Effect of gas filling pressure and operation energy on ion and neutron emission in a medium energy plasma focus device

Self Cite

Plasma focus is a laboratory fusion device that is used to produce pulsed neutrons for a few tens of ns duration. A compact plasma focus tube (volume ≈ 130 cm3) has been developed and this was connected to a newly developed capacitor bank using twenty four coaxial cables, each 10 m long. The capacitor bank was of compact size and this was consisted of four energy storage capacitors (each 6 µF, 20 kV, size:20 cm × 20 cm × 30 cm). The peak discharge current of the capacitor bank was estimated to be 176 kA with rise time of around 3.6 µs at maximum 4.8 kJ operation energy. The average neutron yield was observed to be maximum (3.1±1.0)×106 neutrons/pulse with pulse duration of 15 to 25 ns at an operation energy of 2.7 kJ (15 kV) and deuterium gas filling pressure of 4 mbar. Long coaxial cables allow only the plasma focus head (neutron source) to be moved as per needs, making this a portable pulsed neutron source useful in many applications including in extreme conditions such as in borehole logging applications for oils and minerals mapping. This report describes the details about various components of this portable neutron generator along with its neutron emission characteristics.

Section: Resultssupporting

confidence: 58%

Development of a portable pulsed fast ⩾10⁶ neutron generator based on a flexible miniature plasma focus tube

Niranjan

Srivastava

Joycee

et al. 2023

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“…Neutron energies above 2.45 MeV [estimated using the Q value of d(d, 3 He)n nuclear fusion reaction] were due to high energy deuterium ions transferring their additional energy to neutrons according to beam-target fusion mechanism of neutron production [47]. Variation in neutron energy with filling pressure could be attributed to variation in the energy spectrum of deuterium ions as reported earlier [49]. This has also been confirmed from the observed variation in hard x-ray emission which is produced on collision of relativistic electrons with PF anode as discussed above.…”

Section: Experimental Observationsmentioning

confidence: 78%

“…Compared with the neutron energy curve (figure 4), the maximum neutron yield with maximum neutron energy was observed at the same pressure, 4.5 mbar. This could be due to the emission of a high fluence of deuterium ions with high energy at 4.5 mbar which may have resulted in a greater number of d(d, 3 He) n fusion reactions though the beam-target fusion mechanism [30,31,47,49]. Moreover, the experimentally observed neutron yield (maximum as well as average) were found to be larger than the estimated yield.…”

Section: Experimental Observationsmentioning

confidence: 88%

High yield (⩾10⁸/pulse) DD neutron generator based on a compact, transportable and low energy plasma focus device

Niranjan¹,

Srivastava²,

Joycee³

et al. 2021

Self Cite

A pulsed DD neutron generator based on the plasma focus (PF) device has been developed. The PF device was assembled using a single energy storage capacitor (10 µF) and a triggerable spark gap switch in a compact geometry. The anode of the PF device was made of SS304 material with its tip modified using a high purity tungsten insert. Excluding the power supply, the size of the overall system was 0.6 × 0.6 × 1.0 m and the weight was less than 100 kg. A maximum DD neutron yield of (3.1 ± 0.2) × 108 neutrons/pulse and average DD neutron yield of (2.24 ± 0.16) × 108 neutrons/pulse (pulse duration = 35 ± 4 ns) into 4π sr were observed at a capacitor bank energy of 3.1 kJ (25 kV) and at 4.5 mbar D2 gas filling pressure. The experimentally observed average neutron yield was found to be around 30% more than the estimated yield obtained using scaling laws for neutrons (Y n ≈ 1.7 × 10−10 I 0 3.3; I 0 is the peak discharge current in A). For a peak discharge current of 258 kA at 3.1 kJ, the neutron yield was estimated to be 1.23 × 108 neutrons/pulse. The higher neutron production was attributed to the efficient design of the PF device as well as to the low erosion of the anode tip because of the tungsten insert. Using the time-of-flight method, maximum neutron energy was calculated to be 3.91 ± 0.16 MeV in the radial direction at 4.5 mbar filling pressure. Numerical parametrization using the five-phase Lee model code was performed and found to be similar to PF devices developed across the world.

“…The neutron yield increases with increasing filling gas pressure to a maximum value and then decreases with continued increased gas pressure. This variation in neutron yield is attributed to the deuterium ion velocity distribution (transfer of the kinetic energy of compressing plasma into pinch), which is different at various filling pressures for the same operation energy [17]. This behavior of neutron yield is essentially due to proportionality Y b -t ∼ I 2 pinch .n i .V 0.5 max [5,33], and the neutron yield is strongly related to the square of the I pinch and related to n i .…”

Section: Resultsmentioning

confidence: 98%

“…Saw et al [16] used Lee code on three plasma focus machines, FMPF-3, NX2 and NX3, to compute Y n versus pressure, and compared with experimental results, which show good agreement. Niranjan et al [17] studied the effects of deuterium gas as the operating pressure on neutron yield and other characteristics using Lee code for the MEPF-12 device. Marciniak et al [18] determined the total neutron versus the deuterium gas pressure with a neutron model set in Lee code for the PF24 device, and compared it with measured data; a good agreement between measured and computed Y n for lower neutron emission was found.…”

Section: Introductionmentioning

confidence: 99%

Numerical experiments on the total D–D fusion neutron yield versus deuterium pressure for different energy plasma focus devices using the Lee model code

Wahbe¹,

Abou-Ali²,

Akel³

et al. 2023

Numerical experiments using the Lee model code were carried out to compute the total D-D fusion neutron yield versus initial deuterium pressure for nine different plasma focus devices [PF50, AACS, PF400J, PF2.2, UNU-ICTP, PFZ200, PF24, PF78, Poseidon]. The computed data were compared with the published experimental results. In addition, the maximum discharge current, the pinch current and the pinch ion number density as a function of initial deuterium pressure were discussed as well as their effect on the neutron yield. The optimum pressures that correspond to the maximum neutron yield Yn were obtained for all considered devices, with reference to the specific plasma focus properties. The scaling laws for the D-D fusion neutron production, in terms of storage energies E0 and pinch current Ipinch were derived. The scaling of Yn with Ipinch and E0 over the whole range of investigated energies up to 300 kJ has been obtained as follows: (Y_n~I_pinch^5 ,Y_n~E_0^1.95 ). These laws are important for planning and designing a plasma focus as a potentially powerful pulse neutron source.