Test of SINGLE EVENT UPSETS with heavy particles

The ATLAS SCT/pixel opto-links have already been tested for Single-Event-Upsets (SEU) with a 600 Mbq-Sr90-source which gave a particle flux through the PIN diode and DORIC4 of ~4,3*10⁷ /cm² s. No significant problems were seen.

We have now studied the effects of a high flux of heavy particles (neutrons) on the performance of these links. The opto-link (PIN, DORIC loop VDC, LED) was placed into the beam of the Nuffield Cyclotron in Birmingham.

The fluence was measured with Al foils and the estimated flux of neutrons was ~1.1 *10⁶ n/cm²s. This is about the expected flux in the SCT. The highest particle flux expected in the Pixel B-Physics layer is 2.5 10⁷n/cm²s. The beam energy was 18 MeV and the resulting neutron spectrum had a broad peak centred at 9 MeV. An indication for a change of the overall performance of this link is the minimal light input required for the TTC link to operate with a negligible Bit Error Rate (BER). Two scans of BER vs. optical power were done, with and without beam. The set-up itself was not changed between these measurements.
 

In order to look for occasional more serious errors such as the mis-locking of the DLL in DORIC4 longer scans at higher power levels were also performed when the beam was on. The results of these scans are shown in Table 1 below. No problems of DLL mis-locking were found and the BER was well below the ATLAS specified level of 10^-9 and were typical of values obtained in previous long runs outside the beam area.
 
 
 

LIGHTINPUT	1824 mW	604 mW	538 mW	120 mW *	604 mW
DURATION	7200 sec	7200 sec	3600 sec	9000 sec	3000 sec
ERRORS Cyclotron ON Cyclotron OFF	3	16	2	159	50
Bit Error Rate BER	1,04 E-11	5,55 E-11	1,4 E-11	8,28 E-09	4.17 E-10

 
 

* lighinput below specifications

Conclusions

The ATLAS SCT/pixel optical links have been tested at fluxes up to those expected for the SCT. No significant rate of SEU effects were detected.
 

Comments please mail to:  I.M. Gregor 

last modified : 15. June 1999