ELECTRO-OPTICS

Performance Characteristics ofDetectors Operated

inHarsh Environments

The HEMS 2005 ConferencePoster Paper

Raymond F. Cochran, Bruce N. Laprade,Richard Prunier, Lenny Erickson

and William DunnBURLE Electro-Optics Inc

ELECTRO-OPTICSIntroduction

• Mass Spectrometers are a valuable tool foruse in demanding applications such as drug discovery,semiconductor manufacturing and food processing.The unique capability of a mass spectrometer to identifyminute amounts of unknown materials sets this instrumentapart from almost all others.

• The typical Mass Spectrometer has three key components:The ionization source, the mass filter and the detector.

ELECTRO-OPTICSDiscussion

• Homeland security requirements are nowdriving the development of field portableinstruments that can provide laboratory gradeanalysis.

• In order to reduce the size, weight and powerconsumption of a portable massspectrometer, it is often necessary to deviatefrom the normal operating environment insidethe vacuum system.

ELECTRO-OPTICSDiscussion

• Operation of High Gain Ion Detectors hastraditionally required a vacuum of 10-6 Torr orbetter

• Vacuum systems capable of this performanceare large, heavy, costly and consume largeamounts of power

• Use of High Gain, Low Noise Detectors thatOperate at milli-Torr pressures will permit use ofsimple, low cost and much lighter weight vacuumsystems

ELECTRO-OPTICSDiscussion

• The ideal field portable mass spectrometer must:

• Be small and light weight

• Operate at milli-Torr pressures or higher

• Produce high gain and maintain low noisewhile operating at elevated pressures

• Exhibit long detector lifetime at elevatedpressure

• Must withstand periodic venting to atmosphere

• Should tolerate storage at atmospheric pressure

ELECTRO-OPTICS

• The objective of this project was tocharacterize the performance of varioushigh gain electron multipliers operating atelevated pressures

Objective

ELECTRO-OPTICS

There are 4 main types of Electron Multipliers:

- Single Channel Electron Multipliers (CEMs)(Channeltron®)

-Spiraltron™ CEM Technology

- Microchannel Plate based Detectors

-Discrete Dynode Multipliers

High Gain Detectors

Various Types of Electron Multipliers

Single Channel Electron Multipliers

Magnum® 6-Channel Multipliersusing Spiraltron™ Technology

Discrete Dynode

Microchannel Plates

Microchannel Plate Detectors

Vacuum Requirements• Typical MALDI Time-of-Flight Mass Spectrometers require an ion

flight path length of 1 to 2 meters.• Modern quadrupole based instruments typically operate at

vacuum pressures in the high 10-6 Torr range because ions needto travel 25 cm. or more before they reach the detector withoutcolliding with residual gas molecules.

• If it were possible to shrink the flight path length requirement toless than 5 cm (approx... 2”) then it should be possible to operatea system in the milli-Torr range.

• Milli-Torr vacuum levels can be achieved with simple low costvacuum pumps.

• Multiplier performance outside of the normal 10-6 Torr operatingrange has not been well characterized.

Experimental Apparatus

• BOC Edwards turbo pumped vacuum chamber

• BOC Edwards Turbo pressure monitoring systemwas used as Chamber Pressure Monitor.

• Chamber pressure was modulated using aGranville Philips precision leak valve. Chamberwas backfilled with lab air.

• Dark current measurements made with KeithleyInstruments, Model 600B electrometer.

Detectorsmounted here

Leak Valve

Pressure Sensor

e-gun Ion Source

MAGNUM 5900

5-Micron Pore ChevronMCP Detector

The Effects of Poor Operating Pressure onMultiplier Performance and Lifetime

ELECTRO-OPTICSHistorical DataNoise vs. Operating Pressure For Various Electron Multipliers

0.1

1

10

100

1000

1.00E-06 1.00E-05 1.00E-04 1.00E-03

Operating Pressure (Torr)

Det

ecto

rN

oise

(cts

./sec

.)

5 um MCP Chevron 25 um MCP Chevron Single Channel MultiplierDiscrete Dynode Multiplier Spiraltron™

Back-filled Air

Ref. Characterization of Common Electron Multipliers in Harsh Environments; Pittcon 2005; Bruce Laprade & Ray Cochran

ELECTRO-OPTICSTest Procedure

1.Gain adjusted to 1x106

2.Chamber pressure adjusted with backfilled labair

3.Detector operated at approximately 15,000cts/sec for 5 minutes between readings

4.Readings repeated over two week interval

5.Chamber vented to air overnights and overweekends

Operating limits for selected detectors were explored ingreater depth under the following conditions

MAGNUM 5900Noise vs.Operating Pressure

0.01

0.1

1

10

100

1000

1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02

Operating Pressure (Torr)

