The subject of this review is the field of intense pulsed ion beam generation and its potential application to fusion research Considerable progress has been made in the past six years Power levels of the order of 1000 MW/cm2 have been obtained for pulse-lengths from 10−8 to 10−6 s Light-ion beams with currents approaching 1 MA and energies exceeding 1 MeV have been produced The first half of the paper treats the physics and technology of beam generation Following a unified discussion of the theory of ion injectors, experimental work since 1973 is reviewed Diagnostic techniques appropriate to high-flux ion beams are summarized The general problem of high-current ion beam transport in vacuum and through plasmas is also considered The second part of the paper is devoted to applications to fusion research Applications in both magnetic confinement and inertial confinement fusion are considered Intense ion beams have a number of features which make them ideally suited as inertial fusion drivers Discussions are given of the physics of inertial fusion targets, options for ion beam production, experiments on light-ion beam focusing, and high-current multi-stage accelerators

https://iopscience.iop.org/article/10.1088/0029-5515/20/12/006/pdf

Intense pulsed ion beams for fusion applications

The rod-pinch diode consists of an annular cathode and a small-diameter anode rod that extends through the hole in the cathode. With high-atomic-number material at the tip of the anode rod, the diode provides a small-area, high-yield x-ray source for pulsed radiography. The diode is operated in positive polarity at peak voltages of 1 to 2 MV with peak total electrical currents of 30–70 kA. Anode rod diameters as small as 0.5 mm are used. When electrode plasma motion is properly included, analysis shows that the diode impedance is determined by space-charge-limited current scaling at low voltage and self-magnetically limited critical current scaling at high voltage. As the current approaches the critical current, the electron beam pinches. When anode plasma forms and ions are produced, a strong pinch occurs at the tip of the rod with current densities exceeding 106 A/cm2. Under these conditions, pinch propagation speeds as high as 0.8 cm/ns are observed along a rod extending well beyond the cathode. Even f...

Theoretical modeling and experimental characterization of a rod-pinch diode

Gafchromic EBT radiochromic film is one of the newest radiation-induced autodeveloping x-ray analysis films available for therapeutic radiation dosimetry in radiotherapy applications. The spectral absorption properties in the visible wavelengths have been investigated and results show two main peaks in absorption located at 636 nm and 585 nm. These absorption peaks are different to many other radiochromic film products such as Gafchromic MD-55 and HS film where two peaks were located at 676 nm and 617 nm respectively. The general shape of the absorption spectra is similar to older designs. A much higher sensitivity is found at high-energy x-rays with an average 0.6 OD per Gy variation in OD seen within the first Gy measured at 636 nm using 6 MV x-rays. This is compared to approximately 0.09 OD units for the first Gy at the 676 nm absorption peak for HS film at 6 MV x-ray energy. The film’s blue colour is visually different from older varieties of Gafchromic film with a higher intensity of mid-range blue within the film. The film provides adequate relative absorbed dose measurement for clinical radiotherapy x-ray assessment in the 1–2 Gy dose range which with further investigation may be useful for fractionated radiotherapy dose assessment.

http://iopscience.iop.org/article/10.1088/0031-9155/50/13/N02/pdf

Absorption spectra variations of EBT radiochromic film from radiation exposure

Diagnostic methods pertinent to the probing of intense pulsed ion beams are described. Special emphasis is given to the measurement of delayed radioactivity from nuclear reactions induced in a target by the ions. This nuclear activation analysis provides the most precise, unambiguous means of determining the number of ions per pulse that is presently available. A compilation of yields and cross sections for several nuclear reactions is given. Included among the nuclear techniques is the measurement of prompt radiation such as γ rays and neutrons from ion‐induced reactions. In addition, a scintillator–photodiode detector is described which has proven to be useful for the measurement of time of flight and which may be used to observe the relative pulse shape. Biased ion collectors and difficulties associated with their use are also discussed.

Diagnostics for intense pulsed ion beams

In addition to being initially developed as an energy driver for an inertial confinement fusion, an intense, pulsed, light‐ion beam (LIB) has been found to be applied to materials science. If a LIB is used to irradiate targets, a high‐density ‘‘ablation’’ plasma is produced near the surface since the range of the LIB in materials is very short. Since the first demonstration of quick preparation of thin films of ZnS by an intense, pulsed, ion‐beam evaporation (IBE) using the LIB‐produced ablation plasma, various thin films have been successfully prepared, such as of ZnS:Mn, YBaCuO, BaTiO3, cubic BN, SiC, ZrO2, ITO, B, C, and apatite. Some of these data will be presented in this paper, with its analytic solution derived from a one‐dimensional, hydrodynamic, adiabatic expansion model for the IBE. The temperature will be deduced using ion‐flux signals measured by a biased ion collector. Reasonable agreement is obtained between the experiment and the simulation. High‐energy LIB implantation to make chemical co...

