An Update of The Diagnostic Systems Proposed for
The New Third Generation UK Light Source,
DIAMOND
Stephen R Buckley, Michael J Dufau, Robert J Smith
Daresbury Laboratory, Keckwick Lane, Daresbury, Warrington, WA4 4AD. UK
Abstract. This paper describes the currently proposed systems for electron beam position
monitoring (EBPM) and diagnostics for the DIAMOND synchrotron. Although the basic
requirements have remained unaltered, the philosophy of implementation has been subject to
change, influenced by the experiences of other national light sources, and the emerging
availability of commercial equipment, suited to the needs of DIAMOND. This paper focuses in
greatest detail on the storage ring systems, including data acquisition and control. Details of
Total Current Monitor (TCM) systems, and an active, beam position based interlock system for
protecting ID vessels against thermal damage, by beam mis-steer, are also included.
INTRODUCTION
Diagnostic systems for DIAMOND, the UK's proposed 3GeV 3rd Generation Light
source, will be essential for the rapid commissioning and successful operation of the
new facility. This paper proposes a specification for the expected requirements. The
options to meet these requirements are discussed in turn and technical solutions are
indicated to allow costs to be estimated and to inform design work in other
DIAMOND systems.
Electron beam diagnostics has undergone a period of rapid technological
development. A lot of this technology is now maturing and has been assessed by many
long standing and newer 3rd generation light sources. This now provides the
opportunity to specify and recommend, commercially available and hence more cost
effective diagnostic implementations. It should be borne in mind however that the
development of systems continues apace, and over the period of construction of
DIAMOND, it will be necessary to review and refine some proposals at the onset of
project procurement to capitalise fully on new technology and the experience of
others.
Synchrotron radiation experiments depend increasingly for success on excellent
source properties in terms of the stability of source dimensions and position. It has
been assumed in the following that position stability to 1 micron or better will be
required on all beam lines in both planes measured on time scales from milliseconds to
hours for both local and global feedbacks. In addition and on the microsecond scale,
individual bunch instabilities must also be considered to further reduce the beam size
CP648, Beam Instrumentation Workshop 2002: Tenth Workshop, edited by G. A. Smith and T. Russo
© 2002 American Institute of Physics 0-7354-0103-9/02/$19.00
447
and suppress beam blowup, though such instability feedback is not considered here.
and suppress
blowup,
thoughsystems
such instability
not considered
here.
Although
highbeam
quality
diagnostic
will playfeedback
a majorisrole
in achieving
the
Although
high
quality
diagnostic
systems
will
play
a
major
role
in
achieving
the
required performance, beam stability specifications must be considered at the earliest
required
performance,
beam stability
specifications
be considered
at the
earliestat
design
stages
of all DIAMOND
systems.
The generalmust
problem
of achieving
stability
design
stages
of
all
DIAMOND
systems.
The
general
problem
of
achieving
stability
the user's sample is discussed, leading to some recommendations for considerationatin
thedesign
user’sof
sample
is discussed,
leading to some recommendations for consideration in
the
the facility
as a whole.
the design of the facility as a whole.
STORAGE RING ELECTRON BEAM POSITION MONITORS (EBPMS)
STORAGE RING ELECTRON BEAM POSITION MONITORS (EBPMS)
The proposed storage ring EBPM system is the most extensive and complex of all
The proposed storage ring EBPM system is the most extensive and complex of all
DIAMOND
diagnostics. Each of the 24 cells will be equipped with 7 two plane
DIAMOND diagnostics. Each of the 24 cells will be equipped with 7 two plane
monitors.
At
the ring
ring will
will be
be earmarked
earmarked for
for
monitors. At least
least one
one extra
extra EBPM
EBPM position
position within
within the
installation
as
a
test
station
and
another
for
the
instability
feedback
signal
source.
