Thin Faraday foil collectors as a lost ion diagnostic F.E. Cecil Colorado School of Mines D.S. Darrow and R. Ellis Princeton Plasma Physics Lab W.W. Heidbrink University of California, Irvine V. Kiptily Euratom/UKAEA This work is supported by U.S. Department of Energy Contracts DE-AC02-76CH03073 and DE-FG03-95ER54303 and conducted under EFDA.
Overview of poster Concept Accelerator based proof-of-principle Existing devices K-α-1 on JET (1995) NSTX (1998) DIIID (2001, 2003) Proposed devices K-α-2 on JET (2004) ITER (?)
Faraday foil concept Schematic of lost α detector consisting of four 2.5 µm foils of Ni separated by three 2.5 µm sheets of mica electrical insulator (the range of a 3.5 MeV αparticle in Ni is about 7 µm) 3.5 MeV α Vessel wall Ammeter Ammeter Ammeter Ammeter Ref. F.E. Cecil, Proc EPS Conf (Montpelier) 1994
10000 Range and straggling for protons and alphas in Ni (TRIM2000) Range/straggling (microns) 1000 100 10 1 0.1 alpha range alpha straggling proton range proton straggling 0.01 0.01 0.1 1 10 100 Particle energy (MeV)
Predicted Detector Response (TRIM2000) 0.8 E α = 3.5 MeV; θ max = 30 o 0.6 0.4 0.2 0.0 Current fraction in each foil 0.8 0.6 0.4 0.2 0.0 0.8 0.6 E α = 3.5 MeV; θ max = 45 o E α = 2.5 MeV; θ max = 30 o 0.4 0.2 0.0 0.8 0.6 0.4 0.2 0.0 E α = 2.5 MeV; θ max = 45 o 0 1 2 3 4 5 6 7 8 Foil Number (1=Front)
Proof of principle Accelerator based measurements with α beam; Sandia Nat l Labs 1998. 6.0 µm Al foils with 2.5 µm CH 2 insulator 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 3.7 4.5 Alpha energy (MeV) 5.5 6 6.5 7 7.5 5 3 1 Foil number Ref F.E. Cecil et al, Rev Sci Instrum 70 (1999) 1149
JET K-a-1 Interior of JET showing lost alpha detector mounting on left side near limiter and slightly below torus midplane. Ref O.N. Jarvis et al, Fus. Tech. 39 (2001) 84
Neutrons/sec 8e+18 6e+18 4e+18 2e+18 0 16 MW JET Pulse 42976 Foil 1(V) 2 1 0 Foil 2 (V) 2 1 0 Foil1 - Foil2 (V) 2 [10 V = 200 na] 1 0 51 52 53 54 Time(s) Ref F.E. Cecil et al, Rev Sci Instrum 70 (1999) 1149
NSTX Photograph of fast lost ion probe on NSTX. The three small holes are the apertures for the three Faraday collectors. Ref D.S. Darrow et al Rev Sci Instrum 72 (2001) 784
2 NSTX "Beam-Blip" Shot 105704 neutral beam power 1 0 0.60.15 0.16 0.17 0.18 0.19 0.20 0.21 0.4 neutron source strength 0.2 0.0 0.15 0.16 0.17 0.18 0.19 0.20 0.21 161 cm 0.15 0.16 0.17 0.18 0.19 0.20 0.21 163 cm 0.15 0.16 0.17 0.18 0.19 0.20 0.21 166 cm 0.15 0.16 0.17 0.18 0.19 0.20 0.21 time(sec) Ref WW Heidbrink et al, Nucl Fus 43 (2003) 883
DIIID Photograph of graphite housing of single foil detector on vessel wall with upward facing aperture Ref F.E. Cecil et al Rev Sci Instrum 74 (2003) 1747
neutrons/sec 3e+14 2e+14 1e+14 D III D Shot 113177 Neutron source strength 0 arbitrary units 3 2 1 0 D-alpha brightness 8 Active foil - Blind foil Volts 6 4 2 0-2 Time (msec) 0 500 1000 1500
JET (K-α-2) Fifteen detectors each with four foils at three radial locations for each of five poloidal locations Height above machine midplane (mm) 600 400 200 0-200 -400-600 -800-1000 Poloidal limiter Centers of each foil set -1200 3200 3400 3600 3800 4000 4200 Major radius (mm) Ref. F.E. Cecil et al, Proc EPS Conf (St. Petersburg, 2003)
