6 SMOG2 Gas Feed System Gas

Transcription

1 6 SMOG2 Gas Feed System Gas Giuseppe Ciullo INFN Ferrara Physics and Earth Science Department University of Ferrara Ferrara Italy on behalf of LHCspin Study Group G. Ciullo on GFS for SMOG 2 1

2 SMOG2 vs SMOG Gas Feed System Fig. 20. Feeding of gas in the center of the cell. SMOG: Only one feed line into the VELO Vessel. Monitor & Control on gauge p read-out, low precision and low reproducibility SMOG2: Additional feed line into the center of the cell. The gas flow rate can be accurately set and measured G. Ciullo on GFS for SMOG 2 Gain in higher stability and control on gas flow rate, then better determination of the target areal density. 2

3 6.1 Overview i) ii) A RGA can be connected for the gas analysis. At the Balcony. i) GFS Main Table: hosts the main components and will be located at the balcony in P8 cavern. ii) Gas Supply: reservoirs till 8.6 l each, 17 bar l (at 2 bar) of each gas. At the highest gas flow rate ( mbar l s -1 ) the duration cover more than one year. (balcony) iii) Pumping Station. 70 l s -1 turbo pump, with a dry back pump, and bypass for both pumping (balcony) iv) Feed Lines: the existing one and one additional for the feeding in the center of the cell. 3

4 6.2 Theory of SMOG2 operation V inj keep P inj stable C inj In general the gas flow rate (Q), under constant temperature of the system, is given by the Equ. (6). Q def d( pv ) = dt T=cost dn = dt kt (6) dn/dt =I, I is the intensityof atoms (or molecules) per unit time In Sect. 3 (E. Steffens talk). G. Ciullo on GFS for SMOG 2 4

5 Q and I connections with vacuum quantities V inj keep P inj const C inj The intensity I is connected to the the volume density ρ 0, Equ. (1), and the conductance of the cell (C tot ). From Equ. (1) it is possible to determine the areal density θ in the cell, Equ. (3). ρ 0 = I C tot, (1) θ = 1 2 ρ 0L, (3) From vacuum master equations it comes out: Q inj = Δp C inj =(p inj p vacuum ) C inj ~ p inj C inj p measured directly (precise gauges AG1 and AG2), C inj to be measured indirectly. G. Ciullo on GFS for SMOG 2 5

6 Measuring C inj V inj C inj Start from an initial pressure p inj (0) in a volume (V inj ), with the valve between reservoir and volume closed and gas flows through the injection line, whose C inj has to be determined. C inj is given by a fixed conductances from the volume to the injection point and a tunable conductance DVC, which allows to provide different gas flow rates (Q inj =p inj C inj ). The pressure will decrease following the law: Knowing V inj and from the p inj ( t) = p inj ( 0)e (C inj /V )t inj, (8) decreasing pressure data, it is determined C inj G. Ciullo on GFS for SMOG 2 6

7 From the definition Or more precisely Q inj Q def d( pv ) = dt applied to the decreasing of pressure in a Volume V inj with the gas flowing through a conductance:: 9 8 From p vs t dp dt vs p inj Q = dp inj dt V inj. (9) 7 P cal (mbar) time (min.) Knowing V inj and from the pressure decreasing at a given pressure p inj from the derivative of p inj associate at the pressure in the same time, it is possible to provide: ( p ) inj V Again V inj is required. inj G. Ciullo on GFS for SMOG 2 7 Q inj (p inj ) = dp dt

8 Measuring V inj V cal : known calibrated volume, measured (ex situ), by filling it with liquid (ethanol) and weighing it. In situ (on the GFS) we can fill by the chosen gas the volume to be measured (V main ) and the V cal, at a proper pressure, covering the working condition. Pumping StaFon Then we close the valve between the two volumes, in V cal the pressure will be what we measure as p main(i) in both volumes. Afterwards we pump down V main.. We have to close the valve to the pumping system (PS), then open again the valve between both volume, and expand the gas from V cal in V cal + V main From the law PV=constant p cal ( pmain (i ) ) V after expansion cal = pmain&cal( p main (i+1) ) ( V cal +V main ) The procedure can be iterated (i), till the background contribution is detectable. G. Ciullo on GFS for SMOG 2 8

