Document: 57433 / Release No. 1 / Release Date.:
TRIUMF / / Document: 57433
Design Note TRI-DN-12-13
ARIEL’s E-linac Vacuum System
Document Type: / Design Note
Release: / 1 / Release Date
Author(s): / Dimo Yosifov
Name: / Signature: / Date:
Author: / Dimo Yosifov
Reviewed By: / Rick Baartman
Don Dale
Eric Guetre
Franco Mammarella
Jane Richards
Doug Preddy
Victor Verzilov
Approved By: / Shane Koscielniak
History of Changes
Release Number / Date / Description of Changes / Author(s)1 / 2013-02-01 / Release 1 / Dimo Yosifov
Table of Contents
Document: 57433
Design Note TRI-DN-12-13
ARIEL’s E-linac Vacuum System
1Introduction
1.1Purpose
1.2Scope
1.3Definitions, Abbreviations and Referenced Documents
1.4Requirements
1.4.1Required vacuum levels by subsections:
1.4.2Magnetic fields
1.4.3Radiation resistance and operation in radiation field
1.4.4Beam pipe outside diameter (OD)
2E-linac vacuum system
2.1Names and description of the all electron accelerator sub sections and their vacuum systems
2.2Vacuum system specification
2.2.1Materials
2.2.2Bake-out
2.2.3Venting
2.3Purchased components comprising e-linac vacuum system
2.3.1Flanges and seals
2.3.2Fast closing valve system (FV)
2.3.3Ion pumps (IP)
2.3.4Ion gauges (IG)
2.3.5Convectron® gauges (CG)
2.3.6NEG® Pump
2.3.7Temperature reading gauge
2.3.8Residual Gas Analyzers (RGA)
2.3.9Turbo Pumping carts (TPC)
2.3.10Turbo pumps (TP)
2.3.11Backing/roughing pumps (BP, RP)
2.3.12Leak detectors
2.3.13Vacuum valves of E-linac
2.3.14Heaters for vacuum bake-out
2.3.15Metal-wool foreline trap
2.3.16Purchase components parts count
2.4Cleanliness of the vacuum system
2.5Control system
3Acknowledgement
4References
1Introduction
The new Advanced Rare Isotope Laboratory (ARIEL) is TRIUMF's flagship facility that will expand Canada's capabilities to produce and study isotopes for physics and medicine. Utilizing next-generation technology, it will showcase a made-in-Canada, high-power superconducting electron accelerator to produce exotic isotopes for research and development.
ARIEL is an accelerator based research facility, which is being constructed for scientific research by TRIUMF. It will produce radioactive isotopes by bombarding alkanide targets with high energy electron beam, generated by an electron gun (EGUN) and accelerated with an electron linear accelerator (E-linac). The E-linac is comprised of an EGUN, three main accelerators, and beam transport lines delivering the beam to a beam dump (2014) or to ARIEL targets (2017). To minimize the collision of electrons with air molecules, the E-linac requires an evacuated volume along the electrons path. When beam is running, the pressure in the EGUN has to be at level less than 1.3E-9 mbar, in the three accelerators and the section between the accelerators at level less than 1.3E-8mbar,and in the beam transport lines which deliver beam to the targetsor beam dump at level less than 1.3E-7mbar.
The Vacuum System of the E-linac has to provide an environment with reduced pressure for electron beam acceleration. To achieve this goal, the vacuum system has to comply with Ultra High vacuum manufacturing and assemblystandards. Careful choice of materials and purchased vacuum components will assure that the requirement is met.
1.1Purpose
This document describes the vacuum system of ARIEL E-linac. It identifies all vacuum components as pumps, valves and gauges and names the devices in accordance with the accepted TRIUMF naming conventions. This paper will be the basis for the EPICS interlocks summaries for operating of E-linac vacuum system.
1.2Scope
This document presents the layout of the vacuum system for E-linac as it will be built and installed by the end of 2014: i.e. without the second accelerator cryomodule and without a recirculating ring. It describes the purchased vacuum components, provides parts count and includes information about the operation of the E-linac vacuum system.
