The girls from Daresbury: ALICE and EMMA

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25 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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The girls from Daresbury: ALICE and EMMA

N
on
-
scaling Fixed Fi
eld Alternating Gradient accelerators

were
invented at
the end of the 1990s
because their novel features mean they look

better than existing technology for a variety of
applications. These novel
features
also
mean that
a proof
-
of
-
principle machine has

to
be built
to
demons
trate that the technology works and understand the effects of these features in
detail befor
e their po
tential

can be exploited.

This is
proof
-
of
-
principle accelerator is called
EMMA, the Electron Model for Many Applications. EMMA is under construction at the STFC
Daresbury Laboratory in the UK and will
use
the existing ALICE


Accelerators and Lasers In
Co
mbined Experiments


accelerator as an injector.

ALICE

ALICE is a unique facility that is being
used to investigate and overcome the challenges
presented to scientists in designing and building future generations of accelerators
, in particular
a next gener
ation of
light source
s
.

At its

heart is an Energy Recovery Linac (ERL) acc
elerator
.

Extremely high quality bunches of electrons are produced by i
ntense light pulses from a

laser
bombarding a semiconductor surface. This electron beam
is
accelerated to 35 Me
V

using

superconducting radiofrequency
(RF)
cavities. These bunches

are then
compressed, to
stimulate the production of intense, short pulses of light.


In energy recovery mode, the
bunches are decelerated and
the energy released

used to accelerate the next set of bunches.
For EMMA, ALICE is used to produce a single bunch of electrons with an energy between 10 and
20 MeV. This is transported to the EMMA ring through a purpose built injection line.

EMMA

EMMA has been designed to de
monstrate and study in detail all the features of non
-
scaling
FFAGs. To
do this
,
while keeping costs down,
it was
decided it should

accelerate electrons from
10 to 20 MeV
. In addition, the machine has been designed to be

very flexible and
it
is
instrumente
d with many diagnostic devices to make detailed measurements of the beam
parameters. It is built from 42 magnetic cells, each about 40cm long, making the circumference
16.5m. Each of these cells has two ring magnets and almost every other cell has an RF ca
vity.
The cells in between have vacuum pumps or diagnostic devices. Further diagnostics, that will
significantly degrade the quality of the beam when making a measurement, will be mounted in
an external diagnostics beam line.

Status

EMMA has been under con
struction since April 2007. The injection line was completed In
March 2010 and commissioning of this has already started. The ring
is built on 7 girders and 4 of

these have been complete and in place since before Christmas. Two further girders were put in
place in the middle of May. The last girder is due for installation in the middle of June and will
be closely followed by the start of commissioning of the ring. The diagnostics beam line will
follow later in the year.

EMMA in EuCARD

There are two main EMM
A tasks within EuCAR
D. The first is
the design, construction and
testing of the external beam diagnostics devices and the diagnostics beam line. The second is
the commissioning o
f EMMA and the execution of an

experimental programme to evaluate
the
use non
-
scaling machines

for a variety of applications.


The ALICE and EMMA accelerators at the Daresbury Laboratory


Photograph of the EMMA ring taken on
8
th

June 2010.