No

ise

cts/

sec

4213 SpiraltronOperating Pressure vs. Noise

0.001

0.01

0.1

1

10

100

1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02 1.00E-01

Operating Pressure (Torr)

Noi

sect

s/se

c

5 Micron Pore Chevron MCP DetectorNoise vs. Operating Pressure

1

10

100

1000

1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01

Operating Pressure (Torr)

No

ise

cts/

sec

Lifetime at High Pressure:

1

10

100

0 100 200 300 400 500 600 700Continuous Hours of Operation at 1uA Output Current

Det

ecto

rG

ain

(Mill

ions

)

1 X 10-3 Torr 5 X 10-3 Torr

MCP Chevron, 5 Micron Pore AssemblyBack-filled Air

Ref. Characterization of Common Electron Multipliers in Harsh Environments; Pittcon 2005; Bruce Laprade & Ray Cochran

Lifetime at High Pressure

1

10

100

0 200 400 600 800 1000 1200 1400Continuous Hours of Operation at 1uA Output Current

Det

ecto

rG

ain

(Mill

ion

s)

1 X 10-3 Torr Argon

MCP Chevron, 5 Micron Pore AssemblyBack-filled Argon

Ref. Characterization of Common Electron Multipliers in Harsh Environments; Pittcon 2005; Bruce Laprade & Ray Cochran

ELECTRO-OPTICS

• Minimum detectable noise count in newcharacterization data had a gain of 50,000

• Dark current measurements were madeunder the same conditions to detect noisethat may be present below the 50,000 gainthreshold

Noise Sensitivity

Dark Current at 1,000,000 Gainvs. Operating Pressure

1.00E-16

1.00E-15

1.00E-14

1.00E-13

1.00E-12

1.00E-11

1.00E-10

1.00E-09

1.00E-08

1.00E-07

1.00E-06

1.00E-05

1.00E-04

1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02 1.00E-01

Operating Pressure (Torr)

Dar

kC

urr

ent(

Am

per

es) MAGNUM

Spiraltron

5µ Chevron

ELECTRO-OPTICSObservations

1. MAGNUM, Spiraltron™ and MCPChevron detectors operated well at higherpressures than previously reported

2. MCP detector with Mounting Pad (MP)MCPs tolerated regular venting toatmosphere without apparent damage

3. MP MCPs did not experience bowing as aconsequence of atmospheric exposure

BURLE Electro-Optics’ new, patent-pending MountingPad™Technology Microchannel Plates virtually eliminate warping andcracking problems of MCPs.

It is to resolve these issues that BURLE Electro-Optics developed andintroduced the MCP MountingPad™ technology. This constructionprevents the MCPs from warping and cracking due to hydration. Thedesign is compatible with Chevron™ and Z-Stack configurations, andis available in cartridge and detector assemblies. Simplified storagerequirements allow these MCPs to be stocked for increased efficiency,shorter cycle times, and improved field service performance. Theseproducts are identical in form, fit and function to traditional MCPs,which results in a seamless upgrade.

MountingPad™ MCPs are being implemented as standard in BURLEAdvanced Performance and BiPolar Time-of-Flight detector productsranges. This technology has already been successfully implementedwith major manufacturers

Standard MountingPad™ Configuration

ELECTRO-OPTICS

Discrete dynode multipliers develop ion feedback at pressuresDiscrete dynode multipliers develop ion feedback at pressuresabove 10above 10--55 TorrTorr

Single Channel Electron Multipliers Operate well at pressures inSingle Channel Electron Multipliers Operate well at pressures into theto themid 10mid 10--55 Torr RangeTorr Range

SpiraltronSpiraltron™™ Electron Multipliers operate well into the 10Electron Multipliers operate well into the 10--22 Torr RangeTorr Range

MAGNUM Electron MultipliersMAGNUM Electron Multipliers®® operate well into the 10operate well into the 10--33 Torr RangeTorr Range

ChevronChevron®® style, 5style, 5µµ pore MCP detector with mounting pad MCPs operatepore MCP detector with mounting pad MCPs operatewell into thewell into the 1010--22 Torr RangeTorr Range

Mounting Pad MCPs tolerate long term atmospheric exposureMounting Pad MCPs tolerate long term atmospheric exposure

Summary of Results

ELECTRO-OPTICSConclusions

1. At 1x106 gain, the Spiraltron™ operated at themaximum high pressure, 2x10-2 Torr. It isrecommended for use as a point detector in highpressure applications.

2. The Chevron™ detector operated at 1.5x10-2 Torrpressure. 5µ Pore MCP detectors are recommendedfor applications requiring fast timing, two dimensional orlarge area detection, or a low profile detector design.

3. Low noise, high gain and high pressure operation of adetector is dependent upon proper hardware design.