The
installation as a test station and another for the instability feedback signal source. The
mechanically
the cell
cell is
is shown
shown in
in Figure
Figure 1.1. ItIt isis
mechanically defined
defined positional
positional layout
layout within
within the
proposed
to
add
further
EBPMs
within
the
insertion
device
(ID)
vessels
as they
they are
are
proposed to add further EBPMs within the insertion device (ID) vessels as
installed,
to
provide
facilities
for
stand
alone
vessel
protection
systems
for
vertical
installed, to provide facilities for stand alone vessel protection systems for vertical
beam
high precision
precision beam
beam position
position
beam misalignment,
misalignment, and
and to
to provide
provide additional
additional high
measurement
servos.
measurementtotosupplement
supplement local
local position
position servos.
All
simulations from
from theory
theory[1].
[1].
Allresults
resultspresented
presentedare
areby
bymathematical
mathematical electrostatic
electrostatic simulations
Further
analysis package
package will
will be
be carried
carriedout
out
Furthertests
testsusing
usingan
anelectroststic
electroststic finite
finite element
element analysis
totorefine
refineabsolute
absolutebutton
button pickup
pickup positions.
positions.
FIGURE 1. Positional Layout of EBPMs Within The Cell
FIGURE 1. Positional Layout of EBPMs Within The Cell
448
Primary
Primary Electron
Electron Beam
Beam Position
Position Monitor
Monitor (PEBPM)
(PEBPM) Pickups
Pickups
PBPM Vertical Calibration factor
13
^ ——
12
£12
s/
11
9
m 9
8
|s
7
n ,
£'
6
—n^^i
20.0mm
10
^**^
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a
^»*>»* *°°****~*^
e
\
8
12.0mm
1ZOmm
x
V^—|
*—^i——i——i——y*s
0
2
4
4
6
6
8
J
Horizontal Calibration Factor……..
Of
Of the
the seven
seven EBPMs
EBPMs in
in each
each cell,
cell, the
the two
two devices
devices at
at either
either end
end of
of insertion
insertion straights
straights
will be
will
be of
of the
the high
high performance,
performance, high
high stability
stability type.
type. Mounted
Mounted in
in such
such aa way
way as
as to
to
minimise any
minimise
any mechanical
mechanical movement,
movement, their
their positions
positions will
will be
be constantly
constantly measured
measured in
in
respect to
to machine
machine survey
respect
survey monuments,
monuments, incorporated
incorporated with
with these
these devices.
devices. To
To facilitate
facilitate
this, the
the PBPMs
PBPMs will
this,
will be
be isolated
isolated by
by bellows
bellows from
from the
the rest
rest of
of the
the cell
cell and
and fixed
fixed to
to
individual rigid
individual
rigid stands.
stands. These
These devices
devices will
will provide
provide aa reference
reference beam
beam position
position and
and can
can
also
be used
used to
also be
to determine
determine position
position and
and angle
angle through
through the
the insertion
insertion device
device for
for local
local
correction. Continuous
correction.
Continuous physical
physical position
position measurements
measurements on
on these
these PBPM
PBPM vessels
vessels will
will
also
also be
be made
made to
to discern
discern beam
beam from
from vessel
vessel movements.
movements.
The
The PBPM
PBPM pickup
pickup head
head will
will utilise
utilise the
the standard
standard Daresbury
Daresbury (i.e.
(i.e. modified
modified ESRF)
ESRF)
type
button
feedthroughs
[2]
to
detect
the
internal
electric
field
generated
type button feedthroughs [2] to detect the internal electric field generated by
by the
the beam.
beam.
The buttons
The
buttons will
will be
be arranged
arranged in
in an
an overlapping
overlapping pattern
pattern of
of four
four buttons,
buttons, mounted
mounted on
on the
the
top
and
bottom
faces
of
the
vessel,
with
sufficient
separation
to
allow
installation
top and bottom faces of the vessel, with sufficient separation to allow installation
welding. An
An additional
welding.
additional pair
pair of
of on
on axis
axis vertical
vertical buttons
buttons will
will be
be added
added to
to allow
allow complete
complete
measurement
signals
detection
from
the
horizontal.
de-coupling
of
the
vertical
de-coupling of the vertical measurement signals detection from the horizontal. These
These
will provide
provide an
will
an independent
independent vertical
vertical position
position measurement
measurement ifif required.
