Revision as of 23:18, 6 May 2013

In G4beamline manual "The electromagnetic processes of these physics lists are advertised to be valid above a few hundred electron Volts; Geant4 has a set of low energy electromagnetic processes, indicated by a suffix “_EMX” in the physics list name."

2 MeV Positrons

Measured Electron energy distribution at 10 MeV on 1.mm target

Simulation steps

1.) GEANT4 Simulated Beam energy distribution

2.) GEANT4 Simulated Positrons emitted from 1.x mm thick target

3.) Now use above Positron distribution as the particle source for G4beamline

Positrons hitting Tungsten Converter target

4.) Use GEANT4 to determine 511s from the positrons distribution impinging converter target

Oct 16th 2012 BenchMark

stages:

1. Program to input emittance, output beamsize, beam, divergence and beam energy.

2. e- on W, outcome e+. Incident electron distribution on T1. with general particle source with step 1 histogram. check graph x, y, z theta, En_dis out_put is the input. (directory for each).

3. insert T1 and generate positron distribution.

4. Acceleractor code to transport positron along the beamline. Out put positron theta, beamsize (x,y), energy distribution, out puts transported positron.

5. Geant4 takes step 4 output generates gamma (and other e+,e-) and look at those goes to detectors. beamline, plus shielding, and detectors.

Simulations

Partical Data Ground ID: PDGid=11 is electron. PDGid=-11 is positron. PDGid=22 is photon.

Parameters

Dipole vacuum chamber width is [math] 17 \pm 0.5 [/math] mm

The cavity exit diameter is about 7.3 mm.

Energy Spread Two Skewed Gaussian Fit

Energy spread fitted with two skewed Gaussian.

Beam Distributions Beyond RMS: Media:Beam_Distributions_Beyond_RMS.pdf

Amplitude = 2.13894, mean = 12.07181, sigma_L = 4.46986, sigma_R = 1.20046

Sigma = 2.83516, Skewness = -0.57658

Amplitude2 = 10.88318, mean2 = 12.32332, sigma_L2 = 0.69709, sigma_R2 = 0.45170

Sigma2 = 0.57440, Skewness2 = -0.21360

Electron Distribution Upstream and Positron Distribution Downstream of Target1

simulation: Electron Distribution Upstream and Positron Distribution Downstream of Target1

3067274 Electrons fired.

T1_s=943.5

FDT1_s=$T1_s-26.52

BDT1_s=$T1_s+26.52

Thickness of T1 is 1.016 mm, radius of T1 is 15.875 mm (0.625 inches).

Step 1: Generating positron from electron beam

Detector is after T1 to saple positron distribution. 13,799,743,800 electrons shot at the tungsten target to generate positrons.

step 1: ratio

DDNT1 = Detector DowN from T1

DQ4 = Detector at entrance Quad 4 located right after T1

DD1 = Detector at entrance of the first Dipole.

e-(DUPT1) = 13,799,743,800

e+(DDNT1) = [math]1.095179 \times 10^7[/math]

e+(DQ4) = [math]62780[/math]

e+(DQ4) = [math]6742[/math]

e-(DUPT1)/e+(DDNT1) = 1260

e-(DUPT1)/e+(DQ4) = 219811 = [math]2.2 \times 10^5[/math]

e-(DUPT1)/e+(DD1) = 2046832 = [math]2.0 \times 10^6[/math]

e+(DDNT1)/e+(DQ4) = 174

e+(DDNT1)/e+(DD1) = 1624

e+(DQ4)/e+(DD1) = 9.3

Step 1: Generated Beam on DDNT1

Detector down T1:

Positrons on detector right before Q4.

X profile

Y profile (why is the distribution clipped on the left side in the figure)

X divergence profile

Y divergence profile

Momentum distribution

Sharp drop issue

The Y-position distribution of the beam shown in Figure ~\ref{sim-DDNT1-y-vs-x} has a sharp drop in the region between -25.8 mm and -27.2 mm that corresponds to the boundary of the target T1. Figure ~\ref{sim-DDNT1-T1-geo} shows the geometry of the target T1 and the sensitive detector DDNT1. If the target size was increased, it would eventually intersected the detector DDNT1 at a distance of 25.8 mm from the beam center. A 1.4 mm wide stripe of low counts is visible on DDNT1 that is a result of the target's thickness of 1.016 mm and the 45 degree angle of intersection. ([math]1.016 \sqrt{2}=1.44[/math]). The edge of the target does not produce many positrons compared to the face of the target, and as a result you see the stripe.

As shown in figures ~\ref{sim-DDNT1-theta-vs-y} and ~\ref{sim-DDNT1-theta-vs-y-zoom} (zoomed figure) the positron distribution decrease occures at [math]\theta = 45^o[/math]. Positrons are emitted from both the downstream and upstream side of the target. As shown in the figure, positrons from the downstream side of the target intersect the detector at angles below 45 degrees while positrons from the upstream side of the target begin to hit the detector at angles beyond 45 degrees. The 1.4 mm gap represents the transition of positrons between these two extremes.

Cut off line is around 26.5 mm corresponding to the large angle.

DDNT1 is at 26.52 mm (53.04 mm)downstream of T1.

T1 radius is 25.4 mm (d=50.8 mm)

DDNT1 radius is 31.75 mm (d=63.5 mm).

Step 1: Generated Beam on DQ4

Positrons on detector right before Q4.

X profile

Y profile

X divergence profile

Y divergence profile

Momentum distribution

Step 1: Generated Beam on DD1

Positrons on detector right before D1 - first dipole.

X profile

Y profile

X divergence profile

Y divergence profile

Momentum distribution

Step 2: generate positron

The positrons after T1 is detected on a virtual detector. The positrons beam size, divergence and momentum distributions are extracted and created new positron beam.

Generate positron beam from the detector after T1 and transport it to right before D1.

221032400*16=3,536,518,400 positrons generated.