Casas-Cubillos!!Juan!!Juan.Casas-Cubillos@cern.ch!!CERN!!Division LHC - CERN - 1211 GENEVA 23 - SWITZERLAND!! !! !!SWITZERLAND!!GENERAL INTEREST!!GENERAL INTEREST!!R/M field tolerant electronics!!Preliminary test for radiation tolerant electronic components for the LHC cryogenic system!!990430012

J. A. Agapito**, F. M. Cardeira***, J. Casas-Cubillos*, A. Duarte**, A. P. Fernandes***, F. J. Franco**, M. J. Gil**, P. Gomes*, I. C. Gonçalves***, A. Hernández**, U. Jordung*, M. A. Martín**, J. G. Marques***, A. Paz**, A. J. G. Ramalho***, M. A. Rodríguez Ruiz* and J. P. Santos***.
*CERN, LHC Division, Geneva, Switzerland
**Universidad Complutense, Electronics Dept., Madrid, Spain
***Instituto Tecnologico e Nuclear (ITN), Sacavem, Portugal.


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The typical signal levels involved in the measurement of resistive type cryogenic temperature sensors are in the milli-volt range, with measuring accuracies of about 0.5%, imposing the use of low-noise instrumentation amplifiers. These devices are usually fabricated in bipolar technologies that according to the literature, may exhibit a significant degradation when exposed to the LHC tunnel environment. For 10 years of operation of the LHC machine the expected neutron fluence is 5 x 10^13 n/cm^2 and the gamma dose is 500 Gy.
In order to evaluate and design radiation tolerant electronic systems, irradiation campaigns are being performed at an experimental nuclear reactor (ITN, Lisboa, Portugal) and at CERN. On-line measurements are performed  during irradiation and stand-by periods in order to evaluate respectively total dose and annealing effects. The investigated components include both passive and active devices under normal operating conditions.
The ITN nuclear reactor is operated at a power of 2kW so that the required fluence of 5 x 10^13 n/cm^2 is reached in about 5 days, with 12 hours of operation per day. All components are placed inside a hermetic container immersed inside the reactor pool, over the fuel cells. Thermal neutrons are suppressed by a Cd foil and the gamma radiation is reduced by using a 20 mm thick Pb shield.
At CERN, in the SPS-TCC2 target area, a neutron fluence of 5 x 10^12 and gamma dose of 300 Gy are expected to be reached in 22 weeks.
For measuring the sensor resistance it is necessary to use either a known current (voltage) excitation combined with a voltage (current) measurement, or a comparison technique with a reference resistor. In view of the very stringent accuracy requirements reference devices like high accuracy resistors and voltage references have been investigated. Preliminary results suggest that the radiation hardness of precision resistors with low temperature coefficient (10 ppm/K) is adequate for our application.
Operational and instrumentation amplifiers have been investigated; their noise, input impedance and linearity characteristics have a strong impact on the overall accuracy of any complex electronic apparatus. Their fabrication technologies include bipolar, JFET, DIFET and LINCMOS. The parameters that have been measured are offset voltage, input bias and offset current, open and closed loop gain and their dependence on ambient temperature.
Other elements necessary for fabricating a signal conditioner that have also been investigated include potentiometers, standard resistors and capacitors.

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The LHC accelerator will use about 1600 main superconducting magnets operating below 2K, almost all the tunnel circumference has cryogenic components resulting in a total cold length of over 25 km. The magnets temperature is a control parameter and its target accuracy imposes very severe constraints on both the sensing element (evaluated in another framework) and its signal conditioner. They will both be installed inside the tunnel, thus exposed to a relatively high neutron fluence and gamma dose. It is then crucial to understand the effects of radiation on the performance of the electronic components that will be selected for the signal conditioner.
This paper presents data concerning the radiation effects on typical active and passive discrete electronic components. This is the first step toward building a radiation tolerant signal conditioner.

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