Response of thin foil Faraday Cup lost alpha particle detector in intense neutron and gamma ray radiation fields F.E. Cecil 1, V. Kiptily 2, D. Darrow 3, A. Horton 2, K. Fullard 2, K. Lawson 2, G. Matthews 2, A. Murari 2, and G. Sergienko 2, and JET-EFDA EFDA contributors* 1 Colorado School of Mines, Golden Colorado, USA 2 JET-EFDA, EFDA, Culham Science Centre, OX14 3DB, Abingdon, United Kingdom 3 Princeton Plasma Physics Lab, Princeton, New Jersey, USA supported in part by USDOE *See the Appendix of F. Romanelli et al., Proceedings of the 22nd d IAEA Fusion Energy Conference, Geneva, Switzerland, 2008 1
Measured and calculated responses of a set of thin Faraday foils as a lost alpha particle diagnostic for high yield d-t plasmas to 1) Fast neutrons 2) Energetic gamma rays 3) X-rays 4) UV radiation 5) ICRH 6) Time varying magnetic field and plasma current 7) Beam heating effects In addition: we will present recent observations on JET of lost alpha particles / deuterons with energies up to about 7 MeV generated during ICRH heated 4He plasmas. 2
JET Lost Alpha Diagnostic KA-2; 2005 2.5 um x 25 mm x 75 mm Ni foil 6.3-7.2 MeV alphas 1.7-2.5 MeV p, d, t 4.2-5.9 MeV alphas 1.1-2.2 MeV p, d, t 2.3-3.8 MeV alphas 0.7-1.2 MeV p, d, t 0-1.6 MeV alphas 0.5 MeV p, d, t 58Ni(n,p) 2.5 um x 25 mm x 75 mm mica foil Amp Amp Amp Amp Darrow et al.;fus. Eng. and Design, 74, 853, (2005) 3
Energy resolution Cecil et al., Rev. Sci. Instrum, 70, 1149 (1999 Current fraction in each foil. 1.4 1.2 1 0.8 0.6 0.4 0.2 0 1 1.5 2.2 2.75 Alpha energy (MeV) 3.7 4.5 5.5 6 6.5 7 7.5 5 3 1 Foil number Concept tested with monoenergetic particle beams from linear accelerators
Schematic diagram of poloidal distribution of 5 sets of foils Beam Plasma Faraday cup modules 9 15 21 27 33 Pylon 5
Installation of KA-2; May 2005 6
Response to fast neutrons: calculated Cross sections for 58Ni + n Cross section (b) 1 0.8 0.6 0.4 0.2 0 (n,p) (n,a) 0 5 10 15 20 Energy (M ev) neuts = 6 E13 /cm2 - s; sig = 6 E-25 cm2; tgts = 2.1 E 19 /cm2; Rxns = neuts sig tgts = 7.4 E 8 /cm2-s = - 0.12 na/cm2 7
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Summary of measurements of fast neutron induced currents (per cm 2 target) Machine Flux(n/cm2/s) Msd current Pred current TFTR(95) a 1E12 < 100 na 0.1 na JET(97) b 3E12 <5 na 0.3 na TRIGA(03) c 1E13 1.2 na 0.5 na JAERI(01) d 3E14 30 na n/a ITER 6E13 6 na Refs: a RSI 68, p. 363, b RSI 70, p. 1151, c RSI 74, p. 1749, d FED 56, p. 907 Current predicted using NNDC(BNL) values of cross sections for 58 Ni(n,p) 58 Co and 58 Ni(n,a) 55 Fe current inducing reactions; Predicted current for ITER based upon JAERI data 1% lost alphas on ITER ~ 100 na/cm2 9
Neutron/gamma insensitivity Example: KA-1 on JET for 16 MW d-t pulse JPN42976 F1-F4 3 2 1 0-1 51 52 53 54 JPN42967 F2-F4 3 2 1 0-1 51 52 53 54 10
Response to gamma rays: calculated Calculation based upon known attenuation coefficients Attenuation coefficient at 5 MeV = 0.03 cm2/gm Thickness of 2.5 micron Ni foil =.002 gm/cm2 Gamma ray flux= 6E13 /cm2 - s; Number absorbed= 6E13 (1 e^(- Atten * Thk) = 4E9/cm2-s= 0.6 na 11
Response to x-rays: estimated Calculation based upon known absorption length at 10 kev ~ 7 µ X- ray flux ~ 1E14/cm2 - s; Number absorbed= 1 E 14= 7.2E9/cm2-s= 16µA Conclusion; direct exposure to plasma not possible Solution: face foils outward relying on large gyro radius Alpha particle Rminor Faraday foil X-ray shield X-rays from plasma 12
