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Instrumentation

The main task of the Beam Instrumentation Laboratory (Laboratorio Elettronico Strumentazione, LEST) is the development of the instrumentation for all the accelerators at ELETTRA.

By means of a large number of custom developed boards and instruments integrated into the Control System by more than twenty VME field computers, all main beam parameters, like transverse position, intensity, transverse and longitudinal profiles and other motion related physical quantities, are monitored in real-time.

The basic criteria in our designs are best performances with the highest reliability: as a matter of fact, some instruments are essential for the operation of the laboratory.

By continuously upgrading the installed instrumentation with state-of-the-art solutions, the measurement resolution is permanently pushed down to lower and lower limits, being presently at the picosecond level in the measurements of time domain profiles and at sub-micrometer level in the transverse position measurements.

Recently, the Beam Instrumentation Laboratory has started to provide its service also to some User Groups working in specific fields, like time-resolved spectroscopy or IR analysis techniques.


Knowledge base

The different areas of activity of the Beam Instrumentation group cover:

  • RadioFrequency circuit design
  • Digital circuit design
  • Electro-magnetic sensor design
  • Optical instrumentation design
  • Low Level software development
  • Integration of the "off-the-shelf" instruments in machine measurements

The development tools and instruments routinely used in the Laboratory are:

  • RF measurement laboratory, both in time and frequenmcy domain
  • Digital circuits development tools
  • Integrated CAD environment (PCB design, FPGA synthesis etc.)
  • Software development tools under different Operationg Systems, like OS/9, Linux (also with Real Time extension), Windows, including graphical interfaces
  • 8-bit and 16-bit micro-controller development environments and field buses


Current designs

The following designs are currently active in the Instrumentation Laboratory, listed here with decreasing priority.


Low GAP Beam Position Monitor (LG-BPM)

The Beam Position Monitor (BPM) system provides a measurement of the transverse (X and Y) position of the electrical centre of mass of the electron bunches. The beam is sensed by means of button electrodes housed in the so-called “BPM”. This BPM is a stainless steel block fitted with four 50Ohm SMA vacuum feed-through. The signal induced by the bunched beam (2ns bunches separation) on each electrode is the 500MHz carrier signal, amplitude modulated according to the beam-to-electrode distance. By applying a simple formula (difference-over-sum) to the four output voltages (V1 to V4) of the AM demodulator, it is possible to recover the position information.
 
A new Beam Position Monitor (BPM) system is presently under design for the Storage Ring of ELETTRA. Its performances rely on the new Low-Gap BPM, specifically designed for the low-gap Insertion Device (ID) Aluminum vacuum chamber, presently under installation at ELETTRA. To develop this new system two main projects have been started the mechanical design to provide the Low Gap BPM, fitted with 14mm diameter buttons, and the relative support system and vacuum chamber interface 
the electronic design to provide a new analogue front-end and a digital amplitude demodulator 
Mechanical design At ELETTRA, the low gap ID vacuum chamber has an elliptical section, with L=81mm and H=14mm. To have the maximum sensitivity in the vertical plane, 14mm diameter buttons have been very closely located, with only 12mm center-to-center distance in the horizontal plane (see fig.1). Two bellows will isolate the BPM from mechanical movement possibly induced by the vacuum chamber.


top view of the Low Gap BPM, including two SMA connectors and the two bellows and flanges. 

The support system of the BPM will provide state-of-the-art both short-term (vibrations) and long-term (thermal) stability to the monitor. Furthermore, a monitoring system, based on capacitive sensors (see fig.2), for BPM sensor motion at sub-micrometer level will be installed, providing the information about any sensor motion.


T:Dhe two armatures of the capacitive sensor (20x20mm each).






Electronic design
The electronics (see fig. 3) of the new BPM system can be divided into the following blocks:
- analog front-end
- digital receiver (AM demodulator)
- DSP processor
    The main function of the front-end is to provide high-stability and resolution for the button signals with sufficient bandwidth for the Local Feedback to operate properly. Two front-end solutions are presently under design: a 4-channel Front-end, developed in collaboration with the Swiss Light Source, and a 4-to-1 Multiplexed Front-end, internally developed. In order to keep matched the gains on the four channels, a pilot frequency signal will be injected at the front-end inputs and the amplitudes of the four outputs will be kept equal by tuning each channel gain. The IF outputs of the front-end will be directly under-sampled at 32*frev being the signal band-limited around the IF frequency of 70 MHz.
The digital receiver block will provide x & y position signals by means of state-of-the-art Digital Demodulator (Digital Down-Converter).
Finally a DSP module will manage the data stream and provide filtered values to the central processor of the Local Feedback


User Timing System (UsTiSys)

The Users at ELETTRA are scientists using Synchrotron Radiation for different kind of experiments. One possible application of Synchrotron Radiation is in microscopy and spectroscopy experiments.
Sometimes, there is also the need to synchronise the acquisitions of the experimental set-up with the Synchrotron Radiation light pulses. A low-jitter trigger signal, synchronous to the Light pulses, is then needed close to the experimental station.


To obtain it, a User Timing System is presently under installation at ELETTRA. It is constituted   of a signal distribution system and of many User Timing Units (UTU), each located close to one experimental station.
The RF signal (f=500MHz) from the ELETTRA Master oscillator is distributed around the Experimental Area, by means of a good-quality low-loss coaxial cable. It is, then, locally divided (modulo 432=harmonic number of ELETTRA) to yield the Storage Ring Clock signal (fSRC=1.156MHz).Furthermore, to provide the Users with the information about the Storage Ring filling, an Analogue signal from an Electro-magnetic pick-up located on the ELETTRA Storage Ring is also distributed around the Experimental stations (beam lines).

Block diagram of the User Timing Unit (UTU), showing the digital divide and delay module and the analogue part for the amplification of the Storage Ring filling signal.

The RF signal is first divided-by-432 to generate the Storage Ring Clock (SRC) signal. The SRC signal is then fed to a digitally programmable delay unit which allows to locate it in any point of the Storage Ring time frame (tREV=864ns). Integrated Circuits (ICs) form the ECLinPS (by MotorolaTM) family have been used to keep the jitter at minimum level.

The jitter (defined as time fluctuations of the trigger position with respect to a reference signal) has been measured using the block diagram  using a 50GHz sampling scope by Tektronix.

The measured jitter has shown to be less then 5ps. The slope of the sinusoidal RF signal is acquired using as a trigger to the scope the SRC signal.
Last Updated on Friday, 16 December 2011 14:47