24 research outputs found
Recommended from our members
PHERMEX as an injector to a modified betatron
The PHERMEX accelerator is a pulsed three-cavity, 50-MHz, standing-wave rf linear accelerator. It is used to produce a 30-MeV, 200-ns envelope of electrons for flash radiography and electron beam experiments. The 200-ns electron pulse contains 10 micropulses. The FWHM of a single micropulse is 3.3 ns. Peak micropulse current varies from 350 to 850 A with widths of 3 and 5 ns, respectively. We propose to inject this beam into a solenoidal field with a neutralizing background gas and stack the PHERMEX micropulses in a 28-cm-dia ring to obtain a 3-ns multi-kiloampere beam. Coupled to the background magnetic field will be a ramped field driven by a magnetic flux compression generator. Beam kinetic energy approaching 100 MeV is theoretically possible. Simulations of ring stability with and without the accelerating field are presented. 9 refs., 4 figs
Recommended from our members
Plastic deformation of colliding hemishells. [Steel-ASTM-A 537]
The collision of two hemishells is analyzed where one hemishell is clamped and the other impinges on the inner surface of the clamped hemishell. A model of rigid-perfectly plastic behavior is proposed for the flow of material in the region of contact. An expression relating velocity and deformation is obtained and compared with the results of experiments
Recommended from our members
Intense electron-beam propagation in low-density gases using PHERMEX
Preliminary propagation experiments have been performed using the LASL-PHERMEX 21-MeV electron beam with current densities of 40 kA/cm/sup 2/. Gas densities are varied from 10-m torr to 580 torr. Results indicate the presence of microinstabilities
Recommended from our members
Characterization of diamond film and bare metal photocathodes as a function of temperature and surface preparation
High current photocathodes using bare metal and polycrystalline diamond films illuminated by ultraviolet lasers are being developed at Los Alamos for use in a new generation of linear induction accelerators. These photocathodes must be able to produce multiple 60 ns pulses separated by several to tens of nanoseconds. The vacuum environment in which the photocathodes must operate is 10{sup -5} torr
Recommended from our members
Time-resolved current, current-density, and emittance measurements of the PHERMEX electron beam
The PHERMEX electron-beam pulse is a burst of ten 3.3-ns micropulses separated by 20 ns. Typical accelerator operating parameters produce a mean beam micropulse energy of 26 MeV with peak current of 300-500 A. The purpose of this work is to present experimental measurements of the current, current density, and emittance of a single PHERMEX micropulse. This experiment is part of an effort to completely characterize the PHERMEX electron beam. Understanding the electron-beam parameters is necessary for machine upgrade as related to flash radiography and for both present and future electron-beam experiments
Recommended from our members
Large area polycrystalline diamond films as high current photocathodes for linear induction accelerators
Investigations are underway at Los Alamos to develop a new generation of high current, low source temperature photo cathodes able to operate in vacuum environments with pressures above 10e-6 torr without poisoning or degradation of emission properties. Polycrystalline diamond films are emerging as the ideal material for these photocathodes. Robustness, high quantum efficiency and high thermal conductivity are fundamental necessary attributes that are found in diamond. The high electron/hole mobility in the boron doped diamond lattice and the ability to create a negative electron affinity surface through downward band bending allow for high current density emission with quantum efficiencies of 0.5% when illuminated by a ArF laser. We report the results to date toward the development of a four kiloampere photocathode with a source temperature below 5eV for the DARHT linear induction Accelerato
Recommended from our members
Suitability of high-current standing-wave linac technology for ultra-relativistic electron beam propagation experiments
Near-term development of the existing PHERMEX standing-wave linac would provide a 40 to 60 MeV electron beam with a current of 3 kA capable of answering a number of fundamental issues concerning endoatmospheric, ultra-relativistic electron beam propagation. Inherent high-repetition rate and multiple-pulse capability would allow alternative propagation scenarios to be investigated. Much of the theoretical expertise required to support the technology development and time-resolved beam propagation experiments presently resides within the Theoretical Applications Division
Recommended from our members
Pulsed 4-MeV electron injector with an excimer laser driven photocathode
The Relativistic Electron-Beam Experiment injector at the Los Alamos National Laboratory is used to generate a 4-MV pulse across an anode-cathode gap. A simple metal photocathode is illuminated by a pulsed excimer laser. Time-resolved measurements of current, voltage, and current density are made. The resulting quantum efficiencies are being used to obtain the required laser power for a multikiloampere, high-brightness electron gun to be used as an injector for a linear induction accelerator. 3 refs., 5 figs
Recommended from our members
Electron-beam generation, transport, and transverse oscillation experiments using the REX injector
The REX machine at LANL is being used as a prototype to generate a 4-MV, 4.5-kA, 55-ns flat-top electron beam as a source for injection into a linear induction accelerator of the 16-MeV Dual-Axis Radiographic Hydrotest facility. The pulsed-power sources drives a planar velvet cathode producing a beam that is accelerated through a foilless anode aperture and transported by an air core magnetic lens for injection into the first of 48 linear induction cells. Extensive measurements of the time-resolved (<1-ns) properties of the beam using a streak camera and high-speed electronic diagnostics have been made. These parameters include beam current, voltage, current density, emittance, and transverse beam motion. The effective cathode temperature is 117 eV, corresponding to a Lapostolle emittance of 0.96 mm-rad. Transverse oscillations of the transported beam have been observed via a differenced B-dot technique to be about {plus minus}100 {mu}m at 245 MHz. This beam motion has been correlated via detailed rf measurements of asymmetric transverse cavity modes in the A-K gap. 7 refs., 6 figs
Recommended from our members
Computational support for ITS and PHERMEX. Final report
This report describes calculations carried out over the past year in support of the ITS and PHERMEX radiographic machines. The forces produced by nonaxisymmetric structures in the ITS linac were calculated using 3-D simulations. The quadrupole magnetic field produced by the drive rods in the accelerating cell was obtained. This force can be corrected by a weak static magnetic quadrupole provided the current in the drive rods is constant. The octopole force produced by a 4-hole diagnostic section was also obtained. A new recessed cathode design was modeled using PBGUNS. For a 2 mm recess, the electrostatic focusing due to the recess is sufficient to stop current loss on the anode. The emitted and transported currents are in good agreement with the measured values. The LAMDA code was compared in detail to the LLNL code BREAKUP. The codes are in close agreement. To get the results to overlay identically, however, the beam voltages have to differ by about 100 kV (out of 3 MV). The source of this discrepancy has not yet been identified. A plotting utility for LAMDA was written in the IDL{reg_sign} language. This allows LAMDA output to be viewed on any platform supported by IDL. Experiments on the flat-cathode injector were modeled. Beam radius as a function of magnet strength was compared in detail with measurements, and good agreement was obtained. The effect of the trim coil on reducing beam emittance was investigated further. The trim coil allows one to correct emittance growth due to spherical aberration in the focusing magnet and nonlinear self forces. The measured calibrations for the bucking, focus and trim coils are now in good agreement with the calculated values. A code which optimizes the transport magnet settings was developed. The code iterates on the magnet settings to obtain a beam envelope with some user-specified properties. This procedure may be useful in tuning the ITS or DARHT linacs