ESS-Bilbao Initiative Workshop. Charge to working group: accelerator components/ beam dynamics

Charge to working group:
accelerator components/
beam dynamics
F. Gerigk, C. Prior

ESS-B initiative workshop,
16.-18.03.2009

Outline

goals, expected results,
scope of the session,
accelerator design/beam parameters,
key questions per subject,

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“Accelerator Components”, ESS-B workshop 2009, F. Gerigk

goals, expected results
goal of the workshop:
bring together people working on subjects important to high-power
spallation sources,
identify challenges of next generation machines,
propose necessary R&D programs,
identify common areas/interests with other projects.

expected result:
a summary document highlighting the challenges,
addressing future prospects,
deﬁne potential collaborative developments programmes,

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This workshop is not a design
review of ESS!!

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...instead, this is where we start to develop
recommendations for any future high-power
(long-pulse) spallation source
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scope of the session

high-power, highly reliable front-ends,
high-intensity light ion linacs: component design,
performance of existing machines, reliability,
synergies with ongoing and planned linac projects,
low-energy superconducting structures (< 100 MeV?),

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beam parameter linac design
how the basic target parameters inﬂuence the linac design

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beam parameters linac design

target/instrument
linac design
requirements
beam power ~ 5 MW ?

~ ms ?
pulse width

1 GeV (... 3 GeV ?) ?
beam energy

≤ 20 Hz (15,20,25 ??) ?
repetition rate

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linac constraints (simpliﬁed..)
examples:
150 mA: 6.7 MV
peak power/coupler: max. cavity voltage:
Ppeak≤1 MW Vacc=Ppeak/Ipulse,average
50 mA: 20 MV

cavity gradient (+ n. 704 MHz: 5/6 cells
frequency/number of
of cav. families):
cells per cavity 1300 MHz: 9/10 cells
≤ 20 - 25 MV/m

average power/
2 ms, 20 Hz: 40 kW
coupler: ~50/120 kW
Pav=Ppeak*(tpulse*frep)
(TTF type 1300 2 ms, 40 Hz: 80 kW
MHz/LHC 400 MHz)

high current (150 mA)
space charge: beam stability yields high probability for
(emittance increase,
loss limited machine
beam loss, machine
performance and/or
activation)
need for front-end funnel
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ﬁrst order scaling...

1 GeV, 16.7 Hz, 2 150 mA, Eacc = 6.7
ms, 5 MW MV, linac length = l0

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1 GeV, 16.7 Hz, 2 150 mA, Eacc = 6.7

3 GeV, 16.7 Hz, 2 50 mA, Eacc = 20 MV,
ms, 5 MW linac length = l0

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1 GeV, 16.7 Hz, 2 150 mA, Eacc = 6.7

3 GeV, 16.7 Hz, 2 50 mA, Eacc = 20 MV,

50 mA, Eacc = 20
2.5 GeV, 20 Hz, 2
MV, linac length =
ms, 5 MW l0*16.7/20=0.83*l0

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1 GeV, 16.7 Hz, 2 150 mA, Eacc = 6.7

3 GeV, 16.7 Hz, 2 50 mA, Eacc = 20 MV,

50 mA, Eacc = 20
2.5 GeV, 20 Hz, 2
MV, linac length =
ms, 5 MW l0*16.7/20=0.83*l0

50 mA, Eacc = 20
2 GeV, 25 Hz, 2
MV, linac length =
ms, 5 MW l0*16.7/25=0.67*l0

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target/instrument
linac design
requirements
beam power ~ 5 MW ﬁxed

~ ms ﬁxed
pulse width
high/low pulse
beam energy 1 GeV (... 3 GeV ?) current, length
constant
higher rep. rate
repetition rate ≤ 20 Hz (15,20,25 ??)
shorter linac

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Questions with high impact on linac design/
cost/reliability:
1.) linac:
how strict is the limit of 1 MW/coupler? how difﬁcult are 2 couplers/
cavity?
are 20 - 25 MV/m realistic?
source/front-end limitations (current/time structure)?
2.) beam dynamics:
what are the current limits to avoid a funnel in the front-end?
current limits for low-loss operation in the linac?

3.) target:
how do different energies (1,2,3 GeV) and rep-rates (16, 20, 25
Hz ..) inﬂuence the target design?

