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An optical technique for measuring divergence, beam profile, and aiming direction, of relativistic negative hydrogen ions

Description: A novel, nonobstructive diagnostic technique for high energy H/sup minus/D/sup minus/ ion beams is described. This scheme employs spectroscopic techniques designed to measure beam profile, perpendicular velocity spread (i.e., divergence), and orientation of multiMeV H/sup minus/ beams. The basic principle of this method is to photoneutralize a small portion of the H/sup minus/ beam in a way such that the photodetachment process results in the formation of excited hydrogen atoms in the n = 2 levels. Observation of fluorescence from spontaneous decay of H(sp) andor induced deacy of H(2s) can be readily used to determine beam profile. Doppler broadening measurements can be used to determine velocity spread from which beam emittance is calculated. With off-the-shelf instruments resolutions of 1 mm for beam profile and 2 x 10/sup minus/2) ..pi.. cm-mrad are possible. For photodetachment, the best commercially available laser is found to be ArF eximer laser. The analysis is performed for the 200 MEV BNL Linac. The laser, which has a pulse duration which has a pulse duration which is of 10/sup minus/5) of the linac can produce sufficient signal at a negligible beam loss. In addition, measurements of minute Doppler shifts of this Lyman-Alpha radiation by a spectrograph could in principle resolve beam direction to within 1.57 ..mu..rad. The process under consideration has a resonance known as the shape resonance. As the following literature review indicates, the total cross section is known and there is a reasonable agreement between theory and experiment. There are no experimental measurements of partical cross sections. nevertheless, there are theoretical estimates which agree within 15%. 10 refs., 1 fig.
Date: February 1, 1988
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Method of generating intense nuclear polarized beams by selective photodetachment of negative ions

Description: A novel method for production of nuclear polarized negative hydrogen ions by selective neutralization with a laser of negative hydrogen ions in a magnetic field is described. This selectivity is possible since a final state of the neutralized atom, and hence the neutralization energy, depends on its nuclear polarization. The main advantages of this scheme are the availability of multi-ampere negative ion sources and the possibility of neutralizing negative ions with very high efficiency. An assessment of the required laser power indicates that this method is in principle feasible with today's technology.
Date: January 1, 1986
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Determination of neutral beam direction from radiation emitted by photodetached H/sup -/

Description: Non-destructive diagnostic techniques to determine beam direction of 200 MeV H/sup 0/ atoms are analyzed. These methods are based on excited hydrogen atoms in n=2 and n=3 levels due to photodetachment of H/sup -/ ions. With some development of hot cathodes, an e-beam driven ArF laser can produce H*(2s) atoms for laser resonance fluorescence by photoneutralizing H/sup -/ ions in a quantity comparable to that of a gas cell. Observation of fluorescence from spontaneous decay of H*(2p) or induced decay of H*(2s) can be readily used to indicated beam orientation with a 40 ..mu..rad accuracy. Measurements of minute Doppler shifts of this Lyman Alpha radiation by a spectrograph could in principle resolve beam direction to within 2.8 ..mu..rad. For schemes requiring n=3 hydrogen atoms, a Xe laser can produce H*(3s) or H*(3p) atoms in quantities larger than previously published. 11 refs., 3 figs.
Date: January 1, 1986
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Mark V magnetron with hollow cathode discharge plasma injection

Description: An experiment designed to test the feasibility of negative ion sources based on plasma injection from a hollow-cathode discharge is described. From the plasma column up to 2.3 Amp/cm/sup 2/ of positive ion current were drawn onto a cesiated Mo converter. Strong evidence was found for an H/sup -/ production at a conversion efficiency of 25%. Based on these encouraging results a 2 Amp/H/sup -/ source has been designed.
Date: January 1, 1980
Creator: Hershcovitch, A & Prelec, K
Partner: UNT Libraries Government Documents Department

High current, low emittance, steady state electron guns with plasma cathodes

Description: Major limitations of plasma cathodes have been overcome in an electron gun based on extraction of superthermal electrons from a discharge characterized by a large component of high energy electrons with a low thermal spread. A grid is employed to select these electrons for extraction while retaining the bulk electrons in the discharge. Steady state extraction of electron beams corresponding to over 60% of the total arc discharge current has been observed. A perveance of over 280 microperv was reached with the extraction of 9A at 1 keV from a 6 nun aperture. Some of the characteristics of the electron beam described in this paper are very attractive for electron beam melting.
Date: December 31, 1995
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Electron beam melting at high pressures with a vacuum separator/plasma lens

