2168-4
Joint ICTP-IAEA Workshop on Dense Magnetized Plasma and Plasma Diagnostics
15 - 26 November 2010
Summary of results from POSEJDON Plasma-Focus
H. Schmidt Herrenberg Germany
Diagnostics and Scaling of Fusion- Produced Neutrons in PF Experiments
Hellmut Schmidt
International Centre for Dense Magnetized Plasmas, Warsaw and University of Stuttgart, Germany
Trieste Neutrons in PF 1 November 2010 Experiments Outline
• Introduction • Neutron Detection – Activation – Scintillation – TLDs and Bubble detectors • Neutron Diagnostics – Fusion Reaction Models – Gyrating Particle Model • Scaling of Neutron Yield – Beam Target and Thermal Production of Neutrons
Trieste Neutrons in PF 2 November 2010 POSEIDON Introduction
Trieste Neutrons in PF 3 November 2010 POSEIDON Radial Compression (Pinch) Phase of the Plasma Focus
Trieste Neutrons in PF 4 November 2010 POSEIDON Density sheath of POSEIDON PF Before maximal compression
Trieste Neutrons in PF 5 November 2010 POSEIDON Current and Density Sheaths In a Mather type Plasma Focus
t2 t3
t1 cathode anode
Trieste Neutrons in PF 6 November 2010 POSEIDON Radial Streak Picture, shot 5055 of PF1000
4 cm
0 100 200 t [ns]
Trieste Neutrons in PF 7 November 2010 POSEIDON Radial Streak Picture of PF1000 (shot 5055)
0 100 200 ns m c
4
first pinch „second“ pinch implosion of the current sheath development explosion of instabilities
Typical Behaviour
Trieste Neutrons in PF 8 November 2010 POSEIDON Radial Streak Pictures of POSEIDON (280 kJ)
Bad Behaviour
Typical Behaviour
Trieste Neutrons in PF 9 November 2010 POSEIDON Plasma Focus Phases
Trieste Neutrons in PF 10 November 2010 POSEIDON 5 Schlieren pictures
First neutron pulse
Trieste Neutrons in PF 11 November 2010 POSEIDON 5 Schlieren pictures
Second neutron pulse
Trieste Neutrons in PF 12 November 2010 POSEIDON Trieste Neutrons in PF 13 November 2010 POSEIDON Neutron Detection
Trieste Neutrons in PF 14 November 2010 POSEIDON Neutron Activation
Trieste Neutrons in PF 15 November 2010 POSEIDON Be-detector
Trieste Neutrons in PF 16 November 2010 POSEIDON Silver activation counter Example of a specific design
When used with fast neutrons, the counter is normally placed within a polyethylene moderator
1-mm-thick aluminium entrance window
Back
Lucite Photomultiplier Front light pipe
31 silver foils (101.6 x 203.2 x 0.245 mm), clear silicon aluminium between 32 plates NE 110 plastic scintillator rubber pad housing (102.0 x 204.0 x 3.2 mm)
10 ______
_ counts 10 24-s activity ______background 2.4-min activity _ _ _ _ 10 _ _ _ 450 500 550 600 650 700 750 800 seconds
Trieste Neutrons in PF 17 November 2010 POSEIDON Activity after insertion in a constant neutron flux
Trieste Neutrons in PF 18 November 2010 POSEIDON Bonner spheres with TLDs and silver activation detectors PF1000 in Warsaw
Trieste Neutrons in PF 19 November 2010 POSEIDON Scintillation Detectors
• Scintillators connected to PM- Tubes • Time resolution in the ns range
Trieste Neutrons in PF 20 November 2010 POSEIDON Bubble detectors
They integrate the neutron yield
Bubbles have to be counted
Calibration necessary
Trieste Neutrons in PF 21 November 2010 POSEIDON Neutron Diagnostics
Trieste Neutrons in PF 22 November 2010 POSEIDON Beam Target Processes and their verification
Trieste Neutrons in PF 23 November 2010 POSEIDON Ion Trajectories in the Azimuthal Magnetic Field of the Pinch Current
