Hardware architecture of the data acquisition and processing system for the JET Neutron Camera Upgrade (NCU) project

Transcription

1 EUROFUSION WPJET4-CP(16) M Riva et al. Hardware architecture f the data acquisitin and prcessing system fr the JET Neutrn Camera Upgrade (NCU) prject Preprint f Paper t be submitted fr publicatin in Prceedings f 29th Sympsium n Fusin Technlgy (SOFT 2016) This wrk has been carried ut within the framewrk f the EUROfusin Cnsrtium and has received funding frm the Euratm research and training prgramme under grant agreement N The views and pinins expressed herein d nt necessarily reflect thse f the Eurpean Cmmissin.

2 This dcument is intended fr publicatin in the pen literature. It is made available n the clear understanding that it may nt be further circulated and extracts r references may nt be published prir t publicatin f the riginal when applicable, r withut the cnsent f the Publicatins Officer, EUROfusin Prgramme Management Unit, Culham Science Centre, Abingdn, Oxn, OX14 3DB, UK r Publicatins.Officer@eur-fusin.rg Enquiries abut Cpyright and reprductin shuld be addressed t the Publicatins Officer, EUROfusin Prgramme Management Unit, Culham Science Centre, Abingdn, Oxn, OX14 3DB, UK r Publicatins.Officer@eur-fusin.rg The cntents f this preprint and all ther EUROfusin Preprints, Reprts and Cnference Papers are available t view nline free at This site has full search facilities and alert ptins. In the JET specific papers the diagrams cntained within the PDFs n this site are hyperlinked

3 Hardware architecture f the data acquisitin and prcessing system fr the JET Neutrn Camera Upgrade (NCU) prject M. Riva 1, D. Marcc 1, F. Belli 1, B. Espsit 1, F. Pllastrne 1 J. Bielecki 2,4, L. Giacmelli 3, A. Milcc 2, S. Ppvichev 2 and JET cntributrs* EUROfusin Cnsrtium, Culham Science Centre, Abingdn, Oxn, OX14 3DB, UK 1 ENEA, C.R. Frascati, Via E. Fermi, 45-Frascati, Rme, Italy 2 CCFE, Culham Science Centre, Abingdn, Oxn, OX14 3DB, UK 3 IFP-CNR Via R. Czzi 53, Milan, Italy 4 Institute f Nuclear Physics Plish Academy f Sciences, PL Krakw, Pland Crrespnding authr Marc.Riva@enea.it. * See the Appendix f F. Rmanelli et al., Prceedings f the 25th IAEA Fusin Energy Cnference 2014, Saint Petersburg, Russia The Neutrn Camera (NC) is a Jint Eurpean Trus (JET) diagnstic, based n a set f 19 cllimated lines f sight equipped with plastic (BC418) and liquid (NE213) scintillatrs, with the main functin f measuring the neutrn emissivity prfile due t 2.5 MeV (DD) and 14 MeV (DT). Due t several limitatins f the present data acquisitin system and in view f the JET DT campaign, an enhancement prject (Neurn Camera Upgrade, NCU) was launched. The main bjective was t imprve the measurement capability f NC fr 14 MeV neutrns, by applicatin f a high thrughput FPGA-based digital acquisitin system. The present paper describes the hardware architecture and the FPGA prcessing selected fr the NCU prject and the first tests carried ut at JET. Keywrds: FPGA; neutrn detectrs; digital prcessing; spectrscpy 1. Intrductin The JET NC diagnstic has the main functin f measuring the neutrn emissivity prfile due t 2.5 MeV (DD) and 14 MeV (DT) neutrns ver a plidal plasma crss-sectin using line-integrated measurements alng a number f cllimated channels (lines-f-sight, LOS). The diagnstic cnsists f tw separate shielding cncrete units, each ne including a fan-shaped array f cllimatrs. One unit views the plasma hrizntally (10 LOS), and the ther vertically (9 LOS). Neutrn measurements are perfrmed by means f tw different types f detectrs: NE213 liquid scintillatrs (designed t wrk in DD peratins and lw pwer DT peratins) and Bicrn BC418 plastic scintillatrs (designed fr high pwer DT peratins and fr the detectin f lw intensity DT neutrns in the presence f strng DD neutrn fluxes). During the 1997 DTE1 campaign (recrd discharge #42976; maximum neutrn yield ~ n/s -1 ) the BC418 detectrs wrked up t ~ cps (cunts abve 10 MeV threshld, i.e. ~ cps ttal cunt rate). The presence f higher NBI pwer in future DT campaigns might imply higher rates and a demanding value f ~ cps (cunts abve 10 MeV threshld, i.e. ~ cps ttal cunt rate ) has been set as a target fr the diagnstic. The BC418 detectrs still wrk with an analgue acquisitin electrnics having several limitatins [1]: N raw data (i.e. scintillatr pulses) strage fr mnitring and reprcessing purpses. N prvisin f accurate Pulse Height Spectra (PHS) during plasma discharges (analg discriminatr mdules prvide cunts in 4 energy bands nly). Cmplex calibratin prcedure. The NE213 detectrs are instead cupled t a Field Prgrammable Gated Array (FPGA)-based digital acquisitin system (14 bit 200 MS/s sampling rate, PCIe 1 bus) develped by ENEA [2]. Such system vercmes the limitatins listed abve fr the BC418 analgue acquisitin chain but prcessing is limited t ~ cps in the lab [3]. T address the abve mentined limitatins and in view f future JET DT campaigns, an upgrade prject (Neurn Camera Upgrade, NCU) was launched in the frame f wrk-package JET4 (JET enhancements) with the main bjective f increasing the perfrmance and reliability f the 14 MeV neutrn measurements perfrmed by BC418 detectrs. Such bjective will be achieved by prcuring, setting up, installing at JET and calibrating a new FPGA-based digital data acquisitin system, which will include the fllwing features: High thrughput digital acquisitin fr each BC418 detectr perfrming n-line data pre-prcessing. Raw data (i.e. scintillatr pulses) mass strage n lcal cmputers lcated in the NC cubicles area. Off-line data prcessing (pile-up prcessing, DT neutrn cunt rates, PHS, calibratin, etc.) with dedicated sftware package running n the JET envirnment and n the lcal cmputers. authr s marc.riva@enea.it

