1 Fulvio TESSAROTTO GDD meeting, CERN, 01/10/2008 Trieste THGEM news First indications from...

Fulvio TESSAROTTO GDD meeting, CERN, 01/10/2008 Trieste THGEM newsGDD meeting, CERN, 01/10/2008 Trieste THGEM news 11

First indications from electrostatic First indications from electrostatic simulation exercisesimulation exercise

Goals of the simulation

Parameters of simulated THGEM

Values of Ez

Simulated trajectories

News about UV light source

work done by Gabriele Giacomini


Electrostatic calculations are Electrostatic calculations are essential to optimize our essential to optimize our

THGEMsTHGEMs

We decided to start from simple simulation exercises with ANSYS (and Garfield) in order to estimate the optimal geometrical and electrical configuration for the THGEM

Critical points:

- Effective CsI Q.E. depends on the electric field at the CsI surface

- The backscattering effect depends on the gas and on the field too

-The collection of photoelectrons in the holes for multiplication is

difficult to measure and critically depends on geometry and fields

The optimization of the THGEM geometry and operating parameters

will need some understanding, which can be achieved only

combining measurements and simulations


Focusing is done by hole dipole field.• Maximum efficiency at Edrift =0 (like in GEM).• Slightly reversed Edrift (50-100V/cm) good photoelectron collection & low sensitivity to MIPS (~5-10%) !

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.60.0

0.5

1.0

1.5

2.0

0

Gain~103

1 Atm. Ar/CH4(95:5)

40

20

80

60

100

e- tr

ansf

er e

ffici

ency

[%]

Edrift [kv/cm]

Re

lativ

e

Reverse drift studies at Weizmann

eRef. PC

Edrift

E

EE=0

MIP

Attention: gas and field dependent!


High field on the PC surface (high effective QE)Also at low THGEM voltages (e.g. in Ne mixtures!)

eRef PC

0.4mm thick0.3mm holes0.7mm pitch

>3kV/cm

Electric field on photocathode surfacecreated by the hole dipole field

VTHGEM=2200V

VTHGEM=1200V

VTHGEM=800V

VTHGEM=2200V

VTHGEM=1200V

VTHGEM=800V

C. Shalem et al. NIM A558 (2006) 468

FIELD AT THE THGEM CsI SURFACE

Attention: varies with hole-pitch & hole-voltage


Recent measurement by ElenaRecent measurement by ElenaSingle THGEM, diam. 0.4 mm, th. 0.4 mm, pitch: 0.8 mm


Photocurrent vs field on CsIPhotocurrent vs field on CsI

not acceptable

acceptable good


The operational The operational ΔΔVV of THGEMs depends of THGEMs depends on gason gas

Simulation performed using tools provided by RD51 Colleagues:

based on “ANSYS” and “GARFIELD”


Geometrical parameters of simulated Geometrical parameters of simulated THGEMTHGEM

DEFAULT VALUES

Thickness: 0.6 mm,

Hole diameter: 0.4 mm,

Pitch 0.8 mm,

Rim: 0.0 mm,

Cu thickness: 0.035 mm,

Drift distance:4.0 mm, (cont. plane)

Induction dist.: 3.0 mm, (cont. plane)

Induction field: 0.0 V/cm

Drift field: 0.0 V/cm

ΔV: 1500 V

Basic cell structure

Simulation performed by Gabriele Giacomini, using tools provided by Matteo Alfonsi and Gabriele Croci, based on ANSYS and GARFIELD


Values of Ez along the “z” axis, for different diameters

diameter scan

0

5000

10000

15000

20000

25000

30000

-0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1

z (cm)

Ez

(V/c

m)

0.1 mm

0.2

0.3

0.4

0.5

0.6

holescan along the

“z” axis (hole axis)

Thickness: 0.6 mm,

Pitch: 0.8 mm,




diameter scan

-10000

-7500

-5000

-2500

0

2500

5000

7500

10000

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

y (cm)

Ez

(V/c

m)

0.1 mm

0.2

0.3

0.4

0.5

0.6

Values of Ez along the “y” axis, for different diameters

0.4 mm diam. hole

Thickness: 0.6 mm,

Pitch: 0.8 mm,



diameter:


Values of Ez along the “y” axis, for different pitches

-8000

-6000

-4000

-2000

0

2000

4000

6000

8000

10000

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

y (cm)

Ez

(V/c

m)

0.6 mm

0.7

0.8

1

1.2

pitch:

hole

Thickness: 0.6 mm,

Diameter: 0.4 mm,




field values depend on: field values depend on:

Thickness: Ez = Ez0 × (th0 / th)

