Radiation Safety Designs for LCLS-II FEL Beams Shanjie Xiao, James - PowerPoint PPT Presentation

Radiation Safety Designs for LCLS-II FEL Beams Shanjie Xiao, James Liu and Sayed Rokni SLAC National Accelerator Laboratory Radsynch 2017, Hsinchu, Taiwan

Overview Layout of XTES and Hutches in LCLS-II FEL Parameters • Challenge: high intensity pulses and high power density FEL Stopper System and Related Interlocks FEL Collimators FEL Beam Dump Acknowledgement: • Yiping Feng, Silvia Forcat, Jacek Krzywinski, Eliazar Ortiz, Michael Rowen, Bill Schlotter, Hengzi Wang RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 2

XTES and Hutches Location of XTES (X-ray Transport and Experiment System) in LCLS-II FEE Hallway FEE Rack Room FEE New Entrance SXR HXR EBD FEE NEH HUTCH 1 EBD Electron Beam Dump RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 Courtesy of P. Stephens & T. O’Heron FEE Front End Enclosure 3 NEH Near Experimental Hall

Mirror Configuration in Front End Enclosure SXU: Bendable SXU: Flat Mirror Mirror 0.25 – 2.5 keV SXU: 0.25 – 1.3 keV NEH 1.1 Monochromator NEH 2.1 0.25 – 1.3 keV NEH 2.1, NEH 2.2 SXU: Flat Mirror 0.4-5.0 keV NEH 1.2 SXU: Flat Mirror 0.4 – 5.0 keV SXU: Bendable NEH 1.2 Mirror 0.25 – 1.3 keV NEH 2.1, NEH 2.2 HXU: Flat Mirror 2.5 – 25 keV XPP, XCS, MFX, CXI, MEC HXU: Flat Mirror 1 – 7 keV NEH 1.2 HXU: Flat Mirror 1 - 25 keV NEH 1.2, XPP, XCS, MFX, CXI, MEC RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 4 Courtesy of D. Fritz

Experiment Hutches Original LCLS N2.1 LCLS-II N2.2 Near Hall XCS MFX CXI MEC N1.1 N1.2 XPP Far Hall ~ 50 m ~ 70 m RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 5 Courtesy of D. Fritz

FEL Parameters Experiment systems are designed for 200 W FEL, but LCLS-II can (from simulations) deliver more • S2E simulation results as of September 2016, for 120 kW 4 GeV electrons SXR HXR 250eV 750eV 1.25keV 1.5keV 3.25keV 5keV 20pC (1.5 MHz) 393 (267) 266 (239) 222 (168) 251 (206) 191 (147) 37 (25) 100pC (300 2549 (1205) 1635 (795) 1008 (527) 1731 (1136) 617 (469) 6 (10) kHz) 300pC (100 8801 (5482) 5699 (3844) 3386 (1897) 4567 (2364) 2064 (642) - kHz) Energy in μJ () – values as of Oct. 2015 S2E Simulations by Gabriel Marcus ~ 8.8 mJ/pulse ~ 4.6 mJ/pulse ~ 880 W ~ 460 W RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 6

FEL Stopper Design Grazing incident stopper needs long space – limited space in FEE Beam mode control is not preferred (thermal stability) Multi-layer stopper: • 750 µm CVD Diamond w/ graphite coating + SiC - Good thermal conductivity Burn thru monitor • + Tungsten (for bremsstrahlung) SiC CVD diamond Beam CVD diamond Two considerations • Average power & Instantaneous pulse WHA SiC RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 7

FEL Stopper Design 1D analytical model 4µm Heat graphite Sink • Peak temperature after pulse shot • Quickly cooled • Steady temperature built up gradually 1 st pulse RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 8

FEL Stopper Design Good for hard x-rays • Temperature rising is moderate Combined Steady State and Instantaneous Temperature rise (°C) RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 9

