Ultra High Vacuum Technology Section

Accelerator Programme

Design, Development and Deployment in Major Projects Indus-1, Indus-2, IRFEL, ARPF etc.

1. Vacuum Systems of Undulators in Indus-2 Storage Ring

Indus-2 storage ring is a 2.5GeV synchrotron radiation source (SRS) consisting of eight super periods that contain eight long straightsections (LS). Five of these sections are available to accommodate insertiondevices (IDs) which are special magnetic devices designed to produce SRof special properties includinglarge enhancementof the photon flux. Three of these straight sections namely LS2, LS3 and LS5 have been upgraded and augmented with U1, U2 and APPLE-2 undulators including their vacuum systems and a major boost in the performance of Indus-2 SRS heralding its entry into 3rd generation electron storage ring regime has been accomplished.

SR generated form U1, U2 and APPLE-2 (Advanced Planar Polarized Light Emitter) undulators are to be used for Atomic, Molecular and Optical Science (AMOS) beam line, Angle Resolved Photoelectron Spectroscopy (ARPES) beam line and X-ray Magnetic Circular Dichroism (XMCD) beam line respectively.

Vacuum systems of these undulators were designed, developed and successfully installed within stipulated time schedule. Design of vacuum chamber was so required to satisfy several functional requirements and boundary conditions.Design of vacuum chamber required to satisfy several requirements like: UHV compatibility, low photon induced desorption (PID) yield, lower relative magnetic permeability, good electric and thermal conductivity, low RF impedance, good surface finish and straightness.Aluminium alloy grade 6060-T6 was selected as material of construction for these chambers. Boundary conditions of chamber cross section are minimum pole gap of undulatoron outer side and good field region requirement of circulating electron beam on inner side. To satisfy these boundary conditions, design of the chambers resulted into very low gas conductance. Internal transverse cross section of the vacuum chambers is 17 mm (V) X 81 mm (H) with race track shape. Length of vacuum chambers are 2700 mm and 2500 mm for U1/U2 and APPLE-2 undulators respectively. Attainment of required level of UHV in this low conductance chamber is made possible by deploying nonevaporable getter (NEG) coating as an advanced UHV pumping solution where conventional pumping was not suitable. This NEG coating of ~ 1 micron thickness is a Ti-Zr-V ternary alloy applied on the internal surface of the vacuum chamber by magnetron sputtering. This NEG coating gets masked by stable compound of oxide/nitride layer when exposed to atmosphere whichstops its pumping action. For transforming back to pumping action after installation of vacuum chambers in the ring, this coating required activation cycle. Activation cycle was evolved in-house in the laboratory and applied successfully on these chambers after they were installed in the ring. Programme for automatic baking and NEG activation cycle was also developed.

Major vacuum components developed for undulator UHV systems are: NEG coated vacuum chambers, taper (transition) chamber, corrector chamber, RF-shielded bellow sub-assemblies and RF-shielded sector valves. Fig 1 shows the typical 3D models of undulator system including its vacuum system and Fig 2 shows vacuum system of undulator only. Fig 3 shows the actual photograph of NEG coated vacuum chamber. Prior to installation in ring, all the vacuum components of undulator sectors including IDBPIs were assembled and tested in UHV lab for their UHV performance. Fig 4 shows the undulator vacuum sector on UHV test bench in UHV lab.

Fig 1. 3 D model of undulator system. Fig 2. 3D model of  vacuum system of undulator (Including vacuum system)
Fig 1. 3 D model of undulator system. Fig 2. 3D model of vacuum system of undulator (Including vacuum system)

Fig 3. NEG coated vacuum chamber. Fig 4. Undulator vacuum sector on UHV test bench
Fig 3. NEG coated vacuum chamber. Fig 4. Undulator vacuum sector on UHV test bench

