The Initiation of Electrical Breakdown in Vacuum

Cranberg, Lawrence

doi:10.1063/1.1702243

Cited by 341 publications

(90 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…However, since N e increases dramatically as L → 0, one approaches the limit of HV breakdown which is proportional to d 1/2 ͑the length over which the voltage is applied͒ for d greater than 1 cm. 17,18 Second the Debye length d , is directly related to the degree of shielding of the plasma particles. Even if the extraction field can be maintained, its penetration into the plasma can be drastically reduced.…”

Section: A Plasma Generation and Expansionmentioning

confidence: 99%

The DCU laser ion source

Yeates¹,

Costello

Kennedy

2010

Review of Scientific Instruments

View full text Add to dashboard Cite

Laser ion sources are used to generate and deliver highly charged ions of various masses and energies. We present details on the design and basic parameters of the DCU laser ion source ͑LIS͒. The theoretical aspects of a high voltage ͑HV͒ linear LIS are presented and the main issues surrounding laser-plasma formation, ion extraction and modeling of beam transport in relation to the operation of a LIS are detailed. A range of laser power densities ͑I ϳ 10 8 -10 11 W cm −2 ͒ and fluences ͑F = 0.1-3.9 kJ cm −2 ͒ from a Q-switched ruby laser ͑full-width half-maximum pulse duration ϳ35 ns, = 694 nm͒ were used to generate a copper plasma. In "basic operating mode," laser generated plasma ions are electrostatically accelerated using a dc HV bias ͑5-18 kV͒. A traditional einzel electrostatic lens system is utilized to transport and collimate the extracted ion beam for detection via a Faraday cup. Peak currents of up to I ϳ 600 A for Cu + to Cu 3+ ions were recorded. The maximum collected charge reached 94 pC ͑Cu 2+ ͒. Hydrodynamic simulations and ion probe diagnostics were used to study the plasma plume within the extraction gap. The system measured performance and electrodynamic simulations indicated that the use of a short field-free ͑L =48 mm͒ region results in rapid expansion of the injected ion beam in the drift tube. This severely limits the efficiency of the electrostatic lens system and consequently the sources performance. Simulations of ion beam dynamics in a "continuous einzel array" were performed and experimentally verified to counter the strong space-charge force present in the ion beam which results from plasma extraction close to the target surface. Ion beam acceleration and injection thus occur at "high pressure." In "enhanced operating mode," peak currents of 3.26 mA ͑Cu 2+ ͒ were recorded. The collected currents of more highly charged ions ͑Cu 4+ -Cu 6+ ͒ increased considerably in this mode of operation.

show abstract

Section: A Plasma Generation and Expansionmentioning

confidence: 99%

The DCU laser ion source

Yeates¹,

Costello

Kennedy

2010

Review of Scientific Instruments

View full text Add to dashboard Cite

show abstract

“…In most of the earlier experiments conducted by different workers, 5,6,20 an ultra high vacuum was not available, and the electrodes were frequently of copper, a material which is not easily outgassed. Thus conditioning always occurred, and so it was considered to be a basic property of breakdown.…”

