COMSOL Field Simulation for HV detectors

Himangshu Neog

Priscilla Cushman

Motivation

• Existence of EPot files uptil iZIP detectors but not for HV.

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• The goal is to produce EPot files for HV detectors which can be used in DMC simulations for different detector running conditions like floating phonon channels, non-standard biasing conditions like contact-free bias electrode etc.

Available resources

• iZIP 100mm comsol model https://confluence.slac.stanford.edu/pages/viewpage.action?pageId=182683595
• HV mask design 100mm https://confluence.slac.stanford.edu/pages/viewpage.action?spaceKey=CDMS&title=100mm+HV+SNOLAB
• COMSOL 5.3 License at Minnesota Supercomputing Institute (Each group is limited to 10,000 cpu cores, 8 V100 GPUs, and 40 TB of memory)

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Importing mask design to COMSOL

• HV mask design is in GDS format (2D structures)
• Initially I tried converting GDS to STL/STEP files which are in 3D and can be imported easily into COMSOL. I tried using the github package (https://github.com/dteal/gdsiistl) which gets stuck during triangulation process of the mask structures.
• I found that COMSOL has an extension package (ECAD Import module) which can be used to import GDS files into COMSOL directly (https://doc.comsol.com/5.4/doc/com.comsol.help.ecad/ECADImportModuleUsersGuide.pdf)
• I tried importing the GDS HV Side1 file and it seems to be show progress over an hour and crashes (possibly out of memory for given task).

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Changing Full model to components

Current model tree structure

Mesh settings

Mesh will be made for each domain using virtual Mesh Operation to control meshing size for each component.

(more details once this step have some progress)

HV mask design

1. Simplified geometry: Al disk, consisting of circular disk and arcs to represent individual channel

Things to do

• Importing the GDS mask files to the model
• Whether splitting the full iZIP model into COMSOL components help with memory issue.

izip 100mm model geometry

Questions:

• Was there a reason other than availability of COMSOL license to switch to FEniCS software?
• Who did the mask design part of the iZIP COMSOL model? Is it Noah? I need some input about how this is done, in case the ECAD import feature doesn’t work for the current mask files for HV.

Update 2

Things in this update:

• KLayout modification to HV mask to simplify the structures

QET edited to simple ellipse and propagated to overall mask

Initial QET

Modified simpler QET

Simplified HV mask side1

After editing the GDS file, it is saved as a DXF file for import into COMSOL

Error during Import: Solved

Solution: Split into individual channels and create new file and paste one channel at a time to create DXF files to import.

Error during Import: Solved

Ch A was splitted into inner and outer ring first. Outer ring was successfully imported. Inner ring was further split into right and left half and the right half was copied to make the left half to complete the ring structure and imported successfully.

Note: Left half contains bond pads which might be causing the import issues. The current channel lines going to the bond pads needs to be modified in KLayout so that no lines are intersecting in the modified ChA.

Original mask in Grayscale, Edited mask in Highlighted

Import Details

COMSOL imports DXF files as solid objects, so both mask layer and background is present in the imported geometry. We need to inspect the import and delete background geometry for each channel

Import Details

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Editing errors during Import

Channel B import errors solved

Issue: Inverted QET import structure which cannot be solved with mask layering tricks

Solution: Added two boxes to the two sides of the arc where this issue is present and later deleting those boxes in COMSOL.(I suspect that there is some open boundary somewhere in this region which cause it)

Ch B

Channel A Import Issues

Channel A gives a “No Geometry was imported” error during import.

Solution: Import settings were changed from “Form solids” to “Do not knit” to make a successful import as a curve and then trying convert to solid from the curve.

COMSOL 5.3 Import Summary

• Each detector element is drawn separately in individual COMSOL files and saved as a .mphbin for import.
• Each channel of the simplified HV100mm is imported into COMSOL and saved individually as well as converted to .mphbin for import.
• All channels of the HV100mm mask are imported into one COMSOL mph file and scaled.
• Detector crystal, housing with no dibs/posts and HV100mm mask is imported into a master COMSOL file. This helps to edit individual elements of the detector without consuming much memory as well as making COMSOL more responsive to edits.

HV100mm Mask features to implement for meshing

HV mask has a diameter of 100.0 mm and two 18.0 mm-wide flats on opposite sides.

The faces of the detector are covered with an intricate array of thin-film superconducting electrodes; each one is a small ellipse with major and minor axes of 680 μm and 490 μm, respectively.

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Bias wires (≈ 10 μm wide) run between the ellipses, with a 200 μm-wide gap of open space between TESs and 822 μm-wide gap between two biasing lines.

Desired Specifications:

1 mm cells in the bulk

100 μm cells within 5 mm of either surface

10 μm in the vicinity of the biasing wires

50 μm across the body of the electrodes

Current Status

• Imported HV100mm mask on Side 1. If meshing successful, we will make a mirror of the mask on Side2.
• Defined mask material as Aluminum, Si for crystal and Copper for housing
• Trying to create coarse mesh and will tune this mesh to accommodate the desired specifications.