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