K. R. MacKenzie

Magnetic Multipole Containment of Large Uniform Collisionless Quiescent Plasmas

Over 1200 Alnico magnets (1.3 × 1.3 × 4 cm) are used to contain a conventional discharge plasma produced by 1–20 A of emission from 6–48 small filaments at − 60 V. Densities up to 1012 ions/cm3 are produced in argon at 2 × 10−3 Torr. At 5 × 10−6 Torr typical parameters are: 8 × 1010 ions/cm3; ni / n0 ≈ 0.7; Te ≈ 5 eV; Ti ≈ 0.5 eV; noise 〈 δn/n 〉 ≈ 2 × 10−4; and < 1% nonuniformity over a volume 31 cm diam by 69 cm. Uniform dense plasmas of He, D, and H are also produced. The ion containment appears to be both magnetic and electrostatic.

A Large Double Plasma Device for Plasma Beam and Wave Studies

The DP (or double plasma) device consists of two essentially collisionless plasmas that are separated from each other (for electrons only) by a negatively biased grid. Large cross section beams of ions are produced in one plasma by raising the potential of the other. Ion waves or shocks are produced in one plasma by oscillatory or large sudden (or ramp) potential changes in the other. Electrons emitted from two electrically separate spatial arrays of small filaments produce the two plasmas with densities in the range from below 108 to ∼1010 ion/cm3 with noise levels 〈δn/n〉≈5×10−4.

The Proton Deuteron rf System for the Berkeley Synchrocyclotron

An rf system is described which allows the acceleration of either 190‐Mev deuterons or 350‐Mev protons in the Berkeley 184‐inch cyclotron. The dee is connected to a large cross‐section line, which is in turn connected, through a rotating condenser, to a short section of grounded line of approximately the same cross section. At the upper frequency limit of 23.2 megacycles the dee and dee stem oscillate as a half wave line, while the grounded line, which is about one‐quarter wave long, oscillates in the opposite phase. At the low frequency limit of 9.5 megacycles, the whole system looks like a quarter wave line. The oscillator which feeds the system is described.

A large volume quiescent plasma in a uniform magnetic field

A reasonably uniform cylindrical plasma, 15–20 cm diam, and collisionless for many wave experiments, is generated in fields up to 500 G by applying 200 V of rf at 80 Mc to a fine wire grid stretched across a diameter. Axial containment is provided by opposing sets of μ‐metal strips that gather lines of force and create multimirror fields. Drift waves are inhibited by a short range peripheral alternating shear field, produced by an azimuthal ring of bar magnets. Densities are 108−109 ions/cm3 in argon with electron temperatures up to 12 eV, with a noise level, δn / n ≈ 3 × 10−3, over the ion acoustic frequency range.

Characteristics of Photoionization Plasma Source

A new plasma source is described. A collimated beam of photons of 6 μsec duration generates a plasma by single quantum photoionization of a rarefied gas. A uniform plasma column with sharply defined initial boundaries is produced remote from the container walls and in the absence of currents or fields. At 90 cm from the photon source, plasma densities of 1010 cm3 are produced in argon at a pressure of 5 μ.

Simple method of generating and coupling rf energy to a reactive collisionless plasma

A grounded grid oscillator is placed at the end of an electrical half‐wave line and the plasma generating electrode at the other. This simple one‐mode circuit enables the oscillator to efficiently deliver power in spite of frequency changes caused by the plasma reactance.

Calculator for Some rf Problems in Accelerator Design

A simple mechanical calculator has been developed for solving the transmission line equations when the characteristic impedance is a variable. The speed of computation is some two orders of magnitude faster than analytical methods. The theoretical basis is described and also the way in which it can be used. Some representative problems, which have benefited by use of the calculator, are discussed.

Synthesized Plasma Generator

A cesium plasma with a useful volume of 3 by 15 cm is produced inside a hot cylindrical tantalum cavity at temperatures around 1400 K. Ions are produced by contact ionization at the wall while electrons are obtained from an internal filament. The plasma potential determines the energy of the electrons, and this can be varied such that the electron‐ion temperature ratio ranges from 1 to 2.4. In the vicinity of 1011 ions/cc the background noise is about the same as found in Q machines.

Frequency Modulation of Large Cavities

A model study is described in which a rotating capacitor is coupled to a large re‐entrant cavity. The size and capacitive loading (∼500 pF) are such as to make modulation by ferrites or broadband amplifiers difficult and expensive. A nominal frequency range of 3 to 1 is achieved with a single‐plate six‐bladed rotor. On a possible fullscale cavity with a range of approximately 9 to 3 Mc, the data are scaled to a voltage of 5 kV peak for rf power requirements of 1 to 4.4 kW.