After testing in lab, the non-evaporable getter (NEG) coated vacuum chamber along with the peripheral components like beam position indicators for insertion device (IDBPI), taper chambers, corrector chambers, RF-shielded bellows and sector valves were installed and integrated in Indus-2 ring. The undulator vacuum system is isolated with two RF sector valves from the rest of the Indus-2 ring. After erection of vacuum components, all the vacuum instrumentation cables were routed from the equipment gallery to the undulators well well within stipulated time schedule. Fig 5, 6 and 7 shows the actual photographs of the undulators and their vacuum systems installed in Indus-2 ring. U1 & U2 undulators were installed together in one major shutdown and APPLE-2 undulator was installed in subsequent major shutdown. Subsequent to installation and their integration with adjacent vacuum sectors, in-situ baking and NEG coating activation cycle was carried out for achieving required vacuum level. An ultimate average pressure of 1.5x10-10 mbar was achieved without beam in all the three the undulator sectors and machine was made ready for beam injection trials. Fig. 8 shows the bakeout-cum-activation sequence for undulator vacuum system.

Fig 5. U1 undulator installed in Indus-2. Fig 6. U2 undulator installed in the Indus-2
Fig 5. U1 undulator installed in Indus-2. Fig 6. U2 undulator installed in the Indus-2

Fig 7.  APPLE-2 undulator installed in Indus-2
Fig 7. APPLE-2 undulator installed in Indus-2

The bake-out sequence was optimized to take into account the NEG activation, as given below:

  • In the first part of the bake-out cycle, all non-coated stainless steel components were heated at a ramp rate of ~40ºC/hour to 250ºC and then maintained there for 24 hours, carefully controlling and monitoring with baking software with an auto set point control feature, while the NEG coated Al alloy chamber was ramped up to and maintained at 100ºC in the same duration of ~ 6 hours, to prevent adsorption of water vapor on the inner surface of coated chamber, without an early activation of the NEG.
  • After dwell time period of 24 hours, the temperature of the non-coated parts was ramped down to ~50ºC in such a way that at ~150ºC the degassing of RGA & BAG filaments was completed within a time span of 2-3 hours together with flashing of SIPs intermittently.
  • Together with start of cool down of non-coated vacuum components, the ramp up of NEG coated chamber from 100ºC, at a ramp rate of 16ºC/hour was taken up for ~ 05 hours to attain a temperature of 180ºC, followed by an activation period of 24 hours.
  • By following this baking sequence, all the gases released due to desorption was pumped by SIPs thereby minimizing the adsorption of gases inside NEG coated chambers.
The temperature monitoring and controlling points were optimized by dividing the segment into exactly two halves with one TCU on each side thereby optimizing the electrical hardware. The philosophy behind identification of the temperature controlling points was such as to limit the maximum allowable temperature thereby maintaining the mechanical integrity of chambers and avoiding risk of damage to seals by differential thermal expansion.

Fig 8. Bakeout-cum-Activation Sequence for Undulator Vacuum System
Fig 8. Bakeout-cum-Activation Sequence for Undulator Vacuum System

Fig. 9 shows the spectra of residual gases composition inside undulator vacuum chambers after NEG coating activation. It shows very clean mass spectra, dominated by hydrogen gas in all the three undulator vacuum systems.

Fig 9. Residual gas spectrum of NEG coated vacuum chambers after activation
Fig 9. Residual gas spectrum of NEG coated vacuum chambers after activation


2. Pneumatic Sector & Gate Valve (GV0) Controller in Indus-2

Indus-2, a 2.5 GeV synchrotron radiation source with a circumference of 172 metres, is partitioned in thirteen vacuum sectors using pneumatically operated RF-shielded gate valves. Also, 19 nos. of all metal Gate Valves are installed in the beam lines & TL-3. These valves are opened when the vacuum condition in the whole ring is satisfactory and beam filling is to be done. The valves are to be closed in case of failure of vacuum interlock. The valves are also to be closed for required modifications or repair work or during baking. The opening and closing of the valves is done by means of Valve Controllers which are developed indigenously.These controllers enable safe opening of these valves with interlocks for avoiding any accidental venting of the machine.

