Instrument: Cryostat

Following the light path, the last part of the MEGARA spectrograph is the Cryostat where the deep-depleted E2V CCD231-84 CCD is enclosed. The MEGARA cryostat, an open cycle liquid nitrogen system, is a custom made product that has been designed and will be manufactured by INAOE's "MM-wavelength astronomical instrumentation group". It offers flexibility and modular stages that allows easy changes for detector mounting.

The cryostat mounting is horizontal and it is designed to be kept static, as well as all the other MEGARA spectrograph components. The complete cryostat assembly consists of two main parts: the CCD Head (left panel above) and the Dewar back (right panel above). The main cryostat characteristics are summarized in the next table (Detailed-Design values).

SPECIFICATION	VALUE
Cryostat provider	INAOE, Astronomical Instrumentation lab for mm-λ
Cryostat type	Open cycle, filled with liquid nitrogen
Mass	21 kg
LN2 tank volume	7 lts (6 lts usable)
Estimated LN2 hold time	44 hours
Vacuum requirement	≤ 4.10^-6 mbar
Vacuum flanges	2 ¾ and 1 1/3 CFF
Sorption pump	Active charcoal

Note that the MEGARA cryostat yields a hold time of almost two entire days, reducing the service needs from the GTC staff.

Below we show the Detailed-Design version of the cyrostat whole assemply at the MEGARA spectrograph optical bench.

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