Light Ion Beam Fusion Technology at Sandia National Laboratories

		Ion Source Requirements for Light Ion Beam Fusion Energy Production

For further information, contact

Michael Cuneo, Principal Mem. Technical Staff, 1-505-845-8767, mecuneo@sandia.gov or
Craig Olson, Senior Scientist, 1-505-845-7303, clolson@sandia.gov.

Executive Summary
Beam Requirements
Ion Source Requirements

species, charge state, ion beam purity
divergence, uniformity
density, ionization, neutrals, thickness, velocity
area, geometry
integration, rep-rate operation, lifetime

Specific Pre-formed Non-protonic Plasma Ion Sources
Technical and Programmatic Contacts
References
Critical Elements for High-Brightness Ion Beam Production
Partially Annotated Bibliography

passive ion sources
active ion sources
cleaning techniques
LiF thin film and field-emission theory
"The Maron Files" on spectroscopy
fast neutrals and charge exchange
cleaning techniques background
high voltage gap breakdown
surface flashover
plasma formation in electron beam diodes

Executive Summary

Light ion beams may be the best option for an Inertial Fusion Energy (IFE) driver from the standpoint of efficiency, standoff, rep-rate operation and cost. This approach uses high-energy-density pulsed power to accelerate ions efficiently at fields of 0.5 to 1.0 GV/m, producing a medium energy (30 MeV), high-current (1 MA) beam of light ions that have an appropriate range to couple to an IFE target. Ion beams provide the ability for medium distance transport (4 m) of the ions to the target, and standoff of the driver from high-yield implosions. Rep-rate operation of high current ion sources has also been demonstrated for industrial applications and could be developed for IFE. Although these factors make light ions the best long-term pulsed power approach to IFE, light-ion research at Sandia was placed on hold in 1996 in order to develop a z-pinch-driven approach to ICF capsule research that has an excellent opportunity to achieve the U.S. Department of Energy goal of high-yield fusion on a single-shot basis.

Prior to postponement of the light ion fusion program, experiments on the SABRE accelerator at Sandia confirmed the critical role that the ion source has on the formation of high-brightness ion beams. This work demonstrated, for the first time, well-behaved, pre-formed, non-protonic ion sources with acceptable impedance histories, pulse lengths, and current densities that scale to IFE requirements. The SABRE work gives confidence for further engineering and physics development of a light-ion driver for IFE, since we have shown that ion diodes are able to meet impedance lifetime and current density requirements simultaneously. However, the uniformity (hence source divergence) and purity of these beams did not meet requirements. Much work remains to demonstrate the uniformity and purity of anode plasmas over the required areas.

The lack of an adequate pre-formed ion source greatly limited progress in the light ion program from 1986 - 1996. Pre-formed sources will allow a fundamentally new regime of diode performance to be accessed and will enable the beams generated in applied-B diodes to meet requirements for light ion fusion. Further experimental and theoretical progress needs to be made in the important areas of plasma source formation, uniformity and purity, beam and source non-uniformity and the effects on divergence, and the interaction of plasmas and neutral layers with intense applied electric and magnetic fields. Scalable ion source production/acceleration schemes for appropriate charge states of candidate ions that appear to match to pulsed power systems with 2 < A < 16, e. g., D, He, Li, B, C, N, O, should be developed. This work could leverage an entire technology that was shelved in 1997.

return to Table of Contents

Beam Requirements for Light Ion Fusion

High-current-density, high-energy ion beams are generated in an applied-magnetic-field (applied-B) ion diode coupled to a high-voltage pulsed power accelerator. Beam generation and acceleration are done in one or two short, closely-coupled regions at high accelerating gradients (0.5 - 1 GV/m), well above the threshold for emission of electrons from electrode surfaces. These devices therefore require the use of several-Tesla insulating magnetic fields to restrict electron motion across anode-cathode gaps of order 1 - 3 cm, while accelerating lithium ions to generate ~ 1 kA/cm², 5 - 15 MeV beams. Electrons drift in the E x B direction, forming a virtual-cathode electron sheath.

IFE driver scaling issues are strongly affected by the ion beam power brightness, B ~ JV/ Q², where J, V and Q are the ion current density, energy and divergence, respectively. An ion beam power brightness of about 0.3 to 0.5 GW/cm²/mrad², sustained for a pulse length t = 20 to 40 ns, scales conservatively to IFE requirements (600 TW delivered to a target in 10 ns). The field has been recently reviewed in [1].

Table I presents the separate beam requirements for light ion fusion [2] that combine to meet the power brightness requirements for a lithium ion beam. The primary beam is produced in an injector-acceleration stage. This stage must produce non-protonic ion beams with a current density of 1 kA/cm² at microdivergences of better than 20 mrad, sustained over pulse lengths of 20 to 40 ns. The brightness requirements are to be met through post-acceleration of the beam from the injector stage, with no growth in divergence or transverse beam energy [2]. Post-acceleration of a 7 - 10 MeV beam, at about 20 - 23 MeV, produces a 30 MeV lithium ion to match to ICF target range requirements. If this post-acceleration can be done with no divergence growth, the beam microdivergence is reduced by about a factor of 2. Requirements on microdivergence depend on the method used to transport the beam to the ICF capsule. About 12 mrad is required for self-pinched transport schemes; 6 mrad is required for schemes with an achromatic magnetic focusing lens [3]. Recent experiments have shown the promise of self-pinched schemes [4], offering a higher limit on required microdivergence and a lower limit on beam brightness.

Table I. Beam Requirements for Light Ion Fusion with Lithium

Current Density J (kA/cm²)	Accelerating Potential V (MV)	Ion Microdivergence Q (mrad)	Pulse length t (ns)
Injector Stage:
1	7 - 10	12 - 20	20 - 40
Post Acceleration Stage:
1	20 - 23	6 - 12	20 - 40

Although requirements on J, V, Q, and t have been met individually in separate experiments, they have not been met simultaneously in an integrated experiment. Progress of light ion beam fusion towards these goals has been limited, for the most part, by lack of an appropriate ion source plasma on the surface of the anode. The ion source plasma strongly governs the achievable beam current density and divergence, as well as the impedance history of the diode that impacts the sustainable pulse length. Sources formed through conditions in the high-voltage diode gap such as electron loss or high-electric fields (so-called "passive" sources) are incapable of meeting the requirements for light ion fusion energy production. Pre-formed, or engineered (so-called "active"), anode plasma sources are required to simultaneously meet the purity, current density, uniformity, microdivergence, impedance history and rep-rate requirements for light ion fusion.

