2012
Garfield
Electric Field distribution
The figures represent the simulation of the electric field by using 1/4 hole in THGEM card that is made of FR4 and covered with resistive paste.
The figures represent in order : the THGEM hole model design, electric field simulation of the recent THGEM hole model that has a diameter 0.5mm and 0.9mm rim diameter(we are testing in the lab now), and the last figure represents the THGEM hole simulation after changing the hole's inside shape from the cylindrical shape to cone shape for the top and the bottom part of the hole (so it looks like the hour clock or sand clock shape). The new change in shape will change the E-field strength around and inside the hole to higher values, also it changes the electric field lines distribution outside the hole. The new simulated hole model consists of two cones that have the 0.5 diameter area in contact, each has a an inner diameter of 0.5mm and an outer diameter is 0.8mm, the rim still has 0.9mm diameter without any change.
Garfield simulation for GEM foils
- Single GEM
Garfield simulates a single GEM that has the standard structure
pitch = 0.14 ! Distance between holes, in mm
kapton = 0.050 ! Thickness of the kapton layer, in mm
metal = 0.005 ! Thickness of the meta layers, in mm
r_o = 0.050 ! Hole outer diameter, in mm
r_i = 0.070 ! Hole diameter in the centre, in mm
The simulation results:
Triple GEM:
The results for triple GEM:
ComponentAnsys123::Initialise:
Read properties of 3 materials from file MPLIST.lis.
ComponentAnsys123::Initialise:
Read 31297 elements from file ELIST.lis,
highest node number: 48073,
background elements skipped: 0
ComponentAnsys123::Initialise:
Read 48073 nodes from file NLIST.lis.
ComponentAnsys123::Initialise:
Read 48073 potentials from file field.lis.
MediumMagboltz::SetComposition:
Ar/CO2/CF4 (45/15/40)
MediumMagboltz::EnablePenningTransfer:
Penning transfer parameters for 44 excitation levels set to:
r = 0.55
lambda = 0 cm
Number of materials: 3
The permittivity of material 0 is 1e+10
The permittivity of material 1 is 3.5
The permittivity of material 2 is 1
Sensor::AddElectrode:
Added readout electrode "readout".
All signals are reset.
Sensor::SetTimeWindow:
Resetting all signals.
Avalanche 0 - electrons = 6479, ions = 7113 (started at 0.82 sec)
Avalanche 1 - electrons = 7548, ions = 8340 (started at 1489.31 sec)
Avalanche 2 - electrons = 6801, ions = 7531 (started at 3305.48 sec)
Avalanche 3 - electrons = 7956, ions = 8678 (started at 5048.83 sec)
Avalanche 4 - electrons = 8962, ions = 9860 (started at 6960.89 sec)
Methane percentage calculation if P10 bottle gas totally leaks in the LDS
P10 gas consists if 90/10 Ar/CH4.
A flammability hazard exists when the methane percentage is 5-15 percent (STP) (ref. http://encyclopedia.airliquide.com/Encyclopedia.asp?GasID=41) in the LDS.
The LDS volume in meters is
The volume of the cylinder is =
Assuming the bottle pressure is 2200 psi (149.7 atm), the Methane volume at atmospheric pressure is :
If the Methane is trapped in the LDS room. (assuming the doors are close and there is not any ventilation). The percentage of Methane trapped by the LDS space is .
No more than 20 bottles of P10 may be in the LDS at any given time.
