SQUID Performance in a HV Environment

SQUID Performance in a HV Environment

Young Jin Kim, Chen-Young Jin Kim, Chen-Yu LiuYu Liu

May 21, 2008

SQUIDs pretest

Inserted the probe into the He supply dewar

CryoelectronicsmagnetometerQuantum DesignSuperacon

Cast Pb can

1. Superacon SQUID Noise Signal

00

15 /flux noise 5.35 /

2.80 /rmsV Hz

HzV

-0.1 0.0 0.1 0.2-0.6

-0.4

-0.2

0.0

0.2

0.4 13.92ms , 72Hz

Ba

ckg

rou

nd

of S

QU

ID(V

)

Time (S)

66.5ms , 15Hz

400mV

@ 1kHz

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

0.01

log scale

Vrm

s/sq

rt(H

z)

Frequency(Hz)

0 20 40 60 80 1001E-4

1E-3

0.01

0.1

log scale

Vrm

s/sq

rt(H

z)

Frequency(Hz)

White Noise baseline

1/f noise(pink)

microphonics

FFT

Time trace

2. Star Cryoelectronics SQUID

-0.02 0.00 0.02 0.04 0.06-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01

Ba

ckg

rou

nd

of S

QU

ID(V

)

Time (S)

30mV

60Hz

00

20 /flux noise 3.73 /

5.36 /rmsV Hz

HzV

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

Vrm

s/sq

rt(H

z)

Frequency(Hz)

log scale

0 20 40 60 80 1001E-5

1E-4

1E-3

0.01

log scale

Vrm

s/sqr

t(H

z)

Frequency(Hz)

FFT

Time trace

Superacon SQUID test

Pb superconducting foil

HV feedthrough

(ceramic isolation)

Ferromagnetic NiPlated thread

G10Macor (gradiometer)

SQUID

Second layer of Lead shielding

Lead shielding

First layer of Lead shielding

Superconducting Shield: Pb foil(not liquid tight)

HV in(requires RF shield)

Test Sequence

Outer magnetic shield6.6 3.85 0/Hz (1) (2 layers of Pb)

Closed3.85 0/Hz(SF: 2.88 0/Hz)

Add Semitron6.92 0/Hz (SF:5 0/Hz )

Open shield6.92 0/Hz

Brass Electrode(2mm gap):7.75 0/Hz (0.9mm gap):19.2 0/Hz

Faraday Cage

12 V Car batteries to power the PCI-1000

PCI-1000SQUIDcontroller

There is no AC power inside the faraday cage

Serial to Opticalconverter

HV power supplyGlassman e-series(Powered by ac power,Grounded to the FaradayCage)

Scope to monitor the SQUID, direct current in the ground electrode, and Induced emf in the pick-up coil

A lot of Improvements since the last year0

00

flux noise 30 / at previous measurement

31 /flux noise 5.54 / at 1 at current measurement

2.60 /rms

rms

Hz

V HzHz kHz

V

With improved magnetic shields (2 layers of Pb foils + shield penetrations), and RF shields (around HV input, Faraday cage)

• Flux noise of StarCryoelectronics SQUID is 5 times lower than previous one.• No peak at 60Hz.• Microphonics from 400Hz to 800Hz has been highly suppressed.

However, Some vibrations are still present (from He boil-off).

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 8001E-5

1E-4

1E-3

0.01

0.1

0/sqr

t(Hz)

Frequency(Hz)

previous measurement

current measurement

Tests

• AC power vs Battery powered SQUID control

• 1 vs 2 layers of Pb shielding

• Normal State Liquid Helium vs Superfluid Helium• Induced vibrations

• RF Shielding• Faraday cage, electrical isolation from the AC power ground.

• Grounding • HV test results

• Positive vs Negative Polarities

AC power vs. 12 V battery (floating ground)Supracon SQUID (One layer Pb shielding)

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

0.01

Vrm

s/sq

rt(H

z)

Frequency(Hz)

in the log scale used 110V AC power used 12V battery

0 20 40 60 80 1001E-5

1E-4

1E-3

0.01

0.1

Frequency(Hz)

Vrm

s/sq

rt(H

z)

in the log scale used 110V AC power used 12V battery

No peak

1/f noise is smaller with battery power

69Hz 71Hz

1 vs. 2 layers of Pb shields Supracon SQUID

-0.02 0.00 0.02 0.04 0.06 0.08 0.10

0.0

0.1

0.2

0.3

0.415ms, 69Hz

400mV

Bac

kgro

und

of S

QU

ID(V

)