A recent paper presented at the IAEA meeting in Yokohama, Japan discusses experiments on the SABRE accelerator that were the best attempt at integration of all critical elements for production of a high-brightness ion beam [5]. These experiments confirmed the dominant role that the ion source has on the formation of high-brightness ion beams. This work demonstrated, for the first time, well-behaved, pre-formed, non-protonic ion beams with acceptable impedance histories, pulse lengths, and current densities that scale to IFE requirements. Although complete integration was not achieved, the SABRE experiments have shown a factor of about 10 improvement towards meeting the requirements for light ion fusion in an extraction diode geometry, over the last 6 years. We believe that further development of an improved ion source will allow all requirements to be met simultaneously.

return to Table of Contents

Ion Source Requirements for Light Ion Fusion
The beam requirements discussed above place challenging conditions on those for pre-formed anode plasma ion sources. Current density and pulse length are the principal requirements that make ion sources for light ion fusion fundamentally different than those for other applications. Extraction of space-charge-limited current densities of 1 kA/cm² for 20 - 40 ns require plasma densities exceeding 10¹⁶/cm³. Plasma sources for other applications usually require steady operation at plasma densities in the range of 10¹⁰ - 10¹³/cm³.

Non-protonic beams are required:

to reduce the current density to that for which stable operation is possible
to maximize ion magnetic rigidity and minimize beam current for improved focusing
to minimize electromagnetic-wave-induced divergence [6] from instabilities in the anode-cathode gap

Table II lists specific ion source requirements, with discussion to follow.

Table II. Ion Source Requirements for Light Ion Beam Fusion Energy

Property	Requirement
Species, Charge-State	Ion range that couples well to ICF target and is compatible with pulsed power technology
Purity	Initial: > 50% ion of interest Final: > 90% ion of interest
Divergence	Initial/Final: < 1.3 keV effective source temperature (10 mrad @ 9 MeV).
Uniformity	Initial: < J_i within +20% @ 1 s Final: < J_i within +10% @ 1 s
Density, Ionization	> 10¹⁵ cm^-2ion of interest
Neutrals	< 10¹⁵ cm^-2in front of plasma layer
Thickness	Initial: < 1mm Final: << 1 mm related to plasma gradient, and velocity
Expansion Velocity	< 2 - 3 cm/microsecond
Area	Initial: 1-20 cm² (small-scale experiment) Intermediate: 70-200 cm² (diode-scale) Final: 500 - 1000 cm²
Geometry	Initial: Planar or annular Intermediate/Final: Annular plasma geometry, compatible with B-field coils.
Integration	Compatible with other aspects of ion diode operation and diagnosis
Rep-rate operation	Initial: Single-shot Final: 1 - 10 pulses/s possible ultimately
Lifetime	Initial: 1 pulse Intermediate: 10³ - 10⁵ pulses Final: 10⁶ - 10⁸ pulses

return to Table of Contents

Species, Charge State, Ion Beam Purity
The plasma must have the dominant ion as a single charge state of a single atomic species (>90%), to maximize the efficiency and minimize the size of the facility. The light ion program selected Li⁺ as the ion of interest for two reasons:

Li has a large second ionization energy of 70 volts (i.e., Li⁺ is a closed-shell configuration) so production of only a single charge state in the plasma is possible.
The Li ion range for coupling to an IFE target is readily achievable with pulsed power technology (at 30 MeV).

The production of an adequate Li⁺ ion source over areas of 100 - 1000 cm², under typical pulsed power conditions of a shot per day at 10^-5 Torr, has been more difficult than anyone ever imagined.

A single ion in the plasma also implies minimal contaminants, e.g., H, C, or O in the case of Li. Production of a pure Li⁺ plasma at the base pressures of 10^-7 to 10^-5 Torr compatible with pulsed power technology has been extraordinarily difficult because of lithium's large chemical reactivity. Contaminants are the first species desorbed from surfaces as they heat up because of lower binding energies [7,8]. Other atomic species should be investigated that may be less sensitive to contamination [19]. In particular, closed-shell configurations with boron (B⁺³) and carbon (C⁺⁴) may allow efficient drivers. However, the benefits of Li regarding production of a single charge state may continue to outweigh the difficulties as a result of its increased chemical reactivity. Systems that utilize rapid (< 1 s) in-situ lithium deposition could still meet lithium plasma purity requirements.

This ion must also be the dominant ion extracted from the plasma layer in the applied-B diode. The dynamics of the plasma layer may alter the dominant extracted ion when exposed to the applied voltage pulse in the applied and self-magnetic fields. For example, lithium ion sources are exceptionally sensitive to contamination. Typical contaminants (H, C, O) have higher first ionization potentials (> 11 eV) than Li (5 eV). In a plasma at low temperature (< 1 eV), the contaminants will remain largely neutral and expand across the diode applied-B field. Once ionized by the diode conditions, contaminants will dominate the beam.

Progress could be made with a source supplying greater than 50% of the extracted ion beam in a single ion charge state. Eventually, the source must be optimized to provide > 90% in a single ion charge state. Rep-rate operation of the source might be expected to improve the purity of the plasma through conditioning.

return to Table of Contents

Divergence, Uniformity
Divergence has the largest impact on ion beam brightness. Ion source divergence can be produced by several mechanisms:

The plasma temperature generates a transverse momentum larger than acceptable (1.3 keV at 9 MeV final accelerating voltage). Plasma temperatures below 1.3 keV are the easiest criterion to meet.
The uniformity of plasma current density should be <+20% at 1 s. This non-uniformity is a result of diode and B-field configuration, virtual-cathode dynamics, or as a result of regions of low plasma density. The current density non-uniformity generates a local electric field leading to high effective transverse momentum (> 1.3 keV at 9 MeV final accelerating voltage).
Spatial uniformity of plasma surface coverage or of the extraction surface generates local electric fields, leading to a high effective transverse momentum (> 1.3 keV at 9 MeV final accelerating voltage). The plasma must have a density uniform to within +10% over a spatial scale length of 0.2 mm to 1 cm over the entire anode area. The leading edge must also have a uniform spatial profile along the extraction dimension. This requirement has not been quantified.

These requirements minimize electrostatic deflections that produce divergence near the plasma extraction surface. The net divergence when leaving the vicinity of the plasma layer must be less than 10 mrad, since other mechanisms [6] in the anode-cathode (AK) gap will add a minimum of another 8-10 mrad in quadrature.

return to Table of Contents

Density, Ionization, Neutrals, Thickness, Velocity
As noted, the plasma density must be > 10¹⁶/cm³in order to supply space-charge-limited current densities of 1 kA/cm² for 20 - 40 ns. The plasma must be pre-formed on the anode surface, within 10 - 100 ns of the power pulse arrival at the AK gap. A shorter delay period is believed to improve the diode impedance history and beam uniformity by minimizing expansion into the AKgap and the nonuniformity of the plasma leading edge from which ions are extracted. The plasma should be formed in such a way as to maximize the density gradient. Again, rapid formation and a short-delay time are implied. This also implies a thickness < 1 mm (i.e., less than 5 - 10% of the AK gap), a short delay time, and a small expansion velocity away from the surface. It should also be noted that the plasma expands into a pre-existing, transverse applied-magnetic field that is in the range of 2 - 5 Tesla. Experiments should be prepared to assess the impact of the B-field on plasma ionization, stability, and expansion dynamics.

