LCLS Radiological Considerations Sayed H. Rokni, SLAC April 24, 2002 Radiological safety program at SLAC (S. H. Rokni) Shielding methodology for LCLS (W. R. Nelson) Radiation safety systems for the LCLS (S. Mao) LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Outline of the Presentation Radiological safety program at SLAC ALARA/dose limitation Design criteria Radiation safety systems Passive/active components (BCS) Access control systems (PPS, HPS) Administrative Overview of the systems specific to LCLS Existing facility (FFTB) New components LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Radiation Safety at SLAC Ensure ALARA Provide adequate shield for facilities, beam lines and experimental areas Control access to areas where beam could be present Incorporate dose reduction, contamination reduction, and waste minimization features in planning stage Prevent any person from receiving more radiation exposure than limits LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Radiological Safety at SLAC-Cont. Engineering and administrative systems to implement the program SLAC Radiological Control Manual Radiation Safety Systems, Technical Basis Document Guidelines for Operation Implemented by Radiation Physics, Operational Health Physics, Accelerator and SSRL Safety Offices, Controls Departments LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Engineering Controls for Radiation Safety Passive Bulk Shielding, local shielding: attenuate radiation Protection collimators: limiting apertures prevent beams from striking shielding Active Sensors Beam Containment System (BCS): Sensors that turn beams off when parameters exceed pre-set limits Ion chambers Torroids LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Engineering Controls-Cont. Access Control System Prevents access to areas where potential for beam operations exist Personnel Protection System (PPS) Hutch Protection System (HPS) LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Design of Engineering Controls Radiation Physics Department staff have been involved in design of shielding, BCS and PPS specifications for the LCLS from the start: Design Study Report, Environmental Assessment, Conceptual Design Report Staffing: K. R. Kase W. R. Nelson H. Khater A. Prinz J. C. Liu S. H. Rokni S. Mao H. Vincke LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Radiological Safety at SLAC- Operations Radiation physics has oversight for beam operations in conjunction with: Accelerator and SSRL Safety Offices Administrative controls: Conduct of Operations, Configuration Control Guidelines for operations Beam Authorization Sheets (BAS) Radiation Safety Work Control Forms (RSWC) Accelerator and SSRL safety procedures LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Radiological Safety at SLAC-Cont OHP administers the following services: Training Instrumentation Radiological Postings Dosimetry Radiological Surveys & Monitoring Radiological Hygiene Radioactive Material Inventory Control Radioactive Waste Management Radiological Environmental Protection Emergency Preparedness LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

ES&H Division and Radiation Safety Management LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Shielding Design Criteria Normal mode of operation The integrated dose equivalent outside the the FFTB tunnel must not exceed 1 rem/yr The integrated dose equivalent to personnel working inside and around the experimental hutch shielding barriers must not exceed 0.1 rem Maximum Credible Incident The dose equivalent-rate is limited to less than 25 rem/h, and integrated dose equivalent of less than 3 rem LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Final Focus Test Beam Designed for: 2.5 kW 50 GeV e- or e+ beams FFTB Tunnel 4’ thick concrete side walls 3’ thick concrete roof FFTB Dump 9’ thick iron, concrete walls 60’ of iron to shield muons LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

LCLS Radiation Safety Systems Additional components for the LCLS Injector shielding at sector 20 lateral shielding walls of the optical front end front, back and lateral shielding walls for the electron dump experimental hutches shielding Front End and hutch beam stoppers entrance maze HPS Initial design completed Optimize the design LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

LCLS Radiological Considerations Walter R. Nelson, SLAC April 24, 2002 Radiological Safety Program at SLAC (S. H. Rokni) Shielding Methodology for LCLS (W. R. Nelson) Radiation Safety Systems for the LCLS (S. Mao) LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Shielding Methodology – Outline of Talk Radiation fields around an electron accelerator Electromagnetic cascades (soft showers) Photoproduction of neutrons and muons LCLS geometry “sources of radiation” Shielding methodology (computer codes) Example results using the EGS4, MUON89 and MuCarlo codes will be presented Relevant shielding results will be presented in the talk that follows (by Stan Mao) LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Electron-photon interactions and EM showers Understanding the electromagnetic cascade shower is key to understanding radiation fields at electron accelerators High-energy electrons and positrons produce lots of x-rays X-rays in turn produce more electrons and positrons (in pairs) This continues back in forth – but it eventually stops when all of the energy is used up Process is called an electromagnetic cascade “shower” First observed in photographs like the one shown in the… … next slide LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Cloud chamber photo of a shower (circa 1950) (Note: only charged particles are visible) High-energy electron enters from top Strikes Pb sheet (not visible in photo) Many more charged particles produced They bend because of magnetic field Charged particles are both e+e- (pairs) e+e- get swept out by the magnetic field ------------------------------------------ Take note of the two other Pb sheets Shower regenerated by invisible photons Without the magnetic field, the shower would be very forward-directed LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Monte Carlo simulation showing initiation of a shower 100 MeV electron impinges from the left onto a 1-cm slab of Pb. Particles are produced and are identified by their color. LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Ten 1-GeV electrons strike a 15-cm Cu target All particles are shown Only electrons and positrons shown LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

…Real example of the power of a full EM shower Melt-down at shower maximum e- A Cu beam stopper (PPS/BCS device) that was destroyed by the beam LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

…Real example of the power of a full EM shower (cont.) Note: THREE shower maxima A Cu beam stopper (PPS/BCS device) that was destroyed by the beam LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Photoproduction of other particles (radiation) Although most of the energy in an EM shower goes into ordinary “energy deposition” (i.e., heat), other particles are produced About 0.2% goes into hadron production --- i.e., neutrons Half into low-energy neutrons (giant resonance excitation) Half into high-energy neutrons (hadronic cascade) And muons are pair produced at a rate that is about 1/40,000th that of electron-positron pairs Although these numbers may seem small, these other radiations are more difficult to attenuate than photons LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