Time(sec)

00

10 /flux noise 3.85 /

2.60 /

at 1

rms

rms

V HzHz

V

kHz

0.0 0.1 0.2 0.3-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

91ms, 11Hz

17ms, 59Hz

130mVB

ack

gro

un

d o

f SQ

UID

(V)

Time(sec)

In one layer of Pb foilIn two layers of Pb foil

00

18 /flux noise 6.6 / at 695

2.72 /rms

rms

V HzHz Hz

V

Pb Superconducting shieldingSupracon SQUID

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

0.01

Vrm

s/sq

rt(H

z)

Frequency(Hz)

in the log scale used 110V AC power, one layer of Pb used 110V AC power, two layers of Pb

0 20 40 60 80 1001E-5

1E-4

1E-3

0.01

0.1

Frequency(Hz)

Vrm

s/sq

rt(H

z)

in the log scale used 110V AC power, one layer of Pb used 110V AC power, two layers of Pb

1 layer

2 layers

1 layer

2 layers

Dramatically reduces microphonics; suppress 1/f noise.

Normal State He vs Superfluid He

-0.02 0.00 0.02 0.04 0.06

-0.25

-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

Ba

ckg

rou

nd

of S

QU

ID(V

)

Time(Sec)

normal state superfluid with pumping superfluid without pumping

00

7.5 /flux noise 2.88 / at 1.4

2.60 /rms

rms

V HzHz kHz

V

In superfluid,No semitron electrode

There is no vibration detected in superfluid (w/ pump off).

00

13 /flux noise 5 / at 1

2.60 /rms

rms

V HzHz kHz

V

-0.02 0.00 0.02 0.04 0.06-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

Ba

ckg

rou

nd

of S

QU

ID(V

)

Time(Sec)

normal state superfluid with pumping superfluid without pumping

With Semitron electrode,

Normal State He vs Superfluid (with semitron)

0 20 40 60 80 1001E-6

1E-5

1E-4

1E-3

0.01

0/sq

rt(H

z)

Frequency(Hz)

normal state Superfluid with pumping Superfluid without pumping

0 500 1000 1500 2000 2500 30001E-6

1E-5

1E-4

1E-3

0.01

0/sq

rt(H

z)

Frequency(Hz)

normal state superfluid with pumping superfluid without pumping

In superfluid He, no microphonics in the low region of frequency (<100Hz), But 1/f noise is increased due to continuous temperature change.

The temperature of pumped SF He is around 1.9K.

pumps' frequency:

Adixen: 6000 6000 0.01666667 100

Varian: 1725 1725 0.01666667 28.75

RPM Hz Hz

RPM Hz Hz

Beat phenomena

Induce vibrations in Normal State He

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

0.01 lock mode lock mode with knocking

Vrm

s/sq

rt(H

z)

Frequency(Hz)

0 20 40 60 80 1001E-5

1E-4

1E-3

0.01

0.1

Vrm

s/sq

rt(H

z)

Frequency(Hz)

lock mode lock mode with knocking

4K liquid helium

Vibration induced from knocking on the cryostat increases noise spectrum below 2kHz.

Peaks stay the same amplitudes:He boiling

Induced vibrations in SF (with semitron)

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

Vrm

s/sq

rt(H

z)

Frequency(Hz)

superfluid superfluid with knocking

Microphonics are excited when knocking on the vacuum chamber.No vibrational peaks associated with He boiling.

Vibrations: With and Without the Semitron Electrode

0 500 1000 1500 2000 2500 30001E-6

1E-5

1E-4

1E-3

0.01

0/sq

rt(H

z)

Frequency(Hz)

without electrode semitron electrode

0 20 40 60 80 1001E-6

1E-5

1E-4

1E-3

0.01

0.1

0/sq

rt(H

z)

Frequency(Hz)

without electrode with semitron electrode

00

18 /flux noise 6.92 / at 1

2.60 /rms

rms

V HzHz kHz

V

3.85 0/Hz (no semitron)

Normal State He

Ground Study (with semitron + open Pb shield)

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

Vrm

s/sq

rt(H

z)

Frequency(Hz)

chamber ground after 1 hour from transfering He building ground floating ground chamber ground after 3hours from transfering He