The layer should be fully ionized into the charge state of the ion of interest prior to arrival of the power pulse. Ionization of a neutral layer by the diode conditions could produce large plasma nonuniformities, large divergence, reduce control over the species extracted from the layer and allow rapid impedance collapse and charge-exchange neutral production. A large plasma gradient and minimal neutrals (< 10¹⁵/cm²--i.e., less than a monolayer) in front of the plasma layer will control these effects.

The plasma may need to be created in the vicinity of a conducting boundary to stabilize the system in the presence of an increasing self-magnetic field.

return to Table of Contents

Area, Geometry
Plasma production must eventually be possible over annular areas of 750 - 1000 cm² in order to carry the required current per module (~1 MA) below about 1.5 kA/cm², at 7 - 10 MV. Stable, well-behaved plasma layers, impedance histories, and divergences might be impossible to achieve for 20 - 40 ns at current densities higher than this. Current densities of at least 1 kA/cm² are believed required to scale to the final power density with a two-stage acceleration approach for Li⁺. Larger mass ions may allow an increase in ion energy and a decrease in ion current density for the same required power density. Initial small-scale experiments could demonstrate requirements over at least 1 - 20 cm², in a planar or annular geometry, at current densities that scale to those required. A diode-scale experiment would require at least 70 cm².

return to Table of Contents

Integration, Rep-rate operation, Lifetime
The source should be compatible with other aspects of ion diode operation. The possibility of rep-rate operation and long lifetimes are expected to be developed over several years; however, the initial concept should be compatible with these requirements. Diode operation and beam transport would first be assessed on a single-shot basis.

return to Table of Contents

Specific Pre-formed Non-protonic Plasma Ion Sources

An engineered, pre-formed ion source that meets the requirements for light ion fusion energy production will have a well-understood and controlled mechanism for

storing the atomic species of interest (e.g., Li, B, C, etc.)
releasing the atomic species from storage (desorption)
ionizing the atomic species to the correct ionization state (e.g., Li⁺, C⁺⁴, etc.)
controlling beam contamination (atomic species other than the one desired, e.g., H⁺)
rep-rating the source (eventually)

Methods of storing the atomic species have been:

thin-films (Li, H) [9 - 12, 5]
gaseous species (e.g., H₂, N₂, etc.) [13]
cryogenic gas layers (H₂, N₂, Ne) [14]
solid reservoirs for in-situ deposition systems followed by rapid pulsed deposition on anode surfaces (Li) [15, 5]

Methods for releasing the atomic species from storage have been:

fast laser vaporization (Li, C) [10, 16, 17, 5]
fast, pulsed gas valve for gaseous species (e.g., H₂, N₂, etc.) [13]
20 - 700 ns pulsed, ohmic vaporization from thin films (Li, H) [9 - 12]
conditions in the diode environment that are not desired or controllable

Methods for ionization of the atomic species have been:

fast laser ionization (Li, C) [17, 5]
resonant laser ionization (Li, others) [10, 16, 18 and references therein]
fast gas discharge ionization [11, 12]
inductive ionization (gaseous species, e.g., H₂, N₂, etc.) [13]
vacuum arcs [19] (both desorption and ionization)
flashboards (both desorption and ionization)
conditions in the diode environment that are not desired or controllable

Methods of controlling beam contamination have been:

RF discharge plasma cleaning [5, 7, 8 and references therein]
pulsed or DC heating [9, 5, 7, 8 and references therein]
rapid pulsed in-situ deposition systems at low base pressures [5, 15]
use of C as an ion source appears to be contamination resistant [5, 19]

The only system currently demonstrating rep-rate operation of an intense applied-B diode utilizes gaseous species [13], in a configuration that does not produce acceptable uniformity or divergence. Further work is necessary to apply this source to light ion fusion.

Further experimental and theoretical progress needs to be made in the important areas of plasma source formation, uniformity and purity, beam and source non-uniformity and the effects on divergence, and the interaction of plasmas and neutral layers with intense applied electric and magnetic fields. Scalable ion source production/acceleration schemes for appropriate charge states of candidate ions which appear to match to pulsed-power systems with 2 < A < 16, e.g. D, He, Li, B, C, N, O, should be developed. This work can leverage an entire technology which has been currently shelved. We would like to make systematic progress on the physics and technology of these kinds of ion sources on a smaller scale at universities and national laboratories to a point where full scale experiments on applied-B diodes make sense.

The development of an ion source plasma that meets these requirements is a great technical challenge. The lack of an adequate pre-formed ion source has greatly limited progress in the light ion program for the past 10 years. Pre-formed sources will allow a fundamentally new regime of diode performance to be accessed and will enable the beams generated in applied-B diodes to meet requirements for light ion fusion. With an adequate ion source, pulsed-power-driven light-ion-beam fusion offers a robust technology with efficiency, target standoff and rep-rate at what may be the lowest cost of electricity, and could prove to be the key technology for power generation in the next century.

return to Table of Contents

Technical and programmatic contacts

For technical discussion on applied-B diodes and the development of ion sources, diagnostics, and requirements, contact:

Michael Cuneo, Principal Member Technical Staff
1-505-845-8767, mecuneo@sandia.gov

For information on ion source theory and the development of codes that can model the conditions in anode plasma layers in ion diodes, contact:

Thomas A. Mehlhorn, Target and Z-Pinch Theory Department Manager
1-505-845-7266, tamehlh@sandia.gov

For programmatic issues and technical matters, please contact:

Craig Olson, Senior Scientist
1-505-845-7303, clolson@sandia.gov

return to Table of Contents

References

See also the partially annotated bibliography for a list of relevant papers listed by topic.

[1] T.A. Mehlhorn, "Intense Ion Beams for Inertial Confinement Fusion," IEEE Trans. Plasma Science 25, 1336 (1997).

[2] S. A. Slutz, Phys. of Plasmas 5, 3021 (1998).

[3] C. L. Olson, et al., "Self-pinched transport for ion beam driven inertial confinement fusion," 16th IAEA Fusion Energy Conference, 1996.

[4] P. Ottinger, et al., IEEE Conference on Plasma Science, 1999, abstract to be published, private communication.

[5] M. E. Cuneo, et al., "Generating High-Brightness Light Ion Beams for Inertial Fusion Energy," 17^th International Atomic Energy Authority Fusion Energy Conference, Yokohama, Japan, IAEA-CN-69/IFP/14, 1998.

[6] M. P. Desjarlais, et al., "Evolution and Control of Ion-Beam Divergence in Applied-B Diodes," Phys. Rev. Letters 67, 3094 (1991).

