Thick Target Status

FLASH Collaboration Meeting

2003/07/25

John Belz, Dan Guest

University of Montana

Goals of Thick Target Run:

Confirm proportionality of fluorescence yield to dE/dx by:

• Comparing light yields at different shower depths to GEANT/EGS simulations.

• Comparing the light profile to simulations, at different depths in the shower.

GEANT Lateral Distribution

GEANT Lateral Distribution

GEANT Longitudinal Development

Radiation Lengths

“Gain”

0

1

1

6.7

5

7

62.8

64.5

12

14

21.6

11.0

“Gain” of Electromagnetic Showers:

Proposed Solution

• Steel “pizza box” viewed from 4 sides.

• Three XP3062’s view 20 cm diameter “core” (99.8% at 7 r.l., 97.4% at 14 r.l.)

• Single multianode PMT viewing profile.

Side View

• Recessed on downstream end to reduce light from backscatter.

FLASH Thick Target Setup

• Seven layers of alumina, each layer 2 radiation lengths

• Three PMT’s and one multi anode PMT for cross sectional view

Multianode PMTs

Light Yields: Assumptions • Assume 5 photons/meter (300-400 nm)• View 4 cm path length• Few x107 electrons pulse? (Clive)• GEANT lepton gains

Single Photomultiplier:

• Assume T-461 Entrance pupil (1 cm diameter)• 60 cm from beam (minimize 1/r2 effects)• 9x10-7 p.e./electron ~100 p.e./pulse at 14 r.l.

Light Yield: MPMT

• 1 mm x 1 cm slit• 32 pixels across 20 cm 0.5% of light in outermost slit…• ~ 0.05 p.e./pulse @ 14 r.l. • Options…

• More intense beam?• View < 20 cm profile?• …

To dos…

• Understand mods to thin target “doghouse” necessary to view 20 cm core.

• Can we boost light for lateral measurement? Beam options?

• MPMT readout?

• Vessel manufacture; UM student(s) in collaboration with C.O.T.

• Start talking about beamline insert.