1.3Definitions, Abbreviations and Referenced Documents
For the definitions and abbreviations used for naming E-linac vacuum system sub-sections and their vacuum components the following documents were used
-“ISACDeviseName Convention” - Document -27934
-“ARIEL Name convention” – Document–35040
1.4Requirements
1.4.1Required vacuum levels by subsections:
- 1E-9 mbar – EGUN, ELBT.
- 1E-8 mbar – ELBD, EINJ, EMBT, EMBD, EACA, EABT, EABD, EACB.
- 1E-7 mbar –EHAT, EHDT, EHD, EHBT.
Note: These values are an order of magnitude more demanding than those arising from residual gas scattering [1]. The values are consistent with practise [2] at electronaccelerator laboratories such as CEFAB. The vallues follow the recomendations from [3]
- 1E-6 mbar – Cryomodules insulating vacuum and RF couplers vacuum
Although there are four levels of low pressure, ranging from less than1.3E-9 mbar to 1E-6 mbar, the entire vacuum system will be built and handled by Ultra High Vacuum (UHV) standards.
1.4.2Magnetic fields
Magnetic fields at the beam line, resulting from vacuum devices shall be less than or order of 1 Gauss.
1.4.3Radiation resistance and operation in radiation field
All vacuum components shall be operable in a radiation environment up to 5mSv/hr at 1 meter from the beamline with a mean time to failure longer of several years.
1.4.4Beam pipe outside diameter (OD)
Beam pipe OD constrained to be 2.0”. This value was chosen as a compromise between magnet aperture cost (favored by smaller bore) and beamloss minimization (favored by larger bore). Using one pipe size throughout allows for standardization of components.
2E-linac vacuum system
Figure 1 (below) shows the ARIEL E-linac as it will be built by year 2017. By year 2014 it will have two accelerator sections called Electron Injection Module (EINJ) and Electron Accelerator Module A (EACA). By year 2017 a third accelerator module called Electron Accelerator Module B (EACB) may be added.
Figure 1.”2014”E-linac
The vacuum systems of the individual subsections of E-linacare shown on Figures 2A, 2B, and 2C. On these schematics all parts are shown and identified.
Figure 2A.Vacuum system layout of ARIEL “2014”E-linac. Sections included E-GUN to EINJ
Figure 2B.Vacuum system layout of ARIEL “2014”E-linac. Sections included From EMBT to EACA
Figure 2C.Vacuum system layout of ARIEL “2014”E-linac. Sections included From EABT to end of EHBT and EHDT (EHD)
2.1Names and description of the electron accelerator sub sections and their vacuum systems
-EGUN – electron gun, generating the electron beam (Figure 3). Its vacuum system contains the first of numerous diagnostics boxes (DB). A DB is a multi-port vacuum chamber allowing beam diagnostic devices to be attached to it and inserted into the beam. It also contains the ports for the pumping and the pressure gauges.
Figure 3.E-gun assembly with first diagnostics box
-ELBT – electron low energy beam transport line. For diagnostics reasons, at this section, the beam can be diverted toward ELBD – electron low energy beam dump;
-EINJ – electron injection accelerator module;
NOTE: The cryo- modules - EINJ, EACA and EACB have isolated from each other vacuum systems and vacuum volumes – one is for the beam transport and acceleration, and another for vacuum thermal isolation of a liquid helium installation, used to cool the accelerating cavities. The vacuum system of any of E-linaccryomodule isolation vacuum shall provide pressure lower than 1.3E-3 mbar at room temperature. If this pressure is not achieved, cool-down of the cryo-module can’t be started. The typical operating pressure is expected to be lower than 1.3E-5 mbar at room temperature and lower than 1.3E-7 mbar when cryo-module is cold. For service needs, the cryomodule connections to the beam line should permit the cryomodule to be lifted or lowered vertically from its accelerator position;
-EMBT – electron medium energy beam transport line. For diagnostics reasons, at this section, the beam can be diverted toward EMBD – electron medium energy beam dump;
-EACA – electron accelerating module A;
-EABT – electron accelerated beam transport line. For diagnostics reasons, at this section, the beam can be diverted toward EABD – electron accelerated beam dump;
-EACB – electron accelerating module B - it will be added by year 2017. Until 2017 it will be replace by an evacuated enclosure, transferring the beam further downstream of EABT;
-EHAT – electron high energy accelerated beam (after cryo-module “B”) transport line. This line can deliver the beam to two beam lines: EHDT (high energy dump transfer line, followed by the EHD – high energy beam dump or EHAT can deliver the beam to EHBT;
-EHBT – high energy beam transfer line. This line will deliver the beam to either of two ARIEL targets.