[7] M. E. Cuneo, et al., "Results of Vacuum Cleaning Techniques on the Performance of LiF Field-Threshold Ion Sources on Extraction Applied-B Ion Diodes at 1 - 10 TW," IEEE Trans. Plasma Sci. 25, 229 (1997).

[8] M. E. Cuneo, "The Role of Electrode Contamination and the Effects of Cleaning and Conditioning on the Performance of High-Energy, Pulsed-Power Devices," to be published in the IEEE Trans. Dielectrics and Insulation in Vacuum, 1999.

[9] P. L. Dreike and G. C. Tisone, "Production and diagnosis of a lithium plasma source for intense ion beam diodes," J. Appl. Phys. 59, 371 (1986), also P. L. Drieke, et al., "Development of the BOLVAPS lithium vapor source for the PBFA-II accelerator," Rev. Sci. Instrum. 61, 532 (1990).

[10]G. C. Tisone, et al., "Laser formation of lithium plasma ion sources for applied-B ion diodes on the PBFA II accelerator," Proc. 9th Intl. Conf. on High Power Particle Beams, NTISPB92-206068, Vol. II, p. 800 (1992).

[11]H. J. Bluhm, et al., "Production and Investigation of TW Proton Beams from an Annular Diode Using Strong Radial Magnetic Insulation Fields and a Preformed Anode Plasma Source," Proc. of the IEEE 80, 995 (1992); also H. J. Bluhm, et al., Formation of a Homogeneous Hydrogen Plasma Layer for the Production of Terawatt Ion Beams," IEEE Transactions on Plasma Science 21, 560 (1993), and H. Laqua, et al., "Properties of the non-equilibrium plasma from a pulsed sliding discharge in a hydrogen gas layer desorbed from a metal hydride film," J. Appl. Phys. 77, 5545 (1995).

[12] C. K. Struckmann and B. R. Kusse, "High-purity intense lithium-ion-beam sources using glow-discharge cleaning techniques," J. Appl. Phys. 74, 3658 (1993).

[13] J. B. Greenly, et al., "Magnetically insulated ion diode with a gas-breakdown plasma anode," J. Appl. Phys. 63, 1872 (1988); also W. A. Noonan, et al, "Design and operation of a high pulserate intense ion beam diode," Rev. Sci. Instrum. 66, 3448 (1995).

[14] D. L. Hanson, J. L. Porter, R. R. Williams, "High-purity ion beam production at high current densities with a liquid-helium-cooled series-field-coil extraction ion diode," J. Appl. Phys. 70, 2926 (1991).

[15] K. W. Bieg, et al., "Ion source studies for particle beam accelerators," J. Vac. Sci. Tech. A 3, 1234 (1985), also K. W. Bieg, et al., "Flashover lithium ion source development for large pulsed power accelerators," J. Vac. Sci. Tech. A 4, 772 (1986).

[16] T. J. Renk, et al., "Development of the LEVIS Li Ion Source for PBFAII," to be published, 1999.

[17] A. B. Filuk, et al., "Laser-driven ion sources for high-brightness, high-purity ion beams," 24th Int. Conf. on Plasma Science, 1997.

[18] B. A. Knyazev, "Photo-resonance plasma production by excimer lasers as a technique for anode plasma formation," Nucl. Instrum. and Methods in Phys. Res. A, 525 (1998).

[19] G. Y. Yushkov and A. Anders, "Effect of the Pulse Repetition Rate on the Composition and Ion Charge-State-Distribution of Pulses Vacuum Arcs," IEEE Trans. Plasma Science 26, 220 (1998).

return to Table of Contents

Critical Elements for High-Brightness Ion Beam Production

Experimental and theoretical work from 1990 - 1996 showed that high-brightness beams meeting the requirements for an IFE injector could be possible, but require the simultaneous integration of at least five key conditions. These key conditions are:

diode and magnetic field alignment
rigorous vacuum cleaning techniques for control of undesired anode, cathode, and ion source plasma formation from electrode contaminants to control impurity ions and impedance collapse
carefully tailored insulating magnetic field geometry for radially uniform beam generation
high magnetic fields and other techniques to control the electron sheath and the onset of a high divergence electromagnetic instability that couples strongly to the ion beam
a pre-formed ("active"), pure, uniform lithium plasma for improved beam uniformity and low source divergence that is compatible with the above electron-sheath control techniques.

These conditions have never been simultaneously present in any intense non-protonic ion beam experiment, but we have demonstrated the effectiveness of each condition in experimental tests. Recent SABRE experiments have been the best attempt at integration so far, and have shown significant improvements. A major advance in our understanding is that these conditions are synergistic and tightly-linked. A lack of any one of the elements, in particular a pre-formed ion source, prevents formation of a suitable ion beam.

The SABRE work gives confidence for further engineering and physics development for a light-ion driver for IFE, since we have shown that ion diodes are able to meet impedance lifetime and current density requirements simultaneously. However, the uniformity (hence source divergence) and purity of these beams did not meet requirements. Much work remains to demonstrate the uniformity and purity of anode plasmas over the required areas.

return to Table of Contents

Partially Annotated Bibliography

return to Table of Contents

Anode and Cathode Plasma Formation
in Ion Diodes with Passive Sources
Passive sources are sources that rely on high voltage, high field, and/or electron loss in the diode to turn on a plasma layer on the anode and have been used extensively in applied-B diode research. Passive sources are adequate for understanding many issues of diode operation and for developing diagnostics. These sources are incapable of meeting the uniformity, purity, divergence and pulse length requirements for light ion fusion, but provide insight into important physical mechanisms in high-voltage applied-B ion diodes.

R. B. Baksht, et al., "Cathode plasma in a magnetically insulated diode," Sov. Tech. Phys. Lett. 3, 243 (1977).

D. S. Prono, et al., "Charge-exchange neutral-atom filling of ion diodes, Its effect on diode performance and AK shorting," J. Appl. Phys. 52, 3004 (1981).

D. J. Johnson, et al., "Anode plasma behavior in magnetically insulated ion diode," J. Appl. Phys. 52, 168 (1981). Experimental study of anode flashover using holographic interferometry and UV spectroscopy. Conclude that divergence of beam governed by spatial nonuniformities.

D. J. Johnson, J. P. Quintenz, and M. A. Sweeney, "Electron and ion kinetics and anode plasma formation in two applied B_r ion diodes," J. Appl. Phys. 57, 794 (1985). Postulate anode plasma formation by breakdown of electron-induced desorption of neutral gas.

S. A. Slutz, "Anode Plasma Ionization due to Sheath Heating in Magnetically Insulated Ion Diodes," J. Appl.Phys. 61, 1288 (1987). Theory examination of anode plasma heating due to diamagnetic effect on sheath electrons. Looks at heating effect on Li ion charge state, noting that undesired Li⁺⁺ could be rapidly made if plasma density too high.

