Library of Congress Cataloging-in-Publication Data Karzmark, C. J. Medical electron accelerators 1 C.J. Karzmark, Craig S. Nunan, and Eiji Tanabe. p. cm. : Medical Electron Accelerators: ** Signed gift inscription by co-author Craig Nunan to the previous owner on front endpaper **; Very. Medical Electron Accelerators by Karzmark, C. J.; Nunan, Craig S.; Tanabe, Eiji and a great selection of related books, art and collectibles available now at.
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Operating an electron source in the space charge limited regime provides inherent stability, as the resultant current is dependent only on voltage—something which can be controlled with high accuracy and precision. The temperature can fluctuate due to the large temperature gradients present and due to the energy deposited by back accelerated electrons. Each of these configurations has unique advantages and disadvantages associated with it which have been discussed elsewhere 5 —however, if one considers particle acceleration in isolation, then the in-line configuration is indisputably the superior option.
We have also shown that such a system is far more robust than conventional systems to the presence of in-line magnetic fields, and as such could be an ideal solution for next generation in-line MRI-Linac systems. Note that the asymmetry evident in the plot without the focusing ring is due to the presence of the coupling cavity see color online kqrzmark.
Medical Electron Accelerators
In conventional medical DC electron guns, a relatively low kilovoltage electrostatic field is applied to a thermionic cathode, resulting in space charge limited thermionic emission the space charge of the beam limits the emitted current. A large amount of strategies to mitigate the back-bombardment effect in RF guns has already been published, and given that there is already at least one system in existence operating at karzmarj pulse lengths and energies as would be required for this system the Kyoto University free electron laser injectorit is reasonable to believe that this effect could be managed.
Higher fields further limit the impact of space charge.
Please create a new list with a new name; move some items to a new or existing list; medicl delete some items. One of these is beam stability.
As such, we conclude that a RF-gun based accelerator is capable of robust performance without magnetic shielding in a wide range of in-line magnetic fields.
This distortion can be corrected up to a point, as evidenced by current first generation MRI-Linac systems which successfully utilize magnetic shielding for either the electron gun or the entire Linac. The normalized emittance at the target was calculated using Eq. In general, the field amplitudes obtained from an eigenmode solver are normalized in a manner specific to a given solver implementation, and must then be scaled to levels appropriate for the need at hand Fig.
Metric Single cell values Single cell values published in Ref. However, from speaking to ,edical representatives this appears to be an area to which each accelerator manufacturer has devoted substantial in-house effort. The solver is based on the finite element method and utilizes a tetrahedral mesh with quadratic shape functions.
Exactly the same geometry as in Sec. Note that since the accelerator itself is not strongly affected by in-line fields, the losses in target current are proportional to the losses in the electron gun plotted here.
An estimate of the total space charge limited contribution oarzmark the current can be obtained as follows: The first is to redesign the optics of the electron gun taking the presence of in-line magnetic fields into account such that the modified gun functions within these fields.
As the sources of loss losses to the conducting walls and to the beam are very similar to previously published work, the required input power will also be similar to this—around 2. We were not able to find any published accelerztors on the typical extent of back-bombarded power in medical DC electron guns karzmarl any information on how much back-bombardment would be acceptable or unacceptable. In this work we have proposed a novel medical electron accelerator with robust target current in a wide range of axial magnetic fields.
Each macro particle in this work represented around electrons, and around three million macro particles reached the target in each simulation.
A novel electron accelerator for MRI-Linac radiotherapy
It can be seen that the bunch power rises steadily before plateauing; this behavior occurs because the mean mmedical of the back-bombarded electrons increases as the forward directed beam propagates further down the accelerator. Please verify that you are not a robot. Perhaps the most substantial barrier to clinical implementation of a system such as that described here is the increased back-bombardment power deposited by back accelerated electrons.
B shows the impact of this structure of the radial fields, plotted 1 mm in front of the cathode. Various figures of merit extracted from the simulations. Support Center Support Center.
We have made minimal effort to optimize the RF structure for a temperature-limited cathode—for instance, further optimization of the radial focusing fields around the cathode could be undertaken, and the spatial energy distribution at the target could be optimized by lowering the fields in the first half cavity.
Two solutions for operating the electron gun in in-line magnetic fields acceleratros been proposed. Radiofrequency field calculation The electromagnetic field solution is shown in Fig.
Medical Electron Accelerators : Clarence J. Karzmark :
These numbers take into account all back accelerated electrons. The point at which the cathode becomes temperature limited is then calculated; i. A solution which could meet these criteria and that has not previously been explored is a RF electron gun based system.