Applications of intense pulsed ion beam to materials science

A polarity-reversed 10/sup 12/-W relativistic-electron-beam generator operating in the self-pinched mode is used to produce and propagate intense proton beams. Charge-neutralized beams of 30--50 ns duration consisting of over 4 x 10/sup 16/ 0.5--0.8-MeV protons distributed over a 120-cm/sup 2/ cross-sectional area are routinely produced. The 150--200-kA average ion currents deduced from these measurements are in good agreement with theoretical calculations. (AIP)

Production of Intense Proton Beams in Pinched-Electron-Beam Diodes

A plasma erosion opening switch (PEOS) is used as the opening switch for a vacuum inductive storage system driven by a 1.8‐MV, 1.6‐TW pulsed power generator. A 135‐nH vacuum inductor is current charged to ∼750 kA in 50 ns through the closed PEOS which then opens in <10 ns into an inverse ion diode load. Electrical diagnostics and nuclear activations from ions accelerated in the diode yield a peak load voltage (4.25 MV) and peak load power (2.8 TW) that are 2.4 and 1.8 times greater than ideal matched load values for the same generator values.

/pdf/high-voltage-high-power-operation-of-the-plasma-erosion-ciz6mhxub7.pdf

High Voltage, High Power Operation of the Plasma Erosion Opening Switch.

A plasma erosion opening switch, coupled to a small capacitor bank, conducts 120 kA for 400 ns before opening in 40 ns. Voltages above 170 kV are produced through the use of an electron beam diode. These voltages exceed the initial capacitor bank voltage by a factor of 4. Current and magnetic field measurements indicate that the same current conduction and opening processes observed in earlier erosion switch experiments are involved here at tenfold greater conduction times, verifying the current controlled nature of plasma erosion switch operation.

Long conduction time plasma erosion opening switch experiment

The K-shell radiated energy (yield) from neon Z-pinch implosions with annular, gas-puff nozzle radii of 1, 1.75, and 2.5 cm was measured for implosion times from 50 to 300 ns while systematically keeping the implosion kinetic energy nearly constant. The implosions were driven by the Hawk inductive-storage generator at the 0.65-MA level. Initial neutral-neon density distributions from the nozzles were determined with laser interferometry. Measured yields are compared with predictions from zero-dimensional (0-D) scaling models of ideal. One-dimensional (1-D) pinch behavior to both benchmark the scaling models, and to determine their utility for predicting K-shell yields for argon implosions of 200 to >300 ns driven by corresponding currents of 4 to 9 MA, such as envisioned for the DECADE QUAD. For all three nozzles, the 0-D models correctly predict the Z-pinch mass for maximum yield. For the 1and 1.75-cm radius nozzles, the scaling models accurately match the measured yields if the ratio of initial to final radius (compression ratio) is assumed to be 8:1. For the 2.5-cm radius nozzle, the measured yields are only one-third of the predictions. Analysis of K-shell spectral measurements suggest that as much as 70% (50%) of the imploded mass is radiating in the K-shell for the 1-cm (1.75-cm) radius nozzle. That fraction is only 10% for the 2.5-cm radius nozzle. The 0-D scaling models are useful for predicting 1-D-like K-shell radiation yields (better than a factor-of-two accuracy) when a nominal (/spl ap/10:1) compression ratio is assumed. However, the compression ratio assumed in the models is only an "effective" quantity, so that further interpretations based on the 0-D analysis require additional justification. The lower-than-predicted yield for the 2.5-cm radius nozzle is associated with larger radius and not with longer implosion time, and is probably a result of two-dimensional effects.

J.R. Boller

Papers

Theoretical modeling and experimental characterization of a rod-pinch diode

Production of Intense Proton Beams in Pinched-Electron-Beam Diodes

High Voltage, High Power Operation of the Plasma Erosion Opening Switch.

Long conduction time plasma erosion opening switch experiment

Results of radius scaling experiments and analysis of neon K-shell radiation data from an inductively driven Z-pinch