J. E. Maenchen et al., "Extreme-ultraviolet illumination effects on the PBFAI magnetically insulated ion diode," J. Appl. Phys. 65, 448 (1989). Exptl study of effect of pulsed XUV illumination on anode flashover and virtual cathode formation.

T. W. Hussey, S. A. Slutz, and M. P. Desjarlais, "MHD Calculations of Anode Plasmas," Digest of Technical Papers, Seventh IEEE Pulsed Power Conference, ed. by R. White and B. H. Bernstein (IEEE, New York, 1989), p. 959.

M. P. Desjarlais, "Theory of applied-B ion diodes," Physics Fluids B 1, 1709 (1989). The best analytic theory on the operation of applied-B ion diodes.

Y. Hashimoto, M. Yatsuzuka, and S. Nobuhara, "Effect of Adsorbed Matter on Intense Pulsed Ion Beam Generation," Jpn. J. Appl. Phys. 32, 4838 (1993).

Y. Hashimoto, M. Yatsuzuka, and S. Nobuhara, "Stability of an Intense Pulsed Ion Beam during Successive Operation," Jpn. J. Appl. Phys. 33, 5094 (1994).

M. E. Cuneo et al., "Results of Vacuum Cleaning Techniques on the Performance of LiF Field-Threshold Ion Sources on Extraction Applied-B Ion Diodes at 1 - 10 TW," IEEE Trans. Plasma Sci. 25, 229 (1997).

G. Y. Yushkov, and A. Anders, "Effect of the Pulse Repetition Rate on the Composition and Ion Charge-State-Distribution of Pulses Vacuum Arcs," IEEE Trans. Plasma Science 26, 220 (1998).

return to Table of Contents

Active (Pre-formed) Ion Sources

Pre-formed plasma sources are essential for obtaining the best integrated performance from an applied-B ion diode. The papers by Filuk, et al. and Cuneo, et al. describe the best attempt for non-protonic sources to date.

P. L. Dreike and G. C. Tisone, "Production and diagnosis of a lithium plasma source for intense ion beam diodes," J. Appl. Phys. 59, 371 (1986).

P. L. Dreike, et al., "Development of the BOLVAPS lithium vapor source for the PBFA-II accelerator," Rev. Sci. Instrum. 61, 532 (1990).

R. A. Gerber, et al., "Ion sources for light-ion fusion," Rev. Sci. Instrum. 61, 511 (1990).

J. B. Greenly, et al., "Magnetically insulated ion diode with a gas-breakdown plasma anode," J. Appl. Phys. 63, 1872 (1988).

G. C. Tisone, et al., "Laser formation of lithium plasma ion sources for applied-B ion diodes on the PBFA II accelerator," Proc. 9th Intl. Conf. on High Power Particle Beams, NTISPB92-206068, Vol. II, p. 800 (1992).

H. J. Bluhm, et al., "Production and Investigation of TW Proton Beams from an Annular Diode Using Strong Radial Magnetic Insulation Fields and a Preformed Anode Plasma Source," Proc. of the IEEE 80, 995 (1992). This paper and the following two represent the best attempt at producing a pre-formed protonic source.

H. J. Bluhm, et al., Formation of a Homogeneous Hydrogen Plasma Layer for the Production of Terawatt Ion Beams," IEEE Transactions on Plasma Science 21, 560 (1993).

H. Laqua, et al., "Properties of the non-equilibrium plasma from a pulsed sliding discharge in a hydrogen gas layer desorbed from a metal hydride film," J. Appl. Phys. 77, 5545 (1995).

C. K. Struckmann and B. R. Kusse, "High-purity intense lithium-ion-beam sources using glow-discharge cleaning techniques," J. Appl. Phys. 74, 3658 (1993).

W. A. Noonan, et al., "Design and operation of a high pulse rate intense ion beam diode," Rev. Sci. Instrum. 66, 3448 (1995).

A. B. Filuk, et al., "Laser-driven ion sources for high-brightness, high-purity ion beams," 24th Int. Conf. on Plasma Science, 1997.

M. E. Cuneo, et al., "Generating High-Brightness Light Ion Beams for Inertial Fusion Energy," 17^th International Atomic Energy Authority Fusion Energy Conference, Yokohama, Japan, IAEA-CN-69/IFP/14, 1998.

P. I. Melnikov, et al., "Concentrator of laser energy for thin vapor-cloud production near a surface," Nucl. Instrum. and Methods in Phys. Res. A, 709 (1998). T. J. Renk, et al., "Development of the LEVIS Li Ion Source for PBFAII," to be published, 1999. return to Table of Contents

Cleaning Techniques in Ion Diodes

Cleaning techniques are a critical element in conditioning high voltage gaps for reduction of passively formed anode and cathode plasmas and for reducing plasma contamination to improve ion beam purity. See particularly the last two papers for an extensive discussion of the issues.

K. W. Bieg, et al., "Ion source studies for particle beam accelerators," J. Vac. Sci. Tech. A 3, 1234 (1985).

M. D. Coleman and B. R. Kusse, "Observations of Neutral Impurity Emission During Operation of Intense Pulsed Ion and Electron Diodes," IEEE Trans. on Plasma Science 13, 149 (1985).

K. W. Bieg, et al., "Flashover lithium ion source development for large pulsed power accelerators," J. Vac. Sci. Tech. A 4, 772 (1986).

E. J. T. Burns, et al., "A lithium-fluoride flashover ion source cleaned with a glow discharge and irradiated with vacuum-ultraviolet radiation," J. Appl. Phys. 63, 11 (1988).

J. J. Moschella, et al., "An intense lithium ion beam source using vacuum baking an discharge cleaning techniques," J. Appl. Phys. 70, 3418 (1991).

C. K. Struckmann and B. R. Kusse, "High-purity intense lithium-ion-beam sources using glow-discharge cleaning techniques," J. Appl. Phys. 74, 3658 (1993).

G. C. Tisone, et al., "Laser formation of lithium plasma ion sources for applied-B ion diodes on the PBFA II accelerator," Proc. 9th Intl. Conf. on High Power Particle Beams, NTISPB92-206068, Vol. II, p. 800 (1992).

A. B. Filuk, et al., "Spectroscopic characterization of LEVIS active ion source on PBFA II," Proc. 9th Intl. Conf. on High Power Particle Beams, NTISPB92-206068, Vol. II, p. 794 (1992).

T. A. Mehlhorn, et al., "Progress in Lithium Beam Power, Divergence, and Intensity at Sandia National Laboratories," Proc. 10th Intl. Conf. on High Power Particle Beams, NTISPB95-144317, p. 53 (1994).

M. E. Cuneo, et al., "Cleaning Techniques for Applied-B Ion Diodes," Proceedings Tenth IEEE Pulsed Power Conference, edited by W. L. Baker and G. Cooperstein (IEEE, NJ, 1995), p. 640.

