Abstract
Beam halo is an important factor in any high intensity accelerator. It can cause difficulties in the control of the beam, emittance growth, particle loss, and even damage to the accelerator. It is therefore essential to understand the mechanisms of halo formation and its dynamics. Experimental measurement of the halo distribution is a fundamental tool for such studies. In this paper, we present a new high dynamic range, adaptive masking method to image beam halo, which uses a digital micromirror-array device. This method has been thoroughly tested in the laboratory using standard optical techniques, and with an actual beam produced by the University of Maryland Electron Ring (UMER). A high dynamic range ($\mathrm{DR}\ensuremath{\sim}{10}^{5}$) has been demonstrated with this new method at UMER and recent studies, with more intense beams, indicate that this DR can be exceeded by more than an order of magnitude. The method is flexible, easy to implement, low cost, and can be used at any accelerator or light source. We present the results of our measurements of the performance of the method and illustrative images of beam halos produced under various experimental conditions.
Highlights
Beam halos are typically observed in particle beams [1,2]
The optical system we used for University of Maryland Electron Ring (UMER) is essentially the same as shown in Fig. 1 except that two lenses are used in each channel in order to separately adjust the magnification in each channel, and additional mirrors are incorporated into the design to meet space constraints
We have presented a new high dynamic range method to image beam halo using a digital micromirror device (DMD)
Summary
Beam halos are typically observed in particle beams [1,2]. There is no well-accepted or rigorous definition of halo, but it is usually described as a low intensity distribution of particles that are observed at large radii from a more intense centralized portion of the beam, i.e., the ‘‘core’’. The method usually employs transmissive optics and a fixed size blocking mask to filter out the central area of the beam image, highly polished lenses to avoid scattering, and special apertures (Lyot stops) to partially filter out the diffraction effects produced by the input lens and the blocking mask itself After these steps are taken, the halo is made more visible by increasing the exposure time of the camera. The results showed an effective DR $ 105 These laser studies indicated that the DMD masking method could potentially be more useful than a fixed spatial mask, such as used in the coronagraphy technique described above, to image the halo of a charged particle beam with high dynamic range. The available DR of the optical systems we have developed at both these facilities has been shown to be $107, so that it may be possible to extend the currently measured DR on the beam by one or two additional orders of magnitude
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