GEM gas detectors for Soft X-ray imaging in Fusion devices with neutron-gamma background and polycapillary lenses F. Murtas 2, S. Dabagov 2,4, L. Gabellieri 1, A. Romano 1, D. Mazon 3, D. Hampai and FTU technical team 1 Euratom-ENEA Association, C.R. Frascati, Via E. Fermi, Frascati, Rome, Italy 2 Istituto Nazionale di Fisica Nucleare, Via E. Fermi 40, Frascati, Rome Italy 3 Association Euratom-CEA, CEA Cadarache, DSM/IRFM St Paul lez durance Cedex, France 4 P. N. Lebedev Physical Institute RAS, Leninsky Pr. 53, Moscow, Russia D. Pacella, ENEA-Frascati

Thinking to a Burning plasma……… Triple GEM gas Detector with 2-D pixel read-out Detection of X-ray in presence of a strong background of neutrons and gamma 1 We need to cope with a high radiative background: neutrons (0-14 MeV), gamma-rays, Hard X-ray (for long time we can only ……think it!) 2-D C-MOS imager (Medipix 2) X-ray optics to collect radiation and transport it far away 2 X-ray optics We worked along two directions or a combination of both in the future

1 X-ray detection with n and gamma background Triple GEM gas detector, active area 10cm x 10 cm, 2-D pixel read-out (128), integrated front-end electronics (CARIOCA microchip)

counts Threshold (mV) Digital outputs Summing all the pulses over threshold Threshold scan detector Pulse amplifier and shaper threshold counter CARIOCA chip gain DAQ discriminator Analog signals Pulse amplitude pulse counts Lower gain Higher gain threshold MCA spectrum X-ray 6KeV Photon counting mode per each pixel

Maximum flux n/s cm 2 over the detector Disturbances on the front end electronics occur only at this maximum flux Detector response is linear even at high gain Frascati Neutron Generator (ENEA): D-D (2.5MeV) and D-T (14 MeV) neutrons 14 MeV neutrons Max Intensity n/s over 4 π Tests at Frascati Neutron Generator (FNG)

Discrimination of neutron, gamma and X-rays With the gain we can enable the detection of the different radiations (pulses above threshold) or suppress them (pulses below threshold) At fixed gain, the pulse amplitude distribution (see scan in threshold) is different for the various sources of radiation: almost flat for neutrons, very peaked at low amplitude for gamma, with changeable derivative as function of gain for X-ray X-ray n+ ϒ neutrons ϒ X-ray detector gain Counts vs gain threshold Counts vs threshold n n ϒ

All these processes have to be simulated with a Monte Carlo The components of the detector can be defined to enhance or minimize the detection of the various source of radiation Ar + CO 2 Window (mylar 15  ) GEM 1 (50  ) GEM 2 (50  ) GEM 3 (50  ) read-out Pixels (3 mm ) 3 mm 1 mm 2 mm 1 mm Processes occuring into the detector  (10 -4 ) (10 -6 )   ~ X   (X) > 0.1 n’ n (2.5 MeV) p (~ 1 MeV)  E/E ~ 50 keV R=16  R=35   (n 2.5) ~  (n 14) ~ 10 -5

7500 counts 2-D image of a X-ray through a slit 2000 counts 9000 counts 2-D X-ray image + neutron and gamma background Flux neutrons = n/s Flux gammas = ϒ /s 2000 counts Spatial information of the detected neutron is conserved Neutron source 2-D X-ray image of a source through an oblique slit X source slit detector 2-D X-ray imaging with neutron and gamma background

A previous version (single GEM, lower active area) was developed a Frascati (ENEA) in collaboration with INFN-Pisa (R. Bellazzini and his group) in 2000 and then installed at NSTX (USA) from 2001 to 2004 NSTX The present version (triple-Gem, 128 lines of sight) is now Installed at Tore Supra (see presentation of D. Mazon) Tore Supra July 2011 The potentiality has been proved (NSTX, ). Now a full investigation will be done at Tore Supra (from 2011)

Flux (first wall) ~ n/s cm 2 A. Araujo et al., Brazilian Journal of Physics Vol. 40 (2010) Neutron fluxes expected at ITER Flux ~ 10 8 n/s cm 2 (improved detector) Improvement of one order of magnitude does not seem prohibitive (non plastic window, absorber for protons, optimization of the fields, radiation hard electronics, shielding..) X n,  bare detector at FNG (14 MeV) Flux gammas =  /s Flux ( FNG) ~ 10 7 n/s cm 2 X n,  Flux gammas =  /s Flux ~ 10 8 n/s cm 2 (14 MeV) F. Moro et al., Fusion Engineering and Design, 84 (2009)

2 X-ray polycapillary lenses for imaging and tomography lens Detector Medipix 2: 256 x 256 pixels 55  x 55  15 mm x 15 mm area

80  3.8 mm 500  750  spot size (full lens) spot size (half lens)

Imaging property of the full lens

“Broad view” collector (half lens) 2-3 ˚ ‘Narrow view’ collector (half lens) ~ mrad Array pillar detector Array bent fibers detector Tomography array Possible schemes for MCF plasmas tomography

CONCLUSIONS X-ray detection has been studied in presence of a high radiative (neutron and gamma) background The different physical processes have been estimated, but accurate simulations will be required Thanks to the adjustable detector gain and threshold, the different contributions could be discriminated and evaluated The detector could be designed to tailor it on the detection of the desidered radiation Higher limit for the background radiation are envisaged No tests have been done so far to study aging and degradation at long term Very preliminary tests on X-ray polycapillary optics are encouraging. They could allow the transport of X-ray radiation in configuration imaging and/or tomography Detector for high radiative environments and long distances SXR imaging with polycapillaries could be useful in other field