Beam Diagnostic Laboratory
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Transcript of Beam Diagnostic Laboratory
2FNAL, May 10, 2006
Introduction for Beam Diagnostics Laboratory
• Main Mission: R&D on charged particle beam diagnostics for e+/e- linear colliders (ILC), other demanding e- accelerators (FELs and novel light source concepts) and proton drivers.
• Hardware: A small e- accelerator for
▪ in-house testing/troubleshooting of diagnostics before installing them in other accelerator beamlines (such as ILCTA at Fermilab or AWA at Argonne),
▪ training students, and
▪ doing fundamental beam physics experiments.
3FNAL, May 10, 2006
Phased Plans for Beam Diagnostics Laboratory
Ultimate Goal: Operate a low-average-current, multi-MeV (20-40 MeV is possible) racetrack-microtron accelerator to drive coherent light sources.
• Phase 1: 6 MeV thermionic rf gun
• Phase 2: 6 MeV photoemission rf gun [Phase 2 beam current will be reduced compared to Phase 1]
• Phase 3: 20 MeV racetrack microtron (but we will go as high as permissible per our radiation shielding capability)
4FNAL, May 10, 2006
Basic Design of the electron beam line
Electron gun BPM BPM
BPM
BPM
FC
PS
PS
PS
PS
Q Q
Q
Q Q
BPM – Beam Profile Monitor
FC – Faraday cap
Q – Magnetostatic quad
70 deg. bend
70 deg. bend
PS – pumping station
S S
S – steering system
BCM
BCM
BCM – beam current monitor
Adjustable slits
FC
5FNAL, May 10, 2006
Expected parameters of electron beam
Beam Energy 6 MeV
Energy Spread 5% RMS
Normalized Emittance < 10 mm mrad
Beam Peak Current 10 A
Beam Average Current 6 A
Charge per Bunch 0.44 nC
Bunch Length (total) 10-20 ps
Bunch Rep. Rate 2.856 GHz
Macro Pulse Rep. Rate 1 Hz
Reminder: The eventual photoemission gun and racetrack microtron will operate with significantly less average beam current, i.e., ≤1 μA.
6FNAL, May 10, 2006
Shielding Estimates for Beam Diagnostics Laboratory
Requirement: External dose rates <1.0 mrem/hr per the administrative control levels set by DOE.
Tools & Methods: NCRP Report No. 51, MARS15 Sim. Pkg.
Assumptions:
• Maximum energy & average current
• Simplified geometry: removed electron gun, magnets, most of the beam pipe, maze entrance(s), supports, structural metal inside concrete walls
• Uniform density of all materials
• Initial and final energy of scattered electrons are equal (in NCRP calculation only)
7FNAL, May 10, 2006
BDL shielding estimates
Pb Beam stop
Model layout illustrating neutron scattering, with a cubic beam stop centered 1.25 m from barrier walls
BeamlineElectron gun Beam stop
8FNAL, May 10, 2006
MARS15 Simulations
Parameters (ref. from NCRP calc.):
• 60 cm concrete walls, 20 cm lead beam stop, origin of impingement placed 1.25 m from wall
Results for 20 MeV, 0.06 μA beam:
• Normal-operating scenario: 0.08 << 1.0 mrem/hr
• Worst-case scenarios:
▪ ~100% of radiation impinging fwd-directed barrier wall (w/ Pb beam stop only): 1.0 mrem/hr
▪ Beam misalignment (w/ 10 cm Pb at 10 cm from beam pipe): 0.82 < 1.0 mrem/hr
BDL shielding estimates
9FNAL, May 10, 2006
BDL shielding estimates
Absorbed Dose Rate (Gy/yr), 20 MeV & 0.06 A
10FNAL, May 10, 2006
BDL shielding estimates
Absorbed Dose Rate (Gy/yr) Power density, neutrons (Gy/s)
Both equate to approx. ~0.02 mrem/hr
~5·10-3 ~5·10-11
11FNAL, May 10, 2006
BDL shielding estimates
Problem: MARS results are about an order of magnitude lower than those found by NCRP calculations. Why?
• Methodology of NCRP guidelines are inherently conservative (this is a good thing)
• NCRP data is inadequate to make a thorough analysis
• MARS input code may be incorrect
Solution:
• Reduce margin of error in calculations (updated NCRP reports, alternate sources?)
• Verify MARS code
12FNAL, May 10, 2006
Floor Plan of the Beam Diagnostic Laboratory
Accelerating hall surrounded by concrete shielding
Assembly room with clean tent and related equipment
Accelerator control room
Office area
Laser room
13FNAL, May 10, 2006
Accelerating Hall
Beamline on two optical tables
Sliding door
“Chicane” type entrance from service areas
Concrete shielding covered with lead
14FNAL, May 10, 2006
Conclusions
• The conceptual design of the Beam Diagnostic Laboratory has been prepared
• The basic requirements for the radiation shielding have been established
• To start the actual engineering design of the concrete/lead vault the shielding specifications need to be checked by independent qualified experts