required. These
These vessels
vessels
will be
be of
will
of aa narrow
narrow vertical
vertical aperture,
aperture, to
to give
give enhanced
enhanced performance,
performance, with
with significantly
significantly
improved signal
improved
signal to
to noise
noise ratios.
ratios. Although
Although itit is
is desirable
desirable to
to minimise
minimise the
the vertical
vertical
apertures
the EBPM
EBPM response
response improvement
apertures still
still further
further for
for the
improvement this
this gives,
gives, itit is
is important
important to
to
balance this
balance
this against
against the
the lifetime
lifetime effect
effect that
that this
this will
will have.
have. An
An adequate
adequate response
response
however is
however
is still
still obtainable
obtainable for
for aa PBPM
PBPM with
with aa larger
larger than
than ideal
ideal vertical
vertical aperture
aperture of
of
20mm,
and
a
button
separation
of
12mm
centre
to
centre,
configured
20mm, and a button separation of 12mm centre to centre, configured in
in aa
longitudinally displaced
longitudinally
displaced overlapping
overlapping configuration
configuration as
as described.
described. The
The resultant
resultant vertical
vertical
and
horizontal
electrical
calibration
factors
for
this
geometry
can
be
seen
and horizontal electrical calibration factors for this geometry can be seen in
in Figure
Figure 2.
2.
They are
They
are approximately
approximately the
the same
same in
in both
both planes
planes around
around the
the central
centralregion
regionof
ofinterest.
interest.
22
/
20
y^
18
§">
y1^
16
14
^s^
12
gl210
Vertical Beam Offset (mm)
^^
6
1
10
——-^
8
R -
0
2
4
4
6
6
8
8
10
10
Horizontal Beam Offset (mm)
12
12
14
14
16
Horizontal Beam Offset (mm)
Vertical Beam Offset (mm)
FIGURE 2. Central ‘on-axis’ Electrical Calibration Factor Variation for the DIAMOND PBPMs
FIGURE 2. Central 'on-axis' Electrical Calibration Factor Variation for the DIAMOND PBPMs
As is
is shown
multiplying calibration
As
shown aa multiplying
calibration factor
factor of
of around
around 99 is
is found
found in
in both
both planes
planes
around
the
central
region
of
interest,
which
will
give
adequate
signal
to
noise
around the central region of interest, which will give adequate signal to noise ratios
ratios for
for
the desired
desired positional
positional resolution
the
resolution of
of less
less than
than 11 micron,
micron, in
in the
the vertical
vertical plane.
plane. Further
Further
refining of
refining
of the
the button
button positions,
positions, taking
taking into
into account
account the
the installation
installation of
of the
the on
on axis
axis pair
pair
of
buttons
can
result
in
a
further
improvement
in
calibration
factors
in
one
plane
of buttons can result in a further improvement in calibration factors in one plane only.
only.
Using the
the 44 button
button BPM
the horizontal
Using
BPM only
only for
for the
horizontal plane,
plane, and
and adjusting
adjusting the
the button
button
449
spacing to 24.0mm can produce calibration factors as low as 7. Values below even this
(-6) are obtained from the single on axis vertical buttons. These results should be
balanced however against the increased cost of the detector electronics with which the
PBPM devices will be instrumented.
The extent to which this high accuracy and resolution measurement is useful will
depend on the relationship between the reference in which the user is working or in
which his optics is located and the reference established by the local EBPMs. This in
turn will depend on the details of the building and floor design and the proximity of
the user or his equipment to the source. The same argument can be made for the
relevance of independent white beam photon position monitors, which may be remote
from the user and some distance from his optics. The fast global feedback loop will
however be capable of operating much faster, and in conjunction with fast steering
elements in the ID straights will allow the removal of motions due to ambient
vibration and electrical interference up to ~100Hz.
Standard 'In Vessel' EBPM Pickups
It will not be practical to bellows decouple the remaining 5 EBPMs in the cell from
the vacuum vessel, but they will be kinematically mounted to ensure that thermal
motion is well constrained and repeatable. Global correction regimes lock the beam to
a reference defined by the location of all the EBPM vessels. These in turn will be
referenced to the position of the PBPMs, which define a 'standard' position. However,
in the context of global correction, the reference defined by all the EBPMs is unlikely
to be any more relevant to the facility users than the reference defined by the locations
of the magnet systems and any benefits from this to users will have to be assessed.
