Measuring beam losses in the THI project
L. David, P. Duneau, E. Léorché, P. Lermine, E. Lemaitre, M. UlrichGanil BP 5027 14076 Caen Cedex 5 FranceAbstract
The goal of the THI project (High Intensity Transport)
is to upgrade the GANIL facilities by increasing the beam
by a factor of 15, at least for light ions.
So the actual 1011 pps will be boosted to 2.1013 pps toget 6 kilowatts heavy ion beams at 95 Mev/nucleon.
This higher intensity is required by the radioactive
beam facility SPIRAL starting in September 1997, togenerate the new nuclear species in the solid target-source(ISOL method).
For the control system, the most important issues are
now to tune the accelerators while minimizing the beamlosses at each stage of acceleration and when not possible,
to have a fast beam loss detection signal.
This system is composed of probes which deliver asignal to stop the beam when there too much intensity lost
and when not, a logarithmic value of the beam intensity.
These probes are linked to a front end VME crate on
the network, and in the control room, on the workstations,a graphical user interface program displays the beamvariations using logarithmic scales.
This program is also used to center the beam while
injecting in or ejecting from the main cyclotrons by tuning
the steerers, the magnetic elements inside, and theelectrostatic deflector to be able to separate and extract thelast beam turn.
1 Introduction
The THI project consists in upgrading the GANIL
facilities, while increasing the beam intensity by a factor
around 15, at least for the light ions species up to argon [1].
As an example, an Ar 36 beam now of 7.3 1011 pps will
become 1.1 1013 pps to deliver 6 kilowatts at the output of
the second Sector Separated Cyclotron SSC2 with anenergy of 95 Mev/Nucleon.
This new intensity is necessary for the SPIRAL project
which is the Radioactive Ion Beam facility underconstruction at Ganil [2] following the ISOL production
method. The aim is there to create a sufficient number of
exotic nuclei as the production rate in the SPIRAL
target/source assembly ranges from 1/10000 to 1/1000000.
The SISSI device which already produces radioactiveion beams using the projectile fragmentation method will
also take benefit of the THI project.
The control system must be able to tune the beam
while minimizing as much as possible the beam losses at
every tuning phase, specially in the Separated Sector
Cyclotrons. When these losses happen anyway, the beam
has to be stopped very quickly, to protect the vacuum
chambers or the beam lines pipes called L2 and L3.

Indeed, for the Ar 36 beam at 95 Mev/Nucleon, thebeam power will be 1 kilowatts in the L2 line and 6
kilowatts in the L3 line. Focused on one cm2 of no-cooled
stainless steel, this one will reach his fusion point in 120ms in the L2 line and 40 ms in the L3 line.
2 Acquisition electronic
The sensors to be installed for the THI project must
cope with two needs. First, they have to deliver a signal
proportional to the beam losses and also they have to senda fast response when the beam exceeds predefined
thresholds (Survey mode).
2.1 The probes [3]Before the High Intensity Transport, no diagnostics
were used in the beam lines because the beam losses had
no consequence on the stainless steel pipes. For this newproject, the probes could have been ionization chambers or
isolated shields.
The ionization chambers could take advantage on being
disposed outside the insertion devices but were not sensible
enough at the L2 energy and were too much reactive on
radioactivity ( rays) around the SISSI device.
So we decided to use the shields which were alreadyinstalled to protect the micro-channel profilers.
In the Separated Sectors Cyclotrons, the probes are thesame as those previously existing to measure the injection
or ejection beam. But the electronic acquisition system had
been modified to generate a logarithmic value from theinput signal, in such a way to have a better range.
The intensity transformers, already used, have also
been connected to this logarithmic electronic system withenough dynamic range to measure both a "standard" ionbeam or a "high intensity" one.
2.2 The survey mode
Along the transport lines, the shields are mainly used
for threshold detection. If the beam loss is higher than apredefined threshold, then the electronic acquisition
generates, in a few milliseconds, a signal to reduce thebeam power by activating a chopper.
The other probes in the cyclotrons and the current
transformers are only used for measurement without any
security threshold linked to.
2.3 The input signals
The different probes measure a beam current which istranslated in a voltage proportional to the logarithm of thecurrent by a small CMS mezzanine board, plugged on aVME board based on 68HC11 micro controller. An ADC

converter translate, within 10 µs, the input range of +/- 10
volts in a 12 bits coded numeric value, stored in a sharedmemory between the VME bus and the 68HC11.
Each board has 4 input and every input is compared toa threshold sent by the control system through the VMEbus and the micro controller. This one can also read backthe threshold when asked by the control room.
When the threshold is over, an interrupt is generated on
the VME bus, so that the VME processor is able to know
which board is concerned and which input has detected theovertake.
The VME crate can send an alarm message to thecontrol room, with the right name of the probe between thefour plugged on one board. An other signal is also sent tothe beam interlock to reduce the beam intensity.

