James M. Potter

Acquisition system for the hodoscope spectrometer GAMS-4000

Abstract A data acquisition system with high amplitude resolution (12 bits), high speed conversion (clock frequency 50 MHz), used in an experiment with a large number of counters (∼ 4200) is described. Physical quantities (masses and momentum transfer) are computed during data transmission itself, allowing improved trigger selectivity.

Wideband RF Structure for Millimeter Wave TWTs

LANL has developed a new vane loaded waveguide RF structure for a sheet electron beam traveling wave tube (TWT). The goal was to create a new class of wideband RF structures that allow simple mechanical fabrication and have geometry suitable for interaction with sheet electron beams. We have concentrated on structures at 94 GHz. We have achieved 6% bandwidth and believe that 10% is possible. We have performed 3D electromagnetic simulations using the codes Microwave Studio and HFSS, and fabricated several aluminium cold models of RF structures at 10GHz to confirm the design. Agreement between the 10 GHz cold test data and computer simulations was excellent. An RF structure at 94GHz was fabricated using electrical discharge machining (EDM) with a 0.004 inch wire and cold tested.

MM‐Wave Source Development at Los Alamos

Summary form only given. A sheet-beam traveling-wave amplifier has been proposed as a high-power generator for RF from 95 to 300 GHz, using a microfabricated RF slow-wave structure. The planar geometry of microfabrication technologies matches well with the nearly planar geometry of a sheet beam, and the greater allowable beam current leads to high-peak power (up to 500 kW at 95 GHz), high-average power (up to 5 kW), and wide bandwidths (up to 10%). Simulations have indicated gains in excess of 1 dB/mm, with extraction efficiencies greater than 20%.

A High-Q Ferrite-Tuned Cavity

Rapid cycling proton synchrotrons, such as the proposed LAMPF II accelerator, require approximately 10 MV per turn rf with 17% tuning range near 50 MHz. The traditional approach to ferrite-tuned cavities uses a ferrite which is longitudinally biased (rf magnetic field parallel to bias field). This method leads to unacceptably high losses in the ferrite. At Los Alamos, we are developing a cavity with transverse bias to the bias field) making use of the tensor permeability of the ferrite. Initial tests of a small (10-cm-diam) quarter-wave singly re-entrant cavity tuned by several different ferrites indicate that the losses in the ferrite can be made negligible compared with the losses due to the surface resistivity of the copper cavity. Details of the test results will be presented.

The Klynac: An integrated klystron and linear accelerator

The Klynac concept integrates an electron gun, a radio frequency (RF) power source, and a coupled-cavity linear accelerator into a single resonant system. The klystron is essentially a conventional klystron structure with an input cavity, some number of intermediate cavities and an output cavity. The accelerator structure is, likewise, a conventional on-axis coupled structure. The uniqueness is the means of coupling the klystron output cavity to the accelerator. The coupler is a resonant coupler rather than an ordinary transmission line. The geometry of such a system need not be coaxial. However, if the klystron and accelerator are coaxial we can eliminate the need for a separate cathode for the accelerator by injecting some of the klystron beam into the accelerator. Such a device can be made cylindrical which is ideal for some applications.

Vane Fabrication for the Proof-of-Principle Radio-Frequency Quadrupole Accelerator

The electrodes for the Proof-of-Principle (POP) Radio-Frequency Quadrupole (RFQ) accelerator were machined on a numerically controlled, three-axis, vertical mill. These pole tips, or vanes, were prepared for, and used, in the successful demonstration of RFQ practicality at Los Alamos National Laboratory in February, 1980. The data set that described the vanes contained about 10 million bits of tool position data. The vanes were cut from OFHC copper blanks. The tolerances achieved were approximately ± 0.005 cm. The design and manufacturing procedures are described.

Stability of a bi-resonant klynac

We have built the first-ever klynac, consisting of a klystron and linac combined into a single integrated structure using a single electron beam. This device has two resonant circuits, one for the klystron input and gain section, and one for the klystron output cavity and linac section. Here we describe this devices stability properties driven by its resonant properties.

MM-wave source development at Los Alamos

Summary form only given. A sheet-beam traveling-wave amplifier has been proposed as a high-power generator for RF from 95 to 300 GHz, using a microfabricated RF slow-wave structure. The planar geometry of microfabrication technologies matches well with the nearly planar geometry of a sheet beam, and the greater allowable beam current leads to high-peak power (up to 500 kW at 95 GHz), high-average power (up to 5 kW), and wide bandwidths (up to 10%). Simulations have indicated gains in excess of 1 dB/mm, with extraction efficiencies greater than 20%.

MICROWAVE AXIAL FREE-ELECTRON LASER WITH ENHANCED PHASE STABILITY

Abstract Free-electron laser (FEL) amplifiers in the Raman regime have high efficiencies and high output power at microwave wavelengths; however, the phase stability is not sufficient for driving linear accelerators. Fluctuations in the diode voltage are the largest cause of the shifts in the phase of the output power. Present-day pulse-power technology cannot keep the voltage fluctuations less than 1 4% . In this paper, we study the phase stability by analyzing the dispersion relation for an axial FEL, in which the rf field is transversely wiggled and the electron trajectories are purely longitudinal. It is found that the phase dependence on the beam velocity can be cancelled by the effect of the phase dependence on the beam plasma wave. This cancellation leads to first-order phase stability, which is not possible for standing-wave devices, such as klystrons. Detailed particle-in-cell simulations demonstrate the transverse wiggling of the rf mode and the axial FEL interaction and explicit calculations of the growing root of the dispersion relation are included to verify the phase stability.

X-ray radar imaging technique using a 2 MeV linear electron accelerator

X-ray radar imaging, patented in 2013 by James R. Wood, combines standard radar techniques with the penetration power of x-rays to image scenes. Our project strives to demonstrate the technique using a 2 MeV linear electron accelerator (linac) to generate the S-band-modulated x-ray signals. X-ray detectors such as photodiodes and scintillators are used to detect the signals in backscatter and transmission detection schemes. The S-band microstructure is imposed on the variable-width electron pulse, and this modulation carries over to the bremsstrahlung x-rays after the electron beam is incident upon a copper-tungsten alloy target. Using phase/distance calculations and a low-jitter timing system, we expect to detect different object distances by comparing the measured phase differences. The experimental setup, which meets strict jitter requirements, and preliminary experimental results are presented.