The maximum voltage on a copper THGEM card
The new copper thick GEM cards (t = 0.43 mm , d= 0.3mm, a= 0.8mm) are tested to check the maximum voltage that can be applied between the top and bottom of the card with the least harmful sparking probability. The cards are placed inside the chamber with a vertical distance of 3.4 and 2 mm from the grounded readout plate, then placed again with the same vertical distance but without grounding the readout plate. The results are represented in the following table:
| Card Number | 3.4mm grounded // 3.4mm without ground | ||
| 90/10 ArCO2 | P10 | P5 | |
| 1 | 1500 | 1330 // 1375 | 1200 // 1230 |
| 2 | 1400 | 1140 // 1180 | 1200 // 1180 |
| 3 | 1500 | 1150 // 1183 | 1130 // 1000 |
| 4 | 1300 | 1250 // 1290 | 1120 // 1107 |
| 5 | 1400 | 1500 //1550 | 1350 // 1550 |
| Card Number | 2mm grounded // 2mm without ground | ||
| P10 | P5 | ||
| 1 | 1200 // 1275 | 1121 // 1125 | |
| 2 | 1025 // 1113 | 1100 // 1200 | |
| 3 | 1100 // 1130 | 975 // 1025 | |
| 4 | 1200 // 1130 | 1000 // 1050 | |
| 5 | 1550 // 1650 | 1400 // 1450 | |
What was the max V when the cards were in the detector.
950V, the separation distance was 2mm from the ground (for THGEM2), and 3-4 mm between the cathode and THGEM 1.
V1495_USR_firmware (Warren's thesis)
It is provided by the manufacturer (CAEN) to guide to the V1495 uses.
GEMReadout Firmware Modules
- VHDL Modules
| Module Name | Tasks or description |
| v1495usr.vhd | it contains all I/Os as can be seen on the Pinout |
| tristate_if_rtl.vhd | contains the logic necessary to control the direction of the FPGA data bits found in v1495usr.vhd and the logic to control the direction of the bidirectional I/Os associated with the VME data bus. |
| spare_if_rtl.vhd | contains the logic necessary to control the direction
of the spare bidirectional I/Os included with the Cyclone FPGA. |
| GEMReadout.vhd | This module handles all of the receiving and transmitting functionality to and from the VFAT ICs, the FIFO storage, the PLL timing (if used), control of the LEDs on the V1495 and the ROC interface capabilities via the VME bus. |
| GEMTrigger.vhd | The GEMTrigger module handles the conversion of a single-pulse trigger to a 3-bit (or 8-bit in the case of the Calibration Pulse signal) trigger word which is sent to the T1 line of the VFATs and is in sync with the MCLK. |
| v1495usr_pkg.vhd | contains the offset address for all of the user registers of the v1495. |
| PLLBlock.vhd | replicate the original MCLK signal coming in on G0 and outputting it to the PLLCLK signal. It creates a clock signal that is an exact inverse of this signal (PLLCLK_90), it allows t he user to change the frequency between 15Mhz and 1Ghz. |
| GEMRxEventDataFIFO.vhd/ GEMRxEventSizeFIFO.vhd | contain the specific layout of the DataFIFO and the SizeFIFO and both are extremely similar in layout. |
| GEMRxChannel.vhd | governs the behavior of the data received from the VFATs on their respective DataOut and DataValid channels. |
| GEMTxChannel.vhd | provide debugging methods for the basic functionality of the I/Os on the V1495 |
| GEMReadout_tb.vhd | provides a useful test bench with which to test the basic I/O functionality of the V1495 when one does not have access to VFAT chips for generating and capturing data packets. |
- Verilog Modules
| Module Name | Tasks or description |
| v1495usr_hal.vqm | contains many of the logical functions that serve as a building foundation for the v1495 module, automatically generated using the Synopsys Synplify design entry/synthesis tool which is used to create, synthesize, and optimize a project and then generate a Verilog Quartus Mapping file (.vqm). |
Readout Control libraries
| Function Name | Tasks or description |
| v1495Init | This function establishes a pointer value for the V1495 VME card within the MVME6100 memory map |
| v1495ReadEvent | queries the VFATs and then stores their data into the “V1495ReadoutStatus” struct before getting parsed up and sent to the DAQ. |
| v1495FillData | This function simply takes a pointer to a 32-bit integer and fills it with the data from the structs of type “V1495ReadoutStatus” with 32-bit “chunks. |
| v1495Sprint | This function is a watered-down printout of some of the most useful registers recorded by the V1495 after a query of the VFAT data. |
