2024年4月29日发(作者：)

LIBERA BRILLIANCE AND LIBERA PHOTON WORKING TOGETHER IN

FAST ORBIT FEEDBACK

A. Kosicek, P. Leban, Instrumentation Technologies, Solkan, Slovenia

Abstract

Libera Brilliance is already a standard Beam Position

Processor system, which provides data flows at different

sampling rates and bandwidths. It is widely used in the

Fast Orbit Feedback (FOF) system. For this purpose the

fast acquisition data flow (called FA) at ~10 kHz

sampling rate is used. Two standard protocols can be

employed for integration, GB Ethernet or DLS

Communication Controller, the later being developed at

Diamond Light Source.

Libera Photon is a new photon beam position

processor, which is used on blade-based XBPMs. Similar

to Libera Brilliance, it provides dataflow at different

sampling rates. Sampling frequency of the Libera Photon

FA was carefully chosen to exactly match the Libera

Brilliance FA.

This enables a smooth and simple integration of both

devices into the same Fast Orbit Feedback. Since both

devices also share the same control system interface, their

combination in the same system provides a firm

foundation for further stabilization of the beam.

INTRODUCTION

During last few years, many synchrotron light sources

are successfully implementing local and global FOF. The

use of the FOF suppresses various noise sources

significantly and minimizes the RMS of the electron

beam position oscillations in the frequency range up to

~200Hz, finally resulting in the improved stability of the

photon beam. To obtain even better stability, it is required

to monitor the photon beam and therefore the inclusion of

the photon beam position monitor in the FOF loop(s) was

proposed. The photon beam position monitors can be used

to monitor only the vertical position of the beam (in the

bending magnet beam lines) or to measure also the

horizontal position of the beam (after the insertion

devices).

As a result a better optimized correction matrix for

driving corrector magnets of electron beam is obtained

and more stable photon beam is measured at the target.

The analysis of the later was discussed in [1].

The use of Libera Brilliance and Libera Photon in the

same FOF offers several benefits:

- Full and straightforward synchronization of data

streams from both devices. The data is

automatically synchronized to RF frequency as

well.

- Fast data @ ~10 kHz sample rate and 2 kHz

bandwidth.

- The fast data stream can be implemented via either

GB Ethernet protocol or DLS Communication

Controller, both being proved as reliable and easy

to use solutions.

LIBERA BRILLIANCE

Libera Brilliance is well known state of the art

instrument for electron beam position processing on

synchrotron light sources. Its superb metrological

characteristics and the supported flexibility in software

have made it the BPM electronics of choice. The

instrument is constantly improved through software

release policy, new features and applications being

suggested by both, by users and by development staff.

The device has several possibilities to interface the

accelerator control system.

One of the main strengths of Libera Brilliance is its

performance and flexibility when it is used as the data

source (or even controller) for FOF. The so-called fast

acquisition (FA) data stream, which is used as the input to

the correction matrix, has the sample rate of ~10kHz

(accelerator dependent) and the 3dB bandwidth of exactly

2kHz. The specified beam position RMS of this data

stream is 0.25µm for the input signals above -20dBm, and

is usually kept even lower.

LIBERA PHOTON

Libera Photon is a recently developed photon beam

position processor for electrical current output based

sensors. Its performance is being tested on Soleil and

ESRF. In terms of functionalities it is similar to Libera

Brilliance, except that it is used for photon beam position

monitoring. Due to the principles used it lacks the turn-

by-turn (TBT) data. Anyhow it is of most importance, that

Libera Photon shares the same FA data output as the

Libera Brilliance.

The Libera Photon is an All-in-one device, so it

features:

- Current to voltage conversion

- Digitalization of analogue signals

- Digital signal processing

Four current inputs of the instruments may be used in

different configurations. The internal bias voltage source

may be used to bias the potential of the inputs. Still, the

choice of external bias voltage is provided if higher

voltage is required.

The internal calibration current source is built-in in the

instrument; the calibration itself takes less than 10

seconds. The long term measurements conducted have

shown excellent stability though.

Libera Photon covers broad range of the input signal

levels. The input signal amplitude span is divided into

seven ranges, as presented in table below.

Table 1: Input Current Ranges

The ranges can be set either manually or automatically.

