NZ61

Prof. Czubek Laboratory of Neutron Sources

Plasma Focus PF-24

Plasma focus belongs to a class of research devices in which an electron-ion (e.g., deuterium) plasma is generated by an electrical discharge between coaxial electrodes. The generated magnetic pressure, created by the flow of current through the plasma with an intensity of hundreds of kiloamperes, leads to the compression of the plasma. This results in the fusion reaction of deuterium nuclei, and thus the emission of fast neutrons.

Two images of PF system with the initial and final stage of plasma discharge

Plasma focus is a convenient laboratory device that allows the study of physical phenomena occurring in dense and hot plasma produced from light gases or from light gases doped with other components.

Technical parameters of the PF-24 current generator

Type of device	Mather-type plasma focus
Charging voltage of the condenser bank (U₀)	17-40 kV
Total capacity of the condenser bank (C₀)	116 µF
Energy stored in the condenser bank (E₀)	17-93 kJ
Nominal inductance (L₀)	8.5 nH
Quarter-period of short-circuit (T_1/4)	1.4 µs
Maximum short-circuit current (I_S-C)	3.6 MA
Total resistance (R₀)	3.1 mΩ

Details:
Marek Scholz, Agnieszka Kulińska, The Plasma-Focus device at IFJ PAN Kraków. Status and Perspectives. IFJ PAN Report no 2104/AP, 2020

Primary elements of the PF-24 electrical circuit

Electrical equivalent circuit for a plasma focus discharge

Research objectives and tasks for PF-24

▪ Tomographic 2D and 3D plasma imaging in the magnetic field
▪ Method of reconstruction of the plasma focus
▪ Investigation of advanced fusion reactions in plasma with fast ions, associated with neutron emission
or with lack of neutron emission
▪ Investigation of plasma behavior and the occurrence of D-D fusion reactions during discharges in
mixtures of D₂ with heavier noble gases.
▪ Magneto-hydrodynamic modeling of plasma behavior and radiation emission during plasma focus
discharges.
▪ Investigation of plasma behavior and the occurrence of D-³He and p-¹¹B fusion reactions, during
discharges in a deuterium-helium-3 mixture and during discharges in hydrogen with accompanying
laser ablation of boron-11.

Electrical diagnostics of PF discharge

Plots of 1 total current flowing through the collector 2 derivative after time of total current and during 3 collector voltage, all as a function of time

Neutron and X-ray diagnostics

A photo of neutron pinhole camera. Big cylindrical block of poliethylene visible.

Neutron pinhole camera based on BCF-12 miniature scintillation detectors (Saint Gobain). Time resolution: 5ns, spatial resolution: 5mm.

A photo of small scintillation detector coupled to PMT via optical fibre

Main elements of the PF-24 neutron pinhole camera: BCF-12 scintillation detector coupled to PMT (Hamamatsu) via 25m long optical fibre

A plot of the distribution of the neutron flux along the plasma focus axis during the fusion of deuterium ions registered by a neutron pinhole camera — An example of the distribution of the neutron flux along the plasma focus axis during the fusion of deuterium ions registered by a neutron pinhole camera. Monte-Carlo modeling.

Plots of X-ray and neutron radiation respose of the detectors as a function of time for a PF-24 discharge. — An example of recording X-ray and neutron radiation as a function of time for PF-24 discharge using 3 pcs of scintillation detectors. The delay between the X-ray and neutron peaks is 42 ns.

A photo of the four-frame Camera in soft X-ray energy range.

High-speed, 4-camera pinhole camera operating in the vacuum ultraviolet and soft X-ray (VUV/SXR) range – design and construction by ACS, Warsaw, Poland. Capable of recording 4 images with an exposure of about 2.0 ns and a delay of 4.7 ns (adjustable). Magnification: 2.2. Single pixel size: 43 µm. Spatial resolution: 215 µm.

Imaging example – 3 discharges in PF-24 recorded with the high-speed, 4-frame VUV/SXR pinhole camera.

An image of a discharge in PF-24 recorded with the four-frame Camera.