Cascade Generator Research Articles

Twin-Tank Accelerator for High-Voltage Electron Microscopy (HVEM)

HVEM has become a useful method of research in metallurgy and biology. It was necessary to develop special electron accelerators for the supply of these high-voltage microscopes. In view of ac interference problems with air-insulated accelerators, a commercial 1 MV twin-tank accelerator was introduced in 1967. The voltage in this basic model was extended to 1.5 MV and stability improved from ± 1 x 10-5 to ± 1 x 10-6. The future requirements of the electron microscopists, which are directed towards even higher accelerating voltages and greater stability, can also be met by the principles of the symmetrical cascade generator and twin-tank accelerator.

Electron Accelerators for High-Voltage Electron Microscopy (HVEM)

High-voltage electron microscopes are characterized by accelerating voltages in the megavolt range (500 kV and above). Compared to conventional electron microscopes, with voltages up to 200 kV, the high-voltage instruments offer the advantage of improved resolving power (1 to 10 Å) and greater effective penetration of the electron beam. A basic difference between ordinary and high-voltage electron microscopes is the use of an electron accelerator in place of the electron gun to accelerate the electron beam to the required high energy. The resolving power of an electron microscope is determined by the stability of the accelerating voltage, the mechanical precision of the lenses and specimen stages, the stability of the lens supply current and freedom from mechanical vibrations. The symmetrical cascade generator is the only high-voltage dc power supply to meet these requirements with regard to voltage stability and vibration-free performance.

High Power Cockcroft-Walton Generator

To utilize the full current capability of the regular or symmetrical cascade generator, the conventional selenium rectifiers have to be replaced by a series-connection of silicon diodes which are rather sensitive to overvoltages and overcurrents. The problem of the application and protection of silicon diodes in high voltage generators had to be overcome in connection with the design of an air-insulated 770-kV dc power supply with a rated current of 180 mA dc for the ATOMIC ENERGY OF CANADA, LTD., Chalk River, Ontario and also for a 2 MV, 30 mA test facility.

Pressurized 1-MeV Electron Accelerator of the Twin-Tank Design for Electron Microscopy

A pressurized l-MeV electron accelerator was developed after the principle of the symmetrical cascade generator with fully electronic ac supply and voltage regulating systems. A special feature of the new commercial model is the twin-tank design in which the high voltage generator and the accelerator are separated from each other in individual tanks. The two units are connected by a high-ohmic resistor which is enclosed in a pressurized connecting tube. The ripple voltage is negligible (1 × 10-7) and the overall voltage stability is between 1 × 10-6 and 1 × 10-5 in the voltage range from 100 kV up to 1 MV. The electron accelerator is designed as a production model for the supply of a commercial l-MeV electron microscope.

Electron Accelerator for a 1-MeV Electron Microscope

Highly stabilized electron accelerators are required for the supply of high energy microscopes, such as the 1-MeV microscope installed by RCA at the Research Center of the US Steel Corporation at Monroeville, Pa. As shown in figure 1, the accelerating voltage is generated by a 5-stage Cockcroft-Walton cascade rectifier with an additional filter stack. The accelerator structure is connected to the cascade generator through a high-ohmic damping resistor which also serves as a filter resistor in connection with the capacitive part of the precision voltage divider in parallel to the accelerating tube. The beam tube consists of porcelain isolators sealed together by metal flanges and double 0 rings. The accelerating electrodes are made of highly polished mumetal as well as the cylindrical shields which cover the accelerating gaps. Entire mumetal screening is necessary to minimize the effect of the magnetic field of the earth on the electron beam. The beam tube is surrounded by several insulating cylinders which include the voltage divider, a bleeder-chain, a coupling capacitor for the compensation of the residual ripple voltage, and six insulating shafts which are used to control the electron gun and the injector system at high voltage potential.

A 3 MeV electron accelerator using a pressurized cascade generator

Abstract A 3 MV, 6 mA cascade generator to accelerate electron beams for irradiation has been constructed and tested. The cascade generator circuit is of the symmetrical inverse type using selenium rectifiers operating at a frequency of 10 kc/s. The voltage drop and the capacitive input impedance of the generator due to stray capacitance are compensated by the compensation coils inserted into the circuit at intervals of 5-stages. The 120-stages accelerating tube is made of overlapped μ-metal electrodes for shielding the external field. Special care has been devoted to the protection against the puncture of the scanner window and the surge of the generator. Construction and performance of the accelerator are described. The accelerator is satisfactorily used for irradiation purposes.

Progress in the Development of a 4 Mv Positive Ion Accelerator for High Beam Currents

The symmetrical 4 MV cascade generator is a dc accelerator power supply which provides both high voltage and high current capability at low ripple voltage.1 The problems usually encountered in the accelerating tube like total voltage effect, electron loading, and X-ray generation were solved by utilizing built-in permanent magnets for the deflection of the backstreaming electrons. This design reduces electron loading and brings the X-ray intensity down to a harmless level. With a R. F. ion source of conventional design, proton currents up to 1 mA at 4 MeV were actually obtained on the target. A further increase in the beam current is expected by the use of a duoplasmatron ion source.