00

00

18 /flux noise 6.92 / at 1 in chamber ground

2.60 /

48 /flux noise 18.5 / at 1 in building ground

2.60 /

rms

rms

rms

rms

V HzHz kHz

V

V HzHz kHz

V

0 20 40 60 80 1001E-5

1E-4

1E-3

0.01

0.1

Vrm

s/sq

rt(H

z)

Frequency(Hz)

chamber ground after 1 hour from transfering He building ground floating ground chamber ground after 3hours from transfering He

When the ground electrode is connected to the power-line ground (building ground), flux noise is 3 times larger than that when connected to the chamber as the ground (chamber floats).

0 500 1000 1500 2000 2500 30001E-6

1E-5

1E-4

1E-3

0.01

0/sq

rt(H

z)

Frequency(Hz)

no termination with termination BNC jack

RF Shielding Study 1: Termination of unused BNC connectors

These peaks are suppressed by termination of BNC jack

Termination of PZT connector on BNC box can suppress peaks around from 500Hz to 800Hz (High frequency aliasing?). RF noise leaks through the un-terminated BNC connectors.

0 20 40 60 80 1001E-6

1E-5

1E-4

1E-3

0.01

0.1

no termination with termination of PZT

0/sq

rt(H

z)

Frequency(Hz)

RF Shielding Study 2: HV feedthrough

00

00

20.15 /flux noise 7.75 / at 1 in normal

2.60 /

19.66 /flux noise 7.56 / at 1 with upper HV feedthrough wrapped in 1 layer of a Cu tape

2.60 /

18.85 /flux noise

rms

rms

rms

rms

rms

V HzHz kHz

V

V HzHz kHz

V

V

00

00

7.25 / at 1 with upper HV feedthrough wrapped in 2 layers of a Cu tape2.60 /

20.56 /flux noise 7.91 / at 1 with upper HV feedthrough shielded by RF cage

2.60 /

flux no

rms

rms

rms

HzHz kHz

V

V HzHz kHz

V

00

19.0 /ise 7.31 / at 1 on upper HV feedthrough shielded by RF cage wrapped in Cu tape

2.60 /rms

rms

V HzHz kHz

V

-0.04 -0.02 0.00 0.02 0.04

-0.14

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Ba

ckg

rou

nd

of S

QU

ID(V

)

Time(Sec)

with HV feedthrough exposed and sphere electrode with upper HV feedthrough wrapped in one layer of a Cu tape with upper HV feedthrough wrapped in two layers of a Cu tape on upper HV feedthrough shielded by RF cage on upper HV feedthrough shielded by RF cage wrapped in a Cu tape

with Brass HV electrode

HV-SQUID test 1:

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

Vrm

s/sq

rt(H

z)

Frequency(Hz)

At 0kV At 1kV At 2kV At 3kV At 4kV At 5kV At 6kV At 7kV

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

Vrm

s/sq

rt(H

z)

Frequency(Hz)

At 0kV At 7kV

At HV=7kV, we heard discharge peak’s sound and saw SQUID’s jump. At that time the level of He is low (32%), the HV electrode was probably exposed to the He gas.

AC powered PCI-1000, outside the RF cage

The SQUID survived the spark.

HV-SQUID test 2 (negative polarity)

0 200 400 600 8001E-6

1E-5

1E-4

1E-3

0.01

Frequency(Hz)

0/sq

rt(H

z)

negative polarity 0kV 1kV 2kV 3kV 4kV 5kV 6kV 7kV 8kV 9kV 10kV 11kV 12kV 13kV 14kV 15kV 16kV 17kV 18kV 19kV 20kV

0 5 10 15 200.0000065

0.0000070

0.0000075

0.0000080

0.0000085

0.0000090

0.0000095

0/sq

rt(H

z)

Applied high voltage(kV)

At 779Hz

White Noise measured @ 779Hz

Gap size: 2mmCathode: Brass sphere Anode: semitron planar electrode

cathode

anode

HV-SQUID test 3 (positive polarity)

Gap size: 0.9mmAnode: sphere electrodeCathode: semitron electrode

We heard sparks (breakdown) at 78kV/cm and the supracon SQUID is dead.