One solution adopted by some 3rd generation light sources, which lock the EBPMs to
adjacent quadrupoles will only be effective if the mechanical engineering problems
associated with differential expansion of the vacuum vessels and the magnets under
the influence of varying ambient temperatures and varying stored beam power loading
are solved. Substantial development work continues in this area.
The EBPM pickup head will again utilise the standard Daresbury (i.e. modified
ESRF) type button feedthroughs to detect the internal electric field generated by the
beam. The buttons will be arranged within the standard vessel geometry to give a
reasonable response in both planes. A partially optimised example of such a vessel
response is shown in Figure 3.
The offsets of the electrical centres of the EBPMs will be measured on calibration
rigs before final assembly. However, experience dictates that systems allowing in situ
measurement of the relationship between the electrical centres should be provided.
The simplest way to make this measurement is to modulate the excitation of
individual quadrupoles and look for a minimum response on the beam at the
modulation frequency. The present plan for DIAMOND includes the use of
individually programmed power supplies for each quadrupole which will allow simple
implementation of this measurement technique.
450
Horiz. EBPM Calibration Factor….
T
22
EBPM Vertical Calibration factor
20
18
16
14
38.0mm
12
10
9.50mm
8
6
0
2
4
4
6
6
8
8
10
10
Vertical Beam
BeamOffset
Offset(mm)
(mm)
Vertical
12
12
14
16
28
26
24
22
20
18
16
14
0
2
4
4
6
6
8
8
10
10
12
12
14
14
16
Horizontal
Horizontal Beam
BeamOffset
Offset (mm)
(mm)
FIGURE 3.
3. Central
Central 'on-axis'
‘on-axis’ Electrical
Electrical Calibration
Calibration Factor
Factor Variation
Variation for
for the
the DIAMOND
DIAMOND in
in vessel
vessel EBPMs
EBPMs
FIGURE
DETECTION ELECTRONIC
ELECTRONIC SYSTEMS
DETECTION
SYSTEMS
The installed
installed EBPM
EBPM detection
detection systems
systems must,
must, in
The
in combination,
combination, provide
provide position
position
measurement with
with sufficient
sufficient accuracy
measurement
accuracy and
and range
range in
in several
several situations.
situations. These
These include
include
the storage
storage ring,
ring, where
where capabilities
capabilities of
of instantaneous
instantaneous single/first
the
single/first turn
turn position
position is
is
required, and
and also
also during
during beam
beam transportation
transportation along
required,
along the
the flight
flight paths,
paths, and
and during
during its
its
time within
within the
the booster
booster accelerator.
accelerator. They
They must
must in
time
in addition
addition provide
provide the
the storage
storage ring
ring
with
very
high
quality,
stable
position
information
at
rates
sufficient
to
with very high quality, stable position information at rates sufficient to allow
allow the
the
operation of
of global
global beam
beam feedback
feedback servos,
rates up
to 100Hz.
operation
servos, at
at rates
up to
lOOHz. This
This will
will meet
meet the
the
requirements, of
of both
both long
long and
and short-term
requirements,
short-term stability
stability of
of less
less than
than 10%
10% of
ofbeam
beamsize.
size.
Until
recently,
such
high
precision
detection
electronics
had
to
be
Until recently, such high precision detection electronics had to be built
built in
in house.
house.
Today
however,
commercial
systems
are
available
to
tackle
such
problems.
Today however, commercial systems are available to tackle such problems. Two
Two
systems are
are compared
compared and
and aa suitable
suitable implementation
systems
implementation presented.
presented.
Commercial Systems
Commercial
Systems
The two
two systems
systems discussed
discussed have
have used
used very
The
very different
different approaches
approaches to
to the
the task
task of
of
EBPM
signal
detection,
and
both
have
merits
and
drawbacks.