2.2Diagnostics Box (DB) description (see Figure 4):
A DB is a vacuum chamber containing beam-sensing diagnostic devices and vacuum components. Where space permits, commercially available vacuum crosses may be used. In the EGUN and accelerator sections, where space is limited, a specially manufactured octagonal structure made out of 316L Stainless Steel will be used. The usual location for the ion pump will be the bottom port of a DB or a cross, and for the turbo pump isolation valve is going to be one of the side ports. The image of a DB is shown below:
Figure 4.Diagnostics Box (VECC style)
The flanges are a CONFLAT® (CF) style with the following sizes; 6” CF (two ports), 4-1/2” CF (seven ports), and 1.33”CF (six ports - for beam position monitors and vacuum gauges). The special diagnostics box is built in the TRIUMF Machine shop (Drawing No: TEL0312 – Weld Assembly) The diagnostics box for e-gun will have less ports for BPM.
The shown DB is for VECC Injector; the E-linac DB will have only four ports (vs. eight for VECC injector) for the button Beam Position Monitors and these will be used exclusively for single cable feed-troughs.
-Diagnostics box with most of its devices (missing: beam position monitors and gate valves) attached to its ports (see Figure 5. below). The image bellow shows an assembled typical diagnostics box:
Figure 5.DB with devices.
The diagnostics box with all attached to it devices contain large out-gassing surfacesThere areasareshown in the table below:
Name of device / Outgassing area in cm2E-gun (only) / 11710
Diagnostics box (only) / 2644
Profile monitor (View Screens) / 1246
Faraday Cup / 805
Wire scanner (Fast wire scanner) / 1330
RF Shield / 2000*
Slits Scanner (Linear Profile Monitor) / 1670
TOTAL / 20159
Note *: The surface area of a RF shield is an estimate and any RF shield will be has to be designed with total surface area equal to or less than 2000 cm2.
The e-gun (Fig.3) and its DB with all devices attached to it (Fig.5) has total outgassing surface area of 20159 cm2. A design note describing the e-gun and its vacuum system is not a part of this document.
The gas load of a diagnostics box with all ports taken by devises is 8449 cm2.
To remove the gasses from the vacuum system, at the lower side of the DB is a port for an Ion Pump. The DB also contains ports for pressure gauges and a pumping port with an isolation valve. This port is for a Turbo Pump to be attached to the DB, which pumps out the vacuum system during initial pump down and the following bake-out. Once the bake-out is completed the turbo pump can be isolated via all-metal angle valve and removed from the beam line and stored away from radiation fields created by the e-linac.
2.3Calculating the pressure profile for the beam line leading from EHAT:IV0 to EHD and the beam line from EHBT IV0 to the ends of EHBT.