For people involved with the tuning programs on theworkstations, a software user interface has been written in
Ada to send commands to the front end crate.
Ada is used for all our control software, on the realtime crate but also on the workstations for the graphicaluser in terfaces.
The beam losses software interface contains all thecommands that can be received by the handler. Some ofthem are only used for the survey mode : alarm test, alarm
reset, thresholds read and write. The "read status"
command is used in the survey mode to know the input
number which triggered an alarm and in the measure mode
to check the input channel. The "read input" command is
only used in the measure mode to perform the acquisition.
4 Display software

VME busampli+
filter

I/V log

Mpx

SRAM

ADC

4 analog
inputsThresholds
detection&
Beaminterlocks

4 thresholds

4.1 Beam losses in the cyclotrons

microcontroller
68HC11On the workstations, the tuning program allows toswitch between a display mode and a control panel fromwhich the operator can drive the steerers and the magnetic
injection or ejection devices.

DAC3 Acquisition software
From the control system point of view, the integrationof the beam losses measurement entirely follows thehardware and software architectures adopted for the Ganil
facility [4] and extended to the Spiral project [5].
3.1 Logarithmic handler
In every front end crate, every input-output board iscontrolled by a driver according to the hardware. At an
upper level, a handler manages the function the board has
to perform as seen from the equipment. So, a protocol Jbus
board will be driven by a "Jbus" driver, and will be usedeither by a power supply handler to control power supplies,
either by a stepping-motor handler to manage motors. So, alogarithmic handler has been defined to process the newsensor class as described in section 2.

When one threshold is overtaken, an interrupt isgenerated and the driver reads the status of the board toknow which input had been activated . Then it sends analarm message with this input number to an alarm server
process that is running on the database computer. This
alarm is displayed on an X terminal in the main control
room and stored in the alarm database. So it will bepossible to read it back afterwards, if it is necessary tocompare it with other events.

Also the operator has to choose on which cyclotron hewants to work and if he will tune the beam injection orejection . Before starting the acquisition, the electronicnoise can be suppressed with the offset button.
Most of the injection and ejection devices have four
sensors (top, bottom, right and left). These probes are
displayed on the screen within a cross shape (see above),with the numeric values beside. The more important thelosses are, the more the cross shape is filled.
The summation of all the losses is displayed over eachcross and the beam intensities at injection and ejection arealways shown beside of the cyclotron name.

3.3 User interface

4.2 Injection and ejection centering

3.2 Alarms

In command mode, the bottom side of the screen
displays all the devices used to control the injection or theejection of the beam. That includes two steerers, four
magnetic devices inside the cyclotron and two motors tomove the electrostatic deflector. Each of them is controlled
by a panel like the one below.
With this panel, all the devices can be started, stopped,
set to a value entered either by keyboard or by incremental
steps.

4.4 Future developments
This program doesn't allow automatic tuning while
injecting or ejecting the beam. The human operator has tomanually set the magnetic devices, watch the beam losses
and increase or decrease the current in the steerers.
At the same time, automatic tuning programs havebeen written for beam adaptation and for beam alignment.
Once the alignment program successfully operational,
the next step will be a link between the alignment
algorithm and the centering controls in a way to perform anautomatic centering for injection into the cyclotrons.
In parallel, a new program is under way to organize
and to manage the tuning modes for accelerating highintensity beams. This program will allow the operator to
set the Ganil machine within a predefined procedure bytuning step by step the source, the injector, the SSCs at low
intensity and then switching to the high intensity. The
beam intensities and throughputs will be displayed fromthe main panel of the application being acquired from themeasurement system presented here.
5 References

4.3 The collimators
When the high intensity beam is sent on the radioactive
ion source SISSI, the defining slits of the spectrometer
could be highly activated and have to be protected.
Therefore three collimators have been installed in theL3 line, before the slits. They are water-cooled to support
the beam intensity and are disposed on propellers to beintroduced in for high intensities and moved out forstandard beams.
They are considered as security devices and socontrolled by the program already in use for the beam stops
and pepperpots.

[1] "Upgrading the Ganil facilities for high intensity heavy
ion beams", E. Baron and the Ganil staff. Proceedingsof the 14th International Conference on Cyclotrons. CapTown (1995)[2] "Status of SPIRAL, the radioactive beam project atGANIL", M. Lieuvin and the Spiral group. Proceedings of the 14th International Conference on Cyclotrons. Cap Town (1995)[3] "Dection des pertes faisceau et systeme de protection",
R. Baumgarten, C. Jamet, E. Petit. Internal report Ganil/602.94/EP[4] "Controlling the GANIL from an Operator
workstation", L. David, E. Leorché, C. Maugeais, M.
Ulrich. Proceedings of the 4th European Particle
Accelerator Conference, London, Great-Britain, June
1994.
[5] "Extending the GANIL control system for the Spiralproject", E. Leorché and the Ganil control group. 10 th
Real Time Conference, Beaune, France, September
1997.