Section: Discussionmentioning

confidence: 99%

Electrical breakdown in vacuum

1953

Vacuum

View full text Add to dashboard Cite

The use of vacuum as an insulator has become increasingly important with the development of high voltage electron devices. Much research into the electrical properties of vacuum has been conducted over the past several years, but there remains a considerable diversity in the results and their interpretation. Many of these experiments were conducted however, under conditions of rather poor vacuum, and it was felt that the use of a better vacuum system might produce more consistent results.The present test have been performed using plane parallel electrodes spaced apart by 1 mm., under conditions of extreme cleanliness using ultra high vacuum techniques. The pre-breakdown current was measured as a function of applied voltage, and it was found that pure field emission could be obtained. A small mass spectrometer was designed and built, so that the effect on breakdown of gases absorbed on the electrode surfaces could be investigated. The well known 'conditioning' phenomenon has been shown to be almost entirely a result of this gas desorption, and can be almost completely eliminated by thorough electrode degassing. Electron micrographs have been taken of the surface of the electrodes after breakdown, and these show extreme local heating on the anode. The effect of heating the electrodes and then conducting breakdown tests has also been examined, as has the effect of admitting oxygen to the system at controlled pressures. It should be noted that vacuum alone can be considered to be a perfect dielectric, but its use as an insulator requires metal electrodes. (Cont.)It is really the properties of the combination of the electrodes and the vacuum which constitute the system under investigation in everything which follows. General SurveyInterest in vacuum breakdown was stimulated by Paschen's work in 1889, when he showed that, for a given gas pressuxe p and electrode separation d, the voltage V necessary for a glow discharge was a function of the product of p and d. However if the pressure was reduced such that the mean free path of the molecules in the residual gas became large compared with the dimensions of the system, a charged particle drawn from one electrode to the other would be unlikely to collide with a residual gas molecule and breakdown would not occur.However, it was found that,, even for such low pressures, a current could be drawn from cathode to anode provided that the voltage was sufficiently high. By increasing the applied voltage, a breakdown could be obtained, and this could not be explained in terms of Paschen's Law. Discussion and ProposalsIt can be seen from the foregoing that, in spite of the considerable quantity , of data available concerning vacuum breakdown, several different theories had to be developed to explain the phenomena.It is probable that there are two main reasons for this fact.The first is that, since breakdown is to a great extent a surface phenomenon, several different parameters are involved, and because of the magnitude of the task, no single experimenter has succeeded i...

show abstract

“…A third mechanism was shown by Cranberg [16] in 1952 to apply to gaps > 2 mm that are exposed to DC or long pulses. In this model loosely bound particles acquire surface charge and in-turn are accelerated across the gap.…”

Section: History Of Field Emission and High Voltage Breakdown Researchmentioning

confidence: 99%

Suppression of electron emission from metal electrodes : LDRD 28771 final report.

Stygar¹,

Savage²,

Ives³

et al. 2003

View full text Add to dashboard Cite

This research consisted of testing surface treatment processes for stainless steel and aluminum for the purpose of suppressing electron emission over large surface areas to improve the pulsed high voltage hold-off capabilities of these metals. Improvements to hold-off would be beneficial to the operation of the vacuum-insulator grading rings and final self-magnetically insulated transmission line on the ZR-upgrade machine and other pulsed power applications such as flash radiograph and pulsed-microwave machines. The treatments tested for stainless steel include the Z-protocol (chemical polish, HVFF, and gold coating), pulsed E-beam surface treatments by IHCE, Russia, and chromium oxide coatings. Treatments for aluminum were anodized and polymer coatings. Breakdown thresholds also were measured for a range of surface finishes and gap distances. The study found that: 1.) Electrical conditioning and solvent cleaning in a filtered air environment each improve HV hold-off 30%. 2.) Anodized coatings on aluminum give a factor of two improvement in high voltage hold-off. However, anodized aluminum loses this improvement when the damage is severe. Chromium oxide coatings on stainless steel give a 40% and 20% improvement in hold-off before and after damage from many arcs. 3.) Bare aluminum gives similar hold-off for surface roughness, R a , ranging from 0.08 to 3.2 µm. 4.) The various EBEST surfaces tested give high voltage hold-off a factor of two better than typical machined and similar to R a = 0.05 µm polished stainless steel surfaces. 5.) For gaps > 2 mm the hold-off voltage increases as the square root of the gap for bare metal surfaces. This is inconsistent with the accepted model for metals that involves E-field induced electron emission from dielectric inclusions. Micro-particles accelerated across the gap during the voltage pulse give the observed voltage dependence. However the similarity in observed breakdown times for large and small gaps places a requirement that the particles be of molecular size. This makes accelerated micro-particle induced breakdown seem improbable also. 4

show abstract

The Initiation of Electrical Breakdown in Vacuum

Cited by 341 publications

References 9 publications

The DCU laser ion source

The DCU laser ion source

Electrical breakdown in vacuum

Suppression of electron emission from metal electrodes : LDRD 28771 final report.

Contact Info

Product

Resources

About