Proton damage testing is currently underway at the Harvard Cylotron Laboratory. The test device w159c1 is an unreflexed ccd typical of the ACIS devices. Irradiation is done at room temperature with all inputs shorted. At least two days are allowed after irradiation for any short term activation to subside, then subsequent testing is done under normal calibration conditions. In addition to the standard screening tests a series of dark current maps (hot pixel finder) are made at warmer temperatures. The typical exposure/measurement cycle takes one week. (For low energy proton damage experments go here.)

Date of Irradiation Dose Date of Testing Image Analysis
Dec 15 1997 50 Rads Dec 17 1997 -60c Screening-report
Jan 22 1998 50 Rads Jan 28 1998 -55 c Screening-report
Feb 02 1998 50 Rads Feb 05 1998 -55 c Screening-report
Feb 12 1998 50 Rads Feb 19 1998 -55 c Screening-report
Feb 27 1998 100 Rads Mar 05 1998 -55 c Screening-report
Mar 16 1998 100 Rads Mar 18 1998 -55c Screening-report

Present Status

Even at the lowest doses an oxide charging effect is seen. While the level of this glow increases with accumulated dose it is never visible below -90 c. This is the same behaviour seen with front side ccds overexposed to xrays at 500 eV and 6 keV. No amount of operation or elevated temperature (+40 c) annealing changes the level of the glow. Superimposed on the glow are a number of hot-pixels. The number and intensity of the hot-pixels decreases as the operating temperature of -120c is approached. The hot-pixels are easily distinguished from cosmic-ray or activation by the mean-bias method and because all hot-pixels are "single events". This particular ccd has some problems with repeated temperature cycles, perhaps because of the flexprint. The output noise has been increasing with time but this has nothing to do with radiation damage. Also a nasty feature toward the center and edge seems to be growing. The only screening result which is showing any significant change is the parallel CTI at 5900 eV. The parallel CTI at 525 eV is not reliable because of variable source intensity.