Response to scattered UV: observed Observation of significant (µa) current during Ohmic heating 13
Strong correlation with bolometer which is good measure of UV 14
Comparison of front foil current and bolometric power 15
Suppression or enhancement of front foil current with small DC voltage 16
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Suppression of ICRH (6 MW) induced noise with passive filters at amps Steady state response in KA2 for 75699 @ 57.41 and 59.20 sec 1.E-03 KA2 current (Amperes) 1.E-04 1.E-05 1.E-06 1.E-07 1.E-08 411 412 413 414 415 416 417 418 KA2 foil filters 18
Temperature insensitivity Ni foil with array of 3mm x 3 mm aperture and.037 W/mm 2 (1 ua/cm 2 ) 3.5 MeV alphas with intermediate points anchored at wall temp 20 15 y-dir (mm) 10 600 650 700 750 800 850 900 950 5 5 10 15 20 x-dir (mm)
Foil current induced by changing Bt and Ip for JPN79171; ~ 20 na @ dbt/dt = 0.2 T/sec ~ 5 na @ dip/dt = 0.4 MA/sec 2 nd foil 4 th foil 2 nd foil 4 th foil 2 nd foil 4 th foil ICRH (MW) NBI (MW) Bt (Tesla) Ip (MA) 20
Recent (Sept 18, 2009) observations on JET of lost alpha particles with energies up to about 7 MeV generated during ICRH (up to 6 MW) 4He plasmas and preliminary conclusions JPN 79171 KA2 112 and 114 2.3-3.7 MeV 6.3-7.2 MeV KA2 132 and 134 2.3-3.7 MeV 6.3-7.2 MeV KA2 142 and 144 2.3-3.7 MeV 6.3-7.2 MeV ICRH NBI 21
JPN 79171 KA2 112,113 and 114 2.3-3.7 MeV 4.2-5.9 MeV 6.3-7.2 MeV Just 114 (6.3 to 7.2 MeV) Alphas (6.3-7.2 MeV( or deuterons 2-2.3 MeV 22
Foil currents at increasing RF power 60 Net Foil Current (na) 50 40 30 20 k112 k113 k114 x 2 2.3-3.7 MeV 4.2-5.9 MeV 6.3-7.2 MeV 10 0 0 1 2 3 4 5 6 RF power (MW) 23
Energy spectra at top detector for different RF powers 60 50 Alphas RF 5.7 MW RF4.4 MW RF3.7 MW RF 2.9 MW Net Foil Current (na) 40 30 20 10 0 2 3 4 5 6 7 8 Average energy (MeV) 24
Correlation between foil current and electron temperature Foil current (na) 60 40 20 Foil 114 x 10 Foil 113 Foil 112 0 3.5 4 4.5 5 Electron Temperatute (kev) 25
Comparison of KA2(FC) 112,113 and 114 with KA3(SP) PMT 005 and 016; JPN 79174 KA2 2.3-3.7 MeV 4.2-5.9 MeV 6.3-7.2 MeV KA3 KA3- PMT 016 KA3- PMT 005 26
10 Comparison of Faraday Foil and Scintillator PMT KA3-PMT005 (na) 8 6 4 2 0 0 10 20 30 40 50 60 KA2-112 (na) 27
Focal plane image of KA3 Scintillator Probe of s up to 3.7 MeV or d s up to 1.9 MeV KA2_312 current KA2-31x detector is in the similar poloidal position as Scintillator Probe 500 400 Light integrated in 2.3-3.7 MeV spot KA3 losses, a.u. 300 200 100 0 10 12 14 16 18 20 22 24 t(s) 2.3-3.7 MeV s / 0.9-1.5 MeV d s as in 312-foil (chance to calibrate!!!) 28
Can you separate s from deuterons? de/dx ( kev/µm) Range (µm) Gyroradius(3 T)(cm) 1.2 MeV D 147 6.3 7.4.3.5 MeV 485 6.1 9.0 1.2 MeV d 2 µm 0.91 MeV d.29 MeV 4.4 µm 3.5 MeV.97 MeV 2.63 MeV 4.2 µm 29
Further analysis of these measurements Compare to observation of gamma rays induced by high energy alpha particles (Kiptily) Compare to simultaneous NPA data (Johnson, Medley, Ioffe) Modeling to estimate alpha particle density to infer confinement (JET, PPPL, Innsbruck Uni?) Absolute calibration of -particle losses in Scintillator Probe (JET, PPPL,CSM and Innsbruck Uni) 30
Conclusions Faraday cup lost ion detector capable of operating in ITER like conditions for alpha currents > 10 na/cm2 Lost alpha/deuteron signals measured on JET for ICRH 4He d-t simulation plasmas KA2 data (KA2-3XX at same height as KA3) will allow absolute calibration of KA3 scintillator losses 31