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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.

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Presentation on theme: "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."— Presentation transcript:

1 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 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 testing multiple detectors at the same 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 4 He 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  g 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 Incoming Primary beam 0.2-5.2 MeV (for He) Sample holder backwall Sample holder Thin Au layer on top of carbon foil Backscattering from Au (+ C) to detectors Removable samplesupports

6 Setup at the Pelletron accelerator

7 Reference detector data Flux and energy calibrated from reference detector and multiple targets Implanted Si surface barrier detector ~14 keV FWHM energy resolution FWHM ~16 keV True value for backscattered beam closer to 8 keV

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

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

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15 NPA schematics

16 NPA linearity for Hydrogen

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