Poloidal locations Model of distribution of lost alphas from 42982 d-t plasma Escaping alpha particle impact density 65 389.65 379.65 55 45 35 25 15 5-5 -15-25 -35 Distance above midplane (cm) -45-55 -65-75 -85-95 -105 369.65 359.65 349.65 339.65 329.65 Major Radius (cm) Ref Sean Conroy, private communication 2002
Expected signal level Z=+94.5 mm at center of 8x17 array of 3mm x 3mm holes at θ rad = 52.2 o (outward) and θ tor = 20 o CCW 10000 Signal Current (na) 1000 100 10 1 Front JPF42756 (2 MA, 2T) JPF42983 (4.5 MA, 3.5T) JPF42976 (4.5 MA, 3.5T) Middle 0.1 3860 3880 3900 3920 3940 3960 3980 4000 4020 Major Radius (mm) Back
Comparison of K-a-1and K-a-2 Efficiency (α/source neutron) 1e-6 1e-8 1e-10 1e-12 1e-14 1e-16 K-α 1 K-α-2 (front detector, top pylon) 0 1 2 3 4 Toroidal field (T)
Efficiency of K-a-2 vs Plasma Profile and Plasma Current
Comparison of efficiency for 3.5 MeV alphas and 15 MeV protons 1e-6 Efficiency of a 3 mm x 3 mm Aperture vs Major Radius;Poloidal Limiter at 3752 mm for Z = 393 mm) 15 MeV Proton for Shot 42982 1e-7 Efficiency 1e-8 1e-9 3.5 MeV Alpha particle for Shot 42982 1e-10 3790 3800 3810 3820 3830 3840 Major radius (mm)
K-a-2 Problems Solutions Environmental (dust, Beryllium,x-rays Tilt aperatures Heat load Aperture array Neutron/gamma Thin foils eliminate background Electrical noise Subtract control foil from signal foil
ENVIRONMENTAL Efficiency for JET Shot 42976 at 53.0 sec for 3mm x 3mm aperture at R=3800 mm versus orientation angles Radially outward angle (Radians x 10) 14 12 10 8 6 4 2 2 4 6 8 10 12 14 Toroidally CCW angle (Radians x 10)
HEAT LOAD Ni foil with array of 3mm x 3 mm aperture and.037 W/mm2 of 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)
Neutron/gamma Measured and calculated signal for 4.5 T, 3.5 MA pulse with 10 19 total n/sec n/γ background ~10 13 /cm 2 /sec Expected I α ~ 100 na/cm 2 Predicted I n ~ 0.1 na/cm 2 Predicted I γ ~ 0.01 na/cm2 Measured current from Ni foil in fission reactor core with 10 13 n/γ /cm 2 /sec ~ 0.08 na/cm2 Conclusion (I n +I γ )<< I α Ref F.E. Cecil et al, Rev Sci Instrum 74 (2003) 1747
ELECTRICAL NOISE By subtracting current from control foil from current in signal foil, background electrical noise measured to be ~0.5 na for 50 Hz low pass filter Detail of JET Pulse 42976 0.4 [10 V = 200 na] Foil 1(V) 0.2 0.0-0.2 rms noise ~ 0.2V=>4 na Foil 2 (V) 0.4 0.2 0.0 rms noise ~ 0.2V=>4 na -0.2 Foil1 - Foil2 (V) 0.4 0.2 0.0 rms noise ~ 0.03V=> 0.6 na -0.2 51.0 51.2 51.4 51.6 51.8 Time(s)
ITER 1e+12 ITER Source Profile; Shot 3000; time= 190 sec ITER source strength (reactions-cm -3 -sec -1 ) 8e+11 6e+11 4e+11 2e+11 0 Predicted profile 6.37E11 (1 - (r/rmin) 2 ) 3 0 1 R/R minor Ref. Robert Budny, PPPL, Private communicatiopn (2003) and R. Budny, Nucl. Fus 42 (2002) 1382
ITER ITER Machine Profile 6000 Height above machine mid-plane (mm) 4000 2000 0-2000 -4000-6000 0 2000 4000 6000 8000 10000 12000 Major radius (mm) Ref George Vayakis (ITER), private communication (2003)
ITER Midplane detection efficiency Efficiency (alphas/source neutron for 1cm 2 upward foil) 1e-6 1e-7 1e-8 1e-9 1e-10 8000 8050 8100 8150 8200 8250 8300 Major radius (mm)