Trieste Neutrons in PF 24 November 2010 POSEIDON Trieste Neutrons in PF 25 November 2010 POSEIDON Two Neutron emitting Phases Correlated to Plasma Dynamics
Trieste Neutrons in PF 26 November 2010 POSEIDON Trieste Neutrons in PF 27 November 2010 POSEIDON 8 mbar
Trieste Neutrons in PF 28 November 2010 POSEIDON Trieste Neutrons in PF 29 November 2010 POSEIDON Neutron pinhole measurements
Trieste Neutrons in PF 30 November 2010 POSEIDON Pinhole Measurements Setup for Neutrons
Trieste Neutrons in PF 31 November 2010 POSEIDON Pinhole for Neutrons
Trieste Neutrons in PF 32 November 2010 POSEIDON Array of Scintillators Connected via Light Fibres To Photomultipliers
Trieste Neutrons in PF 33 November 2010 POSEIDON Trieste Neutrons in PF 34 November 2010 POSEIDON Trieste Neutrons in PF 35 November 2010 POSEIDON Neutron
Time of Flight
Measurements
Trieste Neutrons in PF 36 November 2010 POSEIDON Trieste Neutrons in PF 37 November 2010 POSEIDON Trieste Neutrons in PF 38 November 2010 POSEIDON Trieste Neutrons in PF 39 November 2010 POSEIDON Trieste Neutrons in PF 40 November 2010 POSEIDON Large gap (36 mm)
Small gap (28.5 mm)
Trieste Neutrons in PF 41 November 2010 POSEIDON Neutron Yield and
-> relaxation of deuterons
Trieste Neutrons in PF 42 November 2010 POSEIDON Why Reaction Proton Diagnostics?
Trieste Neutrons in PF 43 November 2010 POSEIDON Trieste Neutrons in PF 44 November 2010 POSEIDON Proton Diagnostics
Solid state nuclear track detectors are used for the registration of protons
Individual particles can be registered using an etching process.
Small craters are visible under the Microscope
Spectral information can be obtained using absorbing metal foils
Trieste Neutrons in PF 45 November 2010 POSEIDON Trieste Neutrons in PF 46 November 2010 POSEIDON Trieste Neutrons in PF 47 November 2010 POSEIDON Trieste Neutrons in PF 48 November 2010 POSEIDON Pinhole picture of P i n h o l e
p i c t u r Trieste Neutrons in PF 49 November 2010 POSEIDON Proton spectra
Trieste Neutrons in PF 50 November 2010 POSEIDON Calculated SpectraC a
Trieste Neutrons in PF 51 November 2010 POSEIDON Neutron diagnostics deliver valuable information on various processes which occur in the plasma, such as:
Pinch dynamics
fast ion beams interacting with a target
fast ion energy distributions
Fusion neutron measurements should be complemented by Fusion proton measurements .
Trieste Neutrons in PF 52 November 2010 POSEIDON Trieste Neutrons in PF 53 November 2010 POSEIDON Gyrating Particle Model
Trieste Neutrons in PF 54 November 2010 POSEIDON Trieste Neutrons in PF 55 November 2010 POSEIDON Trieste Neutrons in PF 56 November 2010 POSEIDON Trieste Neutrons in PF 57 November 2010 POSEIDON Trieste Neutrons in PF 58 November 2010 POSEIDON Trieste Neutrons in PF 59 November 2010 POSEIDON Trieste Neutrons in PF 60 November 2010 POSEIDON Trieste Neutrons in PF 61 November 2010 POSEIDON Trieste Neutrons in PF 62 November 2010 POSEIDON Trieste Neutrons in PF 63 November 2010 POSEIDON Trieste Neutrons in PF 64 November 2010 POSEIDON Scaling
Trieste Neutrons in PF 65 November 2010 POSEIDON Michel, Darmstadt, 1974
Trieste Neutrons in PF 66 November 2010 POSEIDON Bernard, Limeil, 1977
Trieste Neutrons in PF 67 November 2010 POSEIDON Krompholz / Herold 1981 /1991
Trieste Neutrons in PF 68 November 2010 POSEIDON Herold 1989
Influence of insulator material!
