’s backwall from where it cannot backscatter to the detectors → virtually no background Sample holder backwall Sample holder Removable samplesupports Thin Au layer on top of carbon foil Backscattering from Au (+ C) to detectors IncomingPrimary beam0.2-5.2 MeV(for He)

  6. Setup at the Pelletron accelerator

  7. True valuefor backscattered beam closer to8 keV FWHM~16 keV Reference detector data • Flux and energy calibrated from reference detector and multiple targets • Implanted Si surface barrier detector ~14 keV FWHM energy resolution

  8. Reference spectra and target • Sample turret can be modified to take up to 20 targets • In current system 5 targets can be loaded same time to the chamber • Logarithmic scale shows that there is a minor background below Au peak • Backscattering starts at the components of steel • Also for part of the background the origin is due to multiple scattering especially for low energies

  9. Flux homogeneity • Can be easily calculated for both energy and intensity Figures of merit for the setup • Energy range • 150 – 5000 keV for He • 150 – 3000 keV for H • Flux • Up to 500 particles per secondper cm2 (100 – 5 s-1 cm-2) • For lowest energies maximumfluxes get lower • Cycle time • During last 2 day test period:He 1st day, H 2nd day, 5-7different accelerator energiesfor 3 different detector setsper day (up to 20 cycles per day). • Multiple detectors at once • 4 minute down-pumping time

  10. NPA – results from the setup • Neutral particle analyzers for Joint European Torus JET • 1st tests showed strange double peak behaviour and bad resolution • 2nd set of detectors performs much better: Improved resolution and effiency, no double peaks but small tail A novel silicon detector for neutral particle analysis in JET fusion research Kalliopuska J, Garcia F, Santala M, et al.NIM A, vol. 591, 1, p. 92-97 (2008)

  11. Future improvements • H - beam currents limited now by ion source • New ion source coming before summer • Order of magnitude increase to H currents • Heavier ions including Li available from new ion source • Beam blanker for the prototype detectors • Total fluxes and energies calibrated from reference detector before letting the beam to the test detector • Full understanding of reference spectrum through Monte Carlo simulations

  12. Thank you for your attention ! Accelerator based materials physics goup in JYFL

  13. NPA schematics

  14. NPA linearity for Hydrogen

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