Status of LAr TPC R&D (2)

2014/Dec./23

Neutrino frontier workshop 2014

Ryosuke Sasaki (Iwate U.)

Table of Contents Development of generating electric field in LAr TPC

・ Introduction

- Generating strong electric field is one of key R&D

subjects toward realization of a large scale LAr TPC

・ Generation of strong electric field

- Methods of generating electric field

- HV generator

- Understanding of characterization using circuit

simulation (LTspice)

- Optimization of elementary device models

- Results of circuit simulation

・ Summary

Introduction Principle of LAr TPC

・ TPC is stored inside the cryostat

・ The cryostat is filled with LAr

1. Charged particles flying in LAr TPC

2. Flying particles reacts with LAr in TPC, the

ionization electrons are generated

3. Ionizing electrons under the force of the

electric field, drift to the anode side

4. The anode is divided into a grid-like, obtains

the position information of the generated

ionization electrons in two dimensions (x, y)

5. And obtaining position information of the z-

direction from the time it took to drift to the

anode from the generation position

6. The track of flying particles can be

reproduced in a three-dimensional

e

Anode

Cathode

Drift

x

y

z

e e

Charged

particles

Ionization

electrons

Electric

field

e

filled with LAr

Agendas to generating electric field

Agendas:

1. Generation of strong electric field

(More than 500V/cm)

2. Uniformity of electric field

When electric field is weak, ionization

electrons can be captured by impurities

before reaching the anode

→ More than ve=1.6mm/msec required

→ More than E=500V/cm required

e

Anode

Cathode

e e

e

Weak

electric field

R&D on fundamental technology of

HV using a small LAr detector

(drift length 10cm)

When electric field is non-uniform,

a mismatch between readout and

generated position can happen

e

Anode

Cathode

e e

e

Electric

field

Today's discussion is about this.

1. 2.

Configuration of TPC Field Shaper placed between the cathode - anode for the uniformity of

the electric field in the prototype (drift length 10cm) in development.

Also, it sets out 500V/cm by supplying voltage to electrode (in the

figure).

Anode 0V

AG, FS1 1kV

FS2 1.5kV

FS4 2.5kV

FS3 2kV

FS6 3.5kV

FS5 3kV

FS8 4.5kV

FS7 4kV

FS10 5.5kV

FS9 5kV

Cathode 6kV

readout region 64mm

110mm

110mm

100mm

150mm

x

y

z

Drift length

100mm

Generation of strong electric field

We adopt option 2:

Consider the Cockcroft-Walton(CW) circuit as the device

→ It’s difficult to supply from the outside of the cryostat by breakdown limit of feedthrough in MV supply

When LAr TPC comes to be a large size (drift length several tens m), it's necessary to supply a voltage of several MV for generating electric field of 500V/cm

Two possible methods of generating strong electric field

1. Supplying HV from the outside of the cryostat through the

feedthrough

2. Generating HV within the cryostat (filled in LAr)

P-05

Half cycle

Half cycle

Cockcroft-Walton(CW) circuit

・ This circuit generates a high DC voltage from a low voltage AC

・ Circuit that combines a capacitor and diode

・ Vout = 2Vin×(Number of stages)

・ Since it can be output from each stage, it’s compatible with TPC structure

Feature

AC source

Each capacitor is charged,

the same role as the power supply

2V

Designed a CW circuit Designed a 10-stage CW circuit for supplying HV in the prototype:

Protection circuit for AC source

Discharge protection circuit

Vdc

(AG,FS1)

V1

(FS2)

V2

(FS3)

V3

(FS4)

V4

(FS5)

V5

(FS6)

V6

(FS7)

V7

(FS8)

V8

(FS9)

V9

(FS10) V10

(Cathode)

Vin

Understanding of CW circuit using circuit simulation (LTspice):

We will compare with an actual measurement in next step.

Circuit simulation is carried out by simulating the actual operating

temperature (-186 deg C)

→ Important to use actual properties of each elementary devices at

the low temperature

We measured the low temperature properties(-196 deg C), and then

create and optimize elementary device model in simulation

sample_1 sample_2 sample_3 sample_4 sample_5 Average

Measurement results

(-196 deg C) 33.63 33.40 33.00 33.32 33.00 33.27

Capacitor PHE450 (EVOX RIFA)

Measurement properties of

elementary device (Capacitor)

Measure the low temperature properties of the capacitor by LCR meter

put a capacitor

in the socket

put in a container

LCR meter (HP 4275A)

filled with LN2(-196 deg C)

According to measurement results,

create a elementary device model as the capacitance is 33.27nF

Measurement result at room temperature(20 deg C) is 32.47nF(average)

Forward characteristic

Measure the low temperature properties of the diode by micro-ammeter

Micro-ammeter

(ADVANTEST R8340)

PC

put in a container

filled with LN2(-196 deg C) put a diode in the socket

Reverse characteristic

Create a model of diode to reproduce the measured results → Making a comparison between the created model and measurement results in the next slide

Diode rgp02-20e (VISHAY)

Measurement properties of elementary device (Diode)

-250

-200

-150

-100

-50

0

0 200 400 600 800

reve

rse

curr

ent

[pA

]

Applied voltage [V]

20 deg C -196 deg C

0

5

10

15

20

0 1 2

forw

ard

cu

rren

t [m

A]

Applied voltage [V]

20 deg C -196 deg C

Optimization of device models

-250

-200

-150

-100

-50

0

0 200 400 600 800

reve

rse

curr

ent

[pA

]

Applied voltage [V]

0

-50pA

-100pA

-150pA

-200pA

-250pA 0 800V

Measurement results(-196 deg C) Created model

0

5

10

15

20

0 1 2

forw

ard

cu

rren

t [m

A]

Applied voltage [V]

20mA

0 2V

15mA

10mA

5mA

1V

200V 400V 600V

The successful creation of a model that low-temperature characteristics match → Characterization by circuit simulation

Forward voltage drop

Vf = 2.03 V

Series resistance

Rs = 9.68 Ω

Forward voltage drop

Vf ≃ 1.95 V

Series resistance

Rs = 9.89 Ω

Saturation current

Is = 1pA

When Vin=800V

I = 200pA

Saturation current

Is = 1pA

When Vin=800V

I = 200pA

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0 1 2 3 4 5 6 7 8 9 10

Results of circuit simulation (LTspice)

Input voltage vs output voltage

Number of stage (N)

1-

(Th

e g

ener

ated

vo

ltag

e) /

(Th

e g

ener

ated

vo

ltag

e at

fir

st s

tag

e) [

%]

The ratio of the generated

voltage of each stage to one of first stage

There is -1.6% of discrepancy of voltage at 10th stage compared with first stage

- A large influence of device characteristics in lower stage

- Since the device is increased along with the increase of the number of stages, the

output voltage becomes non-linear

→ We will compare with actual measurement in next step

0

1000

2000

3000

4000

5000

6000

7000

8000

0 45 90 135 180 225 270

N=1

N=2

N=3

N=4

N=5

N=6

N=7

N=8

N=9

N=10

Input voltage (Vin) [V]

Ou

tpu

t v

olt

age [

V]

Vin=180V

Summary

Development of generating electric field in LAr TPC

Generating electric field is one of key R&D subjects toward realization

of a large scale LAr TPC

Agendas:

1. Generation of strong electric field

We are developing CW circuit HV generator

→ Circuit simulation based on actual measurement of the elementary device

properties at the low temp. is developed

→ We will compare with actual measurement

2. Uniformity of electric field

Understanding with simulation software(COMSOL) is in progress

→ Plan to study with cosmic ray measurement