Description: Plasmas can be used to provide a vacuum-atmosphere interface or separation between vacua regions as an alternative to differential pumping. Vacuum-atmosphere interface utilizing a cascade arc discharge was successfully demonstrated and a 175 keV electron beam was successfully propagated from vacuum through such a plasma interface and out into atmospheric pressure. This plasma device also functions as an effective plasma tens. Such a device can be adopted for use in electron beam melting.
Date: December 31, 1995
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Generation of intense polarized beams by selective neutralization of negative ions

Description: A novel scheme is proposed. This method is based on selective neutralization by laser negative hydrogen ions in a magnetic field. This selectivity is based on the fact that the final state of the neutralized atom depends on nuclear polarization in the magnetic field. A two-scenario approach is to be followed: one in which the resulting neutral atom is in the ground state, and in the other the neutral atom is in the n = 2 level. Limiting factors are discussed. The main advantages of this scheme are the availability of multi-ampere negative ion sources and the possibility to neutralize negative ions with very high efficiency. 15 references, 2 figures.
Date: January 1, 1983
Creator: Hershcovitch, A.I. & Hinds, E.A.
Partner: UNT Libraries Government Documents Department

Cooling high intensity atomic hydrogen beams to liquid helium temperatures

Description: An atomic hydrogen source, designed to operate in the laminar flow range, has been built at BNL. A unique feature of this source is a miniature gap between a teflon tube which guides the beam and an accommodator which cools it. Across this gap a step-function in temperature, with the teflon temperature exceeding 100K and the accommodator temperature as low as 3K, was successfully maintained. This configuration collimates the beam enough to prevent significant diffusive losses without subjecting it to the temperature range of high recombination. Record H beam flux of 3.32 x 10 Y H/sr-sec was obtained at an accommodation temperature of 5.5K. 7 refs., 6 figs., 1 tab.
Date: January 1, 1986
Creator: Hershcovitch, A.; Kponou, A. & Niinihoski, T.O.
Partner: UNT Libraries Government Documents Department

Ring-magnetron ionizer for polarized negative-ion sources

Description: It has been realized for some time that the use of the charge exchange reaction of negative deuterium ions with polarized neutral hydrogen yielding neutral deuterium and polarized negative hydrogen ions to produce polarized H/sup -/ ions could be very efficient. While intense H/sup -//D/sup -/ ion sources exist, one encounters space charge problems when trying to put this scheme into practice. In this paper, a simple method, which uses a self-extracted D/sup -/ beam from a ring magnetron source, is proposed. The basic idea is presented, approximate numbers are given and the expected intensity is estimated. The method not only offers improvement in intensity, but equally important, improvements in reliability and lifetime.
Date: January 1, 1983
Creator: Alessi, J.G.; Sluyters, T. & Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Selective generation and extraction of low emittance electrons from plasmas: A new concept for E-beam cathodes

Description: It is shown that hollow cathode discharges can operate in a mode characterized by a two-component electron energy distribution: bulk electrons with a thermal distribution with a temperature of a few electron volts, and a component of fast electrons with an energy of about 30 eV and a thermal spread of about 0.1 eV. Measurements of both parallel and perpendicular energy spreads confirm the existence of fast, low energy spread electrons. Selective extraction of these electrons can form the basis of a high current, high brightness electron gun which could be well suited for EBIS applications. 8 refs., 4 figs., 1 tab.
Date: September 19, 1991
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Extraction of a steady state electron beam from HCD plasmas for EBIS applications

Description: Experiments to extract high brightness electron beams from hollow cathode discharge plasmas are now in progress. A unique feature of these plasmas, which in principle can facilitate the extraction of large current low emittance electron beams, is the existence of a relatively high energy electron population with a very narrow energy spread. This electron population was identified in a self-extraction experiment, which yielded a 35 eV, 600 mA electron beam with parallel energy spread of less than 0.5 eV. Application of a very modest extraction voltage yielded a steady state extracted electron beam current of 6.5 A of which 5.7 had a preacceleration parallel energy spread of no more than 0.25 eV. The end result of this endeavor would be an electron beam current to 6 A even though, preliminary results strongly suggest that much larger electron beam currents can be produced. 6 refs., 4 figs.
Date: January 1, 1988
Creator: Hershcovitch, A.; Kovarik, V. & Prelec, K.
Partner: UNT Libraries Government Documents Department

