Radiation Protection at Petawatt Laser-Driven Accelerator Facilities: The ELI Beamlines Case

Figures & data

TABLE I Present and Target Parameters of the Laser Systems at ELI Beamlines

Laser	Peak Energy (J)	Peak Power (TW)	Maximum Repetition Rate (Hz)
L1-Allegra
(Present)	0.03	1.5	10^3
(Target)	0.1	5	10^3
L2-DUHA (target)	2	10^2	50
L3-HAPLS
(Present)	30	333	3.3
(Target)	30	10^3	10
L4-Aton (target)	1.5∙10^3	10^4	1 shot per minute

TABLE II Experimental Station at ELI Beamlines Expected to Produce Ionizing Radiation

Station	Laser	Main Goal	Reference
HHG	L1-Allegra	Ultrashort pulses of tunable coherent extreme ultraviolet soft X-ray radiation	Ref. 18
PXS	L1-Allegra	High-brightness X-ray beams with energies varying from 3 to about 77 keV	Ref. 19
E2 X-Ray source	L3-HAPLS	Ultrafast and bright hard X-ray	Ref. 20
LUIS	L2-DUHA L3-HAPLS L4-Aton	Laser-driven electron beams for the generation of initially spontaneous, and subsequently, coherent photon radiation	Ref. 21
ELBA	L2-DUHA L3-HAPLS L4-Aton	Acceleration of electrons up to energies of tens of gigaelectron-volts	Ref. 22
ALFA	L1-Allegra	Electron beams up to energies of 50 MeV	Ref. 23
TERESA	L3-HAPLS	Provide proton beams of 10 to 15 MeV and electron beams of 100 to 150 MeV	Ref. 24
ELIMAIA	L3-HAPLS L4-Aton	Protons acceleration up to 60 MeV (phase 1) and up to 250 MeV (phase 2)	Ref. 25
P3	L3-HAPLS L4-Aton	High-field laser-plasma interaction high-energy density physics	Ref. 26

TABLE III Maximum Legal Exposure Limits for Radiation Workers in the Czech Republic²⁷ and ELI Beamlines Internal Limits*

	Czech Legislation	ELI Beamlines Internal Limits
Effective dose (external and internal)	20 mSv/year (or 100 mSv per five consecutive years with maximum of 50 mSv/year)	1 mSv/year
Equivalent dose to eye lens	100 mSv/5 consecutive years and maximum 50 mSv/year	15 mSv /year
Equivalent dose to skin	500 mSv/cm^2/year	50 mSv/cm^2/year
Equivalent dose to extremities	500 mSv/year	50 mSv/year

*See Ref. 27 for maximum legal exposure limits for radiation workers in the Czech Republic.

Fig. 1. Monte Carlo estimation of the H*(10) rate in the LUIS experimental hall. An electron beam with a peak energy of 400 MeV with 100 pC per pulse was used as the source term for this study. No additional shielding is installed between LUIS and the control room. Radiation leaks through the floor penetrations toward the control room.

Fig. 2. Monte Carlo estimation of the H*(10) rate in the LUIS experimental hall. An electron beam with a peak energy of 400 MeV with 100 pC per pulse was used as the source term for this study. A concrete shielding wall is shown in the figure. The H*(10) rate reduction in the control room is of two orders of magnitude (compared with Fig. 1).

Fig. 3. Picture of the floor penetration in the LUIS experimental hall (a) without and (b) with concrete blocks. The same set is installed on the control room side of the penetrations, but inverted, thus forcing juggled routing of the cabling. These concrete blocks are a redundant shielding easily added in compliance with the ALARA principle (see Sec. IV).

Fig. 4. Monte Carlo ambient dose equivalent rate outside the exit window of the ALFA interaction chamber assuming an electron beam with 3.5-MeV average energy and 2.5-MeV full-width at half maximum. The beam divergence was set to (a) 12 mrad and (b) 100 mrad.

Fig. 5. HEH fluence in the E3 experimental hall for a solid target experiment driven by the L4-ATON laser, estimated via FLUKA simulations.

Fig. 6. Si-1 MeV n_eq fluence in the E3 experimental hall for a solid target experiment driven by the L4-ATON laser, estimated via FLUKA simulations.

Fig. 7. Operators at work on the laser system. Clean room ISO 7 attire and laser-safety goggles limit movement and visibility, increasing the time needed for each intervention, and consequently, the exposure time.

Fig. 8. FLUKA geometry model of the experimental halls at ELI Beamlines. This corresponds to the basement in Fig. 9.

Fig. 9. Diagram of the Laser building, indicating the locations of the main technological units.

Fig. 10. H*(10) rate simulated in an experimental hall hosting a 500-MeV electron source and 1800 shots per day (vertical view). The corridor and control room are treated as a normal workplace, i.e., personnel will be present for daily 8-h shifts.⁵⁴

Fig. 11. Residual dose rate studies of the first quadrupole of ELIMAIA after 1 year of operation and 1 h of cooldown time. H*(10) rates in its proximity are significant. Extra shielding in this area was deemed necessary during maintenance and upgrade periods (see Fig. 12).

Fig. 12. Residual dose rate studies of the first quadrupole of ELIMAIA after 1 year of operation and 1 h of cooldown time with stainless steel shielding. H*(10) rates are significantly reduced with respect to the scenario without the shielding (see Fig. 11).

Fig. 13. View of an experimental hall. Alarms, panels, and detectors are highlighted.

Fig. 14. ELI Beamlines buildings and surrounding areas. The red dots mark the 10 environmental measuring points.

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