General schematic of radiation and shielding Electron beam enters from the left and produces a shower Photons from shower itself must be shielded Neutrons produced by photons must be shielded Muons produced by photons must be shielded (forward direction) LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

A closer look at how radiation gets shielded Low-energy neutrons attenuate rather easily They are followed by the photons When the shield gets “thicker” the high-energy neutron component starts to dominate Ultimately we may be stuck with muons, which attenuate very slowly This is what happens at 0° At 90° things look similar…except we don’t have muons For the LCLS we have to consider both the forward and side directions LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Components along the LCLS (Sources of Radiation) An Injector (at Sector 20) feeds into the main SLAC Linac 15 GeV electron beam with 2 kW of power at the east end 7 x 109 electrons/pulse at 120 Hz (130 nA of beam current) The electrons pass through an Undulator that generates a coherent beam of x-rays A beam line allows x-rays to go to experimental Hutches Another beam line sends the 15 GeV electrons to a Dump Collimators and stoppers are required for PPS purposes All must be considered in the radiation safety analysis LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Sources of radiation (cont.) Undulator Collimators Stoppers Beam dump Electrons will hit all of these components… … and so will the photons The result: radiation !!! LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Sources of radiation (cont.) We have sources resulting from the 15 GeV electron beam Beam halo Gas bremsstrahlung Mis-steering Beam-diagnostic devices The electron dump We also have x-ray sources created by the undulator Coherent (FEL) radiation Synchrotron radiation LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Shielding Methods The Radiation Physics Department has successfully shielded the SLAC Two-Mile Accelerator, and its beam lines, for about 40 years A good starting reference is: Chapter 26: “Shielding and Radiation” in The Stanford Two Mile Accelerator, R. B. Neal, Editor (W. A. Benjamin, Inc., New York, 1968). Many problems can be solved by using existing computer codes, which we categorize into three groups Monte Carlo: EGS4, FLUKA, and MuCarlo Analytic: MUON89, STAC8 and PHOTON Semi-empirical (scaling): SHIELD11 The four codes highlighted above in “blue” were developed within the RP department LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Monte Carlo codes: EGS4, FLUKA, and MuCarlo EGS4 is a program that specializes in the production and transport of electrons, positrons and photons through matter. It is the most thoroughly benchmarked shower code and is generally considered the standard by which other EM codes are judged. FLUKA is a general program for producing and transporting more than 30 different particles, including neutrons, muons, and for solving the EM shower problem. MuCarlo takes muons that are produced by electron beams striking beam dumps and transports them through very complex geometries (including magnet fields). LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Analytic codes: MUON89, STAC8 and PHOTON MUON89 determines the fluence of muons through thick shields after they have been produced in an EM shower initiated by a beam of electrons striking a dump. PHOTON is an x-ray shielding code that was specifically designed to determine radiation levels associated with beam lines at synchrotron light facilities. STAC8 was developed from PHOTON and contains many improvements, such as undulator radiation, build-up factors, angular-dependent coherent and incoherent scattering, self-shielding by scatterers (including inclined scatterers), etc. LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Semi-empirical codes: SHIELD11 SHIELD11 is the “workhorse” code of the department and is based on the scaling of experimental data taken during the early days of SLAC. The components and methods of the code have been used with great success in shielding design not only at SLAC, but also at KEK and Jefferson Lab. LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

An example calculation using EGS4 EGS4 was used to determine where the electron beam produces showers and how much energy gets deposited in stoppers LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

An example calculation (cont.) Energy absorbed all along the undulator Specific peaks at: Collimator C1a Collimator C2 Collimator C3 Stopper ST3 Energy fraction absorbed in ST3 is about 6x10-4, which corresponds to 12 mW (for a 2 kW electron beam) LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Another example calculation using MUON89 We used MUON89 for the forward dump shielding analysis Note the isodose (rate) lines below the ground level LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Summary The shielding of muons from the primary electron beam striking the dump is well understood The energy deposition along the LCLS itself – from the Undulator down through the Hutches – has been quantified Using this information, an extensive shielding analysis has been done by the Radiation Physics Department and the results will be discussed in the next talk (by Stan Mao) LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

LCLS Radiological Considerations Stan Mao, SLAC April 24, 2002 Radiological Safety Program at SLAC (S. H. Rokni) Shielding Methodology for LCLS (W. R. Nelson) Radiation Safety Systems for the LCLS (S. Mao) LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Radiation Safety Systems for the LCLS Injector at LINAC Sector 20 Electron dump line Beam containment system Shielding Front End Enclosure Experimental Hutch Front End Enclosure stoppers and Hutch stoppers LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Injector at LINAC Sector 20 LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Injector at LINAC Sector 20 LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Electron dump line LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Beam containment system (BCS) LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Dump shielding 1 LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Dump shielding 2 LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Front End Enclosure LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Front End Enclosure - continued LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Experimental Hatch LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

Front End Enclosure stoppers and Hutch stoppers LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC

LCLS Radiological Considerations- Summary Radiation safety issues for the LCLS are similar to issues normally encountered at high energy electron linacs and synchrotron radiation facilities. Staff from Radiation Physics Department are involved in the design of shielding and specifications for active radiation safety systems for the LCLS. SLAC has a well established radiological safety program to oversee the safe operation of the LCLS. LCLS DOE Review, April 24, 2002 Sayed Rokni, SLAC