9 Uncertainty (a priori), and calibration (a posteriori) Relative uncertainty on V cal of 0.1 %, and from the capacitive/membrane gauge 0.15 % for the pressure measurement. A priori uncertainty of ~ 0.4 % in the V main, which propagates to Q inj, contributing at a level lower than 1 %. With a similar system in HERMES experiment, on the HERA ring a posteriori uncertainties in the order of a couple of percent were achieved. We call this calibration curve, and Q cal calibrated gas flow rate Data from a system for vacuum technology laboratory in Ferrara a posteriori: Measurement precision 0.5 % Reproducibility 0.5 % G. Ciullo on GFS for SMOG 2 9

10 requirements for Q calibrated For each gas it s required to fix the proper tunable conductance via the DVC opening. Then in a lab, acquire the decreasing of p inj for a proper V inj, which will provide then the calibration curve. According to the calibration curve at the chosen V inj and DVC setting (which means the choosen C inj ) then we can feed the required Q inj just setting the proper pressure p inj in the V inj. This has to be done for each gas. The calibration curves can be found operating the GFS, connected to a Vacuum Vessel which mimic the VELO vessel with its pumping speed, and the feeding into the cell and into the VELO. For the feeding directly in the VELO, if it is required, the parameters can be set for a range of pressure which includes the pressure read-out in the VELO vessel during the injection in the cell. The GFS can be operated in situ just by using settings and conditions obtained in lab tests and calibrations. G. Ciullo on GFS for SMOG 2 10

11 6.3 Technical realization CAD Drawing under design (courtesy of P.M. Gebolis) G. Ciullo on GFS for SMOG 2 11

12 Two Absolute gauges Covering mbar (AG1) mbar (AG2) 0.15 % resolufon Dosing Valve for Stable Pressure (DVS) Dosing Valve for tunable Conductance (DVC) PneumaFc Valves PneumaFc all metal valve G. Ciullo on GFS for SMOG 2 VCR Cajon fizngs provide compactness and easier mounfng

13 6.4 Opera=on and control: Dosing Valve. RVC 300 for dosing valves It Controls one Dosing Valve EVR 116, EVR 116 Dosing Valve Can be programmed via RS232 or RS 485 and controlled also via DIO or AIO as required One RVC 300 can be programmed for the se4ng of the DVS via RS232, for status control and monitoring also via DIO or AIO G. Ciullo on GFS for SMOG 2 The opening of the DVC dosing valve is controlled via 0-10 V DC, 12 W max. 13

14 6.4 Opera=on and control: gauges. TPG 256 (Pfeiffer) can host 6 vacuum Gauges. Can be controlled via RS232 or RS485. It provides from connector 7 the Analog output 0-10 VDC of the read out of the connected gauges. This output can be used for setting Directly the RVC 300 which control The DVS (the Dosing Valve for Stable pressure in the V inj ) It provides also 8 relays which can be programmed on any gauges (hysteresis logic), The controller can host the Absolute Gauges, The Full Range Gauge on the VELO, The gauge for vacuum control on AG GFS Pumping Station G. Ciullo on GFS for SMOG 2 14

15 6.4 Opera=on and control: pneuma=c valves. The peumafc valves can be controlled via one solenoid MS-SOL-1K-BN for each valve The solenoid require 24 VDC and 2 Wac Or with a digital control Device which can control Fll 6 valves. Each Valve can be equipped with indicator Switch in order to check the actual status of the valve. CERN vacuum group suggesfon- a module which allow a Digital I/O control of 6 pneumafc valves. G. Ciullo on GFS for SMOG 2 15