| v1495StatusPrint | outputs a Number of TotalBytes, a Number of TotalFrames, Number of Sent Bytes, VFAT serial data in hexadecimal, 32-bit segments. |
| v1495HextoBin | changes the hexadecimal values reported in the v1495StatusPrint function to their binary equivalent. |
| v1495test | This function prints off several key registers found in the V1495. |
| v1495reload | called from within v1495firmware and simply reboots the User FPGA by writing a ‘1’ to the USER FPGA Configuration Register. |
| v1495firmware | write the “standard” image or the “backup” image,generate files using Quartus II and should have the extension “.rbf”. |
| v1495release | sets the v1495 pointer to a NULL value |
| v1495DataReady | uses the FIFOLength register to determine which VFAT has the greatest number of entries. |
| v1495CalPulse | takes the parameter passed to it to instruct the V1495 to send that number of CalPulses to the VFATs. |
| v1495Reset | resets the V1495. |
| Other VxWorks Debugging Programs | m <32-bit address>,<Number of Bytes>40
The ‘m’ stands for “modify”, command helps one to write to a given register address. Hit Enter if you don’t want to change a value. Enter a ‘.’ and hit enter to exit the function.d <32-bit address>,<Number of Bytes> ‘d’stands for “dump” – displays the values for the requested the hexadecimal number of bytes. Enter a ‘.’ to exit the function. |
Breakout Board
Breakout board tasks
1- employs several noise cancellation techniques which were utilized in this experiment.
2- Built-in radiation protection of the VFAT, charge-discriminating ICs, namely the Single Event Upset (SEU) triplicated logic and the Scan Chain ability for detecting erroneous digital gates.
Breakout board features
- Status Indicator LEDs
Green indicates enough power is provided to the board(2.25V), the green light becomes dim when there is a voltage drop (<2.25V).Yellow or red indicate an error or a problem in the board, and can y be set by the I2C Expander chip.
- I2C Address and Scan Enable Jumpers
By grounding or jumping the pins of the jumpers, these jumpers contain the top three MSBs of a seven-bit I2C address and are labeled “MOST”, “MID”, and “LEAST”. these addresses are 0x16 to 0x112 by multiples of 16 except for 0x32, since it is the default address of the on-board I2C expanded (located in the center of the board) if it is utilized.
- Soft Reset
The Soft Reset pins to the VFATs are all active low.
- Differential-mode vs. Common-mode Signals
Each mode indicate to radiation electric field current , the current has the same direction (common-mode) or an opposite direction (differential-mode)of the circuit current.Considering a Hertzian dipole, in a detector connected with a ribbon cable, the dominant component of the E-field is dependent on the distance, is dominant in far field area, and is dominant in the near field area to the detector.
"The electric fields due to the common-mode currents, however, actually add due to their being driven in the same direction. It is for this reason, despite often being substantially smaller in magnitude than differentialmode currents, that radiated electric fields from common-mode currents are by far the predominant mechanism for producing radiated electric fields"
- Common-mode Chokes
They are chokes on all of the LVDS signals both entering and exiting the board.These chokes are wire pairs wrapped in opposite directions about the same toroidal ferromagnetic core. Ideally this allows the differential signals to pass through completely unabated but any common-mode signals will find these coils to provide a very high impedance.
- Minimizing Current Loops and Geographical Layout of Components
The break out board is built considering the minimum length for the current loops, not to break the ground or power planes in line with the regular currents needed by the VFATs or other components,the highest frequency components should be as far away from the power supply of the board as possible and as the speed decreases and the precision of the voltage values increases (as in the case of the analog components), the components must be physically placed closer to the power supply.
Project-Specific Noise
- Radiation Environment and Inability to Use Active-Network Noise Cancellation Techniques
Techniques such as passive filtering, shielding, and special design techniques in the layout were employed by default and necessity.
