1

G4Beamline Simulated Electron Distribution within the HPRF Cavity

2/15/2012

2Protons Electrons

Beam

CollimatorsCavity

•1000 protons shown (the viewer didn’t like more than that)•Stochastics on•Tracking protons and electrons•Beam originates at vacuum window•4 Detectors (not shown) – 3 in cavity, 1 near origin of beam•6 Detectors (not shown) – 5 in cavity, 1 near origin of beam

2/15/2012

3

Near Vacuum Window

•100,000 protons•p=954.263MeV/c•σx=2.5mm, σy=4.0mm, σp=100keV•Proton X-Y distribution – Top left & right (zoomed in) (mm)•Proton momentum distribution – right (MeV/c vs mm)

2/15/2012

4

Center of the cavity950psi H2, 30MV/m (peak)

X-Y Distribution (mm)

Total momentum (MeV/c) vs r (mm)

r up to 20mm

Radial distribution (mm)

2/15/2012

5

5mm Upstream of the center of the cavity

Total momentum (MeV/c) vs r (mm)

r up to 20mm

Radial distribution (mm)

•More electrons produced upstream•Slightly higher momentum•Roughly same radial RMS at 2cm

2/15/2012

6

5mm Downstream of the center of the cavity

Total momentum (MeV/c) vs r (mm)

r up to 20mm

Radial distribution (mm)

2/15/2012

•Fewer electrons produced downstream•Slightly lower momentum•Roughly same radial RMS at 2cm

7

Fitted Distributions – Electrons contained within r

2/15/2012

•Top left – Fitted radial electron distribution at the center of the cavity (#e- vs mm)•Top right – Fitted normalized radial electron distribution at the center of the cavity (mm)•Right – Fitted normalized radial electron distribution for z= -8, -4, 0, 4, 8mm (0=center, - upstream, + downstream)•Vertical line drawn at r=20mm (radius of downstream collimator)•Horizontal lines at 90 and 95% total e-

Fitted with an exponential of the formy(x)=a+b*exp(c*x)

8

•Left – 5 detector planes hits•Bottom - #e- contained within (r,z)•Strong z dependence can be seen•587/746 e- 8mm upstream of center at r=20mm•231/290 e- 8mm downstream of center at r=20mm

2/15/2012

3D Distribution

x

y

z

r r

zz

Ne

Beam

Beam

92/15/2012

Conclusions

•~80% of electrons fall within the radius of the downstream collimator•Electrons more spread out the further downstream you go•90% of all electrons contained within 35mm radius•95% of all electrons contained within 50mm radius