4.) instruments:
how hard is the limit on the repetition rate (16, 20, 25 Hz ..)?
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Parameter review of
CERN SPL CERN-AB-2008-067

RF frequency & cryogenic
temperature
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SPL (high-power version):
HP-SPL (5 GeV)
102 MeV 160 MeV 732 MeV 5 GeV
50 MeV
3 MeV
H- source RFQ DTL
chopper CCDTL PIMS β=1.0
β=0.65

352.2 MHz 704.4 MHz

kinetic energy 5 GeV
beam power 3-8 MW
repetition rate 50 Hz
pulse length up to1.2 ms
average pulse current 0-40 mA
cavity gradient (β=0.65/1.0) 19/25 MV/m
protons p. pulse 1.5 1014
length (SC linac) 472 m
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RF frequency review: 704 MHz
frequency 704 MHz 1408 MHz
472 m +12%
length
246 +15%
Ncavities
2 3
Nβ-families
5.6/8.2/6.8 6.3/7.8/12.1
ε-growth (x/y/z)
lossy runs for realistic RF
none in simulations
long. beam loss
gradient/phase variations
IBBU,704 1/(8..128)
BBU (HOM)
normal risk 2..4 higher risk
trapped modes
RF power density limit (RF
ok problematic
distribution)
difﬁcult
klystrons comfortable: MBK
overall power consumption
28 MW up to -30%
(RF+cryo, nom. SPL)
more bulky saves tunnel space
power converter

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cryogenic temperature review: 2K
eq. capacity el. power
@ 704 MHz T [K]
@ 4.5 K [kW] [MW]
HP SPL, 2% beam d.c. (4% cryo
2 19.4 4.48
d.c.)
HP SPL, 2% beam d.c. (4% cryo
4.5 104 26.0
d.c.)
LP SPL, 0.24% beam d.c. (0.32%
2 6.1 1.5
cryo d.c.)
LP SPL, 0.24% beam d.c. (0.32%
4.5 11 2.75
cryo d.c.)

not clear that 25 MV/m can be achieved at 4.5 K!

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questions to the working group:

has anyone done a similar analysis?
is there experience with high-power RF equipment at high
duty cycle (~5%) for high frequencies (≥1200 MHz):
klystrons, circulators, RF loads, phase shifters, splitters,...
sensitivity to higher order modes for high-current
machines (50/150 mA)? Is there any relevant experience?

Dedicated workshop on HOMs in high-power linacs will
take place at CERN (~June, exact date to be decided)

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key questions per subject
....common to many SC high-power linacs
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further questions
J. Galambos
1.) instrumentation:
high power proton machines: how can we do proﬁle measurements
during regular operation?
ionisation detector readings disturbed by X-rays from the cavities,
neutron detectors?
halo diagnostics (loss management) 10-5 - 10-6 fractional beam?,
localised beam loss measurements in well shielded low-energy
beam (<100 MeV)?,
P. Ostroumov
high-energy emittance measurements?,
beam instrumentation inside accelerating structures?,
beam centre, proﬁle, emittance to <1%?
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questions II
J-L. Biarotte: fault
tolerance
2.) reliability (spare parts):
for which machine elements are spares necessary? (apart from the
obvious ones..): source, RFQ, cryo-modules (how many),
3.) cryo-modules:
how many layers of insulation?
how many cavities per module? length of cryo-modules?
warm or cold focusing magnets?
conversion of electron modules (TTF/XFEL) for protons?
parallel handling of 2K and 4K two phase circuits?
P. Pierini
pressure vessel codes conformance issues?
interplay of module and cryo-system design?

Dedicated workshop on segmentation of cryo-modules will be
organised by FNAL/CERN (~September, exact date to be decided)
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questions III

4.) power converters: R. Cassel

R&D effort to get a reliable, high duty cycle pulsed power
supply?

can we use a DC power supply with pulsed mod-Anode power
supply for RF test stands? instead of pulsed power supplies (or
even for machine operation?), size? operational impact? droop?
(can it be compensated by LLRF?)

how much distance can we have between a modulator and the
klystrons? 1, 10, 100 m? state of the art in cables? cost
comparison to housing the modulators in the tunnel?

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questions IV
5.) low-beta cavities (<200 MeV): M. Vretenenar

optimum structures (NC or SC) for various beta regions?,

simpliﬁcation/standardisation of mechanical construction/
tuning?,
E. Zaplatin
inﬂuence of low-loss beam dynamics on structure design?

6.) medium/high-beta SC cavities:
S. Bousson
transition energies NC/spoke/elliptical,

how many cavity families,

realistic gradients for each structure type (and beta),

best recipes for surface treatment,
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questions V
S. Belomestnykh
7.) power and HOM couplers:

peak/average power limits?

adaption/re-design of existing devices for different frequencies?

damping requirements (beam dynamics)?

power and HOM couplers for spoke cavities?

8.) RF power splitting:
R. Pasquinelli
how many cavities per klystron?

fast amplitude/phase shifters (high duty cycle)?

ﬂexibility/reliability compared to single sources?

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questions VI
R. Duperrier A. Letchford
9.) Front-ends:

space charge limits?

source, LEBT (space charge compensation), RFQ?
10.) Linac modelling:
J. Stovall
how close are simulations to reality?

code capabilities?
C. Prior
do we understand LEBT modelling?

M. Seidel
11.) machine activation:

beam loss in high-power machines

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questions VII
9.) Collaborations:

Which other projects have similar questions?

A. Mosnier

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