Hole diameter: non trivial (see slides)

Pitch: non trivial (see slides)

Rim: unknown

Drift field: Ez = Ez0 + ED

ΔV: Ez = Ez0 × ΔV / ΔV0

Max. V attained with th. = 0.2 mm ~ 900 V

Max. V attained with th. = 0.4 mm: ~1400 V

Max. V attained with th. = 0.6 mm: ~1700 V


Values of Ez on the CsI surface for various diameters and pitches, compared with active area

0

500

1000

1500

2000

2500

3000

0 0.2 0.4 0.6 0.8 1 1.2 1.4pitch(mm)

Ez

on

TO

P s

urf

ace

0.4

0.5

0.6

0.7

0.8

0.9

1

acti

ve a

rea

diam. = 0.2 mm

0.3

0.4

0.5

0.6

Ez ~ 1/ (pitch)4


Values of Ez on the CsI surface for various pitches and diameters, compared with active area

0

500

1000

1500

2000

2500

3000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

diameter (mm)

Ez

on

TO

P s

urf

ace

0.4

0.5

0.6

0.7

0.8

0.9

1

ac

tiv

e a

rea

pitch = 0.6 mm

0.7

0.8

1

1.2 Ez ~ exp(diam.)


Photoelectron collectionPhotoelectron collection

hole

efficient collection area

dead area

x

y


trajectories for drift = 0 V/cm

x

y scan along the “y” axis

scan along the “x” axis

x

y

Collection efficiency is o.k.

y0- 0.2 0.2 0.5- 0.5

Ez = - 543 V/cm

th. 0.6 mm, diam. 0.4 mm, pitch: 0.8 mm, ΔV = 1500 V


trajectories for drift = -50 V/cm

x

y scan along the “y” axis


x

y

partial collection efficiency

y0- 0.2 0.2 0.5- 0.5

Ez = - 593 V/cm

“full collection radius” = 0.42 mm



trajectories for drift = -500 V/cm

scan along the “y” axis


low collection efficiency

y0- 0.2 0.2 0.5- 0.5

Ez = - 1043 V/cm“full collection radius” = 0.33 mm



trajectories for drift = +500 V/cm



Ez by far too low

y0- 0.2 0.2 0.5- 0.5

Ez = - 43 V/cm x

yy

x



trajectories for drift = +500 V/cm



y0- 0.2 0.2 0.5- 0.5

Ez = + 57 V/cmx

yy

x Loss of e-



Consistency check with other Consistency check with other simulation programssimulation programs

lattice spacing:

50 μm, 30 μm, 20 μm


Consistency check with other Consistency check with other simulation programssimulation programs

diameter scan

-10000

-7500

-5000

-2500

0

2500

5000

7500

10000

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

y (cm)

Ez

(V/c

m)

0.1 mm0.20.30.40.50.6


Main uses of UV lightMain uses of UV light

UVA light (315 nm – 400 nm) is also called photochemical ray because many kinds of adhesives, fluorescence, and other chemistries react to UVA light. For the reason, its potential uses are uncountable, including UV curing/printing/coating, skin therapy, bank note detector, bio-weapon detector, air purification, etc Applications: 1) UV curing systems, UV coating/printing assemblies for PVC, film, glass materials, and etc. 2) Security products such as Bank note detectors, Bio-weapon Detectors, Crime scene inspection, etc. 3) Phototheraphy devices to treat skin diseases including psoriasis, rickets, eczema, jaundice, and atopic dermatitis. 4) Automotive leak detector, Food checking. UVB light (280 nm – 315 nm) is well known that UVB light exposures can be hazardous to human eyes and skin, but also UVB, often called as a dorno ray or a health ray, is assumed to be a beneficial to human health, UVB produces vitamin D in the skin, and prevent skin cancer caused by inefficient UVB exposure.Also in combinations of UVA (or by it self) UVB has become an increasingly popular and effective treatment for psoriasis, vitiligo, eczema, and other skin conditions. Most effective in case of psoriasis is UV light with wavelength of 311 nmApplications: 1) Sterilization systems to purify water, surface, and air 2) Analysis of Minerals 3) EPROM Erasure 4) High Security UV marks UVC light (200 nm – 280 nm) is also called germicidal ray. are the highest energy, most dangerous type of ultraviolet light. With that energy, it destroys DNA & PNA in microorganisms such as bacteria, viruses & mold, Thus, it generates Ozone.Especially 254.7nm is most effective wavelength for disinfectionsApplications: 1) Water/Surface purification system 2) Laboratory testing devices


LED at 255 nmLED at 255 nm

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