Six Ion Gun Fusion Experiment (SIGFE) Findings and Future Work

Transcription

1 Six Ion Gun Fusion Experiment (SIGFE) Findings and Future Work Matt K. Michalak, Brian J. Egle* Gerald L. Kulcinski, John F. Santarius Presented at 1 th US-Japan IEC Workshop 7-8 December 2011 in Sydney, NSW *At ORNL

2 Presentation outline Review of past information presented on the SIGFE Most recent results Diagnostics used 2 Si proton detectors, 1 He neutron detector Fusion Ion DOppler shift (FIDO) Next steps 2

3 IEC fusion reaction modes Basic IEC operation modes Beam-background Beam-embedded Converged core Multiple virtual electrode formation (Poissors) Beam-background and beam-embedded shown to dominate in gridded systems with mid to high pressure (>0. Pa)

4 Experimental results of Hirsch showed tri-modal distribution Relative Intensity [x-ray] Relative Intensity [neutrons] Hirsch-1967 Hirsch-1967 reported a tri-modal spatial distribution of fusion neutrons and bremsstrahlung radiation inside the cathode Theory of virtual electrode formation (poissors) used to explain these results Data taken at pressures between 0. to 1 Pa (2 to 8 mtorr) Source: Hirsch, R.L. (1967). Inertial-electrostatic confinement of ionized fusion gases. Journal of Applied Physics, 8(11), Neutron data X-ray data Radial Position [cm]

5 Comparison of the SIGFE to Hirsch geometry Hirsch SIGFE SIGFE s design attempted to replicate the geometry of Hirsch-1967 as close as possible 5 Major differences that may affect electric fields include: Grounded ring in SIGFE replicates chamber wall as anode Addition of focusing lens Electron suppression on cathode

6 Design to reality December 2007 December 2008 September

7 Total Chamber cathode pressure current [mpa] [ma] SIGFE can operate in a large parameter space Chamber pressure [µtorr] Stable -150 kv operation achieved mm ion beam width at cathode center at cathode voltages from -50 to -150 kv Total cathode Cathode current voltage [ma] [kv] SIGFE Run 266, 9/14/ kv, 10 ma, 44 mpa (0 µtorr ) 8 2 to 1 ma total cathode current 5 to 270 mpa chamber pressure (deuterium) 8 mm 7

8 Neutron rate [n/s] SIGFE neutron rate scaling with pressure is dependent on focus.0e E+07 Unfocused Ion direction 70% V focus Well focused SIGFE n/s has weak pressure dependence 2.0E E+07 Hirsch 100% V focus Over focused SIGFE has direct n/s pressure dependence 1.0E E+06 10% V focus Under focused SIGFE has inverse n/s dependence 0.0E+00 UW Gridded Chamber Pressure [mpa] 100 kv cathode voltage 10 ma total cathode current Under focused SIGFE has similar scaling to Hirsch 1 mpa = 7.5 µtorr 8

9 Neutron Rate [n/s] Defocused SIGFE data matches Hirsch D-D neutron rates 9 5.0E E E+07.5E+07.0E E E E E E E ma of total cathode current 1 mpa = 7.5 µtorr SIGFE 1 mpa focus: 0% Defocused Hirsch 1 mpa SIGFE 1 mpa Hirsch 150 mpa Vfocus: focus 70% SIGFE 150 mpa focus: V focus 70% UW Gridded 270 mpa Hirsch 1040 mpa Cathode Voltage [kv]

10 Calibrated D-D neutron rate [n/s] FIDO diagnostic measured <0.2% of total D-D fusion from cathode center Calibrated D-D proton rate [p/s] 1.0E E E E E+06 Focus voltage percentage 4% 64% 85% 106% 128% 149% 100 kv cathode voltage 5 ma total cathode current 80 mpa (600 µtorr) pressure Linear trend lines D-D proton rate from cathode center only 4 cm 1.0E E+0 8.0E+0 7.0E+0 6.0E+0 D+D 50% 50% n+t p+ He Large difference in protons from center and neutrons from entire volume 5.0E E+06.0E E+06 D-D neutron rate from entire chamber volume cm 5.0E+0 4.0E+0.0E+0 2.0E+0 Virtual potential well formation is not a significant fusion mechanism within the SIGFE parameter space 1.0E E Focus voltage [kv] 10

11 Conclusions from SIGFE D-D experiments D-D fusion rate scaled linearly with current at total cathode currents within the 2-1 ma operation space D-D neutron rate is highly dependent on the focusing of the ion beams Highest neutron rates in the SIGFE observed with defocused ion beams 4.2 x 10 7 n/s at -10 kv cathode voltage, 10 ma total cathode current, 1 mpa chamber pressure 11

12 Evidence of virtual potential well formation not observed in SIGFE Within the parameter space explored (<1 ma total cathode current,-50 to -150 kv, 1 to 270 mpa) Less than 0.2% of the D-D fusion reactions are from center of SIGFE device Virtual potential well structures and other space-charge related physics at the center of the SIGFE cathode are not a significant source of fusion D-D and D- He fusion protons observed from center are consistent with beam-background fusion The results of the SIGFE imply that beam-embedded fusion in the cathode lenses is the dominant D-D fusion mechanism in the SIGFE 12

13 Rational for SIGFE diagnostics Measure energy of reacting particles Determine location of fusion reactions within the cathode Identify the mechanism for high neutron production efficiency Hirsch device was the most efficient IEC, until SIGFE, on a neutron production rate per kilowatt basis 1

14 Proton detector designed to only observe fusion from center Proton detection volume 4 cm Fusion Ion Doppler Shift (FIDO) diagnostic 1 Energy of reactant particles determined from detected fusion proton spectrum 60 cm x-ray noise reduced by bending protons out of lineof-sight of chamber 8 µm of Al foil at cathode edge Designed to detect protons from the center of cathode only Calibrated as a point source of protons at the center of the SIFGE Developed by David Boris

15 Protons from center consistent with beam-background fusion Doppler shift of D-D protons can be from D 1+, D 2+, and D + ion species Experimental proton spectrum consistent with near full cathode energy ions on stationary targets (beam-background) 15 Note: protons from 4 cm volume at cathode center only

16 D- He proton detector D+ He p+ 4 He D- He proton detector Collimated to detect 14.7 MeV protons only from center of cathode Calibrated as a point source of protons at the center of the SIGFE 60 µm of Pb and 8 µm of Al foil between center and detector 90 cm 16

17 Calibrated proton rate [p/s per energy bin] Doppler shift is consistent with D- He beam-background fusion kv cathode voltage 10 ma total cathode current 1 mpa (1000 µtorr) pressure Trend line: 5 pt moving avg 100% focus voltage kv 70 kv Energy deposited in detector [MeV] 17

18 Summary SIGFE has been operated with different fuels and multiple diagnostics over a large parameter space Matched Hirsch results Most likely operated in a beam-embedded mode 18

19 Next steps for the SIGFE Operate in a pulsed mode to achieve higher currents Ohnishi, M., Sato, K. H., Yamamoto, Y., & Yoshikawa, K. (1997). Correlation between potential well structure and neutron production in inertial electrostatic confinement fusion. Nuclear Fusion, 7(5), Explore new operating parameters 19

20 Questions? 20