0 200 400 600 8001E-5

1E-4

1E-3

0.01

0/sq

rt(H

z)

Frequency(Hz)

0kV 1kV 2kV 3kV 4kV 5kV 6kV

positive polarity

Anode (+)

Cathode (ground)

0 20 40 60 801E-6

1E-5

1E-4

1E-3

0.01

0.1

0/sq

rt(H

z)

Frequency(Hz)

18kV

1E-6

1E-5

1E-4

1E-3

0.01

0.1

19kV

1E-6

1E-5

1E-4

1E-3

0.01

0.1

20kV

HV-SQUID test 2 (1/f noise)

0 20 40 60 801E-6

1E-5

1E-4

1E-3

0.01

0.1

0/sq

rt(H

z)

Frequency(Hz)

10kV

1E-6

1E-5

1E-4

1E-3

0.01

0.1

15kV

1E-6

1E-5

1E-4

1E-3

0.01

0.1

16kV

These peaks are suppressed at higher voltage. We can do Gaussian fitting to find width.

Negative polarity (Brass Cathode, Semitron Anode)

HV-SQUID test 3 (positive polarity):

Gap size: 2mmAnode: sphere electrodeCathode: semitron electrode

20 40 60 801E-6

1E-5

1E-4

1E-3

0.01

0.1

0/sq

rt(H

z)

Frequency(Hz)

0kV

1E-6

1E-5

1E-4

1E-3

0.01

0.1

5kV

1E-6

1E-5

1E-4

1E-3

0.01

0.1

10kV

1E-6

1E-5

1E-4

1E-3

0.01

0.1

15kV

0 20 40 60 801E-61E-51E-41E-30.010.1

0/sq

rt(H

z)Frequency(Hz)

16kV

1E-61E-51E-41E-30.010.1

17kV

1E-61E-51E-41E-30.010.1

18kV

1E-61E-51E-41E-30.010.1

19kV

1E-61E-51E-41E-30.010.1

20kV

Positive polarity (Brass Anode, Semitron Cathode)

anode

cathode

Analysis of the noise spectrum

0 5 10 15 20

0.0000

0.0001

0.0002

0.0003

0.0004

0.0005

0/sq

rt(H

z)

Applied High voltage(kV)

At 15.6Hz

0 5 10 15 200.0000

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0/sq

rt(H

z)

Applied High Voltage(kV)

At 1.9Hz

disappearing

0 5 10 15 200.00000

0.00002

0.00004

0.00006

0.00008

0.00010

0.00012

0.00014

0.00016

0/sq

rt(H

z)

Applied High voltage(kV)

At 1.9Hz (positive polarity)

0 5 10 15 20

0.0000

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0.0008

0/sq

rt(H

z)

Applied High Voltage(kV)

At 15.6Hz (positive polarity)

1/f noise(spherical cathode)

1/f noise(planar cathode)

15.6Hz Peak

15.6Hz Peak

HV-SQUID test 4: Star Cryoelectronics SQUID

Comparing noise spectrum of SQUID under High VoltageGap size: 0.9mmAnode: sphere electrode Cathode: semitron electrode

0 20 40 60 801E-5

1E-4

1E-3

0.01

0.1

0/sq

rt(H

z)

Frequency(Hz)

negative polarity

0kV 1kV 2kV 3kV 4kV 5kV 6kV 7kV 8kV 9kV 10kV 11kV

Position of peak is shifted

0 2 4 6 8 10 12

55

56

57

58

59

60

61

position of frequency at peak

Fre

qu

en

cy(H

z)

Applied high voltage(kV)

Structural change under electrical stress?(not seen with the Supracon SQUID.)

Electrostatic force

Charge on the electrode:Q=CV=0.1pF x 10kV = 10-9 Columb

Force between electrodes:F=kQ^2/r^2 = 8.89 x 109 * (10-9)2/(0.001)2 = 0.01N

Equivalent to 1 gram weight, not very large!

Micro discharge or HV noise

-2.0x10-7 0.0 2.0x10-7 4.0x10-7

-0.003

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

TIME(Sec)

gro

un

d e

lect

rod

e(v

)

-0.003

-0.002

-0.001

0.000

0.001

0.002

0.003

Ind

uce

d e

mf(

V)

0.200.150.100.050.00

-0.05-0.10-0.15-0.20

No

ise

sig

nal

of

SQ

UID

(V)

Micro-discharge at 11kV on negative polarity

-2.0x10-7 0.0 2.0x10-7 4.0x10-7

-0.003

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

TIME(Sec)

gro

un

d e

lect

rod

e(v

)

-0.003

-0.002

-0.001

0.000

0.001

0.002

0.003

Ind

uce

d e

mf(

V)

0.20

0.15

0.10

0.05

0.00

-0.05

-0.10

-0.15

-0.20

No

ise

sig

nal

of

SQ

UID

(V)

Micro-discharge at 2kV on negative polarity

There is no HV dependence of these non-random excitations.

