Intense 3~8 MeV Positron Source Introduction Geometry, e + - PowerPoint PPT Presentation

Intense 3~8 MeV Positron Source • Introduction • Geometry, e + production rate • Energy & emission angle distributions • Heat inside target • Target destruction experimental tests • Electrons after the foil? R&D P. Pérez et A. Rosowsky NIM A Vol 532, pp 523-532 2004

Introduction • Beam energy/intensity: 10 MeV 2 ~ 10 mA • Target geometry: thin foil at grazing incidence (3 0 ) – thermal effects: X-rays + e - leak – probability of first interaction (e + and X-rays) • Designed for e + < 1 MeV : – what happens for e + > 3 MeV ?

Thin target at grazing angle Study energy deposit e- beam: as a function of ∆ x = 0.1 mm incidence angle ∆ y = 1 mm Thickness = D equivalent thickness: D’ = D / sin 3 0 D 3 0 D ’

Track length inside target e - track length inside targets 1 mm 90 0 of 1 mm equivalent thickness 50 µ m 3 0 <L> rms 3 0 0.11 0.11 90 0 0.53 0.48

Geant 3.21 Simulation Electrons at target exit 10 MeV electrons

Kinetic energy at target exit positrons electrons Kinetic energy (GeV) Kinetic energy (GeV)

Positrons at target exit 50 µ m tungsten foil Kinetic energy > 3 Mev Kinetic energy (GeV) Pz ( MeV/c ) z at e+ creation location

Positrons at target exit .. Px ( MeV/c ) θ ( degree ) Kinetic energy > 3 Mev

Positrons at target exit … Kinetic energy > 3 Mev Example of selection: 25 0 < θ < 35 0 -95 0 < ϕ < -85 0 Nb e + at target exit / total e − 3 < K < 8 MeV 1.90 e-6 ϕ ( degree ) 3 < K < 5 MeV 1.52 e-6

Geometrical effect on thin target energy leak e - dE/dx at 3 0 e - dE/dx at 5 0 e - dE/dx at 10 0

Experimental target tests (1) e - soldering test on Tungsten 50 µ m 40 kV / 20 mA on 20 mm 2 not perforated at 15 mA Study hypothesis: 1 k W / cm 2 Tungsten foils 5 cm x 5 cm on a tungsten holder (same expansion)

Electron welding tests Illuminated area = 0.2 cm 2 50 µ m 40 KV Welding beam Power (W) Welding beam Power (W) I MAX (mA) I MAX (mA) 40, 50 kV beam leak I MAX 30 kV no leak Power Thickness (mm) Voltage (KV) Power limit < 3.15 kW

Energy deposit in 1cm 2 target Simulation with GEANT E(e - ) = 10 MeV E(e - ) = 100 MeV Deposited power for 1 mA Deposited power for 1 mA Power (W) 90 0 90 0 4.5 kW/mA 3 0 3 0 1.7 kW/mA 4 kW/mA D’ ( µ m) D’ ( µ m)

Maximum input current Simulation with GEANT E(e - ) = 10 MeV E(e - ) = 100 MeV I MAX for 1 kW deposited Current (mA) I MAX for 1 kW deposited Current (mA)  0.3 mA 0.59 mA 3 0 3 0 0.22 mA 90 0 90 0 D’ ( µ m) D’ ( µ m)

Optimal production rates (forward) Power deposited in 1 cm 2 target = 1 kW X 10 9 E(e - ) = 10 MeV X 10 11 E(e - ) = 100 MeV Ne + (s -1 ) Ne + (s -1 ) e + forward e + forward 3 0 1.5 10 14 3 0 5.5 10 12 0.7 10 14 90 0 90 0 D’ ( µ m) D’ ( µ m)

Experimental target tests (2) 10 MeV Linac: Laser driven e - photo-emission Visible target hole: Macro-pulse 70 µ s 10 Hz ~ 1.3 mm x 0.3 mm Tungsten target 100 µ m   2.0 ± 0.6 kW / cm 2 Center: 96 µ m Edge: 99 µ m Beam incident angle : 45 0 Beam energy deposited = 2 %

Experimental target tests (2) .. Target hole Stopping just before the hole …

Rotating disk target? Target: tungsten 50 µ m Deposited at 3 0 ~ 1 kW = 0.58 mA Rotating disk: e − 10 MeV 10 mA 3 0 100 t/s (?) Ø 25 cm → 0.64 mA / cm 2 = 1.1 kW / cm 2 power ~ 1 / 785 x beam 25 0 < θ < 35 0 Beam spot on target: -95 0 < ϕ < -85 0 1mm x 2mm = 2 mm 2 → 1 / 50 cm 2 Number of e + at target exit 1.19 10 11 s -1 3 < K < 8 MeV 0.95 10 11 s -1 3 < K < 5 MeV

Electrons after the target Mimic the collector with an iron cylinder % of total beam energy deposited inside Iron cylinder L = 20 cm R1-R2 = 10-15 cm edge at 10 cm 37.3 % edge at 20 cm 23.7 % edge at 30 cm 12.36 %