The following equation forms the base of a matrix equation (see [19] and [20]):
Qi + Ci-1∙(Pi-1-Pi)+Ci∙(Pi-1-Pi)=Pi∙Si
Where:
Qi =q∙Fi (Torr liter/sec)is the total gas load at element i with surface area Fiin cm2, and outgassing q [1.0E-11 Torr.liter/(sec/cm2)]
Si (liter/sec)is pumping speed,
Pi (Torr)is the pressure at element i,
Ci = 11.6∙Ai∙α (Liter/sec)is the conductance between element i and i+1where Ai is the area of the aperture (cm2) and α is Clausing transmission coefficient
The Clausing transmission coefficient α for circular cross section (beam pipes) is given by Santeler equation as a function of the diameter D(cm) and length L(cm), see [21]:
α1(D,L) = {1+3/4∙L∙[1+(3+6/7∙L/D)∙D-1]}-1
and the Clausing transmission coefficient α for rectangular cross section (diagnostic boxes) is given by Santeler equation as a function of the cross-sectional dimensions H and W (cm) with W ≥ H the and length L(cm):
α2(H,W,L) = [1+ 3∙L∙(H+W)∙(8∙H∙W)-1]-1
The matrix equation is as follows:
For Nnodes, i:=1…Nnode, j:=1…Nnode
M i,j:= │-Ci if i= j - 1˄ j ˃ 1
│-Ci-1 if I = j +1
│S i + C i-1 +Ci if i= j ˄ i ˃ 1
│S1 + C1 if j= i ˄ j = 1
│0 otherwise
And the calculated pressure is:
P:M-1∙Q
The calculated pressure profile and ion pomp position, after optimisation to meet the pressure requirement for the two beam lines, is as follows:
For the beam line connecting ENBT IV0 with the end of EHBT the calculated pressure profile is:
The choice of ion pumps size, their amount and position along EHBT is dictated by the outgassing of the beam line and its effect on the pressure. To meet the requirement for 1.0E-7 Torr static pressure (with no beam) in the beam line, the distances of the pumps are given by their installation at the diagnostic boxes and their pumping speed. Yhe ion pumps shall be able to pump at speed not less than 50 L/s in Nitrogen saturated state. A pump fulfilling this requirement would be Agilent Vaclon Plus 55 by Agilenttechnologies Inc.
For the beam line connecting EHAT IV0 with EHD the calculated pressure profile is:
Note, that at EHAT IV0 the calculated pressure appears to be 5X10-7 Torr. This is due to the calculation being done with the EHAT IV0 closed. With the valve open, the calculated pressure is below 1.0E-8 Torr. At the other end, i.e. EHDT DB6, the calculation doesn’t take into the account the outgassing from the EHD beam dump. The vacuum system for the High Energy Dump is not part of this calculation.
The ion pump for this beam line shall be a pump with performance characteristics of 200 L/s pumping speed in Nitrogen saturated state.
2.4Vacuum system specification
2.4.1Materials
The EGUN, beam diagnostics sections and the beam transport section are built out of materials and components compliant with the UHV practice [8] – 304 SST, 316L SST, OFHC Copper, and Ceramic. The choice of materials is governed by their machine-ability and their low out-gassing properties.
The accelerating cavities of the injector (one nine-cell cavity) and the two accelerator (two nine-cell cavities each) cryo-modules are built out of Niobium (Nb).
The cleanliness of all surfaces exposed to vacuum is of paramount importance for the E-linac vacuum level.
Note: The vertical location of the beam line (electron beam axis) is going to be:
- 76.2cm from the floor of the Electron Hall for the part located in the Electron Hall
- 45.8cm in the tunnel connecting the Electron hall and rising to 137.2 cm after the vertical dogleg leading to the ARIEL targets. In the tunnel section there is a restriction of the space above the beam line – a future proton beam line running from the Cyclotron to the ARIEL west targets will be positioned 91.5 cm above the e-beam vacuum pipe.
2.4.2Bake-out
All components of the vacuum system will be able to withstand a bake-out temperature at about 180 - 200ºC for one week. The cables of the ion pumps and the ion gauges shall be specified to operate at these elevated temperatures. In addition, special feature machined on the body of the diagnostics boxes allows installation of “HOTROD” style heating elements installed in predrilled 9.5mm diameter holes. All diagnostics devices shall be able to withstand 200ºC bake-out temperatures. If necessary, none-metal parts, air-actuators, and electrical motors should be cooled or removed during the bake-out.
