Collective focusing of a charge-neutral ion beam with warm electrons

Robertson, Scott

doi:10.1063/1.336445

Cited by 12 publications

(7 citation statements)

References 4 publications

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“…It is readily seen that an increase in the electron temperature leads to a decrease in the focusing electric field, and the characteristic value of the electron temperature for which thermal effects become pronounced is in good agreement with the estimate in Eq. (20).…”

Section: -4mentioning

confidence: 95%

“…17 In conclusion, we comment on the "thermal" limits of the collective focusing arising from the quasi-adiabatic heating of the co-moving electrons. 18,20 As the effective electron temperature increases during compression, the electron thermal pressure becomes more pronounced, and balances part of the magnetic electron focusing force. As a result, the radial electric field required to provide radial electron force balance decreases, vanishing to zero at the electron stagnation point where 18 T es $ m e x 2 ce R 2 es =4:…”

Section: A Collective Focusing Lensmentioning

confidence: 99%

“…(20) corresponds to T ec ¼ 1255 eV. Results are obtained using the slab (x, z) version of the LSP code.…”

Section: Electrostatic Model Of the Enhanced Self-focusingmentioning

confidence: 99%

“…In the collective focusing scheme originally proposed and experimentally tested by Robertson,19,20 an ion beam pulse enters a magnetic lens carrying an equal amount of comoving neutralizing electrons. Note that in contrast to conventional neutralized magnetic focusing, no preformed plasma is required, and in fact should not be present inside the lens.…”

Section: B Collective Focusing Lens For the Beam Final Focusmentioning

confidence: 99%

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Enhanced collective focusing of intense neutralized ion beam pulses in the presence of weak solenoidal magnetic fields

et al. 2012

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The design of ion drivers for warm dense matter and high energy density physics applications and heavy ion fusion involves transverse focusing and longitudinal compression of intense ion beams to a small spot size on the target. To facilitate the process, the compression occurs in a long drift section filled with a dense background plasma, which neutralizes the intense beam self-fields. Typically, the ion bunch charge is better neutralized than its current, and as a result a net selfpinching (magnetic) force is produced. The self-pinching effect is of particular practical importance, and is used in various ion driver designs in order to control the transverse beam envelope. In the present work we demonstrate that this radial self-focusing force can be significantly enhanced if a weak (B $ 100 G) solenoidal magnetic field is applied inside the neutralized drift section, thus allowing for substantially improved transport. It is shown that in contrast to magnetic self-pinching, the enhanced collective self-focusing has a radial electric field component and occurs as a result of the overcompensation of the beam charge by plasma electrons, whereas the beam current becomes well-neutralized. As the beam leaves the neutralizing drift section, additional transverse focusing can be applied. For instance, in the neutralized drift compression experiments (NDCX) a strong (several Tesla) final focus solenoid is used for this purpose. In the present analysis we propose that the tight final focus in the NDCX experiments may possibly be achieved by using a much weaker (few hundred Gauss) magnetic lens, provided the ion beam carries an equal amount of co-moving neutralizing electrons from the preceding drift section into the lens. In this case the enhanced focusing is provided by the collective electron dynamics strongly affected by a weak applied magnetic field. V C 2012 American Institute of Physics. [http://dx.

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Section: -4mentioning

confidence: 95%

Section: A Collective Focusing Lensmentioning

confidence: 99%

“…(20) corresponds to T ec ¼ 1255 eV. Results are obtained using the slab (x, z) version of the LSP code.…”

Section: Electrostatic Model Of the Enhanced Self-focusingmentioning

confidence: 99%

Section: B Collective Focusing Lens For the Beam Final Focusmentioning

confidence: 99%

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Enhanced collective focusing of intense neutralized ion beam pulses in the presence of weak solenoidal magnetic fields

et al. 2012

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“…A rigid-rotor model has also been used to describe collective focusing of ion beams in thin magnetic lenses,[U]- [13] and in solenoidal fields. [14] This model can be understood in terms of Davidson's results by noting that the electron frequency in Eq.…”

Section: Rigid-rotor Equilibriamentioning

confidence: 99%

Rigid-rotor models of plasma flow

Boercker¹,

Sanders²,

Falabella³

1996

Handbook of Vacuum Arc Science and Technology

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Physics of neutralization of intense high-energy ion beam pulses by electrons

et al. 2010

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Neutralization and focusing of intense charged particle beam pulses by electrons forms the basis for a wide range of applications to high energy accelerators and colliders, heavy ion fusion, and astrophysics. For example, for ballistic propagation of intense ion beam pulses, background plasma can be used to effectively neutralize the beam charge and current, so that the self-electric and self-magnetic fields do not affect the ballistic propagation of the beam. From the practical perspective of designing advanced plasma sources for beam neutralization, a robust theory should be able to predict the self-electric and self-magnetic fields during beam propagation through the background plasma. The major scaling relations for the self-electric and self-magnetic fields of intense ion charge bunches propagating through background plasma have been determined taking into account the effects of transients during beam entry into the plasma, the excitation of collective plasma waves, the effects of gas ionization, finite electron temperature, and applied solenoidal and dipole magnetic fields. Accounting for plasma production by gas ionization yields a larger self-magnetic field of the ion beam compared to the case without ionization, and a wake of current density and self-magnetic field perturbations is generated behind the beam pulse. A solenoidal magnetic field can be applied for controlling the beam propagation. Making use of theoretical models and advanced numerical simulations, it is shown that even a small applied magnetic field of about 100G can strongly affect the beam neutralization. It has also been demonstrated that in the presence of an applied magnetic field the ion beam pulse can excite large-amplitude whistler waves, thereby producing a complex structure of self-electric and self-magnetic fields. The presence of an applied solenoidal magnetic field may also cause a strong enhancement of the radial self-electric field of the beam pulse propagating through the background plasma. If controlled, this physical effect can be used for optimized beam transport over long distances.

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Collective focusing of a charge-neutral ion beam with warm electrons

Cited by 12 publications

References 4 publications

Enhanced collective focusing of intense neutralized ion beam pulses in the presence of weak solenoidal magnetic fields

Enhanced collective focusing of intense neutralized ion beam pulses in the presence of weak solenoidal magnetic fields

Rigid-rotor models of plasma flow

Physics of neutralization of intense high-energy ion beam pulses by electrons

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