2011-07-01_Paris_Francex - the ESS Document Database

closedlavenderΠολεοδομικά Έργα

25 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

85 εμφανίσεις

Beam
Instrumentation

f
or HPM

-
with a strong focus on ESS

Andreas Jansson

Paris, France, 2011
-
07
-
01

P
vs

H
-


An H
-

beam allows for diagnostic methods based on
laser
-
induced photo
-
neutralization.


All sorts of fun non
-
invasive measurements
possible


Not an option in a proton
linac

like ESS, so I won’t
talk about it.


NB. Due to concerns about losses,
unnessecary

use of H
-

is suppressed in e.g. Project X


Diagnostics types in HPA


Diagnostics for daily
operation


Beam Loss


Beam Current


Beam Position &
Phase


Target spot size


Focus on reliability


Non
-
invasive.


Diagnostics for
commissioning and
studies/optimization


Beam size/
emittance


Bunch length/shape


Beam halo


Electron cloud(?)


Focus on accuracy


Could be invasive
and/or use special
beam.

ESS Beam Parameters

Beam Pulse Current:


50
mA (60mA from source
)


Bunch repetition rate:


352
MHz


Bunch
charge:


140
pC


Bunch
length (
r.m.s
.):


10
-
40
ps


Beam
size (
r.m.s
.):


1
-
3 mm

Prel
. ESS Diagnostics Specs


The beam loss monitoring system needs sufficient sensitivity to keep average losses below
1W/m, and enough time resolution/dynamic range to protect the machine from damage in
case of (worst case scenario) uncontrolled fast beam loss.


The
beam position needs to be measured with an accuracy of a couple per cent of the beam
size, or about 0.1
-
0.2 mm. The measurement should have a response time to changes of the
order of 1
μs

or better.


The
time of arrival, or phase, should be measured to a fraction of a degree of RF phase, or
about 2
-
4 ps. A fast response to changes is not needed to phase the cavities, but may be
useful for e.g. LLRF studies.


The
beam size needs to be measured with an accuracy of 10% or better. The beam size is
about 2
-
3 mm at the available locations. The measurement can be an average over the 2
ms

LINAC pulse.


The
bunch length needs to be measured with an accuracy of 10% or better. The
measurement can be taken as an average over the pulse, or on a
single bunch
in the train.
There is no need to measure
the bunch
length of all bunches individually.



Need
to measure halo at the level of 10
-
5 or less
of total
beam.


The
beam profile on target needs to be
measured with
an accuracy of 10%. Since non
-
linear
elements may be used in the final focus, this requirement is best expressed in terms of beam
density rather than size.

Preliminary. Expected to change!

Important Assumption


It is generally assumed that a “special diagnostics
beam” would be low rep rate (perhaps 1Hz or less)

and short pulse (perhaps 100us or less),
but nominal
bunch intensity.


Lowering beam current changes the optics of the
machine, making measurement results less useful


Means nominal bunch charge is unchanged for
diagnstics

pulse


An exception to this rule could be that BPM data
from low current beam might be useful for early
commissioning.

ESS Preliminary System Count

Based on discussions with Beam Physics in Lund, documented in

http://eval.esss.lu.se/cgi
-
bin/public/DocDB/ShowDocument?docid=
43

Intended as starting point for discussions. Expected to change.

Cryomodule

& Diagnostics

Loss monitors


Need
to determine BLM system layout (part of MPS)


includes the type (speed, sensitivity and dynamic
range) of detectors and location


Ionization Chambers


Fast photo
-
multiplier tubes


Neutron detectors


Diamond detectors


Ongoing simulations (L.
Tchelidze
)


Transverse error studies


will generate
l
oss map


result of a several thousand runs with different error
distribution.


Secondary particle shower map along all accelerator


result of a multiple Monte
-
Carlo particle transport
codes (Geant4, MARS, FLUKA).


Beam Position Monitors


One dual
-
plane BPM per cell/
cryomodule
, could
perhaps live with less in high energy end.


Most likely button BPMs in most of
linac

(simpler),
except in front end where
striplines

may be used.


Signal processing most likely digital, narrowband
with bandwidth of order 1
MHz.


Several collaboration/COTS options including
OpenHardware
,
Libera
,
Fermilab
/ATF, ESS
-
B …


In the process of hiring engineer to work on this


Do we need special BPMs to measure/predict beam
position on target (large demagnification)?

Beam Current Monitors


Several BCTs in front
-
end + one between main
linac

sections.


Except for the very front
-
end, will likely only be
used for early commissioning


Available off the shelf.


A
bsolute calibration may be an issue.


Position dependence of reading

Target spot size


SNS experience
with
CrAl2O3 coated target is good,
would like to do something similar.


