# Simultaneous Ultra-Fast Imaging and Neutron Emission from a Compact Dense Plasma Focus Fusion Device

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## Abstract

**:**

**2003**, 27, 77–81), there are notable deviations at low energies due to contributions from both thermonuclear and beam-target interactions (Schmidt, A. et al., Phys. Rev. Lett.

**2012**, 109, 1–4). For low energy DPFs (100 s of Joules), other empirical scaling laws have been found (Bures, B.L. et al., Phys. Plasmas

**2012**, 112702, 1–9). Although theoretical mechanisms to explain this change have been proposed, the cause of this reduced efficiency is not well understood. A new apparatus with advanced diagnostic capabilities allows us to probe this regime, including variants in which a piston gas is employed. Several complementary diagnostics of the pinch dynamics and resulting X-ray neutron production are employed to understand the underlying mechanisms involved. This apparatus is unique in its employment of a 50 fs laser-based shadowgraphy system that possesses unprecedented spatio-temporal resolution.

## 1. Introduction

^{11}n/s [5]. This may be compared to a typical DPF generating 10

^{6}neutrons over a 10 ns pulse: 10

^{14}n/s.

## 2. Materials and Methods

#### 2.1. Diagnostics

#### 2.1.1. Electrical Diagnostics

#### 2.1.2. Radiation Diagnostics

#### 2.1.3. Imaging Diagnostics

## 3. Results

#### 3.1. Example Shot

#### 3.2. Snowplow Model Validation

_{max}, the peak current, and P, the ambient gas pressure, as:

#### 3.3. Shadowgraph Imaging

#### 3.4. Neutron Yield

_{i}which accounts for the intrinsic efficiency of the scintillator, PMT, distance from the DPF, and shielding. For a given yield, the probability of a particular detector, i, registering a hit is p

_{i}= 1 − (1 − pDet

_{i})

^{yield}and the probability of not registering a hit is q

_{i}= 1 − p

_{i}. The four detectors signals are treated as independent events so, given the relevant pDet

_{i}values and the yield, one can calculate the probability of obtaining 0, 1, …, 4 hits among the four detectors for each shot of the DPF. This is summarized in Figure 7. Using these relationships and measured data, we can calculate coefficients of a Poisson distribution for the neutron yield. We note that there is a precedent for using a Poisson distribution to describe neutron yield [35,36]. The best fit distribution is shown in Figure 8. To corroborate these results, the values of pDet

_{i}can be varied either by shielding or changing the distance to the detector (reducing the solid angle coverage). We opted to use paraffin slabs of thicknesses from 5 to 15 cm (backed by 1 cm of lead to stop secondaries) to attenuate the neutron signal in a controllable way. GEANT [37] simulations confirmed that a controllable fraction of the (effectively monochromatic) neutrons initially produced would be unmoderated by the paraffin. By using a time window exclusion and our tightly time resolved neutron detectors, we can still selectively measure full energy neutrons but with less chance of pileup.

_{0}is the peak current in kA. Based on this scaling law and our system parameters we expect to produce about 30,000 neutrons per shot. The overall predictions of the Soto model have been validated, or even exceeded in this device.

#### 3.4.1. Double Strike

#### 3.4.2. Noble Gas Doping

## 4. Discussion

## 5. Patents

## Acknowledgments

## Conflicts of Interest

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**Figure 2.**Rendered image of DPF electrodes with insulator around anode base, and a multi-post cathode configuration.

**Figure 4.**(

**Top**) Current dip in dI/dt signal from the B-dot probe (blue trace), along with the PMT time-of-flight measurements (red and green traces); synchronized with (

**bottom**) a series of framing camera images separated by 30 ns.

**Figure 6.**The

**top**row shows shadowgraph images showing the progression of the plasma sheath run-in. The

**bottom**row is a schematic representation of the run-in to clarify the shadowgraphy.

**Figure 7.**The probability of getting exactly k detected neutrons from a single shot, given the detection system parameters used and the shot yield.

**Figure 9.**CAD model of a proposed stroboscopic imaging system showing four independent delay lines and cameras.

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**MDPI and ACS Style**

Majernik, N.; Pree, S.; Sakai, Y.; Naranjo, B.; Putterman, S.; Rosenzweig, J.
Simultaneous Ultra-Fast Imaging and Neutron Emission from a Compact Dense Plasma Focus Fusion Device. *Instruments* **2018**, *2*, 6.
https://doi.org/10.3390/instruments2020006

**AMA Style**

Majernik N, Pree S, Sakai Y, Naranjo B, Putterman S, Rosenzweig J.
Simultaneous Ultra-Fast Imaging and Neutron Emission from a Compact Dense Plasma Focus Fusion Device. *Instruments*. 2018; 2(2):6.
https://doi.org/10.3390/instruments2020006

**Chicago/Turabian Style**

Majernik, Nathan, Seth Pree, Yusuke Sakai, Brian Naranjo, Seth Putterman, and James Rosenzweig.
2018. "Simultaneous Ultra-Fast Imaging and Neutron Emission from a Compact Dense Plasma Focus Fusion Device" *Instruments* 2, no. 2: 6.
https://doi.org/10.3390/instruments2020006