D. R. Welch, et al., "Simulations of H₂ layers in Applied-B Ion Diodes," Proceedings Tenth IEEE Pulsed Power Conference, edited by W. L. Baker and G. Cooperstein (IEEE, NJ, 1995), p. 969.

P. R. Menge, M. E. Cuneo, "Quantitative Cleaning Characterization of a Lithium-Fluoride Ion Diode," IEEE Trans. Plasma Sci. 25, 252 (1997).

M. E. Cuneo, "The Role of Electrode Contamination and the Effects of Cleaning and Conditioning on the Performance of High-Energy, Pulsed-Power Devices," to be published in the IEEE Trans. Dielectrics and Insulation in Vacuum, 1999.

return to Table of Contents

LiF Thin Film experiments and theory of field-emission in ion diodes

The LiF thin-film ion source has been the best passive, non-protonic ion source used in the light ion program. The LiF ion source is known not to meet the requirements for light ion fusion. The last three papers are the most detailed studies of this source that have been done and provide important background on high-power ion diode experiments.

K.W. Bieg et al., "Lithium fluoride ion source experiments on PBFA II," Rev. Sci. Instrum. 61, 556 (1990). Use "20-micron-grade" roughened stainless substrate coated with 1 - 3 micron LiF to observe ~50 mrad total divergence on PBFAII. Using a "2-micron-grade" substrate resulted in ~25 mrad. Characterizing substrate gave typical roughness points' radius, separation of ~ 25, 150 microns for the "20-micron" surface and ~12,70 microns for the "2-micron" surface. Simple source divergence roughness scaling agrees with observed divergences and indicated total divergence dominated by source.

P.F. McKay et al., "Ion production on the PI-110A accelerator," Rev. Sci. Instrum. 61, 559 (1990). Observed that Li ion current roughly proportional to enhancement of electric field a stainless surface (from changing roughness of substrate for various shots).

A.L. Pregenzer et al., "Ion production from LiF-coated field emitter tips," J. Appl. Phys. 67, 7556 (1990). Results similar to Schwoebel & Panitz - ion emission at ~10 V/nm seen. It was discovered after the publication that the LiF film was being removed prior to ion emission, probably at much lower fields than needed for ion emission.

P.R. Schwoebel & J.A. Panitz, "The behavior of LiF coated metal anodes in pulsed electric fields," J. Appl. Phys. 71, 2151 (1992). Use field-emitter tips w/ 20 ns pulsed voltage to study thin (<50 nm) and thick (>100 nm) LiF films. Observe that Li ion emission at 10-15 V/nm follows film removal. Notes that 1 V/nm is in range of LiF mechanical yield strength. Li ion emission seen after LiF film is completely pulled off!

T.A. Green, et al., "Production of lithium positive ions from LiF thin films on the anode in PBFA II," Sandia Report SAND95-1794, September 1995. Available from NTIS. Reviews observations of Li ion emission in previous expts and PBFAII. Considers properties of LiF and processes that can occur on fast timescale. Determines flashover of thin LiF coatings cannot occur. Calculates that LiF anode should be conductor due to electron bombardment in an ion diode. Based on analogy to observations of Li ion emission at few MV/cm in hot, ionically conducting LiF, postulates that electronically-conducting LiF in ion diode will also emit at low (<<100 MV/cm) field threshold.

J.A. Panitz, "Electrostatic removal of lithium fluoride from field-emitter tips at elevated temperatures", J. Vac. Sci. Technol. B 12, 2889 (1994). Visualizes LiF removal at 9 - 18 MV/cm in electron microscope with DC voltage applied. Higher temps require lower E field. Attributes film removal to field-induced fatigue failure. Comments that significantly higher fields needed to remove films in fast-pulsed fields, and that ion emission probably not associated with film removal.

Stintz & J.A. Panitz, "Field desorption of lithium fluoride," J. Vac. Sci. Technol. A 13, 169 (1995). Applies ~DC voltages to very thin (10 nm) films and sees clusters in mass spectrometer: (LiF) n attached to Li⁺. n=1 dominates at < 40 MV/cm, then simple Li⁺ ions dominate emission at > 40 MV/cm. Film is not catastrophically torn off unless thickness increased to ~ 50 nm. If cluster-ion emission happens in fast-pulsed ion diode why do we see only tiny fraction of beam is F ions in Thomson parabola?

J.E. Bailey et al., "Measurements of acceleration gap dynamics in a 20 TW applied-magnetic-field ion diode", Phys. Rev. Lett. 74, 1771 (1995). Exptl measurements of Efield vs space and time in PBFA II using Stark shifts. Notes high-anode-field LiF, azimuthally perturbed fields, and does comparison of fields with 3D PIC simulations.

A. B. Filuk, et al., "Charge-Exchange Atoms and Ion Source Divergence in a 20 TW Applied-B Ion Diode," Phys. Rev. Letters 77, 3557 (1996).

M. E. Cuneo, et al., "Results of Vacuum Cleaning Techniques on the Performance of LiF Field-Threshold Ion Sources on Extraction Applied-B Ion Diodes at 1 - 10 TW," IEEE Trans. Plasma Sci. 25, 229 (1997).

return to Table of Contents

"The Maron files" - Ion diode & flashover anode plasmas
via spectroscopy

These papers are the most detailed studies of conditions in an anode plasma layer in an ion diode. These anode plasmas are produced via surface flashover. Flashover sources are known not to meet the beam requirements for light ion fusion. Although the initial conditions in pre-formed plasma sources are expected to be different, modification of the plasma layer by the intense electric and magnetic fields in the ion diode may show some of the same phenomenon discussed in these papers.

Y. Maron, et al., "Measurements of the electric field distribution in high-power diodes," Phys. Rev. Lett. 57, 699 (1986). Measurements of AK gap electric field with space and time resolution, showing confined electron sheath. See rapid gap reduction at very early time in pulse.

Y. Maron, et al., "Measurements of ion transverse-velocity distribution in the gap of an ion-beam diode," J. Appl. Phys. 61, 4781 (1987). Exptl measurements of ion transverse velocities in AK gap, measuring divergence across the gap! Not time-resolved.

Y. Maron, et al., "Experimental determination of the electric field and charge distribution in magnetically insulated ion diodes," Phys. Rev. A 36, 2818 (1987). Exptl measurements of AK gap E field via Stark shift, showing gap reduction early in pulse and electron diffusion across gap later. Comparisons made with 1D Brillouin flow model.

Y. Maron & C. Litwin, "Local ion direction of motion and electron flow in a magnetically insulated diode," Phys. Fluids 30, 1526 (1987). Exptl study of ion deflections crossing AK gap as evidence for transverse electric field perturbations. Growth rates suggest deflections due to nonuniform anode plasma expansion. Transverse fields seen were up to 20% of main accelerating field.

C. Litwin & Y. Maron, "Thermal-resistive instability and magnetic insulation breakdown in ion diodes," J. Appl. Phys. 64, 1078 (1988). Postulates explanation of burst phenomenon in ion diodes as due to unstable cathode plasmas, causing loss of electron insulation.

