ESS Docs Document 163-v1

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Estimations of Residual Dose Rate and Beam Loss Limits in the ESS Linac

Document #:
ESS-doc-163-v1
Document type:
Tech Note
Submitted by:
Karin Rathsman
Updated by:
Karin Rathsman
Document Created:
07 Feb 2012, 12:13
Contents Revised:
07 Feb 2012, 12:13
Metadata Revised:
07 Feb 2012, 12:13
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Abstract:
The ESS linac will accelerate protons from rest to 2.5 GeV through a variety of accelerating structures. One of the advantages of modern linear accelera- tors compared with their circular cousins is that they can typically provide very strong confinement for very high beam currents. While in the linac, the protons will be bunched and focused by electromagnetic fields to prevent them from striking the walls of the accelerator and being lost. Any protons that escape these confining fields cannot be recaptured and will eventually interact with the materials from which the linac is constructed via various processes. The nuclear reactions between the errant protons and the atoms of the parent materials of the accelerator itself will result in:
• in-situ production of ionizing radiation fields (prompt radiation) and • theproductionofradioactivenucleiinsidetheparentmaterial(induced
activity).
In this report we address only the induced radioactivity in which radioactive isotopes are produced within the accelerator components. These isotopes decay, mainly by emitting betas and gammas, until they reach the valley of stability. Since the half-lives of the radioactive isotopes can range from fractions of seconds to years and beyond, the radiation fields will always be present in the machine once it becomes operational and are the source for the residual dose rates.
The purpose of this report is to evaluate the residual dose rates resulting from proton beam losses in the RFQ (radiofrequency quadrupole), MEBT (medium energy beam transport) and DTL (drift tube linac) sections of the ESS accelerator. Based on these results we propose beam loss criteria that can be used by accelerator designers that will ensure residual activation levels in the early part of the accelerator which will be consistent with safe hands-on maintenance as defined by both statutory regulations and ESS administrative requirements.
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