Radiation Safety Aspects of LCLS-II Accelerator at SLAC Sayed Rokni, Johannes Bauer, Jan Blaha, James Liu, Stan Mao, Ludovic Nicolas, Mario Santana and Shanjie Xiao SLAC National Accelerator Laboratory RadSynch 2017, NSRRC, Hsinchu, Taiwan April 19-21, 2017
Overview • Introduction: LCLS-II Project • Radiation Protection Issues • Radiation Safety Systems • Beam Containment System • Summary RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 2
New Injector and LCLS-II New Superconducting Linac New Cryoplant Existing Bypass Line New Transport Line Two New Undulators Repurpose Existing Experimental Stations 61st Annual HPS Meeting, July 17-21, 2016, Spokane, WA Slide 3
LCLS-II- SC Linac, LCLS-I Linac GUN proposed LCLS-I Linac 750 keV LCLS-II SCRF Linac FACET-II 3-17 GeV SXU Sec. 11-20 Sec. 21-30 L2 L3 L1 HXU 0.25 1.6 4.0 BSY GeV GeV GeV CM02 CM03 • Thirty five 1.3 Ghz Cryomodules HCM01 • Two 3.9 Ghz Cryomodules HCM02 • 300 pC, 1 Mhz, 4 GeV, 1.2 MW 4 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017
LCLS-II- Undulators 0.2-1.3 keV (<1 MHz) proposed LCLS-I Linac 0.1-20 keV* (120 Hz) LCLS-II SCRF Linac FACET-II 3-17 GeV SXU Sec. 11-20 Sec. 21-30 L2 L3 HXU 0.25 1.6 4.0 1-25 keV (120 Hz) BSY GeV 1-5 keV (<1 MHz) GeV GeV RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 5
Dump Hall and FEE 0.2-1.3 keV (<1 MHz) proposed LCLS-I Linac 0.1-20 keV* (120 Hz) LCLS-II SCRF Linac FACET-II 3-17 GeV SXU Sec. 11-20 Sec. 21-30 L2 L3 HXU 0.25 1.6 4.0 1-25 keV (120 Hz) BSY GeV 1-5 keV (<1 MHz) GeV GeV Photon stoppers FEE Electron beam dumps 2x120 kW @ 4GeV NEH (240 kW @8 GeV) RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 6
LCLS-II Status 7 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017
LCLS-II Status 8 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017
LCLS-II Commissioning Plans • Early Injector Commissioning: January 2018 • HXR Commissioning with Copper Linac: 6/12/2019 • HXR Commissioning with SC Linac:10/3/2019 • SXR Commissioning with SC Linac:10/3/2019 • Power Up Ramp:11/12/2019 – 8/7/2022
• High average electron beam power, MHz rep rate machine • No MW dump, must rely on interlocks and distribute power in several lines • Fast shut-off time is required to terminate errant beam conditions • Pre-existing facility • Beam Transport Hall, Dump Hall, FEE designed for LCLS-I • Over 450 penetrations from the Linac to the Klystron Gallery • Personnel working in experimental hutches located near zero-degree with respect to the electron beam direction and at short distance • Containment of FEL RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 10
11 SLAC Radiation Safety Systems R adiation S afety S ystem Access Control System R adiation C ontrol S ystem (keep people away from radiation ) ( keep radiation away from people ) Beam Containment System B eam S hut- Shielding • Beam Parameter Monitors O ff I on • Beam Loss Monitors C hambers Protection of Safety Devices Stoppers, Collimators
17 mSv/h 12
Beam Transport Hall (designed for 5 kW) o Beam Power = 2 x 120 kW 2 x 240 kW @8 GeV o Normal Beam Loss = 1 W/m LION setting = 35 W S.B. Long BTH detectors 6’ (1.8 m) 18’ (5.5 m) Local shielding around 13 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 collimators
Beam Containment: Protection Collimators o Tunnels and shielding implemented in FLUKA o Cu-Line, HXR, SXR and DML imported from MadX twiss files into FLUKA with MadFLUKA. This includes geometry & optics o Optics perturbations with one independent failure in magnetic routine Uncontained rays towards ESA Collimator added with optimized dimensions 14 14 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 Courtesy of Mario Santana
Beam Containment: Protection Collimators o Tunnels and shielding implemented in FLUKA o Cu-Line, HXR, SXR and DML imported from MadX twiss files into FLUKA with MadFLUKA. This includes geometry & optics o Optics perturbations with one independent failure in magnetic routine 15 15 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017
Containment of the Electron Beam D. Walz et al., SLAC-PUB-1224 1973 • Copper beam stopper (personnel safety device: 4" in diameter 30" long -53.6 r.l.) that was destroyed by the SLAC electron beam 500 kW, 18 GeV, (11 s for radial blow out, 49 s for burn through) •The 1 MW ~ 30 micron beam can be very destructive if steered onto a component and hazardous if sent towards walls / shielding: •Beam needs to be shut-off very fast 16