- GEM Trigger Pulse
- Frequency Dependent Noise
- Thermal Noise of the GEM High-voltage Distribution Network
Summary Sorma 2012
Due to the demand on robust, economical, large active area compatible and gamma discriminating detectors, we started our work to build then measure the efficiency of Thick Gaseous Electron Multiplier Preamplifiers (THGEM) as a Neutron Sensitive Detector in the range of 1-14 MeV. The THGEM is constructed using an FR4 substrate that has been coated with a resistive paste or a thin layer of copper. A staggered array of millimeter size holes are machined in the THGEM. The resistive paste is removed from the perimeter of the holes in order to reduce the spark discharge probability. By doping the resistive paste with a neutron sensitive material A determination of the neutron sensitive material type and optimal doping strategy to produces a high detection efficiency.
ACNS 2012
A neutron detector is being constructed that uses Thick Gaseous Electron Multiplier preamplifiers (THGEM) and a thin film of a fissionable material. The THGEM is constructed using an FR4 substrate that has been coated with a resistive paste to reduce disharge events uncorrelated with an incident neutron. A staggered array of millimeter size holes are machined in the THGEM. The detector includes a segmented charge collector which is used to determine the potisiton of the neutron as it enters the detector's acceptance. The detector's efficiency for neutrons having energies between 1 and 14 MeV will be quantified using an accelerator based neutron source.
The Gaol in participating in ACNS school
Being a neutron detector research student, I am always interested in all neutron science developments and applications. A recent goal of my work is developing a fast response neutron detector using THGEM (thick gaseous electron multiplier) preamplifier, and neutron imaging using segmented charge collector technology. Such a combination between two technologies requires a knowledge of the latest neutron detectors' uses and of other instrumentation used in experiments. Participating in your school is a step to gain experience in this field, and offers a golden opportunity to communicate with specialists and scientists who have remarkable achievements in this field.
ISU research symposium
http://www.isu.edu/bulletinboard/student/xcall-03_19_2012_so.html
Due to the demand on robust, economical, large active area and gamma discriminating detectors, we started our work to build then measure the efficiency of Thick Gaseous Electron Multiplier Preamplifier (THGEM) as a Neutron Sensitive Detector in the range of 1-14 MeV. The THGEM is constructed using an FR4 substrate that has been coated with a resistive paste or a thin layer of copper. A staggered array of millimeter size holes are machined in the THGEM. The resistive paste is removed from the perimeter of the holes in order to reduce the spark discharge probability. Basically , the incident particle causes an ionization within the active area, most of the free electrons will drift through the holes by the the electric field causing an electron multiplication. The project THGEM model has a hole diameter of 0.5mm and rim size of 0.2mm, which allows the voltage between the top and bottom side of the Preamplifier to go up to 2kV. We are expecting a gain of 105 electron when a gas chamber filled 90/10% Ar/CO2 gas mixture has four THGEM Preamplifiers, each has a voltage close to 2kV. By doping the resistive paste with a neutron sensitive material A determination of the neutron sensitive material type and optimal doping strategy to produce a high detection efficiency.
THGEM test 2/15/12
Four THGEM Card Model were tested and the pulses below were observed.
The distances in of : Cathode is 11.5mm, THGEM card distance is 4.6mm, readout distance : 6.9mm
Nothing is observed on the readout card!
THGEM#9 test 12/23/12
Don't increase voltage and risk a spark!
Measure the rate using a scaler to determine if ithere is a difference between shutter open/clsoed.
Perform as many measurement as possible before raising voltage.
If the rate changes with the shutter, move the DAQ from the HRRl control room back into the LDS and prepare to use an ADC.
Three of THGEM#9 Cards Model were tested and the pulses below were observed.
The distances in of : Cathode is 3.4mm, THGEM card distance is 2.4mm, readout distance 2mm.