HV noise

0.00000 0.00001 0.00002 0.00003-0.004

-0.002

0.000

0.002

0.004-0.004

-0.002

0.000

0.002

0.004

Time(sec)

ind

uce

d e

mf(

V)

gro

un

d e

lect

rod

e(V

)

Periodic pulses in both the direct current monitor and the pick-up coil: 110 kHz (related to the HV supply)

6 59.0 10 , 1.1 10s Hz

SQUID Noise Spectrum

0 200 400 600 8001E-5

1E-4

1E-3

0.01

0.1

0/sq

rt(H

z)

Frequency(Hz)

0kV 7kV 8kV

2 4 6 8 10 12

20

40

60

80

100

120

140

160

Am

plit

ud

e o

f no

ise

sig

na

l of S

QU

ID (

mV

)

Applied Hign Voltage (kV)

Low frequency filtered signal: integrated signal from 2.5MHz ~ 500 MHz(HV related, but could be averaged out).

Squid rms noise vs HV

Breakdown

0.0000000 0.0000008 0.0000016-100

-50

0

50-40

-20

0

20

40

gro

un

d e

lect

rod

e(V

)

Time(sec)

ind

uce

d e

mf(

V)

A breakdown spark occured at - 12kV.

E=121kV/0.9mm = 133kV/cmNegative polarity on the Brass spherical electrode

The instantaneous current of the spark is measured to beAmplitude > 80V/3 = 27 Amps.Time scale < 100 ns.

This killed the Star CryoelectronicsSQUID. (Battery power is floating).

FFT of break down’s spark

5.0x107 1.0x108 1.5x108 2.0x108

0.0

2.0x103

4.0x103

6.0x103

8.0x103

1.0x104

1.2x104

1.4x104

1.6x104

133MHz84MHz

62MHz

49MHz

35MHz FFT of induced emf

Ma

gn

itud

e

Frequency(Hz)

11MHz

5.0x107 1.0x108 1.5x108 2.0x108

-2.0x103

0.0

2.0x103

4.0x103

6.0x103

8.0x103

1.0x104

1.2x104

1.4x104

1.6x104

1.8x104

2.0x104

11MHz

5MHz

78MHz

46MHz

16MHz FFT of ground electrode

Mag

nitu

de

Frequency(Hz)

Summary Sufficient shielding (both magnetic & RF) can be

implemented to operate SQUIDs.

Applying HV does not increase the white noise baseline (up to 20kV, 130kV/cm). However, it does increase the 1/f noise.

HV affects some features on the microphonics. structural deformation or something else? Provide a mean to monitor the HV magtinude

SQUID survival under sparks When the SQUID and the electronics is kept floating,

sparks readily kill SQUID sensors. Tying the SQUID ground to the RF shield might alleviate the SQUID failure rate (need more tests).

Backup slides

Star Cryoelectronics Magnetometer

00

25.7 /5.49 /

4.68 /

with Cu electrode and HV feedthrough shielded

rms

rms

V Hzbaseline Hz

V

00

19.0 /4.52 /

4.20 /

with no electrode and HV feedthrough shielded

rms

rms

V HzBaseline Hz

V

00

27.64 /6.05 /

4.57 /

with no electrode and HV feedthrough Shielded

rms

rms

V Hzbaseline Hz

V

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

0.01

Vrm

s/sqr

t(H

z)

Frequency(Hz)

no Ni and Cu electrode no electrode and Ni no electrode and Ni

Measured at November in 2007

3. Quantum Design SQUID

-0.02 0.00 0.02 0.04 0.06-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

Time (S)

Ba

ckg

rou

nd

of S

QU

ID(V

)

400mV

00

850 /flux noise 229 /

3.70 /rmsV Hz

HzV

0 500 1000 1500 2000 2500 30001E-3

0.002

0.003

0.004

0.005

0.006

Vrm

s/sq

rt(H

z)

