Chandra Bhat

Dated September 16, 1997

The Main Injector (MI) is a high intensity 150 GeV proton synchrotron. This accelerator replaces the existing Main Ring for collider operation of the Tevatron and has an additional capability of providing 120 GeV proton beam year round, for the fixed target experiments like NuMI and experiments in the Switchyard area [1]. The beam line towards Switchyard comprises of a part of the Main Ring remnant from F0 to A0 and the existing beam line which is being used for transporting 800 GeV proton beam towards the Switchyard experimental areas. In this report we concentrate on the radiation shielding of the 120 GeV beam transport line for the region from F0 to "D" road. Any special administrative control procedure for the operation of the beam line is omitted here. The radiation shielding assessment related to the Main Injector extraction losses will be dealt with in a separate document.

Presently, it is planned to accelerate the proton beam from 8 GeV to 120 GeV in MI and perform slow resonant extraction at MI-52 location for one second. The beam intensity limits and some details of the cycles of operation of the MI are given in Table I. Recently, a shielding assessment has been carried out for the Tevatron (Main Ring) enclosure and the beam line downstream of the A0 straight section for beam intensities up to 4E13 protons per pulse/min at 1000 GeV [2] and the necessary precautions have been taken. For the present assessment we have been suggested [3] to assume 5.7 x 1016 p /hr @120 GeV delivered to the Switch Yard experimental area during MI era.However, during the Main Injector era the total beam power delivered to the Switchyard area will be a factor of three higher than the existing operating scenarios. Hence it is necessary to do the shielding assessment again from the point of view of the MI operating conditions.

The Main Injector Preliminary Safety Report [4] specifies that the MI enclosure should have a minimum of 24.5 ft of soil equivalent to achieve unlimitted occupancy limits. This specification is derived using Dugan's Criteria ([5], also see Appendix A) for accidental beam losses and CASIM calculations for normal losses. Hence, the MI enclosure is built with a shielding of 24.5 ft soil equivalent (and is designed to carry additional 1.5 ft of soil equivalent shielding on the top). The region over the beamline berm are generally considered as minimum occupancy area and the Dugan's criteria for such region suggests that required shielding to be in access of 22.8 ft of soil shielding.

For the rest of this report we use the Dugan's Criteria to estimate radiation dose over the berm for accidental beam loss conditions with the existing shielding and also estimate required shielding to achieve minimial occupancy limit at all locations along the F0 to Switchyard MI 120 GeV beam line.

Table II summarizes the results of analysis of the existing shielding of beam line enclosure from F0 to Switchyard. The beam line enclosure has over 19.5 ft of soil equivalent shielding at most of the locations. Meeting the requirement of 24.5 ft of passive shielding for no occupancy (or 22.8 ft for minimal occupancy) over the entire beam line is prohibitively expensive. Hence, it is suggested to adopt a combination of instrumentation with some passive shielding to limit the radiation dose below acceptable level in compliance with the Fermilab Radiological Control Manual [6]. In column seven of Table II, we have listed our recommendations for the MI operating scenarios (special administrative exceptions are not considered in this report). We find that adding an electronic berm [7] (Particle Physics Division has used one electronic berm in the M-East beam line and another in neutrino test area) down stream of Transfer Hall will be more economical than using one interlock detector for every 30 ft to 40 ft over the berm (i.e., more than 15 interlock detectors on the berm and their associated electronics).

In conclusion we have estimated the radiation dose over the 120 GeV proton beam transfer line from F0 to Switch Yard experimental area with the existing shielding during accidental beam loss conditions assuming 5.7 x 1016 proton@120 GeVare lost in one hour. We also estimate the required extra passive shieding to be added to achieve minimum occupancy limit. Suggestions have been made to add fences with signsup to location A13 ; add interlocked detectors or e-berm in the region of A13 to D -road.

References ( * Implies these references are included as attachments)

[1] Fermilab Main Injector Technical Design Handbook (1994 and Updated 1997).

[2] MAD Shielding Assessment for the 1996 Fixed Target Run.

[3] S. Holmes, Project Manager (Private Communication 1997).

[4] Fermilab Main Injector Preliminary Safety Analysis Report-(1992).

[5]* Dugan Criteria " Radiation Shielding Calculations for Booster Operations with Main Injector", Memo to Vinod Bharadwaj, July 29, 1991.

[6]* Fermilab Radiological Control Manual ( dated January 1997).

[7] "Eberm Electronic Berm Interlock Module - Functional Description", P.C. Czarapata (October 20, 1995) and "Description and Calibration SEM/Ion Chamber Current Digitizer" Daniel Schoo (Jan. 20, 1992).