The voltage distribution in Volts as the following:
| V_cathode | THGEM_1T | THGEM_1B | THGEM_2T | THGEM_2B | THGEM_3T | THGEM_3B |
picture | |||
| 3089 | 2950 | 2450 | 500 | 1950 | 1200 | 750 | 995 | 100 | 895 | 
|
Te cathode voltage was increased gradually up to 4089V, it affected the pulse rate, but not its height.
| V_cathode | THGEM_1T | THGEM_1B | THGEM_2T | THGEM_2B | THGEM_3T | THGEM_3B |
picture | |||||
| 4089 | 2950 | 2450 | 500 | 1950 | 1200 | 750 | 995 | 100 | 895 |  |
 |
|
Closing the shutter affected only the pulse rate of the pulse in the 3rd picture.
- Increasing the Voltage of THGEM-1
The voltage of THGEM-1 increased to 300V more compared the to the its voltage in the first table. The results were as the following:
| V_cathode | THGEM_1T | THGEM_1B | THGEM_2T | THGEM_2B | THGEM_3T | THGEM_3B |
picture | |||||
| 4600 | 3250 | 2450 | 800 | 2000 | 1250 | 750 | 885 | 100 | 785 | 60px | 60px | 60px |
3/28/12
- Conical copper THGEM cards are in the machine shop and may be done by next week
- 5 resistive paste cards are in the LDS
- Succeeded to run Garfield example GEM.C (error message: couldn't reach a Garfield text file)
To Do:
- Tomorrow install 4 THGEM cards into test chamber with advisor
- Document Garfield results from GEM.C
U-238 fission cross section in EPS format for Dr. Forest
File:ENDF GEAN4 U238 fxsection.eps
5/11/12 3-THGEM copper card detector testing results
- There was not any signal observed from the detector for cosmic rays or for the gamma source, the maximum voltage applied on each card (top and bottom) was 1.7 kV, and the trasmission voltage was 0.9 kV (between the cards), the distance between the cards was 2.3 mm, the same distance used to separate the cathode from the first THGEM card.
- Strong sparking was observed when the applied voltage on the cards was equal or more than 1.8 kV (as the THGEM cards and the cathode were placed with the same distances mentioned before), the sparking wass not in the holes area but on the other areas around the holes on the surface of the THGEM card. The spark was strong enough to damage a 1kV rated capacitor (for the fifth time by today morning), to damage a 50 ohm terminator (0.5 W), and to cause an offset on the scilloscope channel if it was connected. (it is not recommended to connect the oscilloscope over night with the detector even if the voltage is 1.7 kV!)
- The cathode distance varied from 6.9 to 2.3 mm, but the changing the distance did not forbid creating the sparks in the holes area (for the largest seperation distance), or around the holes (for the smallest one).
- The next step (if you agree) is to reproduce the results of the published paper for using the THGEM copper cards to build an alpha detector, simultaneously I repeat the testing steps using 3 resistive paste card detector in the old gas chamber, then compare the results with the THGEM copper cards' results .
Efficiency of an alpha double-THGEM detector
Two THGEM copper foils (the foil has cone shape holes with inner diameter of 0.5 mm,and outer of 0.66mm, and a pitch distance of 1.25mm.) and a cathode was installed in the gas chamber with a separation of distance of 1mm, U-233 button source was also fixed in holes' shadow area on the cathode.
a signal observed of width of 50ns and 1.5Hz frequency (in average).
A counting experiment is in progress to count the trigout signal from the THGEM detector, then another counting experiment for the U-233 source will be set up using an alpha proportional counter that has an efficiency of 30% (Roy will help in providing the equipment for the second part).
Result: the detector showed very low counting rate.
11/26/12 :Testing three copper THGEM cards (THGEM#9)
Three THGEM copper foils (the foil has cylindrical shape holes with diameter of 0.3 mm, and a pitch distance of 0.86 mm.) and a cathode was installed in the gas chamber with a U-233 button source was also fixed in holes' shadow area on the cathode.
The following table shows the observation on the pulse observed as the difference voltage between top and the bottom of each card is changed.