An
overview
EBPM signal detection, and both have merits and drawbacks. An overview of
of the
the
operational techniques
techniques is
is given
given below.
below.
operational
The Bergoz
Bergoz Instruments,
Instruments, Multiplexed
Multiplexed BPM
The
BPM (MBPM)
(MBPM)
This device is the more mature of the two commercial types, and its function is
This device is the more mature of the two commercial types, and its function is
based around analogue circuitry to produce DC values, relating to X and Y beam
based around analogue circuitry to produce DC values, relating to X and Y beam
position within a normal type four button pickup EBPM head [3]. A schematic
position within a normal type four button pickup EBPM head [3]. A schematic
showing the detector hardware can be seen in Figure 4.
showing the detector hardware can be seen in Figure 4.
The key to the operation of this device is that each button pickup from the EBPM
The key to the operation of this device is that each button pickup from the EBPM
head, is processed through the same electronic detector. This is achieved by a
head, is processed through the same electronic detector. This is achieved by a
switching multiplexer, that passes all signals in turn through a series of filters and gain
switching multiplexer, that passes all signals in turn through a series of filters and gain
control, to the detector chip, based around a standard television technology detector,
control, to the detector chip, based around a standard television technology detector,
running at 21MHz. The resultant voltages are held in sample and hold devices that
running at 21 MHz. The resultant voltages are held in sample and hold devices that
allow the appropriate summing and differences to result in X and Y positions being
allow
the appropriate summing and differences to result in X and Y positions being
produced as DC Voltages. These voltages are then digitised by a separate ADC to
produced
as DC Voltages. These voltages are then digitised by a separate ADC to
interface them to the control system.
interface them to the control system.
451
Cask 90*9FIGURE 4. Bergoz Instrumentation Detector Electronics Schematic (MBPM)
FIGURE 4. Bergoz Instrumentation Detector Electronics Schematic (MBPM)
Since this detector uses a multiplexer on its input, it uses the same detector for each
Since this detector uses a multiplexer on its input, it uses the same detector for each
button signal, and produces excellent results, with compensated electronic drift,
button signal, and produces excellent results, with compensated electronic drift,
however
the multiplexer means that it has limitations with regard to its position
however the multiplexer means that it has limitations with regard to its position
reading
update
on the
the SRS
SRS for
for over
over two
two
reading updaterate.
rate. Bergoz
Bergoz MBPM
MBPM cards
cards have
have been
been used
used on
years
for
BPM
measurements
and
active
machine
protection
for
insertion
devices.
years for BPM measurements and active machine protection for insertion devices.
The
BPM (DBPM)
(DBPM)
TheInstrumentation
Instrumentation Technologies
Technologies (I-Tech)
(I-Tech) Digital
Digital BPM
This
method is
is based
based
This device
device isis relatively
relatively new
new to
to the
the market,
market, and
and its
its detection
detection method
around
the
technique
of
processing
all
four
button
pickups
down
identical
separate
around the technique of processing all four button pickups down identical separate
channels.
and difference
difference required
required for
for
channels.The
Theresults
results are
are then
then digitised
digitised and
and the
the summing
summing and
beam
or other
other higher
higher level
level
beamposition
position readings
readings carried
carried out
out within
within the
the VME
VME controller,
controller, or
computer
within the
the Swiss
Swiss Light
Light Source
Source
computer [4].
[4].AAblock
block diagram
diagram of
of its
its implementation
implementation within
(SLS)
(SLS)isisshown
shownininFigure
Figure5.5.
FIGURE5.5. I-Tech
I-Techfour
fourchannel,
channel,'Quad-Receiver'
‘Quad-Receiver’ Schematic/Overview
Schematic/Overview installed
installed in
in the
the SLS
SLS EBPM
FIGURE
EBPM Configuration
Configuration
I-Techthemselves
themselves are
are becoming
becoming established
established with
with this
this and
I-Tech
and
around
BPM
technology,
including
tune
measurement
and
around BPM technology, including tune measurement and
systemfront
frontend
enddetectors.
detectors.