Y. Maron, et al., "Time-dependent spectroscopic observation of the magnetic field in a high-power-diode plasma," Phys. Rev. A 39, 5856 (1989). Detailed exptl measurements of magnetic field in anode plasma using Zeeman effect, showing B penetrates plasma early in pulse. Indicates ~10X classical anomalous resistivity required.

Y. Maron, et al., "Particle-velocity distribution and expansion of a surface-flashover plasma in the presence of magnetic fields," Phys. Rev. A 39, 5842 (1989). Detailed exptl measurements of ion velocity distribution in anode plasma, showing higher-charge ions have higher energies. Noted that measured plasma pressure gradient can explain observed anode plasma expansion, and requires anomalous resistivity. Resistivity consistent with lower-hybrid drift instability. Notes probable difference in ion velocities parallel to anode inside and outside anode plasma.

Y. Maron, et al., "Electron temperature and heating processes in a dynamic plasma of a high-power diode," Phys. Rev. A 40, 3240 (1989). Detailed exptl measurements and modeling of line ratios with CR calculations to determine electron temp and small gradient. Measurements clearly inconsistent with classical conductivity. Concludes electron heating dominated by pressure-driven current in plasma.

Y. Maron, et al., "Spectroscopic determination of particle fluxes and charge- state distributions in a pulsed-diode plasma," Phys. Rev. A 41, 1074 (1990). Exhaustive exptl and CR modeling study of measured particle fluxes into anode plasma, showing continuous injection during pulse. Determined that mainly multiply-charged ions and protons reach front of anode plasma, and results agreed with extracted beam ions.

R.E. Duvall, C. Litwin, Y. Maron, "Space-charge-limited ion flow through an ionizing neutral layer," Phys. Fluids B 5, 3408 (1993). Studies shut-off of SCL ion current as a neutral layer in front of anode plasma ionizes. Complement to Litwin & Maron Physics of Fluids B 1,670 (1989).

R.E. Duvall, et al., "A model for energetic ion generation in an anode plasma," Phys. Fluids B 5, 3399 (1993). Studies various mechanisms to explain injection of energetic ions into anode plasma via strong electric fields between physical anode and anode plasma.

E. Sarid, Y. Maron, L. Troyansky, "Spectroscopic investigation of fluctuating anisotropic electric fields in a high-power-diode plasma," Phys. Rev. E 48, 1364 (1993). Exptl study of fluctuating E fields in anode plasma by polarization spectroscopy. Fluctuations affect line widths, forcing some corrections to earlier Maron papers (e.g., electron temp would be 10 eV, not 5 - 8 eV previously).

C. Litwin, Y. Maron, E. Sarid, "Plasma flows and fluctuations in intense ion beam diodes," Phys. Plasmas 1, 758 (1994). Examines E field fluctuation data of Sarid et al (above) and various mechanisms that could be responsible for fluctuations in anode plasma. Rather than due to lower-hybrid drift instability, they suggest ion flow destabilizes an electrostatic mode similar to 2-stream.

L. Perelmutter, et al., "Plasma properties near the anode surface of an ion diode determined by high resolution laser spectroscopy," Phys. Rev. E 50, 3984 (1994). Very nice exptl study of anode plasmas w/ high-spatial-resolution resonant absorption and induced-fluorescence techniques. See ions accelerated to ~ 15 eV within 30 microns of solid surface, indicating electric field accelerating layer between physical anode and anode plasma.

return to Table of Contents

Fast Neutrals, Charge Exchange

Charge-exchange fast neutral acceleration has been observed in many passive sources used for diode development. Production of fast-neutrals may also be an issue for pre-formed sources with inadequate ionization or a shallow gradient.

D.S. Prono, et al., "Charge-exchange neutral-atom filling of ion diodes: Its effect on diode performance and A-K shorting," J. Appl. Phys. 52, 3004 (1981). Propose charge exchange (CX) neutral filling of gap based on indirect evidence from 0.25 MV, 1000 ns, reflex ion diode. Use observations of plasma effects, framing camera gap light, Faraday cups with B field-filtering, secondary-emission detectors. Quantitative model and notes that only few monolayers needed to supply the 10¹⁶-10¹⁷/cm³ necessary.

H. Bluhm, et al., "Intense ion beam source development experiments," Beams81 Proceedings (Palaiseau, France), p. 87. Describes on p. 90 huge fast-neutral fluxes observed on 0.1 MV, 800 ns ion diode. Notes that neutral flux down by factor 200X on 0.8 MV, 90 ns ion diode.

R. Pal & D. Hammer, "Anode plasma density measurements in a magnetically insulated diode," Phys. Rev. Lett. 50, 732 (1983). Spectroscopic measurements of anode plasma and neutral expansion in a 0.5 MV, 30 ns ion diode. See H-beta in front of plasma, speculate that ~ 10¹⁶/cm³ neutral density present and ionizing to cause anode plasma expansion.

C. Litwin & Y. Maron, "Role of neutrals in plasma expansion in ion diodes," Phys. Plasmas B 1, 670 (1989). Detailed attempt to explain initial anomalously fast expansion of flashover anode plasma to observed 1-2mm thickness by ionization of CX neutrals.

M.P. Desjarlais, "The effect of charge exchange processes on ion diode impedance," J. Appl. Phys. 66, 2888 (1989). Models CX effects on diode impedance and virtual cathode motion. Concludes V-star can be raised/lowered relative to no-CX case depending on whether CX localized near anode or distributed across AK gap.

T.D. Pointon, "Charge exchange effects in ion diodes," J. Appl. Phys. 66, 2879 (1989). Uses 1-D code NEUTRAL to evolve neutral transport across AK gap, using an assumed H layer of 1-4mm thickness and 10¹⁶-10¹⁷ cm^-2 areal density. Sees rapid neutral filling of gap to ~10¹⁵/cm³.

M. Tuszewski, W.J. Waganaar, M.P. Desjarlais, "Electron Density Measurements in a Magnetically Insulated Ion Diode," J. Appl. Phys. 77, 6188 (1995). 2-color interferometer measurements on 0.5 MV, 600 ns, 2 cm-gap ion diode with flashover plasma source, showing lack of anode plasma build-up/closure until after end of ion beam. Sees a brief negative phase shift that could be explained by dense neutrals. Infrared interferometer can resolve electron line density >10¹⁴ cm^-2.

return to Table of Contents

Cleaning Techniques for Tokamaks and Storage Rings

These papers provide important background on cleaning techniques.

M. H. Achard, R. Calder, and A. Mathewson, "The effect of bakeout temperature on the electron and ion induced gas desorption coefficients of some technological materials," Vacuum 29, 53 (1978).

H. F. Dylla, "A Review of the Wall Problem and Conditioning Techniques for Tokamaks," J. of Nuc. Mater. 93 & 94, 61(1980).

