R. L. Garwin

Efficient Precision Current Regulator for Low‐Voltage Magnets

A simple, inexpensive current regulator has been built using power transistors and a chopper amplifier to regulate magnet currents to <0.001%. Thus far, the regulator has been used to 20 amp and 40 v, and at ∼100 amp and ∼200 v. With minor modifications, it will give very much better regulation.

Simple Continuous He3 Refrigeration System

A simple continuous He3 refrigerator which uses a minimal amount of gas (80 cc STP) has been built. Temperatures below 0.5°K may be attained for as long as He4 remains in the cryostat. Commercial components are used throughout.

Efficient Precision Current Regulator for High‐Power Magnets

Using paralleled power transistors driven by a transistor and a chopper amplifier, supplemented by a coarse feedback loop to the generator field, we have regulated to <0.001% the field of an electromagnet requiring 80 amp at 200 v. The dissipation in the regulator is 250 w. The magnet current may be varied from zero to maximum by setting the reference potentiometer to the appropriate voltage, and sufficient protective measures are incorporated so that the circuit is not injured by misuse. The circuit is usable to perhaps a megawatt.

Production of Beams of Polarized Protons by the Acceleration of Protons Derived from Polarized Hydrogen Molecules

A conventional Stern‐Gerlach separation of hydrogen molecules is proposed for the supplying of a radio‐frequency or PIG ion source of standard type to produce microampere beams of polarized protons for acceleration in electrostatic accelerators, cyclotrons, etc. The long nuclear relaxation time of molecular hydrogen gas allows the accumulation of polarized protons (as molecules) for the production of microampere average beams by means of a pulsed ion source. The polarized protons after acceleration have the energy‐ and angular‐spread characteristic of the machine with which they were accelerated. There is no apparent reason why polarized H− may not be produced in the same strong‐field rf ion source, accelerated in a weak field to preserve polarization and stripped in a tandem machine, all without significant depolarization.

What is to be Done

It is now time to turn from theory to a brief consideration of practice—to ask the question, if something like the analysis given in the preceding chapters is correct, then what, if anything, does it demand that we do? At the end of chapter one, it was pointed out that, considered analytically, Holt’s works consist of three main components. First, they contain a positive or constructive account of what he considers the ‘best learning’, the sorts of conditions that promote such learning, and the sorts of conditions that are hostile to it. Secondly, they contain a critique of education, which is justified by appeal to the foregoing account of ‘best learning’. And thirdly, they contain a range of practical strategies, aimed at mitigating the problems of education (especially compulsory schooling) and maximising the opportunity of acquiring the ‘best learning’. This third component was of great significance to Holt. Although there is a sense in which Holt’s work is ‘utopian’, in that it criticises some foundational cultural assumptions and envisages a possible society that exists nowhere, he is, at the same time, a deeply practical, realistic thinker. He does not offer airy plans for grand social reconstruction, addressed to nobody in particular; rather, he tries to answer the question of what can be done by us, here and now. In the words of one of his book titles, he wants to answer the question: What do I do Monday?

Proton Magnetometer and Stable Oscillator for Remote Measurement of Strong Magnetic Fields

A simple apparatus for proton‐resonance magnetic‐field measurement permits remote location of the rf source and indicator. A high stability variable‐frequency oscillator is also described.

Transistorized, Crystal‐Controlled Marginal Oscillator

A simple, crystal‐controlled, transistorized marginal oscillator magnetometer has been built. It is self‐contained except for an oscilloscope and modulation power supply. Circuit and construction details are given.