Beam shutoff studies o FLUKA used to compute energy deposition in various materials and irradiation conditions (beam energy & size, geometry, impact parameter) o FHeat3D heat transfer code developed to compute heat transfer: • Interfaced ‘directly’ with FLUKA output Copper block • Conduction, convection, radiation Al body Steel sleeve Return/Supply 30 cm o Collimators (W) pipes t r > 150 μs @ 120 kW damage • t r > 1 s @ 120 kW melting • t r > 1 ms @ 1200 kW melting • Vacuum pipe • Alternatives: Ti or Al o 250 kW Al/Cu dump (2 cm Raster): • t r (cooling loss) = 15 s; t r (1.2 MW) = 1.5 s; t r (raster failure) = 1.5 s 17 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 Courtesy of Mario Santana-RP-14-07, April 2017
LCLS-II BCS Functions • Much higher repetition rate, much higher beam power • These considerations require fast response, different processing and a much wider dynamic range • Beam Parameter Monitoring: - Average Current Monitor (5 ms) - Average Current comparator • Beam Loss Monitoring: - Fiber Cherenkov Monitor (1 s) • Beam Loss Monitoring – protection of safety devices: - Diamond sensor (200 µs) • Magnet Current Monitor RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017
BCS Devices • Average Current Monitors RF cavity ACMs with FPGAs to directly detect and limit beam current • Diamond Detector Metallized diamond chip, 10 × 10 × 0.5 mm 3 • Fast response: output pulses of ≈5 ns • • No accumulation from prior pulses Dynamic range: 1–10 5 (B2) and 10 4 –10 9 (B4) • Optical Fiber • Cherenkov light • Photomultiplier (PMT) at end of fiber measures beam loss RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 19
Status of Accelerator Radiation Protection • Completed: • Modelling of field emission from CMs • Dump design and associated shielding • Collimator design and associated shielding • Shielding for penetrations • Access Control requirements • Decommissioning of S0-10 of SLAC Linac • Radiological Environment Protection requirements - Air, skyshine, groundwater, residual dose rate, LCW system • Underway: • Testing and evaluation of performance of BCS (sensors, electronics) RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 20
Summary • Radiological analysis for LCLS-II has been conducted with extensive use of FLUKA code and leveraging experience from LCLS-I design and operations, as well as high power beam operations • Sections of LCLS-II will be housed in enclosures that are designed for lower power beam. Repurposing of the existing accelerator facility for higher average beam power has posed several challenges • Local shielding (penetrations) & increase of distance (fences of beam-line modification), and Beam Containment System controls have been applied to maintain safety and provid cost-effective solutions RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 21
Thank You • Adds a new, 4 GeV superconducting linac in an existing SLAC tunnel, avoiding the need for excavation • Repetition rate up to 1 MHz (currently 120 Hz) • World’s only xFEL to supply uniformly-spaced train of pulses with programmable repetition rate • Two new adjustable gap undulators: tunable source of X-rays • Intermediate X-ray energy range studies of new materials, chemical catalysis and biology • Extends the operating range to ~25 keV • Latest seeding technologies fully coherent X-rays • Maintains the existing copper-based warm linac 22 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017
Test of BCS Devices Fisher – LCLS-2 Beam-Loss Monitoring RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 23
LCLS-II (SCRF) Baseline Parameters Parameter nominal range units Electron Energy 4.0 2.0 - 4.14 GeV Bunch Charge 100 10 - 300 pC Bunch Repetition Rate in Linac 0.62 0 - 0.93 MHz Avg. e − beam power at linac end 0.25 0 - 1.2 MW RF frequency 1.3 - GHz Avg. CW RF gradient (powered cavities) 16 - MV/m Photon energy range of SXR ( SCRF ) - 0.2 - 1.3 keV Photon energy range of HXR ( SCRF ) - 1 - 5 keV Photon energy range of HXR ( Cu-RF ) - 1 - 25 keV 24
Design Limits, Criteria • Protect workers, users, general public, and the environment on-site and off- site from radiation of accelerator and beam operations 5 µ Sv/hr • Bulk shielding 0.5 µ Sv/hr • Experimental hutch 50 µ Sv/yr • Site boundary dose 740 Bq/L for 3 H • Ground water activity 1 µ Sv/yr • Air activation dose • Maintain doses as low as reasonably achievable (ALARA) Prompt dose rates, Residual dose rates, Impact on the environment 25 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017
LCLS-II Schedule RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 26
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