Fig 10: Modular Valve controllers with front & back panels view
Fig 10: Modular Valve controllers with front & back panels view

This controller is microcontroller based aiding easy modifications for interlocking scheme, software debouncing, and multiple status indication by the LED without modification in hardware. It also helps to add features of serial communication (RS232 & RS485) along with hardwired potential free relay contacts. The overall design is such that units can be used independently or in a stack of 4 in a 19”card frame in modular fashion allowing easy replacement & maintenance. Provision of Key-switch is kept for selection of LOCAL/REMOTE mode for avoiding unauthorized access of the unit. Failsafe operation is in the sense that any breakage in the interlock cables, solenoid coil wire or power failure should result in the closing of the valve. The unit supports operation of 24V/230V solenoids.
For providing safety to the valve, the status of valve is also integrated with the Machine Safety Interlock System (MSIS) which dumps the beam if valve is not found in open condition during machine operation. The interlock for operation is implemented in the following way:

  1. For opening of the valve the pneumatic pressure required for operation must be in therange of 4-8 bar andthe interlock is set at 5 bar. Vacuum on either side of the valve must be better than set value on the gauge controllers.
  2. For closing of the valve pneumatic pressure must be present. The pneumatic pressure interlock is taken through a mechanical pressure switch.

The LED’s on the front panel indicate different states providing friendly interface for easy fault finding to the operator.

3. Baking System

Baking is an essential process for achieving Ultra High Vacuum in vacuum systems. Optimized bake-out procedures are very important for overall reliability of any vacuum system. In this process the UHV components like Sputter ion pump (SIP), Titanium sublimation pump (TSP) along with the vacuum chambers are subjected to baking for sufficiently long period of time, ~60 hrs. INDUS-2 vacuum chambers are made of Aluminium alloys, which demands very slow and controlled baking. In order to achieve this, an intelligent ON/OFF control system is designed & developed incorporating modular baking system with distributed controls.

This system contains Temperature controller unit (TCU), Pressure Monitoring Unit (PMU), as well as Baking Application GUI. Each TCU is an eight channel temperature controlling unit. A PMU is an eight channel pressure monitoring unit to which analogue data from various gauges like Penning Gauges, BA Gauges, are fed. Baking Application is a user interface software developed for controlling up to 6 TCUs. In this way, 48 channel temperature data logging &control, along with eight channel pressures monitoring is realized.

TCU:

Each TCU is having a provision of 8 channels. It is capable of monitoring as well as controlling the temperature & able to communicate to computer through half-duplex RS485 network. K-type thermocouples are used temperature sensors. TCU temperature measurement range isup to 500ºC, with a resolution of 1ºC. Each channel is able to handle grounded as well as ungrounded thermocouple. In input section, differential as well as common mode RC filter is used.

Fig 11: TCU & PMU
Fig 11: TCU & PMU

Each channel is having short circuit protected SSR (Solid state Relay-zero crossing) which can give ON/OFF type of control to heaters (up to 4 kW/Channel). These relays can be controlled remotely as well as locally. Heat sink and cooling fan provision is made for reliable operation of SSR.

Specifications of TCU

Number of channels : 8
Thermocouple Type : K-type
Resolution : 12 bit
Sampling Rate : 20 mS
I/P Signal range : 500 ºC. (+/- 20mV)
I/P Coupling : DC
I/P Impedance : 10 GΩ
I/P Bias current : 1 nA
I /P offset voltage : 50 µV
I/P Offset current : 0.5 nA
CMRR : 100 dB @ gain = 10
Filter : RC-type
Differential frequency BW : 8 Hz
Common frequency BW : 16 KHz
Heater Power/Channel : kW

PMU:

During bake-out, pressure in the system has to be monitored continuously by using Penning Gauge (1.0E-2mbar to 1.0E-9 mbar) whereas after bake out by using BA Gauge (1.0E-3 mbar to 1.0E-11 mbar). These gauge controllers provide logarithmic 0-10V signal. This signal is used for data logging of pressure readings by using PMU. Each PMU can monitor pressure of 8 channels. These units also support RS485 communication. PMU converts analogue data to digital count by multiplexing the 8channels and using, 12 bit successive approximation ADC and 89S52 micro-controller.

