Simulation studies using Garfield and ANSYS for SπRIT TPC

Yaofeng Zhang for the SπRIT TPC collaboration

Outline:

1. Introduction to

• Garfield program

• field cage of SπRIT TPC

• some simulation results based on the program

2. 3D Electric field calculations for SπRIT TPC using ANSYS

3. Summary and Conclusions

1. Introduction

Widely used program for gas detectors—Garfield:

GARFIELD: • gas detectors simulations

• open source program

• electric field calculation(2D or simple 3D)

• nearly exact boundary method

• Can do 2D/3D simulations using E-field data from other

finite element method programs, such as OPERA-3D, ANSYS

• Can not save a data lib file, need field calculation for each

new running

SπRIT and its simulations:

SπRIT-TPC has been constructed to constrain the symmetry-energy term in the nuclear Equation of State (EOS).

Cathode Plane

Pad Plane

Gating Wires

Strips

Anode Wires

Window Beam

Ground Wires

Strips

Field cage of SπRIT TPC

Avalanche region:

Windows region

Drift region:

Electrons will be pre-amplified and collected in avalanche region, and that is why we can get signal.

Electrons will drift in this region. The strips here will help to achieve a very uniform electric field in this region.

Beam will go through this region and collide with the target.

Electric field & drift simulation in the drift region:

Size range of the field cage :

A large number of strips were added to hold a uniform electric field inside the field cage.

Typical size of strips:

6mm(y)*0.035mm(z)*1m(x)

Drift simulation

Drift simulationEqual potential distribution

Avalanche region:

Electrons will be pre-amplified and collected in avalanche region, and that is why we can get signal.

Electric field & drift simulation in the avalanche region:

-115 V

By=0.5T

anode wires

Ground wires

Gating grid wires

gating grid is open open: Vgg=-115; Voff=0

-80 V-150 V -150 V

gating grid is closed

-80 V-150 V -150 V

By=0.5T

Closed: Vgg=-115; Voff=35

Comparison for transparency results by different methods

for By=0

The transparent ratio was

calculated by:

T = 1−σg+||σp|

open

By=0T

The experimental parameters:

anode wire: 680V

cathode: -6637.15V

By=0

Vgg=-114.84V

Transient condition(from open to closed)

Reason for difference:

The e-field near gating wires varies dramatically so that electrons will not strictly drift following the e-field lines.

GARFIELD with direct simulations

Analytic solution

Experiments

GARFIELD using mc-simulations

By=0T

Windows region Beam will go through this region and collide with the target.

Window region :

The window contains many layers of strips, and has a very complicated geometry.

We need to carefully analyze the e-field in the region nearby.

We have to do 3D electric field calculation and drift simulation!

SπRIT TPC simulations using Garfield only:

• Electric field calculation• Detector simulations

• 2D calculation: OK

• 3D calculation: failed

• Needs more

memory(100G to start)

• Program often

terminated

• Needs a few weeks,

and often finally fails

• Solution: using external FEA program: ANSYS

The pros for TPC simulations by GARFIELD using the e-field data from ANSYS:

• Can do 2D/3D simulations for TPC detectors

• Can generate a binary e-field file, which could be read by GARFIELD very

quickly(a few seconds). So we will save a lot of time for TPC’s repeated

simulation.

2. 3D Electric field calculations for SπRIT TPC using ANSYS

The workflows for the electric field calculations in ANSYS:

build the geometry model

mesh the model

electric field calculation

apply the boundary condition

to refine the grids in the

region near wires and strips

to apply the BC according to

the position of each node

3D meshed model

¼ of the whole body

Region of strips

Region of rear strips

Pad plane & wire regions

Window frame

Top plate

drift area

x

y

z

electric field equalpotential

distribution

avalanche area

Drift simulations for electrons based on 3D electric field data

Window region

Drift regionDrift region

1cmaway

Window region

4. Summary and Conclusions

• Garfield program can be used to do 2D e-field calculation and drift simulations for SπRIT TPC.

• ANSYS program could be employed to do 3D e-field calculation, and 3D drift simulation for SπRIT TPC can also be finished with combination of Garfield.

• The simulation results agree well with the experimental data in the test stage.

• Simulation results could help us to get the optimal parameters for SπRIT TPC

Acknowledge:

Suwat Tangwancharoen, Jon Barney, Justin Estee, Bill Lynch, Betty Tsang.

Funding of DOE.

Funding from BNU.

Thanks!