FEL Stopper Design Potential issue for soft x-rays: around carbon K-edge (~285 eV) • High temperature around carbon edge - Combined steady state and instantaneous temperature rise (°C) Power (W) 100 200 300 400 500 600 + mJ 1.0 2.0 3.0 4.0 5.0 6.0 250 103 173 242 315 393 480 290 569 947 1304 1658 2016 2382 500 425 699 959 1218 1488 1773 750 337 554 763 980 1213 1472 1300 225 380 541 724 943 1209 - Mainly from single pules instantaneous temperature rise (°C) mJ 1.0 2.0 3.0 4.0 5.0 6.0 250 40 64 81 94 105 115 290 504 834 1135 1426 1712 1996 500 352 567 758 937 1112 1286 750 257 404 529 647 760 872 1300 132 200 252 300 347 394 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 10

FEL Stopper Design • CVD diamond phase transition at ~1300°C • Graphite sublimation starts from ~1500°C - Sublimation rate increases exponentially with pulse energy (mJ) Graphite sublimation rate 4 4 5 5 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 11

FEL Stopper System for SXR Lines 1. Additional BCS (beam containment system) FEL absorber before stoppers 2. Limit FEL power to known safe levels (safety interlock, details later) 3. Bootstrap - Have a test absorber upstream to demonstrate absorber is undamaged - Gradually increase beam power BCS FEL absorber RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 12

FEL Intensity Interlock Difficult to upgrade gas monitors to safety components Indirect method • Monitor e- energy, e- bunch charge, undulator K-parameter (gap), number of undulators in resonance • Assume optimized FEL yield and determine if stoppers will be safe • Pros: can be a safety interlock • Cons: limit actual FEL  actual FEL yield will be less than the optimized one in most time RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 13

FEL Intensity Interlock Predefined limiting temperature: T limit , ex. 1000°C Get prohibited photon energy range Electron Pre- calculated temperature map ΔT Energy • Based on optimized FEL yield Calculate prohibited Electron undulator gap range Bunch Undulator Charge gaps 1000°C >2/3 undulators in prohibited gap range && Any PPS stopper NOT OUT Yes Trip Off Use bootstrap to gradually increase T limit and update the temperature map RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 14

Test the Integrity of the Stoppers Graphite coated CVD sample irradiated with 100,000 shots (left) and uncoated CVD sample irradiated with 500,000 shots (right) • Single shot (focused) maximum dose is estimated to be 0.6±0.15 eV/atom • Calculated instantaneous max temp. 2500°C • Testing samples for surface morphological changes Graphite coated diamond Uncoated diamond • Seeking for further tests, e.g. high rep-rate tests at XFEL RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 15

FEL Collimators Similar design with stopper • CVD diamond + SiC + W • Same issue: may be damaged by soft x-ray FEL CVD Diamond + SiC • Collimators should not see beams in normal operations + W - Use photo diodes to catch mis-steered beams Scattered Photo radiation Diodes RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 16

FEL Dump: H1.1 TMO Preliminary Normal beam path: • Project requests to separate experiment beam terminator (CVD diamond, not a safety component) with the beam dump • Dump will be out of vacuum • KB with fixed focal length will make beam size large at dump location • BeO (water cooled) is the current choice Mis-steered beam path KB set 2 • Air + solid absorber KB set 1 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 17

Air Attenuation for High Rep-Rate FEL Beams Hard to simulate precisely ( plasma, fluid dynamics, etc. ) 300 K Trying to find a conservative model • Steady status calculation (no flow, air can freely leave the volume) FEL • 409 eV (N 2 edge), 900 W, 1mm beam radius Temp (K) Density (n/n 0 ) 50cm long air, r (mm) r (mm) x5 attenuation z (mm) z (mm) RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 18

Summary Challenge design for high power and high pulse intensity FEL • Single pulse + average power • Use CVD diamond as the main FEL absorber for stoppers and collimators - May be damaged by strong FEL beams around carbon K-edge - FEL intensity interlock for stoppers - Photo diodes for collimators • Preliminary stage for beam dump - Out of vacuum and will not see beams in normal operations - Plan to use BeO - Plus air for mis-steered beams This work is supported by the U.S. DOE, Office of Science, Office of Basic Energy Sciences, under Contract No. DE- AC02-76SF00515 RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017 19