M. Grunder, and J. Halbritter, "On Surface Coatings and Secondary Yield of Nb³Sn and Nb," J. Appl. Phys. 51, 5396 (1980).

H. F. Dylla, et al., "Initial conditioning of the TFTR vacuum vessel," J. Vac. Science Tech. A 2, 1188 (1984).

J. Burt, et al., "RF Glow Discharge Cleaning of the DITE Tokamak," Fusion Technology 6, 399 (1984).

H. C. Hseuh, T. S. Chou, and C. A. Christianson, "Glow discharge cleaning of stainless steel accelerator beam tubes," J. Vac. Sci. Tech. A 3, 518 (1985).

H. F. Dylla, "Glow discharge techniques for conditioning high-vacuum systems," J. Vac. Sci. Tech. A 6, 1276 (1988).

P. A. Redhead, et. al., The Physical Basis of Ultrahigh Vacuum (Chapman and Hall LTD, 1968).

return to Table of Contents

High Voltage Gap Breakdown

These papers describe the role of surface contaminants, conditioning and cleaning in high voltage gap breakdown and insulator flashover in vacuum. Conditioning techniques for high-voltage gaps are important for improving the operation of applied-B ion diodes.

P. N. Chistyalov, "A method of revealing residual dielectric films on metal surfaces," Sov. Phys. Tech. Phys. 8, 1037 (1964).

P. N. Chistyalov and N. V. Tatarinova, "Small postdischarge emission as an indicator of the surface state of electrodes in experiments on vacuum breakdown," Sov. Phys. Tech. Phys. 10, 1035 (1966).

P. N. Chistyalov, et al., "Vacuum breakdown with controlled electrode surfaces. I," Sov. Phys. Tech. Phys. 14, 807 (1969).

P. N. Chistyalov, et al., "Vacuum breakdown with controlled electrode surfaces. II," Sov. Phys. Tech. Phys. 17, 646 (1972).

A. A. Advienko and A. V. Kiselev, "Outgassing from Insulator Surfaces in a Strong Electric Field in Vacuum," Sov. Phys. Tech. Phys. 12, 381 (1967).

B. Mazurek, et al., "Point-to-plane Breakdown in Vacuum at Cryogenic Temperatures," Physica 104C, 82 (1981).

J. Halbritter, "On conditioning: Reduction of secondary- and rf-field emission by electron, photon, or helium impact," J. Appl. Phys. 53, 6475 (1982).

J. Halbritter, "On contamination on electrode surfaces and electric field limitations," IEEE Trans. on Electrical Insulation 20, 671 (1985).

G. A. Mesyats, D. I. Proskurovsky, Pulsed Electrical Discharge in Vacuum (Springer-Verlag, 1988).

G. A. Mesyats, "Pulsed Electrical Discharge in Vacuum at Cryogenic Electrode Temperatures," 13th Intl. Symp. on Discharges and Electrical Insulation in Vacuum," Paris, France, June 27-30, 1988.

R. V. Latham, ed., High Voltage Vacuum Insulation: Basic Concepts and Technological Practice, Academic Press, 1995.

return to Table of Contents

Surface Flashover

S. P. Bugaev, et al., "Investigation of the Pulsed Breakdown Mechanism at the Surface of a Dielectric in a Vacuum, I. Uniform Field," Sov. Phys. Tech. Phys. 12, 1358 (1968).

A. A. Advienko and M. D. Malev, "Flashover in vacuum," Vacuum 27, 643 (1977).

A. A. Advienko, "Surface breakdown of solid dielectrics in vacuum, I. Characteristics for breakdown of insulators along the vacuum surface," Sov. Phys. Tech. Phys. 22, 982 (1977).

A. A. Advienko and M. D. Malev, "Surface breakdown of solid dielectrics in vacuum, II. Mechanism for surface breakdown," Sov. Phys. Tech. Phys. 22, 986 (1977).

R. A. Anderson and J. P. Brainard, "Mechanism of pulsed surface flashover involving electron-stimulated desorption," J. Appl. Phys. 51, 1414 (1980).

E. W. Gray, "Vacuum Surface Flashover: A High Pressure Phenomenon," J. Appl. Phys. 58, 132 (1985).

return to Table of Contents

Anode and Cathode Plasma Formation in Electron Beam Diodes

These papers also provide important background for conditions in applied-B ion diodes, particularly those related to cathode plasma formation, and anode plasma formation from electron thermal desorption of surface contaminants.

R. K. Parker, R. E. Anderson, and C. V. Duncan, "Plasma-induced field emission and the characteristics of high-current relativistic electron flow," J. Appl. Phys. 45, 2463 (1974).

D. L. Hinshelwood, "Cathode plasma formation in pulsed high current vacuum diodes," IEEE Trans. Plasma Science 11, 188 (1983).

D. L. Hinshelwood, "Cathode plasma formation in pulsed high current vacuum diodes," Ph. D. Thesis, MIT, 1982.

D. W. Swain, S. A. Goldstein, et al., "Observation of anode ions associated with pinching in a relativistic electron beam diode," J. Appl. Phys. 46, 4604 (1975).

J. G. Kelley and L. P. Mix, "Measurements of high-current relativistic electron diode plasma properties with holographic interferometry," J. Appl. Phys. 46, 1084 (1975).

J. G. Kelley, et al., "Influence of anode composition on the electrical properties of relativistic electron-beam diodes," J. Appl. Phys. 46, 4726 (1975).

D. W. Swain, et al.,"Measurements of large ion currents in a pinched relativistic electron beam diode," J. Appl. Phys. 48, 118 (1977).

D. W. Swain, et al., "The characteristics of a medium current relativistic electron-beam diode," J. Appl. Phys. 48, 1085 (1977).

A. E. Blaugrund, G. Cooperstein, S. A. Goldstein, "Relativistic electron beam pinch formation processes in low impedance diodes," Physics Fluids 20, 1185 (1977).

D. J. Johnson, "Impedance characteristics of heated REB diodes," Appl. Phys. Lett. 32, 614 (1978).

R. E. Shefer, et al., "Evolution of high current, cold cathode diodes to steady state," Phys. Fluids 31, 930 (1988).

T. W. L. Sanford, et al., "Measurement of electron energy deposition necessary to form an anode plasma in Ta, Ti, and C, for coaxial bremstrahlung diode," J. Appl. Phys. 66, No. 1, 10 (1989), and references therein.

M. E. Cuneo, "Characterization of the Time-Evolution of a Microsecond Electron Beam Diode with Anode Effects," Ph. D. Thesis, Univ. of Michigan, 1989, Univ. Microfilms Intl., 89-20519.

M. E. Cuneo, et al., "Spectroscopic study of anode plasmas in a microsecond electron beam diode," IEEE Trans. Plasma Science 15, 375 (1987).

return to Table of Contents