Development of software for baking application

In consideration with requirement of conducting baking cycles on regular basis, the process is simplified & made reliable with in-house developed distributed 48 channel temperature controlling system. The system includes six 8-channel Temperature Controlling Units (TCU) and one 8-channel Pressure Monitoring Unit (PMU) distributed over RS-485 multi-drop network. A GUI is developed for overall supervision & control and data logging of temperature & vacuum. The pressure monitoring unit is used for providing data logging of vacuum in the system supporting various types of pressure gauges being used. The GUI for this setup is completely redesigned & redeveloped for adding more user friendly features using VB.NET.
In this process the temperature of the component is elevated to a desired temperature level from room temperature with required ramping rate, after which it is maintained for about 24 - 48 hours. The temperature is then ramped down to room temperature. In this period turbo molecular pump is kept ON which evacuates the vacuum system bringing down the pressure to a level around 1.0E-06 mbar. The vacuum level is further improved by using ionisation pumps.

Fig.12: Screenshot of software showing overall GUI
Fig.12: Screenshot of software showing overall GUI

Fig.13: Result of a baking cycle conducted for ID BPI
Fig.13: Result of a baking cycle conducted for ID BPI

The benefits of the newly added features are user can configure eight sets of profiles defining starting & maximum temperature. Additional settings which are common for all the profiles like ramp time, temperature band, free fall temperature, need to be set before starting of the cycle. Any channel can be configured for one of the eight suitable profiles, before or during running of the cycle. After starting of the cycle, the set point for each channel is updated automatically for full cycle as per selected profile,at the same time maintaining temperature difference between all channels within required limits. This overcomes the need of manual updating of the set points by the operator at regular intervals. The software also auto detects serial port to which system is connected, the number of units connected at start, minimising further inputs required from operator. Data is logged in .CSV format. This helps in removing dependency on Microsoft office & limitation of installation of old software on a PC with higher version of OS.

The software has more user friendly features like observing serial data communication status & information, data logging status etc. Any channel can be set for one of the profilesand if required, switching between the profiles during operation of cycle is also possible. The state of cycle & running time duration including delay required for holding the cycle for restricting the temperature difference between all channels is also displayed. Provision is there for saving operator notes, channel names etc.Provision is also there for configuring auto set point or manual set point for any channel. The channels which are used only for temperature monitoring must be set to manual mode. The PMU interface now supports selection among eleven types of various vacuum measuring gauges used in UHV Lab.

The software auto detects power failure and provides option of auto reloading after restarting. If a user opts to reload the software, the software restores all the previous settings, channel names & starts appending data log in the original file. This developed software has been successfully used in the baking cycles conducted during commissioning of the Undulators U1, U2 and U3 in Indus-2 as well as in various setups for performing vacuum qualification tests in UHV Lab.

4. 160 Channel Distributed Temperature Monitoring System in Indus-2

In Indus-2 ring, temperature of vacuum components is monitored at different points. This is done considering the interaction of synchrotron radiation (SR) with the vacuum components. At 2GeV, 300mA, estimated radiated power in the ring will be 187 kW and it may cause material damage to chamber walls. 64 water-cooled photon absorbers & 48 water-cooled end flanges are installed on dipole chambers to dissipate SR power. It is necessary to ensure that the temperaturesof these components are under control. This will also ensure low out gassing rate of photon absorbers. The developed system has provision of monitoring 160 channels. The data is being successfully logged along with alarm & trip event occurrences.

This distributed monitoring system has 20 TMUs. Each TMU (Shown in Fig.1) monitors temperature of eight channels. The front panel has communication status LED, Trip status LED, cold junction compensation (CJC) sensor & thermocouple terminating connectors. The back panel has RS485 in & out 9-pin D-connectors. The cabling has been extensively minimised sending temperature of 160 channels over a pair of wires with a facility to define customized commands & easy future modifications. The set point trip relay contacts of all units are taken in series with the help of second pair of wires in communication cable. The mains power supplies of all units are distributed from single point making hardware reset easy for all units, at once.