Compact, energy EFFICIENT neutron source: enabling technology for various applications

Description: A novel neutron source comprising of a deuterium beam (energy of about 100 KeV) injected into a tube filled with tritium gas and/or tritium plasma that generates D-T fusion reactions, whose products are 14.06 MeV neutrons and 3.52 MeV alpha particles, is described. At the opposite end of the tube, the energy of deuterium ions that did not interact is recovered. Beryllium walls of proper thickness can be utilized to absorb 14 MeV neutrons and release 2-3 low energy neutrons. Each ion source and tube forms a module. Larger systems can be formed from multiple units. Unlike currently proposed methods, where accelerator-based neutron sources are very expensive, large, and require large amounts of power for operation, this neutron source is compact, inexpensive, easy to test and to scale up. Among possible applications for this neutron source concept are sub-critical nuclear breeder reactors and transmutation of radioactive waste.
Date: December 1, 2009
Creator: Hershcovitch, A. & Roser, T.
Partner: UNT Libraries Government Documents Department

Single pass electron beam cooling of gold ions between EBIS LINAC and booster is theoretically possible!

Description: Electron beam cooling is examined as an option to reduce momentum of gold ions exiting the EBIS LINAC before injection into the booster. Electron beam parameters are based on experimental data (obtained at BNL) of electron beams extracted from a plasma cathode. Many issues, regarding a low energy high current electron beam that is needed for electron beam cooling to reduce momentum of gold ions exiting the EBIS LINAC before injection into the booster, were examined. Computations and some experimental data indicate that none of these issues is a show stopper. Preliminary calculations indicate that single pass cooling is feasible; momentum spread can be reduced by more than an order of magnitude in about one meter. Hence, this option cooling deserves further more serious considerations.
Date: January 1, 2011
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

R&D ERL: Beam Dump

Description: As its name suggests, the beam dump is where electron bunches end up while depositing energy unrecovered by the ERL. The process of removing unrecovered energy must not have any adverse effects on the ERL system like outgassing or backstreaming electrons. Electron beam dumps are widely used in various applications ranging from radiation generating devices like klystrons and traveling wave tubes to EBIS sources and electron beam coolers, as well as to large machines that include LINACs and electron colliders. Energy of discarded electrons range from a few electron volts to 10's of GeV. This beam dump has a couple of unique issues that determine the design concept: cascade showers and seals that can withstand high radiation dosage.
Date: January 1, 2010
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Part II/Addendum Electron Beam Cooling between EBIS LINAC and Booster; Is Single Pass Cooling Possible?

Description: Due to some miscommunication, incomplete data was erroneously used in examining electron beam cooling for reducing momentum of gold ions exiting the EBIS LINAC before injection into the booster. Corrected calculations still indicate that single pass cooling is, in principle, feasible; momentum spread can be reduced by an order of magnitude in about one meter. Preliminary results suggest that this cooling deserves further consideration.
Date: July 1, 2008
Creator: Hershcovitch,A.
Partner: UNT Libraries Government Documents Department

Emittance Reduction between EBIS LINAC and Booster by Electron Beam Cooling; Is Single Pass Cooling Possible?

Description: Electron beam cooling is examined as an option to reduce momentum of gold ions exiting the EBIS LINAC before injection into the booster. Electron beam parameters are based on experimental data (obtained at BNL) of electron beams extracted from a plasma cathode. Preliminary calculations indicate that single pass cooling is feasible; momentum spread can be reduced by more than an order of magnitude in less than one meter.
Date: April 1, 2008
Creator: Hershcovitch,A.
Partner: UNT Libraries Government Documents Department

Issues concerning high current lower energy electron beams required for ion cooling between EBIS LINAC and booster

Description: Some issues, regarding a low energy high current electron beam that will be needed for electron beam cooling to reduce momentum of gold ions exiting the EBIS LINAC before injection into the booster, are examined. Options for propagating such an electron beam, as well as the effect of neutralizing background plasma on electron and ion beam parameters are calculated. Computations and some experimental data indicate that none of these issues is a show stopper.
Date: March 1, 2009
Creator: Hershcovitch,A.
Partner: UNT Libraries Government Documents Department

High current magnetized plasma discharges and electron beams for capture and cooling of charged leptons and hadrons