ESS baseline target is now a He cooled solid
tungsten wheel, need to adapt.


Would like to see if we can measure spot size on
beam window as well (using coating or OTR)


“Cross
-
functional task force” with Target Division for
integration issues


W.
Blokland
, BIW10

Bunch Length/Shape

A.
Feshenko
, LINAC04


Due to very short
bunches,
Feshenko

type monitor prime
candidate


Alternative design
based on x
-
ray
detection proposed by
Ostroumov
, may have
significant advantages


Both use physical wire
in beam. Possibility to
use ionization electrons
(GSI)

Wire Scanners


SNS studies concluded that carbon
wires would work for short pulse.


Straight forward in NC
linac
.


GANIL wire sublimation test
suggests carbon wires bad for SC
cavities, tungsten (and
Nb
) OK.


Tungsten will likely have issues with
thermionic emission, may need to
measure downstream loss signal


Potential space/geometry issue,
need study


May be able to use welded bellows
-
> simpler than SNS design


Wire scanner baseline profile
device!



SNS SCL WS

IPM/Gas Jet/BIF


Except in front
-
end, IPM/BIF would likely need long
integration time, possibly
neeed

to be operated in
counting mode (slow), and may require gas injection.


Gas injection compatible with SC cavities?


Gas jet to be investigated for use in SC
linac

(discussion with
Cockroft

Institute)



NB. Profile measurement is

primarily an issue in the cold
linac

Kuehnel

et al, EPAC08

Other profile/beam size options


Electron beam
scanner





Quadrupole

pick
-
ups

W.Blokland
, HB2010

+

+

-

Halo Diagnostics


Options for halo
measurements
include instrumented
scrapers,
v
ibrating
wires, and high
dynamic range wire
scanners


Best option may be
wire scanner with
coincidence
counting
detector/telescope

LEDA WS, LANL

Vibrating Wire,
Bergoz

3
4
W
i
r
e

S
c
a
n
n
e
r
s
P
M
T
s

























A
N
D

(
C
o
i
n
c
i
d
e
n
c
e

u
n
i
t
)


S
c
a
l
e
r









T
i
m
e
r
1
2
3
4
W
i
r
e
p
o
s
i
t
i
o
n
N
o
r
m
a
l
i
z
e

c
o
u
n
t
s

t
o

t
i
m
e

i
n
t
e
r
v
a
l
!
R
e
d
u
c
e
d

b
a
c
k
g
r
o
u
n
d

f
r
o
m

d
a
r
k

c
o
u
n
t
s

a
n
d

b
e
a
m

l
o
s
s
e
s
!
S
t
a
r
t
S
t
o
p
H
u
g
e

d
y
n
a
m
i
c

r
a
n
g
e

(
1
0
8
)

b
y

c
o
i
n
c
i
d
e
n
t

c
o
u
n
t
i
n
g
:

W
i
r
e

S
c
a
n
n
e
r
s

a
t

J
e
f
f
e
r
s
o
n

L
a
b
L
a
r
g
e

D
y
n
a
m
i
c

R
a
n
g
e

B
e
a
m

P
r
o
f
i
l
e

M
e
a
s
u
r
e
m
e
n
t
s
F
r
e
y
b
e
r
g
e
r
,

D
I
P
A
C
0
5
WS Telescope,
eg

ANL

Other Diagnostics/Open Questions


Specific front
-
end diagnostics (Faraday cups, slit
scanners, …).



Do we need to measure
uncaptured

beam?



Do we need to measure e
-
cloud?



Do we need to measure something else?

Diagnostics Girder/Side Spurs

19

19

It is foreseen to use a temporary movable diagnostics plate/girder with

addtional

destructive diagnostics only for commissioning


May make sense to design one of more permanent diagnostic side spurs


Allows the use of (semi
-
)destructive diagnostics


May resolve the wire scanner contamination question


No throw
-
away diagnostics for initial commissioning


May help reduce the need of warm space between sections


Could potentially divert every Nth pulse for monitoring.


Side spurs may be useful in the future (e.g. parasitic experiments)


But needs to be designed into the lattice

50kJ pp

20kJ pp

5kJ pp

250kJ pp

Summary


Work to define the ESS diagnostics is progressing


Have preliminary specs and systems count,
mainly based on discussions with Beam Physics
in Lund


Will be discussed with the persons responsible for
the different parts of the
linac
, to make sure all
needs are covered and enough space is reserved.


Beam
Diagnstics

group in Lund is responsible for
diagnostics in the entire
linac
, but we welcome your
input and help.


Conceptual design, locations/count and cost by 2012
(ADU), prototyping as part of P2B