4 A pssible replacement f the NE213 acquisitin system with the same presented in this paper fr BC418 detectrs is als freseen. The decisin will be taken after 14 MeV neutrns irradiatin tests at high rate t be carried ut at the Frascati Neutrn Generatr (FNG). 2. Hardware architecture The hardware architecture selected fr the NCU acquisitin system is based n a set 5U-rack units (figure 1). Each unit is equipped with a 4-slts backplane (figure 2) hsting up t 4 PC bards (SBS - i7 3.4 GHz Ivy Bridge, (figure 3)) and each PC bard accmmdates a tw-channel digitizer thrugh a PCIex8 carrier bard. Tw rack units with all backplane slts ccupied (16 acquisitin channels) and ne rack unit with 2 backplane slts ccupied (4 acquisitin channels) are used t prvide full cverage f NC lines f sight and a spare acquisitin channel. The 10 tw-channel digitizers (X6-400M, prduced by the Innvative integratin cmpany ([4]) are equipped with a XilinxTM Virtex 6 FPGA, 4 GBytes f Lw Pwer Duble Data Rate Memry (LPDDR2), tw 1 GS/s DAC, external clck and trigger; each digitizing channel features a 14 bit ADCs with sftware selectable sampling rate up t 400MS/s. The FPGA bard is munted n the PCIex8 carrier as a high speed Switch Mezzanine Card (XMC) mdule, shwn in figure 4. Fig. 3. PC bard SBS- i7 3.4 GHz Ivy Bridge. Fig. 4. X6-400M XMC mezzanine Card. Sme specific design chices were made in rder t cpe with the high data thrughput freseen in future DT campaigns: Fig. 1. 5U rack unit cntaining fur acquisitin systems. Fig slt backplane, hsting the acquisitin and prcessing units. Large n-bard RAM (4GBytes) and use f a fast bus fr FPGA data buffering and data transfer (PCIex8, > 1GB/s) Maximizatin f prcessing resurces per acquisitin channel. Single FPGAs and PCs are allcated fr each cuple f acquisitin channels, thus prvide the system with rbustness bth against data verlad n the FPGA/CPU and acquisitin bard/pc failure. A secnd PCIex8 slt is anyway available n the PC bards, allwing 2 additinal acquisitin channels t be installed. Sampling rate flexibility. The pssibility f dwngrading via sftware the 400Ms/s maximum sampling rate allws, depending n the need, t easily select between high perfrmances (in terms f energy reslutin, pile-up analysis and, in case f use with NE213 detectrs, n/γ separatin) and data reductin. It is als t be mentined that the acquisitin bard supplier prvided full access t FPGAs, thus allwing the use f the custm firmware specifically designed in ENEA fr pulse acquisitin and pre-prcessing [5]. The firmware takes advantage f a nn-cntinuus acquisitin plicy in which a selectable number f samples (data windw) are acquired when a pulse is detected and the size f the windw is dynamically extended depending n the presence f additinal pulses; such a prcedure reduces the amunt f stred data and increases the maximum cunt rate sustainable by the system. A layut f the verall system, as it will be installed at JET, is shwn in figure 5. Each detectr signal passes thrugh a fast amplifier and is then split in tw paths, the first ging t the digital system and the ther t the ld analgue system. Nnetheless, the pssibility t split the detectr signal befre the amplifiers is als being

