Peter Hobson - Brunel University, UK 3 July 2003

VPT 4 Tesla testing

An automated characterisation facility based at Brunel has been commissioned to handle VPT devices.

Samples (about 10%) from the production batch (of 15000 total) are now being tested at Brunel.

Currently processing about 60 tubes per month.

Small improvements over the last 6 months to improve stability of pulsed and DC LED and to minimise the effect of humidity on DC leakage currents.

Developing a new VPT carrier which could allow us to test around 200 per month or more.

Peter Hobson - Brunel University, UK 3 July 2003

4T System at Brunel

Floating unit1.5 kVmaximum

HV Anode

SR PS310

HV Dynode

SR PS310

DVM(General)

Keithley2700

GPIB BusIsolator

NI GBIB-120A

DVM(Floating)

Keithley2000

PCNT4 WorkStn

IEEE 488.2

Non-Floating0.5 kVmaximumDAQ Card

NI 6033E

Step Motor

Maclennan

PCI bus

RS 232

Automated VPT testerat Brunel. Mainly uses IEEE488.2 instruments.ADC is multiplexed and PCI based.

VPT andPre-amp

Anode current

Cathode current

Peter Hobson - Brunel University, UK 3 July 2003

4T System at Brunel •4.0T Superconducting solenoid at Brunel

•Persistent current, no power supply

•“Zero” field region is actually about 0.5 mT

All tubes operated at 1000V on anode and 800 V on dynode.The photocathode is held at 0V.

Peter Hobson - Brunel University, UK 3 July 2003

DC illumination data

Tube 3273

0.00E+00

5.00E-02

1.00E-01

1.50E-01

2.00E-01

2.50E-01

1 11 21 31 41 51 61 71 81 91

Measurement number

Rec

ord

ed v

olt

age

acro

ss s

ensi

ng

res

isto

rs

Anode, illuminated

Cathode, illuminated

Dark currents

~ 180 nA (at 0T)

30 seconds

Peter Hobson - Brunel University, UK 3 July 2003

Pulsed LED data

Tube 3273

-5.00E-02

0.00E+00

5.00E-02

1.00E-01

1.50E-01

2.00E-01

2.50E-01

3.00E-01

1 1001 2001 3001 4001

Measurement number

AD

C v

olt

age

fro

m a

no

de

(pu

lsed

LE

D)

Signal

Pedestal

0T

4T

LED pulsed at 500 Hz

10 seconds

Peter Hobson - Brunel University, UK 3 July 2003

Measurement correlations

Gain ratio (4T/0T) for production tubes

70.0%

90.0%

110.0%

70.0% 90.0% 110.0%

Relative DC gain

Re

lati

ve

pu

lse

d g

ain

•Different illuminated areas•Problem of DC leakage current correction

Encouraging!

DC gain = (Ianode – Idark)/ (Icathode – Idark)

Peter Hobson - Brunel University, UK 3 July 2003

Batch acceptance test at 4T

Arrows indicate angular regions of

end caps

Production tubes

0

20

40

60

80

100

120

140

0.8 0.85 0.9 0.95 1 1.05 1.1 More

Relative 4T/0T pulsed gain (upper bin edge)

Nu

mb

er

in b

in

PassedVPT Axis at 15o to Magnetic Field

Central illumination

Peter Hobson - Brunel University, UK 3 July 2003

VPT Summary

About 10% of all delivered tubes have been measured at 4T, only one working tube failed to pass the acceptance criterion.

Some tubes noisy at 1.8T are also noisy at 4T. All tubes noisy at 4T were found to be noisy at 1.8T (or at 0T).

Almost all tubes at Brunel are measured by the same skilled technician consistency.

Problems with tubes (or system) are found rapidly due to on-line display of measured DC and pulsed data.

All raw measurement data is archived at Brunel, processed (summary) data is archived in a database at RAL.