Richard J. Adler

Collective acceleration of protons in relativistic electron beam propagation in evacuated drift tubes

The results are presented of a series of experiments investigating the mechanisms leading to the collective acceleration of protons occurring in electron beam propagation through evacuated drift tubes. Detailed measurements have been made of the electron and ion beam propagation and of the ion energy spectra. The results show that the acceleration cannot occur as a result of a beam head or deep potential well mechanism. It seems likely that the acceleration is due to the self‐excitation of a wave on the beam, possibly the electron‐ion two‐stream instability.

Experimental results of phase locking two virtual cathode oscillators

Experiments have been completed on electrostatic and electromagnetic phase locking of two independent virtual cathode oscillators (VCO). The experiments were accomplished by using the Gemini electron beam accelerator. The Gemini accelerator was used to generate each VCO with a chosen time separation. The phase locking was observed by beating microwave signals generated in each anode‐cathode gap and noting the time intervals during which the phase difference remained constant. The phase locking was observed during both electrostatic and electromagnetic coupling of the microwave power between the VCOs. We did find that one must prefill the coupling cavity with microwave power to enable one VCO to phase lock the other.

Radial isolated Blumlein electron beam generator

A new high‐voltage pulse‐forming line, the radial isolated Blumlein (RIB), is described. The new configuration produces an output voltage pulse into a matched load equal to the charge voltage on the line (as in a conventional Blumlein circuit); however, the prepulse level is negligible and both sides of the load remain at electrostatic ground potential. The RIB is rapidly charged to allow 24 oil dielectric spark channels to close within ∼2 ns. With this number of channels, 94% of the theoretical peak voltage is achieved even though the pulse duration is only 15 ns. Using a foilless diode load, the device has been used to generate 4‐MeV, 100‐kA electron beam pulses.

IBEX magnetic field extraction and propagation experiments of intense high-energy electron beams

We have investigated the extraction and propagation of intense relativistic electron beams from an immersed foilless diode into a magnetic field‐free region. It was established experimentally that under matching conditions, the extracted beam propagates into and through the axially varying magnetic field region with minor perturbation of the equilibrium. The independent variables of the experiment were beam current, beam radius, magnetic field strength, and gas pressure in the field‐free region. The accelerator used was IBEX. [J. J. Ramirez, J. P. Corley, and M. G. Mazarakis, in Proceedings of the Fifth International Conference on High‐Power Particle Beams, San Francisco (Physics International, San Leandro, CA, 1983), p. 256.] The propagation of the extracted beam was studied up to 60 cm downstream from the extraction foil. A strong, fast growing filamentation instability was observed after extraction. Time‐resolved measurements of the beam current, net current, and current distribution were performed by ...

IBEX Foilless Diode Experiments

A new high voltage isolated Blumlein accelerator (IBEX) has been designed and constructed. A new accelerator pulse-forming-line (PFL) configuration produces an output voltage pulse equal to the PFL charge voltage for a matched load (as in a conventional Blumlein circuit); however, the prepulse level is negligible and both sides of the diode remain at electrostatic ground potential. With a matched planar diode load, IBEX has generated a 4 MeV, 100 kA electron beam. In the present stage of experimentation, a foilless diode load is being used to produce 3-4 MeV, 20-30 kA annular electron beams with an applied magnetic field strength of ~10 kG.

Conservation of axial momentum in intense ion beam systems

In a number of systems, interaction between electrons and ions results in acceleration of ions. Because of the large ion/electron mass ratio, the efficiency of intense ion beam sources can often be low. A macroscopic momentum conservation law is presented which allows the efficiency of collective accelerators and ion diodes to be evaluated. The application of the equation is straightforward and does not depend on the specific dynamical processes involved. A number of new relations are derived from the basic equation including the efficiency of a collective accelerator, the average ion velocity for collective acceleration in vacuum, the ratio of electron and ion currents in a pinched beam diode, and a relation for current enhancements in magnetically insulated diodes. These relations also serve to elucidate the role of magnetic pressure in intense ion beam systems.

Collective acceleration of metallic ions

Preliminary results of collective acceleration of aluminum and iron ions from metal foils are presented. Aluminum ions of up to 15 MeV have been produced from a 0.6‐MeV electron beam. Results also suggest that all particle species accelerated reach the same velocity (∼0.035c), indicating that the acceleration may occur in a moving potential well.

Energy spectrum diagnostics for collectively accelerated proton beams

An account is presented of the proton energy spectrum diagnostic techniques employed in a Collective Ion Accelerator study. The emphasis is on a newly developed neutron time of flight diagnostic which yields the complete (E≳2 ⋅ 5 MeV) proton spectrum on every shot. A brief account is also presented of the stacked foil activation technique employed, and results from the two measurements are compared. Finally, we describe a stacked foil Faraday cup which provides temporal resolution of the proton acceleration.

Ion‐acceleration mechanisms in vacuum diodes

A study of proton acceleration in a Luce diode has been carried out. Measurements of beam‐neutralization times, electron and ion energy distributions, and induced radioactivity have been made. These measurements show that the effective potential‐well depth at the beam head is less than the electron‐accelerating voltage. Also, the relative activity of Mylar and copper foils indicates that ion energy increases with mass for Z=1 particles. Both of these observations are consistent with ion acceleration resulting from a moving potential well.

Proton Injection into a Large Amplitude Space Charge Wave

An account is presented of some aspects of recent progress in the Collective Ion Space Charge Accelerator (CISCA) program at Cornell University. The object of this program is to explore the potential of the slow space charge wave on an electron beam for use in an ion accelerator. We describe in this paper the results of a study of a Luce diode as an ion source and outline initial results obtained when the proton beam is injected into a space charge wave growth section. We find that it is possible to inject a beam of protons through a vacuum diode, used to generate the beam for wave growth, and for the conditions achieved to date to maintain the growth of a coherent wave.