5 investigated. JET reference CLOCK/GATE signals and netwrk will be ruted t each acquisitin bard/pc by means f dedicated distributin units. A 10 channels Keybard Vide and muse (KVM) system will allw lcal access t PCs fr set-up, mnitring and calibratin purpses. Acquisitins will be synchrnusly triggered n all units by the JET PRE signal, active n the pulse start; scintillatr pulses data will be stred in PCs RAM memry during plasma discharges and saved in the JET database as raw signals immediately after the end f the discharge. Prcessing f raw data will take place n the JET chain1 cmputer system (respnsible fr generating prcessed physics and engineering data after JET pulses) by means f a dedicated C++ cde, prviding PHS and 14 MeV neutrn cunt rates fr the different NC LOS. Lcal prcessing f raw data n NC PCs in the cubicles will be als pssible fr ptimizatin purpses. Fig. 6a. Energy calibrated Na22 PHS fr the hrizntal JET neutrn camera. Fig. 5. Neutrn Camera Upgrade: verall system architecture 3. JET tests A prtable acquisitin system based n a X6-400M bard has been used fr a set f preliminary tests perfrmed at JET. T verify the adequacy f the ADCs input range (1.1 V) when using default HV settings fr the BC418 detectrs, all NC channels have been energy calibrated by means f the Na22 gamma surces embedded in the NC detectr bxes and the relatin between neutrn energy and ADC channels has been determined. Gamma calibratin data were prcessed using the pulse peak t determine the pulse energy, s that the channels f the gamma pulse height spectra can be directly related t ADC channels. Figures 6a and 6b shw the energy calibrated (electrn equivalent energy, E ee ) PHS respectively fr the hrizntal and the vertical camera channels. Fig. 6b. Energy calibrated Na22 PHS fr the vertical JET neutrn camera. The neutrn energy (E) vs. ADC channel curves deduced frm gamma calibratin are depicted in figures 7a and 7b. Cnversin frm electrn equivalent energy t neutrn energy (E) was made accrding t reference [6,7,8], i.e. using the frmula: E ee ( ( )) ( MeV ) = a " 1 1 exp a 2 E a 3 # MeV a 1 = 8; a 2 = 0.1; a 3 = 0.9; a 4 = 0.95 $ % + a 4E MeV ( ) Results indicate that the ADCs input range is adequate t enable 14 MeV detectin. Fr sme NC channels (especially fr the vertical camera) the maximum detectable neutrn energy is anyway clse t 14 MeV; mrever PMT gain variatins due t high cunt rate culd further reduce such maximum detectable energy. Therefre, the use f resistive attenuatrs may be needed in rder t reduce the amplitude f the pulses in input t the acquisitin system. (1) Fig. 7a. E Vs. ADC channel plt fr the hrizntal JET neutrn cameras

