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Beam-intensity measurements

Most of the diagnostics concept for monitoring the Super-FRS beam intensity and transmission are FAIR accelerator based: particle detection combination (PDC), with three types of particle detectors (SEM, IC, plastic scintillator or diamond detector) at the entrance of the Pre-Separator (target) and the Main Separator to measure the beam current and counting. Special care is needed at the target region for the signal transportation and the front-end electronics location due to the high radiation level.

As an example, a two-gap IC with 50 mm diameter active area used to measure 12C ion-beam intensity is shown, see figure below. The detector was fit in a gas sensitive housing with stainless steel foils (0.1 mm) separating it from the vacuum. The IC analogue signal was fed into a current to frequency converter.

[1] S. Schlemme et al., GSI Scientific Report (2015) p. 369

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Two-gap IC with active area of 50 mm diameter.
Intensity curve measured for 12C at 62 MeV/nucleon [1].
Two-gap IC with active area of 50 mm diameter.
Intensity curve measured for 12C at 62 MeV/nucleon (May 2015).

At the highest particle rates it is foreseen to operate a SEM transmission monitor equipped with thin metallic foils (SEETRAM) in current mode. The IC/SEETRAM current is calibrated by using a fast-counting diamond detector.

[2] F. Schirru et al., Diam. Relat.  Mater. 49 (2014) 96

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scCVD diamond detector (2x2 mm2) [2].
scCVD diamond detector (2x2 mm2)

The signal properties (amplitude, slope and charge) of a pcCVD diamond detector exposed to 60 h of irradiation corresponding to an integrated flux of 6.2⋅ 1013  12C/cm2
were studied as a function of the accumulated flux [3].

[3] S. Schlemme et al., Diam. Relat. Mater. 99 (2019) 107536

/fileadmin/Super-FRS/BI/pcCVD_AmpSlope_Distr.jpg
Amplitude and slope of the pcCVD-DD signals as a function of the irradiation time at two different beam attenuation factors f1 and f2.
Amplitude and slope of the pcCVD-DD signals as a function of the irradiation time at two different beam attenuation factors f1 and f2.

Partners: TU Darmstadt and GSI