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

▶
radiation safety designs for lcls ii fel beams
SMART_READER_LITE
LIVE PREVIEW

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

May 01, 2023 346 likes •549 views

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

slide-1
SLIDE 1

Radiation Safety Designs for LCLS-II FEL Beams

Shanjie Xiao, James Liu and Sayed Rokni

SLAC National Accelerator Laboratory Radsynch 2017, Hsinchu, Taiwan

slide-2
SLIDE 2

2

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

slide-3
SLIDE 3

3

XTES and Hutches

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

Location of XTES (X-ray Transport and Experiment System) in LCLS-II

Courtesy of P. Stephens & T. O’Heron

FEE EBD FEE Hallway NEH HUTCH 1

SXR HXR

FEE Rack Room FEE New Entrance

EBD Electron Beam Dump FEE Front End Enclosure NEH Near Experimental Hall

slide-4
SLIDE 4

4

Mirror Configuration in Front End Enclosure

SXU: Flat Mirror 0.4 – 5.0 keV NEH 1.2 SXU: Flat Mirror 0.4-5.0 keV NEH 1.2 SXU: Bendable Mirror 0.25 – 1.3 keV NEH 2.1, NEH 2.2 HXU: Flat Mirror 1 – 7 keV NEH 1.2 HXU: Flat Mirror 2.5 – 25 keV XPP, XCS, MFX, CXI, MEC SXU: Monochromator 0.25 – 1.3 keV NEH 2.1, NEH 2.2 SXU: Bendable Mirror 0.25 – 1.3 keV NEH 2.1 HXU: Flat Mirror 1 - 25 keV NEH 1.2, XPP, XCS, MFX, CXI, MEC SXU: Flat Mirror 0.25 – 2.5 keV NEH 1.1

Courtesy of D. Fritz

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

slide-5
SLIDE 5

5

Experiment Hutches

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

Original LCLS XCS MFX CXI MEC Near Hall N1.1 N1.2 XPP N2.1 N2.2

~ 50 m ~ 70 m

LCLS-II Far Hall

Courtesy of D. Fritz

slide-6
SLIDE 6

6

FEL Parameters

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

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

S2E Simulations by Gabriel Marcus

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 kHz) 2549 (1205) 1635 (795) 1008 (527) 1731 (1136) 617 (469) 6 (10) 300pC (100 kHz) 8801 (5482) 5699 (3844) 3386 (1897) 4567 (2364) 2064 (642)

  • Energy in μJ

() – values as of Oct. 2015

~ 8.8 mJ/pulse ~ 880 W ~ 4.6 mJ/pulse ~ 460 W

slide-7
SLIDE 7

7

FEL Stopper Design

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

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
  • + Tungsten (for bremsstrahlung)

Two considerations

  • Average power & Instantaneous pulse

Beam

WHA Burn thru monitor SiC CVD diamond SiC CVD diamond

slide-8
SLIDE 8

8

FEL Stopper Design

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

1D analytical model

  • Peak temperature after pulse shot
  • Quickly cooled
  • Steady temperature built up gradually

4µm graphite Heat Sink 1st pulse

slide-9
SLIDE 9

9

FEL Stopper Design

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

Good for hard x-rays

  • Temperature rising is moderate

Combined Steady State and Instantaneous Temperature rise (°C)

slide-10
SLIDE 10

10

FEL Stopper Design

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

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)
  • Mainly from single pules instantaneous temperature rise (°C)

Power (W) + mJ 100 1.0 200 2.0 300 3.0 400 4.0 500 5.0 600 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 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

slide-11
SLIDE 11

11

FEL Stopper Design

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

  • CVD diamond phase transition at ~1300°C
  • Graphite sublimation starts from ~1500°C
  • Sublimation rate increases exponentially with pulse energy (mJ)

4 4 5 5

Graphite sublimation rate

slide-12
SLIDE 12

12

FEL Stopper System for SXR Lines

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

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

slide-13
SLIDE 13

13

FEL Intensity Interlock

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

Difficult to upgrade gas monitors to safety components Indirect method

  • Monitor e- energy, e- bunch charge, undulator K-parameter (gap), number
  • f 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
  • ne in most time
slide-14
SLIDE 14

14

FEL Intensity Interlock

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

Get prohibited photon energy range Calculate prohibited undulator gap range >2/3 undulators in prohibited gap range && Any PPS stopper NOT OUT Trip Off Electron Energy Undulator gaps Yes

Use bootstrap to gradually increase Tlimit and update the temperature map

Predefined limiting temperature: Tlimit,

  • ex. 1000°C

1000°C Pre-calculated temperature map ΔT

  • Based on optimized FEL yield

Electron Bunch Charge

slide-15
SLIDE 15

15

Test the Integrity of the Stoppers

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

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
  • Seeking for further tests, e.g. high rep-rate tests at XFEL

Graphite coated diamond Uncoated diamond

slide-16
SLIDE 16

CVD Diamond + SiC + W

16

FEL Collimators

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

Similar design with stopper

  • CVD diamond + SiC + W
  • Same issue: may be damaged by soft x-ray FEL
  • Collimators should not see beams in normal operations
  • Use photo diodes to catch mis-steered beams

Scattered radiation Photo Diodes

slide-17
SLIDE 17

KB set 1 KB set 2

17

FEL Dump: H1.1 TMO Preliminary

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

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

  • Air + solid absorber
slide-18
SLIDE 18

18

Air Attenuation for High Rep-Rate FEL Beams

RadSynch 2017, NSRRC, Hsinchu, April 19-21, 2017

Trying to find a conservative model

  • Steady status calculation (no flow, air can freely leave

the volume)

  • 409 eV (N2 edge), 900 W, 1mm beam radius

300 K FEL

Hard to simulate precisely (plasma, fluid dynamics, etc.)

z (mm) z (mm) r (mm) r (mm) Temp (K) Density (n/n0)

50cm long air, x5 attenuation

slide-19
SLIDE 19

19

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