FEL-1 intensity monitor calibration procedure
The procedure to calibrate the online intensity monitors (I0M) of FEL-1 is based on the cross-calibration of the gas-based I0M with respect to a previously-calibrated (on Elettra BEAR beamline) diagnostic composed by a photodiode attached to an Al-coated Ce:YAG crystal.
The radiation ionizes the Nitrogen (pressure = 3E-5 mbar) in the I0M, which is basically an ion chamber, and creates a cloud of ions that are collected by one of the plates of the condenser in the ion chamber. The charge generated in this way, and deposited on the plate, is then collected by an XPI picoammeter that gives the corresponding reading in terms of number of counts (depending also on the measuring scale used, e.g. 50pC, 100pC, 200pC, …,1.8nC). In this way, each FEL pulse is correlated to the generated charge in the gas, giving an absolute determination of the pulse energy (i.e., the number of photons per pulse).
Calibration table
The data collected during the calibration of the I0M are then put in a calibration file organized like in a matrix-like structure:
I0         lambda1          lambda2          lambda3          …                     …                     …
0          XXX                 XXX                 XXX                 XXX                 …
100      XXX                 XXX                 XXX                 XXX                 …
200      XXX                 XXX                 XXX                 XXX
300      …

where the rows refer to the counts read by the XPI (measuring scale: 1.8nC - normal range of operations) and the columns refer to the different wavelengths. Whenever the XPI reads a certain number of counts at a certain wavelength it gives out the corresponding energy per pulse in µJ.
[counts from 0 to 2^20=1048576 corresponding to 0--1.8nC]
For the wavelengths not explicitly reported in the calibration file bi-linear interpolation is performed.
Calibration 2012 – May 2016
In 2012 an I0M calibration procedure was carried out at the following wavelengths: 21.8nm, 28nm, 32.5nm, 37nm, 43.3nm, and 52.5nm. The corresponding calibration table was used since then on.
Calibration file 2012
The calibration file used since 2012 (up to May 2016) is attached and named “Calibration_FEL1_2012.txt”.
Calibration May 2016 - present
In May 2016 a new I0M calibration procedure was carried out, and the following wavelengths were used: 21.8nm, 23.8nm, 26.2nm, 29.1nm, 31.2nm, 32.3nm, 37.4nm, 41.6nm, 43.6nm, and 51.7nm.
Calibration file 2016
The calibration file used since May 2016 is attached and named “Calibration_FEL1_2016.txt”.
As a conclusion, the new calibration (2016) has shown that the old one was under-estimating the energy per pulse especially at some wavelengths around 30nm. 

Calibration_FEL1_2012.txt                                                Calibration_FEL1_2016.txt 


GAS ABSORBER - Gas injection procedure pdf

                                   Gas Control Panel jpg

                                   Initialization of the VLVR_G1_PFE.01 valve pdf

ENERGY SPECTROMETER - CCD server reboot  txt

                                                       LE and HE grating positions txt

KB MIRROR SYSTEM - KB system reboot txt



PADReS HDB - http://padresproxy/docs/padres/hdb.php
Ultima modifica il Martedì, 07 Marzo 2017 18:55