Simulations of various aspects of the PPS

Various members of the collaboration, to be enumerated

later

We Need to Know?• Properties of the discharge

– Voltage required– Current delivered– Development time– Decay time– Recovery time (deadtime)

• Properties of the device– Electric field distribution– Electric field uniformity in drift regions– Electric field intensity in discharge regions

• How to trigger the discharge– Minimum Number of electrons– Minimum Energy of the electrons

• How to produce the electrons– Energy loss from ions traversing the device– “Converters”

• Properties of the output pulses– Risetime – Decay time– Crosstalk

What to simulate

• Arriving particle spectrum• Particle energy loss, multiple scattering• Gas ionization• Electric fields• Output electrical signal• Plasma discharge dynamics

Particle scattering

• Principal tool is GEANT4– Widely used in nuclear physics– Gives event-by-event output for later analysis– Open source, easily available

• Example: 106Ru (R. Varner)

106Ru example

106Ru Example

Electric FieldsY. Silver

• COMSOL has been the most used tool• Examples:

Cell capacitance estimates

Electric Field MapDrift Region

Dielectric10mm k=10

Discharge(15 x 75mm) (1mm deep)

80 fFcapacitance

Sense(10 x 25mm)

Applied HV(20 x 25mm)

Resistive (0.0051 siemens/meter)

Modeling and simulation• Initial geometry: two

orthogonal copper strips separated by a 400 µm gas gap. One strip at ground, one at 1V.

• Initial strip dimensions: 1 cm X 1 mm X 25 µm. Initial two-strip capacitance: 0.1845 pF

• Incrementally changed dimensions

• Right: Electric potential plot of initial strip geometry

Capacitance v gas gap

Right: Plot of capacitance vs. gas gap, keeping strip geometry constantChanged gas gap from 400 microns to 2000 microns, in 100 micron incrementsData fitted with 4th degree polynomial

Capacitance vs Electrode WidthRight: capacitance plotted vs width of terminal electrodeWidth changed from 1 mm to 10 mm, in 1 mm increments

HV sensitivity of cells

Output electrical Signal

• Develop equivalent circuit• Evaluate the circuit using SPICE to simulate the

output pulse properties– Amplitude– Width– Ringing

Cell Schematic

Full Schematic

Plasma discharge• Many approaches considered

– None found to be practical or sufficient• Possibilities

– Fully dynamical (Y. Silver)• Boltzmann equation• Maxwell equation• Atomic physics cross-sections• Somewhat developed for Plasma Display Panels• Expensive to run

– Drift chamber models (C. Ferretti)• CERN GARFIELD• Electron production• Gas amplification

– Geiger counter models• Semi-empirical

– Require calibration• “Rules of thumb”