Frequency(Hz)

log scale

0 20 40 60 80 100

0.005

0.01

0.015

0.02

0.025

log scale

Vrm

s/sq

rt(H

z)

Frequency(Hz)

FFT

Time trace

AC power vs Battery power (with semitron)

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

Vrm

s/sq

rt(H

z)

Frequency(Hz)

AC power battery AC power after superfluid

0 20 40 60 80 1001E-5

1E-4

1E-3

0.01

Vrm

s/sq

rt(H

z)

Frequency(Hz)

AC power Battery after superfluid

Noise spectrum using AC power was measured with no termination of PZT BNC connector, while rest one was measured with termination. So noise spectrum in the region of from 500Hz to 800Hz on rest one is strongly suppressed. Therefore we can conclude that noise peaks at this region come from pickup signals by BNC connector.

Warming up from SF to Normal State Helium:1/f noise is increased due to temperature change

Summary: Supracon SQUID Spectrum

Comparing noise spectrum of SQUID under different conditions

Flux noise of SQUID measured in clean state has obviously less than others

0 500 1000 1500 2000 2500 30001E-6

1E-5

1E-4

1E-3

0.01

Frequency(Hz)

0/sq

rt(H

z)

clean state with semitron electrode with semitron electrode and HV feedthrough exposed with semitron electrode and HV feedthrough exposed and sphere electrode

0 20 40 60 80 1001E-6

1E-5

1E-4

1E-3

0.01

0.1

0/sq

rt(H

z)

Frequency(Hz)

with semitron electrode, HV feedthrough exposed and sphere electrode with semitron electrode with semitron electrode and HV feedthrough exposed clean state

RF Shielding Study 2: (Brass electrode)

Comparing noise signal of SQUID under different RF shielding

Measurement under upper Ni with RF cage looks worst between them. But difference is not big.

0 500 1000 1500 2000 2500 30001E-6

1E-5

1E-4

1E-3

0.01

0/sq

rt(H

z)

Frequency(Hz)

with HV feedthrough exposed and sphere electrode with upper HV feedthrough wrapped in one layer of a Cu tape with upper HV feedthrough wrapped in two layers of a Cu tape on upper HV feedthrough shielded by RF cage on upper HV feedthrough shielded by RF cage wrapped in a Cu tape

0 20 40 60 80 1001E-6

1E-5

1E-4

1E-3

0.01

0.1

0/sq

rt(H

z)

Frequency(Hz)

with HV feedthrough exposed and sphere electrode with upper HV feedthrough wrapped in one layer of a Cu tape with upper HV feedthrough wrapped in two layers of a Cu tape on upper HV feedthrough shielded by RF cage n upper HV feedthrough shielded by RF cage wrapped in a Cu tape

SQUID Noise Spectrum (positive polarity)

0 20 40 60 801E-6

1E-5

1E-4

1E-3

0.01

0.1

positive polarity

0/sq

rt(H

z)

Frequency(Hz)

0kV 5kV 10kV 15kV 16kV 17kV 18kV 19kV 20kV

HV-SQUID test 2

0 200 400 600 8001E-61E-51E-41E-30.01

0/sq

rt(H

z)

Frequency(Hz)

no turn on HV

1E-61E-51E-41E-30.01

0kV

1E-61E-51E-41E-30.01

1kV

1E-61E-51E-41E-30.01

2kV

1E-61E-51E-41E-30.01

3kV

1E-61E-51E-41E-30.01

4kV

1E-61E-51E-41E-30.01

5kV

0 200 400 600 800

1E-6

1E-5

1E-4

1E-3

0.01

Frequency(Hz)

6kV

1E-6

1E-5

1E-4

1E-3

0.01

0/sq

rt(H

z)

7kV

1E-6

1E-5

1E-4

1E-3

0.01

8kV

1E-6

1E-5

1E-4

1E-3

0.01

9kV

1E-6

1E-5

1E-4

1E-3

0.01

10kV

Gap size: 2mmCathode: sphere electrodeAnode: semitron electrode

We didn’t see any micro-discharge.

cathode

anode

Negative polarity

0 200 400 600 8001E-61E-51E-41E-30.01

0/sq

rt(H

z)

Frequency(Hz)

15kV

1E-61E-51E-41E-30.01

16kV

1E-61E-51E-41E-30.01

17kV

1E-61E-51E-41E-30.01

18kV

1E-61E-51E-41E-30.01

19kV

1E-61E-51E-41E-30.01

20kV

HV-SQUID test 2

0 200 400 600 8001E-6

1E-5

1E-4

1E-3

0.01

0/sq

rt(H

z)

Frequency(Hz)

11kV

1E-6

1E-5

1E-4

1E-3

0.01

12kV

1E-6

1E-5

1E-4

1E-3

0.01

13kV

1E-6

1E-5

1E-4

1E-3

0.01

14kV

1E-6

1E-5

1E-4

1E-3

0.01

15kV

1/f noise starts increasing?