system
452
other
other products
products based
based
multibunch
multibunch feedback
feedback
The basic methodology used here is to detect each input signal down its own
detector channel, in order to provide very high speed (single/first turn) Beam position
signals. Each single input channel is mixed down to an intermediate frequency of
36MHz and gain equalised against a separate pilot frequency, applied to all channels,
generated on board before final filtering. This pilot frequency is essential to help keep
all channel gains close together, to maintain the reading accuracy. These four 36MHz
signals are digitised by an adjacent dedicated 14 bit ADC, with 16 bit resolution being
achieved by oversampling. Hence the 14 bit mode is available for the single/first turn
mode, and the 16 bit data at much slower rates for high precision read back for use
with global servos, typically at frequencies up to lOOHz. Further enhancements to the
system include a dedicated DSP module (installed one per VME crate), to fully exploit
the single turn capabilities. A major feature of this system is its ability to store up to
16,000 turns of data, allowing a 'black box' mode to investigate beam losses and some
instabilities exhibiting sufficient positional change to be observed at single turn.
COMPARISON OF KEY SPECIFICATIONS
Table 1 reviews and compares the major technical specification, features and
performance of the two systems.
TABLE 1. Key Specification Comparison
Dynamic Range (Beam
Current)
High Speed Resolution
(Turn by Turn/'Pulsed')
Memory Depth
(No. of selectable turns)
Low Speed Resolution
(Closed Orbit)
Output X, Y, 2
Wide Range Beam Current
Dependence
Narrow Range Beam Current
Dependence
Long Term Stability
Form Factor
/-Tec/7
Bergoz
>100dB
>90dB
±20jim
(500kHz Bandwidth)
1k to 16k
Not Supported
<1um
(2kHz Bandwidth)
14 bits Digital
(16 bits -oversampling)
25um
(-65dBm to -5dBm)
2.5um
(in any 14dB range)
2.5um
VME 64X Compatible
<1um
(9kHz Bandwidth)
Analogue +/-10V
Not Supported
1 urn (SLAC Test)
(-SOdBm to -3dBm)
>1.0um
(in any 14dB range)
>1 urn (LEP Test)
3D Eurocard
Detection Electronics Summary
Commercial systems are available for DIAMOND EBPM application, thus
avoiding the considerable time/cost outlay in the development of further in-house
systems, which invariably are more expensive. One is a mature, established system,
the other becoming so and still under considerable development.
The system offered by Bergoz Electronics is a simple fully analogue design but
offers resolution, accuracy and stability compatible with the requirements of a third
generation light source. Being an analogue system digitising of the output is required
prior to any software interface and unlike its I-Tech counterpart the Bergoz system is
453
unsuitable for pulsed beams. It is however well established, it has a proven reliability
unsuitable
commission in
in most
most of
of the
the light
light sources
sources around
around the
the world.
record and is in commission
The relative performances of the two systems are naturally reflected
reflected in their
respective costs. BPM channel for BPM channel the I-Tech system is several times as
expensive as the Bergoz system, and thus may possibly only be justified
justified for
applications that will truly exploit the full potential of the system.
system. The I-Tech DBPM
applications
specified elsewhere for all EBPM locations within the DIAMOND predetector is specified
injector. Its transient beam capabilities will allow instantaneous beam position within
all transport lines and
and also
also provide position/tune measurement for the Booster
all
synchrotron. The dynamic range of this system
system is also
also adequate for top up mode, low
synchrotron.
level electron beams.
beams.
Within the storage ring, a combination of the two systems following
following the
the examples
examples
given in Figure 6, will provide DIAMOND with first class EBPM systems, for the best
value for money.
Control System
System Data
Data Network
Network
Control
VME 64X
SLS Type
DBPM
Shielded
Eurocrate
Bergoz Type
EBPM
X and
and Y
Y Analogues
Analogues
X
To local
local 16
16 channel,
channel,
To
16bit,VMEADCCard
16
bit, VME ADC Card
Additionally Instrumented
Vertical PBPM
button
66 button
PBPM
PBPM
button
44 button
EBPM
EBPM
PBPM == Primary
Primary Beam
Beam Position
Position Monitor
Monitor (Isolated
(Isolated for
for high
high mechanical
mechanical stability)
stability)
PBPM
EBPM == Electron
Electron Beam
Beam Position
Position Monitor
Monitor (normally
(normally mounted
mounted within
within vessel)
vessel)
EBPM
FIGURE 6.