Different components of the beam line will require different solutions for the bake-out:
- The ion pumps heaters are going to be operated remotely from the ion pump controllers, located in electrical cabinets at the roof of the e-hall.
- The beam line pipe, valves and any other components will be bake-out with heaters, which are going to be powered locally.
For practical reasons it is beneficial to bake-out several adjacent sub sections at a time. The name for the several sections is a domain. There are 7 domains comprising the e-linac vacuum system. The schematic shows the domains which require electrical power for local and remote bake-out heaters:
Fig.6 E-linac bake-out domains
The power in kW and the time in weeks to bake out the e-linacare estimated in the table below:
Domain / Local powerin kW / Remote power
in kW / Time to vacuum bake-out in weeks
1 / 63 / 9 / 2
2 / 48 / 11 / 6
3 / 42 / 7 / 2
4 / 42 / 8 / 4
5 / 72 / 7 / 6
6 / 175 / 16 / 2
7 / 50 / 7 / 2
totals / 492 / 65 / *
Note “*”: The bake-out of several sections can happen simultaneously, for example: during the bake-out of a domain with a long bake-out time, another section with a shorter bake-out time can be baked.
2.4.3Venting
For operational need, when it is necessary to vent a section of the E-linac, a source of ultra high purity, filtered Nitrogen shall be used as backfill..
All work related to removal or installation of E-linac components exposed to vacuum, should be performed under a movable tent, which is equipped with air filtering system. The above recommendations are necessary to eliminate the possibility from dust particles entering the vacuum system of the E-linac and contaminating the internal surfaces of the Nb cavities.
Operating procedures:
Cryo-modules isolation vacuum / Rest of accelerator sectionsPump-out procedure
- Initialcondition:the volume is vented. /
- Ensure that all ports and valves are closed.
- Ensure that all pumps are off.
- Turn on the backing pump.
- Open the backing pump valve.
- Open the turbo pumps isolation valves. Leave the turbo backing valves closed.
- Open the cryo-module roughing valve.
- When the pressure in the cryo-module tank is lower than 150mbar, close the roughing valve and immediately open the turbo-pumps backing valves.
- Turn the turbo-pumps on.
- When the turbo pumps are up to speed, turn the ion gauge on.
- Ensure that all ports and valves are closed.
- Attach a turbo pump to the closed pump–out valve of the section
- Attach the backing /roughing line to the turbo pump
- Make sure that the pressure in the beam line and the pressure at the turbo-pump port are the same.
- Open the pump out valve of the section to the turbo-pump
- Wait until the vacuum is better then 1.3E-6mbar before continuing with turning the heaters for the bake-out.
Bake-out procedure
- Initial condition: the volume is at 1.3E-6mbar or lower pressure. / N/A /
- When the vacuum in the subsection is lower than 1.3E-6mbar, turn the heaters on and for about 6-8 hours rise the temperature to about 200ºC.
- Keep the temperature at 200ºC until the pressure in the beam line does not show further improvement.
- Turn on the ion pump
- When ion pump is at normal operation, close the pump-out valve, turn off the ion gauge, remove the turbo from the pump-out valve and remove the turbo pumping cart out of the electron hall.
Venting procedure
- Initial condition: the volume is under vacuum /
- Attach a source of filtered and dry ultra high purity Nitrogen to the vent valve. The line should have a pressure relieve valve set at 10 PSIG pressure. Purge several times the line.
- Turn off the ion gauge.
- Close the isolation valves of the turbo-pumps
- Ensure that the helium tank is at room temperature
- If the helium tank is at room temperature open the vent valve.
- Once the tank is vented, close the vent valve.
- Turn off the ion pump.
- Attach a source of filtered and dry ultra high purity Nitrogento the vent valve. The line should have a pressure relieve valve set at than 10 PSIG pressure. Purge several times the line.
- Open the vent valve to allow the Nitrogen to vent the section.
2.5Purchased components comprising e-linac vacuum system
2.5.1Flanges and seals
All flanges installed on an E-linac vacuum system part, which will take beam, will be of CONFLAT® style. [10], [11], [12].