6 Fig. 7b. E Vs. ADC channel plt fr the vertical JET neutrn cameras As a test n sampling rate requirements pulses frm 22 Na surces were acquired at 400 Ms/s and 250 Ms/s (figure 8). A slight reductin in pulse height reslutin is bserved which des nt translate int a relevant change in the calculated psitin f the Cmptn edges (i.e. in the calibratin lines) and therefre int a significant change in the psitin f the 10 MeV threshld nrmally used fr r DT cunting; 250 MS/s and 400 Ms/s appear therefre equally suitable fr sampling f BC418 detectr pulses frm JET NC. cunts (A.U.) Fig. 8. Energy calibrated Na22 PHS acquired at 250 Ms/s and 400 Ms/s. Abut 50 DD plasma discharges (in the range # #87595) were als acquired cupling the digitizer t a central vertical NC channel (#15); PHS data frm these discharges were summed in rder t have enugh statistics n 14 MeV burn-up neutrns. In figure 9 the verall PHS is shwn, highlighting the different regins in which cntributins frm DD neutrns, DT neutrns and gammas are expected. Cunts ADC channel LOS# MS/s LOS#15 400MS/s DD+DT+γ DT+γ DT E(MeV) Figure 9. Energy calibrated BC418 PHS frm the sum f ~50 JET discharges. Indeed, since BC418 detectrs have n neutrn/gamma capabilities, the detectin f 14 MeV neutrns with BC418 is btained by setting a threshld (typically 10 MeV neutrn energy) n the energy abve which ne can cnsider the cunts in the PHS t be slely due t 14 MeV neutrns. 5. Cnclusins A new digital acquisitin system fr the JET neutrn camera detectrs devted t the measurement f 14 MeV neutrns was designed in the frame f wrk-package JET4 (JET enhancements), with the bjective f vercming the limitatins f the presently running analgue system (n strage f pulse data, n prvisin f pulse height spectra) and matching the demanding data thrughput requirements f future DT campaigns. The key design elements f the prpsed system are: separate resurces fr prcessing (FPGA/PC), fast data transfer (PCIex8 bus) and data strage allcated t cuples f neutrn camera channels; selectable sampling rate up t 400Msps; large FPGA n-bard memry; custm FPGA firmware fr nn-cntinuus acquisitin f scintillatr pulses. Preliminary tests perfrmed at JET with a prtable single 2 channels acquisitin bard identical t that t be used fr the final system indicate adequacy f ADCs input range t enable 14 MeV neutrn measurements when using default HV settings f BC418 detectrs and suitability f sampling rates lwer than 400Ms/s in setting f energy threshlds fr 14 MeV neutrns cunting. Acknwledgments This wrk has been carried ut within the framewrk f the EUROfusin Cnsrtium and has received funding frm the Euratm research and training prgramme under grant agreement N This views and pinins expressed herein d nt necessarily reflect thse f the Eurpean Cmmissin. References [1] M. J. Lughlin et al., Neutrn prfile measurements fr trace tritium experiments, Review f Scientific Instruments 70 (1999) [2] M. Riva, B. Espsit, D. Marcc, F. Belli and B. Syme, The new digital electrnics fr the JET Neutrn Prfile Mnitr: Perfrmances and first results, Fus. Eng. Design 86 (2011) [3] L. Giacmelli et al., Physics Prcedia 62 (2015) [4] [5] M. Riva, B. Espsit, D. Marcc, A new pulse-riented digital acquisitin system fr nuclear detectrs, Fusin Engineering and Design 82 (2007)1245. [6] R. Madey et al., The respnse f NE-228A, NE-228, NE- 224, and NE-102 scintillatrs t prtns frm 2.43 t MeV, Nuclear Instruments and Methds 151 (1978) [7] [7] G. Grini, L. Ballabi, and J. Källne, Plasma Phys. and Cntrlled Fusin 39 (1997) [8] [8] F. Belli et al., IEEE Transactin n nuclear science 59 5 (Octber 2012)