6. Proposed
Proposed Storage
Storage Ring
Ring Detector
Detector Implementation
Implementation
FIGURE
MACHINE PROTECTION SYSTEMS
Beam mis-steer
mis-steer damage
damage protection,
protection, of
of narrow-gap
narrow-gap insertion
insertion device
device vessels,
vessels, is
is aa
Beam
fringe
area
of
beam
diagnostic
systems,
thus
it
is
therefore
appropriate
to
detail
fringe area of beam diagnostic systems, thus it is therefore appropriate to detail the
the
system in
in this
this section.
section.
system
DIAMOND is
is intended
intended to
to be
be essentially
essentially an
an insertion
so eventually
DIAMOND
insertion device
device machine
machine so
eventually
most straights
straights will
will be
be fitted
fitted with
with narrow-gap
narrow-gap beam
most
beam vessels
vessels introducing
introducing attendant
attendant beam
beam
steering limitations.
limitations. Theoretical
Theoretical analysis
analysis has
has shown
shown that
steering
that mis-steer
mis-steer of
of the
the electron
electron
beam, could
could cause
cause catastrophic
catastrophic thermal
thermal damage
damage to
to the
the vessel
vessel in
in less
beam,
less than
than one
one second.
second.
Front line
line protection
protection systems
systems have
have been
been developed
developed for
for the
SRS narrow
Front
the SRS
narrow gap
gap vessels
vessels to
to
help prevent
prevent such
such damage
damage [5],
[5], and
and are
are suitable,
suitable, with
with minor
for
help
minor modification,
modification, for
installation on
on DIAMOND
DIAMOND insertion
insertion devices.
devices.
installation
454
Machine Protection Hardware Installation
When dangerous mis-steering conditions prevail, the electron beam will be
switched off by tripping the RF power to the beam. The main interlock signals to
achieve this will have been generated by excessive vertical beam displacement (shown
as Beam Position Upstream and Downstream), and excessive rise in vessel wall
temperature (Thermal Trip). The single Thermal Trip interlock will be generated from
a strategically placed array of thermocouples, affixed to the vessel wall and monitored
by a Programmable Logic Controller (PLC).
Since initial injection at low current is deemed to be a safe operating area, a current
sensitive bypass will be included as shown. This will facilitate beam steering through
the narrow gap of the vessel at low currents, by permitting a wider tolerance on
position.
Because confidence in the reliability of beam position measurement and interlock
operation is paramount, secondary interlock signals will be required to become active
when the integrity of electronic hardware and associated support signals is suspect.
These are shown in Figure 7, an expanded organizational diagram, as BPM
Electronics Failure Upstream and Downstream, Total Current Monitor Failure, Power
Supplies Failure and Thermal Monitoring (PLC) Failure. A keyswitch controlled
override of Beam Position interlocks is included for possible Accelerator Physics
application, to permit wider beam positioning at high current levels, or unrestricted
control under special user conditions (e.g. ultra low current running).
Interlock
£>s
Beam Position Upstream
Beam Position Downstream
Current
NSensitive
BPM Electronics Failure Upstream \
1
BPM Electronics Failure Downstream
Total Current Monitor Failure
Interlock
FIGURE 7. Full Interlock Organisation
There will be provision for full status monitoring interface to the DIAMOND
control system, and local (Control Console) real time display of beam positions and
current sensitive bypass status.
Because experience has shown that there is interaction between the vessel
protection system and beam loss when an unrelated fault occurs, i.e. beam loss creates
numerous vessel protection interlock failures, Event Sequence Discrimination circuitry
will be installed to distinguish cause from effect. The result of the discrimination
process will be displayed through the Control System and visually at the Control
Console.
455
When the time for installation of vessel protection systems arrives, all development
from both a design philosophy and engineering aspect will be complete and
installation should be modular on demand.
