GEM Foil Cleaning Methods

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Method used at CERN

  1. When the leakage current is above 10 nA and below 200 nA when the GEM HV is 600 Volts, the GEMS are cleaned.
  2. First try high pressure (2000 PSI) distilled water (10 Mohms quality) spray. CERN has what looks like a power washer and they spay it against a tub wall in a workshop.
  3. After spraying with distilled water they bake it at 80 celsius in an oven for 1 hour
  4. If this doesn't work they will repeat the above after immersing the foil in a degreaser bath at 60 degrees celsius for 1 minute. Then rinse with a non pressure (not high pressure) spray of DI.
Ask RUI which degreaser he uses

When the leakage current is below 200 nA we just clean the GEMs with sprayed DI water (DI water 10Mohms quality)

The above info came from Alexis Rodrigues ( . Alexis did not recommend the alcohol method.

Power Washers

Power washer similar to what RUI is using

the smaller model below may be better for the LDS


Clean room Ovens

Terra Universal: Class 100 Cleanroom Oven Cat# 3700-70 $8,992, 2.8 cu. ft.

Warming tank

A degreaser solution is stored at 60 celsius so foils can be dipped for 1 minute to clean the copper.

check TerraUniversal Ultrasonic Cleaner with heating

2.5 gallon, cat #2619-00 $964.

Need a stainless steel tank to hold the solution and keep it warm


1600 PSI Electric Pressure Washer


The basic procedure followed for cleaning GEM foils suggested by Bob Azmoun, a researcher in the PHENIX Group at Brookhaven National Lab. Media:Georgia_3GEM_Detector_UR_Report_F04-1.pdf, Media:UG_Research_Report_David_Fall_04-1.pdf.

The procedure, which is done under a laminar flow hood, is outlined below:

1.Spray down the foils (always at “grazing incidence”) with dry N2

2.Spray down the foils with ethyl-alcohol until foils are completely drenched, using a Windex-type dispenser spray

3.Before the ethanol has a chance to air dry (which could absorb particulate deposits from the air onto the GEM surface), quickly spray down the foils again with dry N2 (again, always at “grazing incidence”)

One should keep in mind that after this process the GEM impedance should drop dramatically, due to the conductivity of the remaining alcohol. However, usually after 5hrs of purging with dry gas, the impedance returns to its original value. "