Automatic gain control is based on observation and quick

analysis of the ADC buffer, the principle was proven on

the Libera Brilliance already. A hysteresis is introduced to

avoid frequent switching between adjacent ranges.

The Libera Photon preliminary position RMS

performance was measured at four lower ranges, the setup

and the results are outlined below:

Figure 1: The measurement setup at lower ranges.

Table 2: The RMS at Lower Current Ranges

Libera Photon also uses the same software structure as

the Libera Brilliance; the same principles are used for

interaction with the control systems. This makes the

integration into common operational system even more

straightforward.

LIBERA PHOTON AND BRILLIANCE

WORKING TOGETHER

Among the main ideas during the Libera Photon

development was to make it compatible with Libera

Brilliance from the FOF point of view. A lot of effort was

in creation of the mechanism for the synchronization of

the data streams. The only non-synchronized data

available from the two devices is the ADC rate data;

anyhow this is obvious since the ADC sample rate on

Libera Brilliance is at ~115MHz (16bit), while the ADC

rate on Libera Photon stays typically at ~100KHz (24bit).

FA data rate

The FA data rate is used as an input to the FOF

correction matrix. When the Libera Brilliance is

customized (specific requirement of each light source to

adjust to the particular revolution time, retrieving so

called TBT data), a suitable FA data rate is chosen at

around 10kHz rate. Exactly the same data rate is used on

Libera Photon. This makes the integration of both devices

into the FOF straightforward. The integration of Libera

Photon into a Libera Brilliance based FOF, is just the

same as an addition of yet another Libera Brilliance.

The synchronization of the FA rate is realized in the

same way on both devices; they are based on the same

timing inputs. First, the synchronization in frequency is

achieved through the Machine Clock. Then, on the Set-

time trigger, the synchronization of phase is done by

tweaking the phase-locked loop on sampling VCXO. The

process is schematically shown on the figure below:

Figure 2: The FA data synchronization process.

In addition to perfect synchronization of phase and

frequency, the FA data packets are equipped with 16bit

counters. These are reset on the set-time trigger to assure

that the samples originating from the right moment in

time are taken into account for the correction calculation.

Setup

Libera Photon and Libera Brilliance are measuring the

positions of two totally different types of beam, photon

and electron beams. But as the photon beam originates

from electron beam, the measurements on photon beam

can reveal a lot of information of the behaviour of the

electron beam. Having this information, the correction of

the electron beam orbit can be significantly better.

To make the FOF containing both devices feasible, a

dedicated fast LAN must be in place, connecting all BPM

devices around the ring and beamlines. The final

architecture of the FOF layout differs from accelerator to

accelerator and it takes into the account different criteria

like the accelerator size, minimum latency, existing

connecting hardware, the amount of data concentrators,

etc. Below is the scheme of the local FOF setup involving

Libera Brilliance and Libera Photon:

Figure 3: The setup.

As the Libera Brilliance and Libera Photon are identical

from the FA point of view, they can be inserted in the

setup in arbitrary succession.

The integration into control system

From the Control System point of view, the devices are

also very similar. Although the Libera Photon is less rich

with settings and options, main parameters are the same.

As mentioned, the only data from Libera Photon that

differs is the ADC raw data, which is 24-bit deep at

100kHz. Also, there is no TBT data from Libera Photon.

Below is the schematic [1] of the Libera Photon

software structure, the architecture is identical with

Libera Brilliance:

Figure 4: The Libera control system integration structure.

Although this is not a pure “plug and play” solution, for

existing Libera Brilliance users this almost identical

interface diminishes a lot of the effort and manpower

needed for the integration of a new device into the

Control System.

CONCLUSION

The addition of Libera Photon to the existing FOF is

interesting for users mainly since:

- By having the same data properties it is very

simple to extend the correction matrix of the

existing Libera Brilliance FOF.

- Its integration into Control System is simple as it is

using the same principles as Libera Brilliance.

- It helps to improve the global electron beam

stability by adding a new dimension into FOF.

- It measures reliably the photon beam position,

which is critical for the quality of the light source.

As already known, users can also count on

Instrumentation Technologies extensive technical

support during system planning, setup and

commissioning.

REFERENCES

[1] D. Tinta, “Libera Photon”, ppt presentation, Libera

Workshop 2009, Solkan Slovenia, September 2009.