Figure 14: Front & Back Panel of TMU
Figure 14: Front & Back Panel of TMU

Technical Description

Temperature measurement is done using K-type thermocouples. RC filter is used for rectifying common mode & differential mode noise. The circuit is compatible for both grounded & un-grounded type of thermocouples. It also has provision for detection of open thermocouple. This ADC is chosen for keeping the design universal for faster signal measurement. Temperature resolution is 1°C. The linearization of thermocouple is done with the help of lookup table. Half Duplex RS485 communication is used in which all units are acting as slaves while computer in control room works as master. RS485 driver is optically isolated from the circuit for overcoming the ground loops & limiting the interference of noise sources in analogue measurement circuit. Resistors are terminated on the extremesof the units to get rid of signal reflections. Twisted, shielded cable is used with one pair of wires along with shield to each unit. The power supply transformer is with a shield between primary & secondary windings to minimise noise coupling. For restricting CJC error, sensor (LM35) is located close to the front panel and terminatedwith compensating cables.

Operation and Interlock

There is provision for two types of set points called Alarm Set Point & Trip Set Point. Alarm set point can be changed remotely whereas trip set point is programmed in EPROM. The operator is supposed to find out the cause behind the alarm & take appropriate action as soon as an alarm is detected. Since alarm has the second priority, it’s raised in computer software itself after observing the temperature data. Trip set point is hardwired interlock (single contact). In PC software, user can identify the unit generating the alarm as this data is passed by the unit through the communication frame. In the controller unit, status of spare contact of trip relay is read back & its status is sent in the frame. Considering the importance of trip relay, a maintenance frame is incorporated. After issuing this command, all the trip relaysare activated & their status is read back. This ensures normal behaviour of all trip relays from control room only. Each unit has single trip relay with failsafe logic (normally activated). The N/O (normally open) contacts of all trip relays are connected in series & single contact is given to Machine Safety Interlock System (MSIS). If any channel among the 8, crosses trip set point, the trip relay is deactivated which results in opening of the contacts. Necessary action is taken through the interlock to dump the beam in the ring.

5. Industrial LINAC-ARPF

Vacuum System:

Electron bean quality depends on vacuum level in electron Linear accelerator (LINAC) and desired vacuum required is less than 10-6 mbar. Vacuum in the order of 10-8 mbar is maintained in the LINAC. Vacuum condition is necessary for following purposes:

  • Avoid oxidation of electron gun cathode at high operating temperature.
  • Prevent collision of electron beam with residual gas molecules resulting in beam energy loss.
  • Inhibit microwave arcing and electrical breakdowns in side structure.
  • To avoid impurities inside the structure and multi-pactring.

The vacuum envelope of LINAC consists of electron gun, beam collimator, vacuum manifold-1, accelerating structure with RF input and reflected power RF window coupler, adopter chamber, UHV gate valve, vacuum manifold-2,FCT, bellow chamber and scanner horn assembly. The vacuum system is divided into two sections, the electron gun with accelerating structure and scan horn section using UHV gate valve for maintenance point of view.

In order to minimize the vacuum gradient between different sections due to conductance limitation, distributive pumping scheme was adopted. The electron gun section pumped by two 70 l/s Triode Sputter Ion Pumps (SIP) connected in vacuum manifold-1. One SIP of 70 l/s connected in vacuum manifold-2 just after the gate valve and one SIP of 70 l/s is provided in scanner horn assembly. Leak tightness of vacuum system was maintained < 1x10-9 mbar-l/s order. Leak tightness is checked with HMSLD and base vacuum of 10-8 mbar order was obtained in the LINAC. The detailed specifications of SIP’s used are as follows:

Make : RRCAT made
Pumping speed : 70 l/s for Nitrogen at 10-6 mbar
Configuration : Triode ion pump
Pressure range : 10-3 mbar to < 10-10 mbar
Life time : 50,000 hrs. @ 10-6 mbar
Baking temperature : 250°C
Inlet flange : DN 100 CF-F

Two numbers of cold cathode full range vacuum measuring gauges and controllers are provided for pressure measurements at two locations i.e. at electron gun section (in vacuum manifold-1) and Scanner section at vacuum manifold-2. The schematic of LINAC vacuum system is as shown in the following Fig.

