Nationaal instituut voor subatomaire fysica


Colloquium Harry van der Graaf (Nikhef)

Tuesday 20 November, 11:00h, at Nikhef in H331

Speaker: Harry van der Graaf (Nikhef)

Title: "ERC-Advanced 2012 'MEMBrane': The Tipsy photon detector and the Trixy tracking detector"

We propose to develop a stack of ultra-thin membranes, in vacuum, which are put at decreasing potential, acting as dynodes of a photomultiplier. After an electron, with energy ~ 200 eV hits the top membrane, a multitude of electrons are emitted from the bottom side of the top membrane. These electrons are accelerated towards the 2nd membrane, where the multiplication repeats. With N membranes, with secondary electron yield of M, the number of electrons leaving the bottom dynode equals M**N, being the gain of the electron multiplier. A pixel readout chip, placed under the stack of membranes, receives this charge signal on the pixel input pads. Since the source capacitance of the input can be as mall as 5 fF, a gain of ~ 30 k will provide a digital signal on the pixel input pad. The rise time of this signal is determined by the crossing time of the (free) electrons between the bottom membrane and the pixel input pad (~ 2 ps). 

The (MEMS made) assembly of electron multiplier and pixel anode chip, combined with a classical and continues photocathode forms a new photomultiplier with potentially a superb time and position resolution per single soft photon, and capable to operate in magnetic field. 

Combined with an electron emission membrane 'e-brane', the multiplier-chip unit would form a tracker with ps time resolution. If a MIP crosses the surface of an aluminium or copper electrode in vacuum, at least one low-energetic electron is emitted in about 4 - 6 % of the events. By means of material selection (low work function for electron emission), surface fractalizing, and a high electric extracting field, we hope to develop an e-brane with a yield higher than 50 %.

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