Optical diagrams for electrostatic lenses applied in high voltage accelerators

Optical data for two similar electrode configurations generally used as electrostatic lenses in high current cascade generators are presented in the form of P-Q diagrams and cardinal characteristic obtained by the application of theGans’ method.

Factors controlling the performance of cascade rectifier circuits

A method is derived of distributing the stage capacitances of a single-phase cascade generator which minimises the output ripple caused by load current. The design of a generator must also take account of the voltage-regulation characteristic, and a procedure is outlined for optimising the generator performance.The characteristics of symmetrical cascade generators are analysed, and a new fullwave circuit of improved regulation characteristics is described.The presence of stray capacitance between the feed and load columns of the generator causes output ripple and loss of output voltage; the amplitude of ripple due to this cause is calculated.At low load currents the limitation upon performance is imposed by the characteristics of the rectifying components. This has been examined for the case of metal rectifiers. It is shown that the minimum output ripple obtainable is determined by the reverse conductivity of the rectifiers; the voltage regulation depends, upon the ratio of forward to reverse conductivity.

A traveling wave cascade generator ? a new high-voltage supply for accelerator tubes

The construction and performance of a traveling-wave cascade generator of 250 kw, 1.5 mu a (operation frequency 7 to 10 k hertz), with cascade heights of 25 mm each, and using a selenium rectifier are analyzed. The generator can be effectively utilized with a strong point, direct-action accelerator of 5 to 6 Mev and current beam up to 1 mu a. (R.V.J.)

Electrostatic charged-particle accelerators

A survey is given of studies on electrostatic particle accelerators. The main attention is given to problems of increasing the energy of the accelerated particles and the beam power in electrostatic generators. A comparison of the different methods of voltage stabilization is made. In conclusion a brief discussion is given of cascade generators designed for the production of high-power beams.

Spin and parity assignments to the Ep=504 keV and Ep=506 keV resonance levels in 27Al(,γ)28Si

The resonance doublet of Al/sup 27/(p, gamma )Si/sup 28/ at E/sub p/ = 504 and 506 kev was investigated with the Utrecht 850-kev cascade generator, and the following results were obtained. The angular distribution of the ground- state transition of the 504-kev level is W( theta ) approximately 1 + (0.01 plus or minus O.O2)cos/sup 2/ theta , and that of the first excited state transition of the 506-kev level is W( theta ) plus or minus 1 -- (0.08 plus or minus O.02)cos/sup 2/ theta . Both levels decay to both the ground state (0/sup +/) and the first excited state (2/sup +/) of Si/sup 28/. The 504-kev level emits alpha particles to the ground state of Mg/sup 64/(0/sup +/), whereas the 506-kev level does not. lt is concluded that the spins and parities of the 504- kev and 506-kev resonance levels are 2/sup +/ and 1/sup +/, respectively; the reasons for these assignments are given. (D.L.C.)

The Utrecht 850 kV cascade generator I. Beam deflection and energy control

The beam deflection magnet and energy control system of the Utrecht cascade generator are described. The uniform-field magnet has entrance and exit slits located outside the magnetic held. Since the cascade generator produces a vertical beam, the most convenient choice for the angle of deflection was 90 degrees. The radius of curvature of the beam in the region of the uniform-field is 20 cm, which makes it possible to deflect a one MeV beam of He + or D e T ions with a field of 14.5 kilograms. The value assembly of the magnet and slits can be repeated about the incoming beam in order to direct the beam to different experimental arrangements. Energy control is achieved in two steps: first the exciting current of the magnet is stabilized, the magnetic field being measured with a proton magnetic resonance fluxmeter, and second the high tension is controlled so as to maintain the deflected beam centered on the exit slit of the magnet. The expected energy resolution of the system has been verified down to an energy spread (full width at half maximum) of 0.15% in proton energy. At the resolution a useful beam ( ∼ 2 μ A is obtainable with a high-frequency ion delivering a total beam of about 40 μA protons.

The effect of source and sink thermal resistance on thermoelectric generator performance

A static analysis of the thermoelectric generator is necessary in order to specify the electrical loading condition for maximum energy conversion efficiency and to determine the corresponding efficiency. Ioffe has done this for the simple case of a single p-n junction thermocouple, and his analysis has been extended to include the effect of temperature dependent parameters by Borrego, Lyden, and Blair.1,2 Harman has considered a cascade generator and has shown how its design can be optimized.3

A high output DD neutron generator for biological research

A description is given of an apparatus capable of producing a fast neutron flux exceeding 10 10 neutrons per second from a DD reaction. The set consists of a pressurized cascade generator and an accelerator tube with a rotary heavy ice target. The rectifiers used are of the selenium type.

Half-lives of short-lived activities with a pulsed neutron source and a ten channel time analyser

The half-lives of He6 and Pb207m have been measured by pulsing the neutron source from a 1 Mev cascade generator and observing the decay with a ten channel cathode ray tube time analyser. A scintillation counter with anthracene crystal served as the detector. Using least squares fitting, the half-lives of He6 and Pb207m were found to be respectively 0·852±0·016 second and 0·948±0·014 second. Comparison with previous determinations is given.