Description: Nowadays most magnetic lenses used to capture and to focus pions and muons utilize azimuthal magnetic fields generated by large axial currents, like horns or lithium rods (or even a Z-pinch at GSI). Capture and focusing angle is proportional to the product of the current and length of the lens. State-of-the-art for these lenses is no more than 750 kA and 70 cm. A meter long, multi-MA, magnetized axial discharges were generated by the early days of fusion. Lenses based of such devices can increase the capture angle of pions, e.g., by more than a factor of 2. Electron beam cooling is presently achieved in storage rings by having charged particles interact with a co-moving electron beam. In these devices, typical parameters are electron beam currents of about 1 A, an interaction length of about 1 meter, and interaction time of about 30 msec. Multi-MA electron beams can be used for single-pass final stage cooling in a number of machines. Calculations for some applications, as well as other advantages indicate that these schemes deserve further more serious consideration.
Date: July 1, 1997
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Review of electron beam macroinstabilities and other EBIS related stability and issues

Description: Plasma magnetohydrodynamics and macro-instability theories are briefly reviewed. Although the configuration of any EBIS is inherently susceptible to a number of classical beam instabilities, the small radial dimension of an EBIS plasma prevents modes from occurring in EBIS traps with low beam compression due to physical limitations. In EBIS devices with high electron beam compression, where the potential for beam instabilities is great, the radial dimension is smaller than the Debye length, which renders any plasma theory invalid. However, a RHIC EBIS is expected to have a diameter which is much larger than the Debye length. Hence, it may be the first EBIS, in which the various plasma theories could be valid. For this and future devices like it, a framework is established to analyze and offer remedies plasma instabilities in EBIS.
Date: November 1, 1997
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

INVESTIGATION OF A PLASMA MODE IN EBTS.

Description: A plasma related mode has been identified when EBTS operated with long trap length. The mode frequency scaling showed monotonic increased with confinement time. Initial scaling qualitatively suggested the mode to an electron beam driven ion cyclotron instability. However, a more quantitative evaluation is indicative of a drift mode. Nevertheless, the possibility of a structure mode, though unlikely, can not be completely excluded. The process of proper instability identification and stabilization is described.
Date: November 6, 2000
Creator: HERSHCOVITCH,A.
Partner: UNT Libraries Government Documents Department

PLASMA WINDOW FOR VACUUM - ATMOSPHERE INTERFACE AND FOCUSING LENS OF SOURCES FOR NON-VACUUM MATERIAL MODIFICATION.

Description: Material modifications by ion implantation, dry etching, and micro-fabrication are widely used technologies, all of which are performed in vacuum, since ion beams at energies used in these applications are completely attenuated by foils or by long differentially pumped sections, which ate currently used to interface between vacuum and atmosphere. A novel plasma window, which utilizes a short arc for vacuum-atmosphere interface has been developed. This window provides for sufficient vacuum atmosphere separation, as well as for ion beam propagation through it, thus facilitating non-vacuum ion material modification.
Date: September 7, 1997
Creator: HERSHCOVITCH,A.
Partner: UNT Libraries Government Documents Department

Comments on velocity space relaxation in high charge-state plasma neutralizers

Description: Scaling of velocity space relaxation rates, which affect the final temperature of a natural beam, with ion charge state in plasma neutralizers is examined. Overall, this scaling indicates a substantial enhancement in emittance growth of the neutral beam with increase in the charge state of ions in plasma neutralizers. 9 refs.
Date: January 1, 1989
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Development of multiampere negative ion sources

Description: The Neutral Beam Development Group at BNL is developing H-/D- surface plasma sources as part of a high energy neutral beam injector. Uncooled Penning and magnetron sources have operated at a maximum beam current of 1 A (10 ms pulses, Mk III) and a maximum pulse length of 200 ms (0.3 A, Mk IV). A magnetron source with focusing grooves on the cathode and an asymmetric anode-cathode geometry operates at a power efficiency of 8 kW/A and a 6% gas efficiency. As the next step, a water cooled magnetron, designed to give a steady state beam of 1 to 2 A, has been constructed. Experiments are in progress to test a modification of the magnetron which may significantly improve its performance. By injecting a sheet of plasma, produced by a highly gas efficient hollow cathode discharge, into a magnetron type anode-cathode geometry, we anticipate a reduction of the source operating pressure by at least three orders of magnitude. Initial experiments have given indications of H/sup -/ production. The next plasma injection experiment is designed to give a steady state beam of approx. = 1 A.
Date: January 1, 1981
Creator: Alessi, J.; Hershcovitch, A.; Prelec, K. & Sluyters, T.
Partner: UNT Libraries Government Documents Department