Fig 15: Schematic of LINAC Vacuum System
Fig 15: Schematic of LINAC Vacuum System

The gauges are having pressure measurement range from atmosphere to 5x10-9 mbar. The details of gauges used are as follows:

Specification of Vacuum gauge

Make : Pfeiffer PKR 251
Type : Cold cathode full range gauge
Measuring range : Atm. To 5 x 10-9 mbar
Controller : TPG 262 Dual channel
Safety interlock : User defined Pressure trip setting.

Initial vacuum is created with Turbo molecular pumping station connected with both the vacuum manifolds equipped with the all metal right angle valves for isolation purpose. Completely oil free TMP station is utilized to protect the system in case Linac pressure rises above preset value of 1x10–6 mbar.

Figure 16: Industrial Linac
Figure 16: Industrial Linac

6. IRFEL

Vacuum system

Free electron lasers (FEL) are used for research in different areas of science and technology using short pulse high power electromagnetic radiation. An infrared free electron laser (IRFEL) is being installed in RRCAT. It is designed to lase in 12.5-50 µm wavelength band. Initially it will be used for study of materials in low temperature and high magnetic field environment.
The IR-FEL machine is divided in four sections, first is Linac section, second is beam transport line prior to optical cavity, third is optical cavity and fourth is beam dump line post optical cavity. Total length of the system is more than 17 meters. Each section is separated from other with the help of a gate valve, this facilitates evacuation and maintenance of an individual section without breaking the vacuumin other sections. The general layout details of the machine is given in figure (17).

Fig. 17 General layout of IR-FEL
Fig. 17 General layout of IR-FEL

For smooth transport of the electron beam, pressure in the beam pipes should be less than 3x10-8mbar. In Linac section, the electron gun, pre buncher cavity and both the Linac’s are individually pumped by 140 l/sec. sputter ion pump, four pumps are deployed in this section. To maintain desired vacuum level with uniform pressure profile another 15 sputter ion pumps are deployed in remaining three sections which include one 140 l/s, twelve 70 l/s and two 35 l/s capacity pumps. Based on physics design requirements beam pipes of different cross section/sizes were designed and fabricated to accommodate shape and size of the electron beam in respective section of the beam transport line. Material of construction was S.S. 304L. The first beam transport line pipe was fabricated from a 50.8 O.D. pipe. After first bending magnet chamber, to accommodate specific shape and size of the beam in a given magnetic aperture, a 2040mm long rhombus chamber having inside cross section of 40x80mm is fabricated from 2mm thick S.S. 304L sheet. Sheet pieces were formed to make two halves of the chamber, long sides were machined for accurate matching of both the halves. The schematic details of rhombus chamber are given below.

Fig. 18 Shows actualphotograph of IRFEL beam transport line.
Fig. 18 Shows actualphotograph of IRFEL beam transport line.

Fig. 19 Scheme and actual photograph of rhombus vacuum chamber during installation
Fig. 19 Scheme and actual photograph of rhombus vacuum chamber during installation

The undulator vacuum chamber is fabricated from extruded Al alloy section to avoid any attenuation of magnetic field by the chamber material. It is a 2630mm long chamber with race track type aperture of 17mm x 81mm. Figure (20) shows thephotograph of undulator vacuum chamber.

Fig. 20 Al alloy undulator vacuum chamber
Fig. 20 Al alloy undulator vacuum chamber

The beam dump line is fabricated from 60mm O.D. pipe. There are four bending magnet chambers, three of them are fabricated form S.S. 304L sheet and fourth one is fabricated from S.S. 304L pipe. Ports have been fabricated in the beam transport line to assemble beam diagnostic devices. There are 11 BPM assembled in the line, details of other diagnostic devices are given elsewhere. There are eleven B.A. gaugesmounted at different locations to accurately monitor pressure of the complete facility. The whole line was assembled on appropriate supports fabricated for this purpose. Section wise vacuum commissioning was done by closing entry and exit gate valve of respective section. All the gate valves were opened after achieving desired vacuum in each section. Presently vacuum in all the sections except electron gun and pre buncher is in lower order of 10-9 mbar which shows the healthy condition of the vacuum system.

