Monte Carlo versus bulk conductivity modeling of RF breakdown of helium

Thoma, C.; Hughes, T.P.; Bruner, N.; Genoni, T. C.; Welch, D. R.; Clark, Robert E.

doi:10.1109/tps.2006.873255

Cited by 18 publications

(11 citation statements)

References 8 publications

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“…Computational modeling of the fundamental processes associated with the breakdown of high pressure gases is an important aspect in the design of a number of pulsed power switching components [1][2][3][4]. New models of high pressure gas breakdown are presently under development for use in particle-in-cell (PIC) codes.…”

Section: Introductionmentioning

confidence: 99%

Computational modeling of high pressure gas breakdown and streamer formation in external electric fields

Rose

Welch

Thoma

et al. 2007

2007 16th IEEE International Pulsed Power Conference

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The development of new computational models of gas breakdown for use in particle-in-cell (PIC) codes is described. These modeling efforts include fundamental processes associated with the breakdown of high pressure gases and represent key components in the comprehensive study of the physics of high-pressure gas switches. Two computational algorithms are discussed; a Monte Carlo type collision (MCC) model whereby PIC macro-particles undergo random elastic and inelastic interactions, and a semi-fluid scattering model.A newly implemented attachment algorithm, important for electronegative gases such as SF 6 , has been developed. Cross-section compilations for H 2 and SF 6 for use in the MCC algorithm are summarized along with the modeling assumptions used to make this model computationally tractable. The results of detailed swarm calculations using these cross-sections are presented along with comparisons to experimental data.An implicit semi-fluid collision PIC model is used to carry out the streamer simulations. These simulations track the formation and evolution of a streamer from a small seed electron population in different applied electric fields. The results of H 2 and SF 6 streamer simulations are discussed, including comparisons between the semi-fluid and MCC model for streamer formation and evolution in H 2 .

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Section: Introductionmentioning

confidence: 99%

Computational modeling of high pressure gas breakdown and streamer formation in external electric fields

Rose

Welch

Thoma

et al. 2007

2007 16th IEEE International Pulsed Power Conference

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“…A detailed description of such a comparison, for He instead of H2, is given in Ref. [13]. The figure shows that at a ratio of electric field to gas number density E/N =100 Td (a "Townsend" is defined as: 1 Td = 10 -17 V-cm 2 ), the PIC-MCC calculation evolves in time with an exponentially-increasing number of free electrons and an energy distribution that remains essentially constant after an initial transient.…”

Section: Figure 3: Results From Lsp and Eedf For H2 At 100 Td (A) Elmentioning

confidence: 99%

Hydrogen-filled RF Cavities for Muon Beam Cooling

Charles¹

2009

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TECHNICAL ABSTRACT (Limit to space provided)Statement of the problem or situation that is being addressed -typically, one to three sentences.Ionization cooling requires low-Z energy absorbers immersed in a strong magnetic field and high-gradient, large-aperture RF cavities to be able to cool a muon beam as quickly as the short muon lifetime requires. RF cavities that operate in vacuum are vulnerable to dark-currentgenerated breakdown, which is exacerbated by strong magnetic fields, and they require extra safety windows that degrade cooling, to separate RF regions from hydrogen energy absorbers.General statement of how this problem is being addressed. This is the overall objective of the combined Phase I and Phase II projects RF cavities pressurized with dense hydrogen gas will be developed that use the same gas volume to provide the energy absorber and the RF acceleration needed for ionization cooling. The breakdown suppression by the dense gas will allow the cavities to operate in strong magnetic fields. Measurements of the operation of such a cavity will be made as functions of external magnetic field and charged particle beam intensity and compared with models to understand the characteristics of this technology and to develop mitigating strategies if necessary.What was done in Phase I -typically, two to three sentences.Fermilab MuCool Test Area (MTA) delays precluded beam tests during Phase I, allowing more diagnostic and simulation development, including an important experimental breakdown study with SF6 dopant to verify the computer model. An optical fiber system was added to the test cell to be used in the first beam tests. A 1.3 GHz test cell was built and tested which can operate under pressure or in vacuum in order to extend our understanding of RF breakdown as a function of frequency and geometry and to correlate with previous vacuum cavity experience.What is planned for the Phase II project -typically, two to three sentences.The Fermilab MTA will be exploited to extend measurements of maximum stable RF gradient in strong magnetic fields and in the presence of ionizing radiation. Beam-induced gas breakdown will be studied by improving computer simulation models that include the use of electronabsorbing dopants, external magnetic fields, and variations of cavity geometry and materials. RF cavities will be built or improved to verify the models using MTA RF, beam, and magnetic field.COMMERCIAL APPLICATIONS AND OTHER BENEFITS as described by the applicant. (Limit to space provided).Bright muon beams are needed for many commercial and scientific reasons. Potential commercial applications include the use of muon beams to screen cargo containers for homeland security, low-dose radiography, and muon catalyzed fusion. Scientific uses include low energy muon beams, muon spin resonance, and muon beams for neutrino factories and muon colliders.KEY WORDS: hydrogen, RF cavity, muon, collider, ionization, beam cooling, high pressure, gas breakdown. SUMMARY FOR MEMBERS OF CONGRESS: (LAYMAN'S TERMS, TWO SENTENCES MAX...