16 Some opera=ons of GFS. We can disfnguish different operafons of the GFS, which will be organized with well detailed flow charts, including preparing steps and final sezngs. In following we provide some of them. Evacuation of the GFS and/or the long pipe: The GFS PS with a proper sezng of valves can pump down indipendently the GFS or the long pipe, or both togheter. The Pumping stafon, has to operated for a rough vacuum first with the rough pumping, without stopping completely the turbo, then, closing the bypass, by the turbo pump. Selecting a gas: after the evacuation of the whole volumes, the long pipe and the previous connection to the valve of the reservoir. The DVS has to be completely closed and then the Valve upstream open in line with the proper reservoir. Feeding a chosen Q: before setting the feeding parameters, all volumes and the long pipe is under the PS pumping, then the Safe Valve, the Velo Valve and the Cell Valve are open. Just after safe check that there is no gas which can blow in the VELO, if the feeding into the cell is required, the Valve on the GSF PS in closed the VELO Valve is closed, and the parameter on the RVC 300 for DVS will be set slowly step by step to the nominal pressure, the RVC 300 for the DVC are set to the proper percentage opening for the required Q inj. Feeding into the VELO vessel Q: the same procedure as feeding into the Cell, unless, that the operation will be performed with the Cell Valve close. All opera=ons will be in details performed and described in carefully lab tests. G. Ciullo on GFS for SMOG 2 16

17 Opera=on: evacua=on before feeding gas. Any operation of the GFS will reach the working conditions in steps, under safe control of the status of the devices, and the status of the pressure in any critical place. Here we report the final status of pumping down the system, just in preparation of setting the proper gas rate flow to be injected. G. Ciullo on GFS for SMOG 2 17

18 Opera=on: feeding a given high Q inj. The use of the main volume and the supplementary volume provides a more stable condition in case of high gas flow rates. This is the final condition, just after closing the valve on the PS, then afterwards the DVS is closed, simoultaneously the DVC is set to the proper opening, the gas valve open, and the setting of the DVS starts step by step. G. Ciullo on GFS for SMOG 2 18

19 6.5 Commissioning and opera=on. The whole system can be commissioned and operated in a laboratory, connected to a vacuum chamber which can mimic the VELO vessel and the proper connecfon between the GFS table and the feedthrough into the VELO and into the cell. The influence of the conductance of the connec=ng lines can be studied, together with the calibra=on procedures and uncertainty es=ma=ons, during laboratory tests, using the same final configurafon. The working parameters set to both RVC 300s can be obtained recording calibra=on curves and studying the reproducibility of the system in the lab. These measurements have to cover the required range of gas flow rate for the different gases. Once determined, they can be used at the experimental site. The final commissioning of the system mounted on the experiment can be performed aier all tests just with checking the calibrafon curves, and eventually adapfng the parameters. The purity of injected gas, can be performed via a standard RGA during the commissioning, and in case of evident strange behavior of the GFS, during the runs, also remotely, just including the remote control of the RGA. Also the calibrafon curves, if required, can be acquired in situ on the balcony. G. Ciullo on GFS for SMOG 2 19

20 Conclusions / proposals. Based on the esperience and exisfng design of calibrated gas flow rate in the HERMES experiment, in the COSY experiment, and also in laboratory of vacuum technology, we agreed in a new design for feeding well controlled and stable gas flow rates in the or in the center of the cell. and for BG studies also in the exisfng VELO vessel feedthrough. The system once assembled and commissioned can be implemented in the VELO VACUUM System Control, with a collabora=on between proponents and responsibles of the CERN TE/VSC-ICM. The components are piloted by controllers which are equipped for different kinds of communica=ons, also for by I/O both digital and hardware controls. Meanwhile we can adapt (in Ferrara) and assemble available components and devices in order to test the present proposed design and train young students, which eventually can join as fellowship or technical students the CERN group. Under the supervision of a senior researcher, there will be support and the students can take part in the implementafon and commissiong of the system at CERN. G. Ciullo on GFS for SMOG 2 20