In the region of E>75kV/cm, 1/f noise keeps increasing.

Negative polarity

Normal State He vs Superfluid He

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

0.01

Vrm

s/sq

rt(H

z)

Frequency(Hz)

At 4K without pumping in superfluid without pumping in superfluid with pumping

0 20 40 60 80 1001E-5

1E-4

1E-3

0.01

Vrm

s/sq

rt(H

z)

Frequency(Hz)

At 4K without pumping in superfluid without pumping in superfluid with pumping

4K liquid He, no pump

Superfluid w/ pump on

Superfluid, no pump

RF shielding Study 2: HV feedthrough

-0.02 0.00 0.02 0.04 0.06-0.040

-0.035

-0.030

-0.025

-0.020

-0.015

-0.010

-0.005

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

Ba

ckg

rou

nd

of

SQ

UID

(V)

Time(Sec)

with Ni after 3 hours from transfering He with upper Ni wrapped in a Cu tape on upper Ni with RF cage on upper Ni with RF cage wrapped in Cu tape

00

00

0

18 /flux noise 6.92 / at 1 in normal

2.60 /

17 /flux noise 6.54 / at 1 with upper HV feedthrough wrapped in a Cu tape

2.60 /

18 /flux noise 6.92

2.60 /

rms

rms

rms

rms

rms

rms

V HzHz kHz

V

V HzHz kHz

V

V Hz

V

0

00

/ at 1 with upper HV feedthrough shielded by RF cage

18 /flux noise 6.92 / at 1 on upper HV feedthrough shielded by RF cage wrapped in Cu tape

2.60 /rms

rms

Hz kHz

V HzHz kHz

V

semitron open Pb shield

Studies on RF shielding of the HV line (Semitron + open Pb shield)

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

Vrm

s/sq

rt(H

z)

Frequency(Hz)

with Ni after 3 hours from transfering He with upper Ni wrapped in a Cu tape on upper Ni with RF cage on upper Ni with RF cage wrapped in Cu tape

0 20 40 60 80 1001E-5

1E-4

1E-3

0.01

0.1

Vrm

s/sq

rt(H

z)

Frequency(Hz)

with Ni after 3 hours from transfering He with upper Ni wrapped in a Cu tape on upper Ni with RF cage on upper Ni with RF cage wrapped in Cu tape

Measurement under upper Ni with RF cage looks worst between them. But difference is not big.

AC power vs. 12 V batterySupracon SQUID (One layer Pb shielding)

-0.02 0.00 0.02 0.04 0.06 0.08 0.10

0.0

0.1

0.2

0.3

0.415ms, 69Hz

400mV

Ba

ckg

rou

nd

of S

QU

ID(V

)

Time(sec)

00

18 /flux noise 6.6 / at 695

2.72 /rms

rms

V HzHz Hz

V

-0.02 0.00 0.02 0.04 0.06 0.08 0.10-0.3

-0.2

-0.1

0.0

0.1

0.2

14ms, 71Hz

350mV

Ba

ckg

rou

nd

of S

QU

ID(V

)

Time(sec)

used battery for running PCI-1000

With feedback on,

120Vac power PCI-1000 12V battery power PCI-1000

SQUID with and without Faraday cage

0 200 400 600 8001E-6

1E-5

1E-4

1E-3

0.01

0.1

0/sq

rt(H

z)

Frequency(Hz)

with Faraday cage without faraday cage

00

00

50 /flux noise 19.2 / at 1 with 0.09 of gap size and Faraday cage

2.60 /

20.15 /flux noise 7.75 / at 1 with 0.2 of gap size and without Faraday cage

2.60 /

rms

rms

rms

rms

V HzHz kHz mm

V

V HzHz kHz mm

V

The baseline of SQUID with Faraday cage is larger than that without Faraday cage. But we guess that this comes from the gap size of electrodes. With Faraday cage it’s hard to see SQUID jumped. So it is obvious that we can reduce RF interference by Faraday cage.

