Positrons Using The HRRL

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The purpose of this research is to evaluate the veracity of a positron beam line using the quad triplet method to collect positrons produced when a 10 MeV electron beam impinges on a 1.25 mm thick Tungsten target.

Positron Beam Properties

Tungsten thickness

The optimal Tungsten target thickness to produce positrons using a 10 MeV incident electron beam appears to be 1.25 mm.

PositronProduction-vs-Energy 10MeVelectrons.png

Reference Serkan Thesis

Positron Momentum and Phase space distribution

Assuming a 10 meV electron beam having a gaussian spot size with a [math]\sigma_{xy}[/math]= 3mm.

PositronMom Phase 10MeVelectrons.png

We may want the achromat to have a 10% or less energy spread to measure the above distribution but we will also wan to open the slits to maximize positron current. This may mean accepting an energy spread of 30%.

Reference serkan thesis

GEANT4 simulation of 100 Million , 10 MeV electrons hitting a 0.8 mm thick Tungsten target at an angle of 45 degrees.

HRRL PosPdist 10MeV1mmW 71912.png

GEANT4 predicts about 1 , 2 MeV positron for every 10,000 electrons. To get a single positron in a pulse you need a peak current of at least

[math]\frac{10^5 \times 1.6 \times 10^{-19} Coul }{300 \times 10^{-9}} = 50 [/math]nA
collection and detection efficiency would need to be 100% for this to happen.

Electron Momentum Distributions

According to GEANT4

The electrons which penetrate a 1 mm Tungsten foil have the momentum distribution below

Accelerating 100,000 6 MeV electrons onto a 1 mm thick Tungsten target

HRRL 6MeVePdist 71812.png

If the incident beam is 100 mA then you might get a current of 100*400/100000 = 0.4 mA of 3 MeV electrons.

Accelerating 100,000 10 MeV electrons onto a 1 mm thick Tungsten target

HRRL 10MeVePdist 71812.png

Accelerating 100,000 15 MeV electrons onto a 1 mm thick Tungsten target

HRRL 15MeVePdist 71812.png

Measured HRRL emittance

HRRL beam line

HRRL BeamLine 20101022.png

Fig.1 HRRL beamline for positron generation.