1. Min Huang g2p/GEp Collaboration Meeting April 18, 2011

2. SNAKE Overview Simulate how particles pass through the target-septa-HRS system, traces trajectories through a series of boxes Directive file: define the whole system  Magnetic field defined in each box  Runge-Khuta raytracing  Analytic: dipole, quadrupole, fringe field, helmholtz …  Field map 3D, two 3D …  End-planes (e-p) with aperture options (trapezoid/ellipse): septa window, Q/D entrance, Q/D exit, … Trajectory file: the trajectory parameters  Total # trajectories initiated  Position, angle, momentum … (min, max) g2p/GEp collaboration meeting - Min Huang

3. y: electron direction x: straight down g2p/GEp collaboration meeting - Min Huang Side View – Vertical Plane

4. y: electron direction z: point to left Bird View – Horizontal Plane g2p/GEp collaboration meeting - Min Huang

5. SNAKE Raytrace Simulate the trajectories from target plane to focal plane (fp), e-ps along the way Record coordinates on any two e-p  x i, θ i, y i, φ i, x f, θ f, y f, φ f, p, l Use MUDIFI to fit the trajectories between two e-p  For optics, reverse function from fp to target  delta(x,m), theta(x,m), phi(x,m), y00(x,m)  x is an array in which x(1->5) are x f, theta f, y f, phi f, and x 0  For MC simulation (eg. G4), forward function from target to different e-p, i.e. different planes of septa, QQDQ  function: {x,t,y,p,l}+ _e_ + {fp, septa, q1en, q1ex, …} (x,m)  x is an array in which x(1->5) are x 0, theta 0, y 0, phi 0, delta The fitting functions are tested to reach the requirements for optics study g2p/GEp collaboration meeting - Min Huang

6. σ=2x10 -4 GeV σ=0.3 mrad σ=0.1 mrad σ=0.2 mm δx=Rev(fwd(x))-x x: delta, theta 0, y 0, phi 0

7. SNAKE Input Update Target box field: Helmholtz coil model  Field map from SANE Large target field  large vertical angle shift  large scattered angle (polar angle)  Vertical shift angle (θ 0 tr ) and scattered angle (θ 0 ) consistent with G4 results from Jixie Q2 coverage shift! Ryan Zielinski g2p/GEp collaboration meeting - Min Huang

8. Q2 Coverage Solution – Target raised up 9cm, 2.5T Scattered angle significantly smaller Q2 coverage improved a lot! Karl Slifer, Ryan Zielinski g2p/GEp collaboration meeting - Min Huang

9. New configurations Different target position + field for different beam energies + in-plane angles Acceptance does not change much Need more study on 12.5 deg. g2p/GEp collaboration meeting - Min Huang E (GeV)θ (deg)Target Field (T) Target Elevation (cm) Acceptance (msr) (SNAKE simulation) 0.562.594.7 162.594.33 2659 36504.81

10. Acceptance Distribution g2p/GEp collaboration meeting - Min Huang Same with 2 GeV 9cm 5T

11. reference g2p/GEp collaboration meeting - Min Huang

12. Summary & Plan SNAKE cross check with G4, consistent and reliable Study the acceptance of different configurations Provide ray traces to fit the trajectories (forward/backward) with MUDIFI Change the configuration to see the effect of raising 9cm on Gep: 20 deg. field Get a set of reverse and forward functions for all the new configurations  Esp. change posi. and ang. of boxes for 12.5 deg. g2p/GEp collaboration meeting - Min Huang

13. backup g2p/GEp collaboration meeting - Min Huang