Tune vs Lock mode

-0.02 0.00 0.02 0.04 0.06 0.08 0.10

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

14ms, 71Hz

3V

Ba

ckg

rou

nd

of S

QU

ID(V

)

Time(sec)

In the tune mode (feedback circuit is off)

Amplitude of noise signal in the tune mode is 10 times larger than that in the lock mode

00

121 /flux noise 8.55 / at 695

14.16 /rms

rms

V HzHz Hz

V

Supracon SQUID (one layer Pb shielding)

Tune vs Lock mode

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

0.01

0.1

Vrm

s/sq

rt(H

z)

Frequency(Hz)

tune mode

0 20 40 60 80 1001E-5

1E-4

1E-3

0.01

0.1

1

Vrm

s/sq

rt(H

z)

Frequency(Hz)

tune mode

Noise Spectrum with feedback off

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

0.01

Vrm

s/sq

rt(H

z)

Frequency(Hz)

in the log scale used 110V AC power used 12V battery

0 20 40 60 80 1001E-5

1E-4

1E-3

0.01

0.1

Frequency(Hz)

Vrm

s/sq

rt(H

z)

in the log scale used 110V AC power used 12V battery

Noise Spectrum with feedback on

Supracon SQUID (one layer Pb shielding)

5 10 15 20 25 30 35

0.00000

0.00005

0.00010

0.00015

0.00020

0.00025

0.00030

0.00035

0/sq

rt(H

z)

Frequency(Hz)

Gaussian fitparameter Value Error----------------------------------------y0 0.00002 3.5997E-6xc 16.44983 0.05842w 4.19372 0.13665A 0.0016 0.00006----------------------------------------

At 0kV Gaussian fit

Gaussian fitting of the 15.6Hz peak

Example of Gaussian fit

2

2

( )2

0/ 2

cx x

wAy y e

w

10 15 20 25

0.00000

0.00005

0.00010

0.00015

0.00020

0.00025

0.00030

0.00035

0.00040

0.00045

0.00050

0.00055

0/sqr

t(Hz)

Frequency(Hz)

0kV 1kV 2kV 3kV 4kV 5kV 6kV 7kV 8kV 9kV 10kV 11kV 12kV 13kV 14kV 15kV 17kV 18kV 19kV 20kV

0 5 10 15 20

2.0

2.5

3.0

3.5

4.0

4.5

0/sq

rt(H

z)

Applied High Voltage(kV)

Supracon SQUID test (open Pb shield)

00

18 /flux noise 6.92 / at 1

2.60 /rms

rms

V HzHz kHz

V

In the lock mode

The flux noise is same as a previous value.

The system needs a few hours to settle.

In the beginning of measurement, noise signal keeps going down very fast and is easy to jump. But after 3hours system is much more stable, but noise signal still goes down slowly.

-0.02 0.00 0.02 0.04 0.06-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

48ms, 21Hz

42ms, 24Hz

22ms, 45HzBa

ckg

rou

nd

of S

QU

ID(V

)

Time(Sec)

with HV feedthrough exposed after 1 hours from transfering He with HV feedthrouhg shielded with HV feedthrough exposed after 3 hours from transfering He

SQUID Noise Spectrum (open Pb shield)

At the low region of frequency, noise spectrum after 1 hours from transfering He is very noisy. Due to boiling of He?

0 20 40 60 80 1001E-5

1E-4

1E-3

0.01

0.1

Vrm

s/sq

rt(H

z)

Frequency(Hz)

with HV feedthrough exposed after 1 hours from transfering He with HV feedthrough shielded with HV feedthrough exposed after 3 hours from transfering He

0 100 200 300 4001E-5

1E-4

1E-3

0.01

0.1

Vrm

s/sq

rt(H

z)

Frequency(Hz)

with HV feedthrough exposed after 1 hours from transfering He with HV feedthrough shielded with HV feedthrough exposed after 3 hours from transfering He

0 500 1000 1500 2000 2500 30001E-5

1E-4

1E-3

Vrm

s/sq

rt(H

z)

Frequency(Hz)

with HV feedthrough exposed after 1 hours from transfering He with HV feedthrough shielded with HV feedthrough exposed after 3 hours from transfering He