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“…Reaction channels for SF 6 The MCC model used here is an extension of the model described in Ref. 33. This model, including electron elastic, inelastic, and ionization processes with neutrals, was benchmarked for noble gases, such as He and Ar, in which no significant electron sink is present.…”

Section: Simplified Sf 6 Chemistrymentioning

confidence: 99%

“…33. Energy transfer to electrons from the neutrals through scattering is included, but the reverse process is neglected.…”

Section: Elastic Collisionsmentioning

confidence: 99%

“…However, the MCC algorithm does not make any assumptions a priori about the distribution function and should generate the correct kinetic behavior for an adequately small time step and large enough particle number. 33 The results of the Boltzmann and PIC methods should be the same as long as enough angular terms are retained in the Boltzmann treatment to yield good convergence.…”

Section: B Sf 6 Cross Section Datamentioning

confidence: 99%

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Towards a fully kinetic 3D electromagnetic particle-in-cell model of streamer formation and dynamics in high-pressure electronegative gases

et al. 2011

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Streamer and leader formation in high pressure devices is dynamic process involving a broad range of physical phenomena. These include elastic and inelastic particle collisions in the gas, radiation generation, transport and absorption, and electrode interactions. Accurate modeling of these physical processes is essential for a number of applications, including high-current, laser-triggered gas switches. Towards this end, we present a new 3D implicit particle-in-cell simulation model of gas breakdown leading to streamer formation in electronegative gases. The model uses a Monte Carlo treatment for all particle interactions and includes discrete photon generation, transport, and absorption for ultra-violet and soft x-ray radiation. Central to the realization of this fully kinetic particle treatment is an algorithm that manages the total particle count by species while preserving the local momentum distribution functions and conserving charge [D. R. Welch, T. C. Genoni, R. E. Clark, and D. V. Rose, J. Comput. Phys. 227, 143 (2007)]. The simulation model is fully electromagnetic, making it capable of following, for example, the evolution of a gas switch from the point of laser-induced localized breakdown of the gas between electrodes through the successive stages of streamer propagation, initial electrode current connection, and high-current conduction channel evolution, where self-magnetic field effects are likely to be important. We describe the model details and underlying assumptions used and present sample results from 3D simulations of streamer formation and propagation in SF6.

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Monte Carlo versus bulk conductivity modeling of RF breakdown of helium

Cited by 18 publications

References 8 publications

Computational modeling of high pressure gas breakdown and streamer formation in external electric fields

Computational modeling of high pressure gas breakdown and streamer formation in external electric fields

Hydrogen-filled RF Cavities for Muon Beam Cooling

Towards a fully kinetic 3D electromagnetic particle-in-cell model of streamer formation and dynamics in high-pressure electronegative gases

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