TOTAL CURRENT AND BUNCH CHARGE MONITORS (TCMS AND BCMS)
Accurate and stable measurement of the DC component of the stored charged
DIAMOND beam is an important requirement, since it will be a measure of the light
intensity and the parameter from which lifetime will be calculated. The parameter of
critical importance, for monitors which are designed to non-intrusively measure
charged particle beam currents, is resolution, a specification that is dictated by zero
drift. For a third generation machine such as DIAMOND a zero drift figure in the
order of 5.0 microamps is required.
Zero drift of a monitor is defined primarily by the thermal properties of the core
material that is employed for the toroidal monitor head. In this area the current
generation of monitors use amorphous magnetic materials for the cores, materials that
demand extensive expertise and resources to process. Consequently the manufacture
of modern monitors has tended to remain within the province of the commercial
sector.
In the commercial field a leading manufacturer of high specification Total Current
Monitors TCMs (now more commonly referred to as Parametric Current
Transformers, PCTs) is the French firm Bergoz Electronics. This company has
supplied PCTs to most of the leading synchrotron radiation laboratories world wide;
their products have a good reputation for performance and reliability and the company
has demonstrated its long term commitment to product support.
Thus in line with the cost effective policy to be applied to DIAMOND of
implementing systems by use of commercial instrumentation, it is intended to equip
DIAMOND with a Bergoz Electronics PCT, with the assurance that the potential for
obsolescence is minor.
A standard production model from the Bergoz Company offers zero drift of 5.0
microamps. This specification satisfies both the measurement and lifetime calculation
demands of DIAMOND, but to achieve the quoted performance figure, careful
consideration will have to be given to the magnetic and electrostatic screening
requirements of the toroidal monitor head. To implement the full theoretical monitor
head screening required to guarantee the demanded performance, a free beam pipe
length of approximately 0.6 metres is required.
Finally, since DIAMOND is to operate in a top-up, mode it is recommended that
two PCTs be installed in the DIAMOND Storage Ring to crosscheck beam current
measurement by comparison. This is important if the top-up operation is to be
performed at a defined and repeatable level of beam decay. Additionally a PCT is
required for the DIAMOND Booster ; this device can be of a lower specification than
that for the Storage Ring, but there would be little economic gain in purchasing an
inferior instrument.
The potential user community for DIAMOND have expressed a desire for
customised bunch charge fill patterns on request, a facility that will require selection
456
and charge fill of individual beam bunches. This in turn will require the capability of
measuring the individual bunch charge content.
Selection of an individual bunch can be achieved through the DIAMOND timing
system by variable delay from the Orbit Clock ; measurement of the bunch charge
content will require the installation of a Beam Charge Monitor.
Again in order to adhere to the policy of using commercial instrumentation, a Beam
Charge Monitor manufactured by Bergoz Electronics will be installed. This device has
an integrate - hold - reset capability on an individual pulse basis, that offers a
maximum sensitivity < 60 pico Coulombs per volt and a resolution of approximately 3
x 106 particles.
These devices will also be installed as part of the beam loss monitoring throughout
the DIAMOND to assist with radiation protection system, in order to assess and
interlock if necessary, the effective beam injection/transport efficiency.
REFERENCES
1. T. Ring, "Beam Position Monitors for the High Brightness Lattice", Daresbury Report, DL/SCI/TM41A
(1985).
2. M J Dufau, D M Dykes, R J Smith, "Electron Beam Position Monitor (EBPM) Diagnostics for DIAMOND",
Proceedings, PAC99, New-York (1999)
3. J. A. Hinkson, K. B. Unser., "Precision Analogue Signal Processor for Beam Position Measurements in
Electron Storage Rings", Proceedings, 2nd DIPAC, Travemunde, Germany, (May 1995)
4. Brown, M. P., and Austin, K., M. Dehler, A. Jaggi, P. Pollet, T. Schilcher, V. Schlott, R. Ursic, "New Digital
BPM System for the Swiss Light Source", DIPAC99, Chester, UK (May 1999).
5. M J Dufau, R J Smith, "a fast protection system for narrow-gap insertion Device vessels", DIPAC99, Chester,
UK (May 1999)
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