Scattered hard X-ray and <i>γ</i>-ray generation from a chromatic electron beam

Coleman, J. E.; Welch, D. R.; Miller, Carol

doi:10.1063/1.4935480

Cited by 3 publications

(3 citation statements)

References 27 publications

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“…These are generated due to lower energy electrons (<3 MeV) during the rise and fall of the diode extraction voltage scraping the beam pipe. 32 Processing the difference between total photons in black and the high energy X-rays and c-rays in red, we can determine the temporal profile of visible light generated by the cathode shown in blue in Fig. 10(a).…”

Section: A Pmt Measurementsmentioning

confidence: 99%

“…The third image at 205 ns indicates the X-ray speckle evident on the CCD due to the off energy (E < 3 MV) electrons scraping the beam pipe. 32 The triggering of the camera gate is synchronized with the onset of the diode voltage and is monitored in parallel with the E-dot and BPM diagnostics to verify the gate time is accurate as shown in Fig. 5(b).…”

Section: A Cathode Facementioning

confidence: 99%

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Temporal response of a surface flashover on a velvet cathode in a relativistic diode

et al. 2015

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Surface flashover of a carbon fiber velvet cathode generates a discharge from which electrons are relativistically accelerated to c ranging from 4.9 to 8.8 through a 17.8 cm diode. This discharge is assumed to be a hydrocarbon mixture. The principal objective of these experiments is to quantify the dynamics over the $100 ns pulse of the plasma discharge generated on the surface of the velvet cathode and across the anode-cathode (A-K) gap. A qualitative comparison of calculated and measured results is presented, which includes time resolved measurements with a photomultiplier tube and charge-coupled device images. In addition, initial visible spectroscopy measurements will also be presented confirming the ion species are dominated by hydrogen. V C 2015 AIP Publishing LLC.

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Section: A Pmt Measurementsmentioning

confidence: 99%

Section: A Cathode Facementioning

confidence: 99%

Temporal response of a surface flashover on a velvet cathode in a relativistic diode

et al. 2015

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“…This result confirms the influence of energy on the beam envelope dynamics. Electrons produced during the rise and fall of the pulse are mostly lost in the pipe, inducing bremsstrahlung as shown by Coleman and co-workers [32]. In order to complement their study, simulations were carried out to extract all particles striking the tube, as can be seen from the time-integrated energy distribution of the "lost" electrons at 201 A shown in Fig.…”

Section: Characterizing the Beam Dynamics Within The Injectormentioning

confidence: 99%

High power electron diode for linear induction accelerator at a flash radiographic facility

Plewa

Bernigaud

Barnes

et al. 2018

Phys. Rev. Accel. Beams

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We investigated a new cathode design and beam transport with the EPURE axis-1 injector in order to increase the beam characteristics at 3.8 MeV, 80 ns FWHM from the 2.0 kA nominal current to 2.6 kA corresponding to an average current density of 82 A=cm 2 . Such current increase is highly desirable for improving the x-ray dose and hence radiographic performances. To achieve this, a time-dependent model based on the particle-in-cell method was developed in order to simulate the injector. Using results from calculations based on this model, a 17.2 cm AK gap diode with a larger radius cathode (3.175 cm) was designed, manufactured and tested. Experimental and calculated currents and emittances are qualitatively compared. The study provides a detailed understanding of the beam dynamics inside this type of high current, high energy injector.

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Modeling and experimental characterization of the plasma produced by a velvet cathode in a linear induction accelerator

et al. 2018

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A high power electron diode is used to generate an intense high quality pulsed electron beam (2.6 kA, 4 MeV) in order to produce a bremsstrahlung radiation pulse for the first axis of the flash radiography facility named Epure. The plasma created by surface flashover of the velvet cathode provides a zero work function emitter used to produce the space-charge-limited electron beam. In order to optimize the design of diodes and to better understand the plasma dynamics, we have developed a 0D Collisional-Radiative Model (CRM) which describes the time-dependent evolution of the density of the plasma species in three plasma compositions: 100% H, 95% H + 5% C, and 64% H + 31% O + 5% C. The non-equilibrium electron energy distribution functions (EEDFs) are pre-calculated for a large range of electron mean energies for each mixture. EEDFs and cross sections of electron impact processes are then used to tabulate the electron rate coefficients needed to simulate the time-dependent plasma species densities. The evolution of the electron mean energy is estimated through the electron beam current density itself inferred from particle-in-cell calculations experimentally validated. Visible emission spectroscopy measurements were performed in order to investigate the plasma composition, to measure the Hα/Hβ intensity ratio, and to estimate the electron density. It was shown that the electron density in our setup is between 1014 and 1016 cm−3. Experimental results were compared to the 0D CRM. Results from the time-dependent CRM show that for the three studied plasma compositions, maximum electron densities range from 0.9 × 1014 cm−3 to 1.7 × 1014 cm−3 and that the electron energy averaged over the time interval of the electronic beam pulse is about 3.5 eV. An estimate of the electron energy inside the plasma during the relaxation provides values ranging from 0.10 eV to 0.12 eV based on comparison between the calculated and measured Hα/Hβ intensity ratio averaged over 5 μs. Moreover, main reactions involved in the evolution of the electron density were pointed out.

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Scattered hard X-ray and γ-ray generation from a chromatic electron beam

Cited by 3 publications

References 27 publications

Temporal response of a surface flashover on a velvet cathode in a relativistic diode

Temporal response of a surface flashover on a velvet cathode in a relativistic diode

High power electron diode for linear induction accelerator at a flash radiographic facility

Modeling and experimental characterization of the plasma produced by a velvet cathode in a linear induction accelerator

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