Trieste Neutrons in PF 69 November 2010 POSEIDON Scholz 2010
Ic - Current on collector probe, at the max current on ACMP Ip - Max current on ACMP, measured at 40/12 mm
Trieste Neutrons in PF 70 November 2010 POSEIDON Scholz 2010 Results for probe position at r = 40 mm
Ic - Current on collector probe, at the max current on ACMP Ip - Max current on ACMP, measured at 40/12 mm
Trieste Neutrons in PF 71 November 2010 POSEIDON Lee 2009
Figure 4. Assembly of experimental data to obtain Yn scaling with current; loosely termed as the current or pinch current in the literature. This is the experimental curve from which a calibration point is obtained, at 0.5 MA, to calibrate the neutron yield equation (3) for the Lee model code.
Trieste Neutrons in PF 72 November 2010 POSEIDON L Lee, 2009 e e
Trieste Neutrons in PF 73 November 2010 POSEIDON Geometry for Lee-Model
Trieste Neutrons in PF 74 November 2010 POSEIDON Spherical Geometry – Different results for scaling expected
Trieste Neutrons in PF 75 November 2010 POSEIDON Trieste Neutrons in PF 76 November 2010 POSEIDON Trieste Neutrons in PF 77 November 2010 POSEIDON Conclusions • Neutrons from a plasma focus, measured as a function of time, location and direction of emission reveal quite a number of important parameters on fusion reactions occurring in the dense high current phase of the experiment. In addition determination of the energy spectra of the emitted neutrons are important for understanding of the mechanisms taking place for the neutron production. The two main reasons for neutron diagnostics are 1) to determine the fusion yield, i.e. the efficiency of a device and its scaling; and 2) to learn the characteristics of the fusion reactions. • Correlations of the neutron emission to other properties of a plasma focus such as pinch current, plasma density and temperature as well as electron beam and ion beam emission are of importance as well. • Methods and results of neutron diagnostics for large experiments such as the former experiment Poseidon in Stuttgart and PF 1000 in Warsaw were presented and discussed. • Neutron diagnostics presented include nuclear track detectors, plastic scintillators coupled to photomultipliers, activation measurements, time-of-flight methods as well as pinholes for spatial resolution of the neutron source. • The well known scaling law according to which neutron yield scales roughly with the square of the energy input and the fourth power of the current was commented. Reasons for strong deviations from this law for high energy – know as saturation – are still a subject of debate.
Trieste Neutrons in PF 78 November 2010 POSEIDON References:
Liberman, A.M., De Groot, J.S., Toor, A., Spielman, R. Physics of High-Density Z-Pinch Plasmas Springer, 1998
Schmidt, H. Plasma focus and z-pinch Proceedings of the II Latin-American Workshop on Plasma Physics and Controlled Thermonuclear Fusion, CIF Series, Vol. 12, pp. 1-30 Medellin, Colombia, 16-28 Feb. 1987 Editor: R. Krikorian
Schmidt, H. Neutron Yield Optimization of Plasma Focus Devices J. Tech. Phys. 41 , 2, Special Issue, 93-108 (2000)
Knoll, Glenn F. Radiation Detection and Measurement, Second Edition John Wiley & Sons, 1989
Vikhrev, V.V. and Korolev, V.D. Neutron Generation from Z-Pinches Plasma Phys. Rep. 33 , 356-380 (2007)
Velikovich‚ A.L.et al. Z-pinch plasma neutron sources Phys. of Plasmas 14 , 022701 (2007)
Schmidt, R. and Herold,H. A method for time resolved neutron spectroscopy on short pulsed fusion neutron sources Plasma Physics and Controlled Fusion. 29 , 523 – 534 (1987)
Trieste Neutrons in PF 79 November 2010 POSEIDON