7. A Differential Pumping System for Soft X-ray Beam Line of Indus-2

Differential vacuum pumping system provides windowless transition between high vacuum region and low vacuum region by using series of vacuum pumps and conductance limited openings (tubes). It is highly useful for the SRS beam lines where 10-6 to 10-7 mbar pressure is maintained at an experimental station. This has to be isolated from the beam line region towards machine side where 10-9 to 10-10 mbar pressure is to be maintained. A differential pumping system does this job without physically obstructing the beam at any point. As there is no physical barrier in the beam path it eliminates the beam loss, heating and mechanical issues of mounting the physical window.

Fig 21: Outline drawing of the Differential Pumping Setup
Fig 21: Outline drawing of the Differential Pumping Setup

A two stage differential pumping system is designed, fabricated in house, assembled, tested and integrated with beam line – 3 of Indus-2. It is designed to fit in available linear space of 415mm in the beam line. It is supposed to maintain a pressure ratio of 1000 across its both ends i.e. 1x10-6 mbar on experimental side (input pressure) and 1x10>sup<-9 mbar on machine side (output pressure). Outline drawing of the system is shown in figure 21.A unique 35 l/s. in-line sputter ion pump is designed and fabricated in house for this purpose. It has a clear opening to pass beam through its anode assembly. It also acts as conductance limited path and thus helps in reducing the integrated length of the system. Details of the pump are shown in figure 22 (a) and (b).

Fig. 22: (a) 35 l/s SIP showing through opening in anode Assy. (b) 35 l/s in-line SIP Assy.
Fig. 22: (a) 35 l/s SIP showing through opening in anode Assy. (b) 35 l/s in-line SIP Assy.

Complete system contains a conductance limited opening in a flange, a 35 l/sin-line SIP, another conductance limited tube and a 70-l/s SIP connected in series. System assembly is shown in figure 23.

Fig 23: Differential pumping system
Fig 23: Differential pumping system

This differential pumping system has been tested from 5x10-4 mbar pressure to 2x10-10 mbar pressure. The maximum pressure ratio of 2400 has been observed at 1x10-4 mbar input pressure. At input pressure of 1x10-6 mbar the pressure ratio is found to be around 1000 which is a desired result. The system is integrated with the beam line and is working satisfactorily. The plot of input v/s output pressure is shown in figure 24.

Fig. 24: Input v/s output pressure (mbar)
Fig. 24: Input v/s output pressure (mbar)

8. Installation and commissioning of upgraded transport line-1

The new transport line-1 was fabricated to augment its performance in electron beam transport from Microtron to booster synchrotron. It has upgraded vacuum beam pipes with all knife edge sealing flange joints. Old sputter ion pumps were replaced and two new pumps were added to take care of additional gas load due to increased diagnostic devices. A branch line is also added to it for measurement of energy spread of the 20 MeV microtron beam. The line is equipped with diagnostic devices such as six beam slit monitors, four upgraded beam profile monitors, two fast current transformers and two secondary emission wire monitors. The signal processing and control network was also augmented to accommodate new diagnostic devices. The transportline-1 was divided in three sections with the help of gate valves for easy operation and maintenance, each section has a vacuum gauge for pressure monitoring. Prior to installation complete line was assembled and vacuum qualified in Lab. Before installation of new transport line the old transport line was removed. First section of new line was assembled, leak tested with HMSLD to have a leak tightness of better than 1x10-9 mbar. All the three sections were assembled and tested with similar procedure. Complete line was vacuum qualified and a base vacuum of 2x10-8 mbar was achieved without any baking. The transport line-1 is functioning satisfactorily after commissioning.

Fig 25: Upgraded Transport Line-1
Fig 25: Upgraded Transport Line-1

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