2. ESSnuSB Accumulator Work Plan
E. Wildner
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

3. ESSnuSB on ESS site
Tord is laying out the transfer from Linac !
> 2 GeV
2 GeV p H-
Neutron
spallation
target
E. Wildner, CERN
~1 BEuros for the neutrino facility including detector
NOW 2014, 10/9

4. Accumulator_Uppsala_Oct_14, E. Wildner
One accumulator
The originally proposed 4 Accelerators for accumulation seem costly and not necessary
One accumulator could pulse 4 times with ¼ of the linac pulse length
The injection bumper is too slow
Rise time for the PS Booster bumpers is10 ms (same for the fall time)
Modern bumpers?
We propose to make 4 linac pulses of length 2.86/4 ms (same beam power)
They would be injected sequentially into accumulator
Spaced using timing such that bumpers are comfortable
However a price has to be payed…
NB: accumulation for ESS neutrons need H- but considerably longer pulses at extraction from accumulator: this is not forgotten but is less straight forward, needs more design work
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

5. Linac Pulsing 70 Hz, present baseline
neutrino
neutron
71.4 ms, 14 Hz
35.7 ms
28 Hz
Four Accumulators
2.86 ms
71.4 ms, 14 Hz
One Accumulator
(baseline)
14.28 ms
70 Hz
0.7 ms
2.86 ms
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

6. Accumulator_Uppsala_Oct_14, E. Wildner
70 Hz linac pulsing
Fill time of the superconducting cavities:
For loaded Q, this is about 0.2 ms
For two 3 ms beam pulses, this is 6.6% of the beam pulse length
This corresponds to an inefficiency of 6.6%
4 pulses at 0.75 ms and one pulse of 3 ms:
5 x 0.2 ms = 1 ms filling time, 16.6% inefficiency (10% extra)
Keep in mind: 4 rings are 4 times operation and maintenance cost, not less
Foil heating in accumulator (see later)
Communication D. Mc Ginnis
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

7. ESSnuSB Accumulator Lattice Version 0
Circumference
376 m
Dipole field
0.635 T
# Dipoles 64
# Quads 84
Bending radius
14.6 m
Injection region
12.5 m
Revolution time
1.32 μs
C=376 m
J. Jonnerby
Straight Arc
SNS straight section for injection used “as is” for simulations of foil stripping
Less bending strength to ease energy upgrade
No magnet considerations yet
Collective effects not yet completed
SNS
C=278 m

8. H- injection foil stripping
24 m
Courtesy W. Bartmann

9. Injection area optics (foil/laser)
Contradicting requirements for foil and laser  two different optics settings (however: the layout is the same!)
Foil optics
Laser optics
Courtesy W. Bartmann

10. Feasibility of Stripping foil injection
Foil stripping feasibility: first stage approach
Simulations of MW accumulator projects have been done with the ACCSIM Code.
The results are compared with the ORBIT results (courtesy M. Plum, J. Holmes) for representative SNS beams.
H. Schönauer, CERN
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

11. ESS Linac + Exteded SNS Lattice
Comparison of Foil Heating Simulations for some Project Lattices with the SNS
TEST CANDIDATE:
ESS Linac + Exteded SNS Lattice
CERN SPL
PDAC 2001
1Foil
2Foils
SNS
C [m]
318
943
242
T [GeV] 2
2.2 1
P beam
5 GW / 4
2 GW
1 GW
f rep [Hz]
70 / 14 50 60 Np
2.8E14
2.3E14
1.5E14
N turns
650
850
1060
 Norm (95%)
100 / 200*)
150
200 
 Linac (95%)
1.33 
2 
1.5 
Nmacro
33000
41000
156000
Foil [mg/cm2]
750
2 x 750
400
*) 100 too small;
better 200
like in SNS
H. Schönauer, CERN
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

12. Accumulator_Uppsala_Oct_14, E. Wildner
Comparison of Phase space Occupation for 100  vs. 200  normalized Emittance
For an emittance of 100  the average Nr of foil hits of the circulating beam approximately doubles - the linac beam remains about the same
Space Charge Detuning (approx.):
-0.15 (100 ), (200 )
H. Schönauer, CERN
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

13. ESS Foil (Extended SNS Lattice): Peak Temperatures
H- Linac
H- Linac+ p circulating
Maximum Foil Temperatures:
1797 K (H- Linac Beam))
2050 K (H- + p circulating Beam)
H. Schönauer, CERN
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

14. ESS stripping foil heating considerations I
Table 1: ESS beam characteristics at injection
Parameter
Value
Ion kinetic energy
2 GeV ( = 3.1)
H pulse duration
0.715 ms = 2.86 ms/4
H pulse repetition rate
70 Hz, ms
H mean pulse current
62.5 mA
RMS normalized emittances
and preferred beam size
x,y  0.33m & x,y = 2 mm
with at injection x,y 36 m
Carbon foil dimensions (x, y, z)
Thickness area density
17  62 mm2  3.9 m (tc [m])
= 750 g/cm2
H total stopping power at 2 GeV
Sp = 4.98 MeV cm2/g
To keep constantly the foil temperature below 2500K the pulse RMS spot size should be about 2 mm (x & y dir.) which needs betatron functions at accumulator ring injection close to 36m.
Protons and electrons in H- having the same velocity at foil entrance (same  & ) the electron energy is then 1.09 MeV and its total stopping power is 1.61 MeV cm2/g. So the H- total stopping power is 4.98 MeV cm2/g.
M.Martini, CERN

15. ESS stripping foil heating considerations (2)
M.Martini, CERN

16. ESS stripping foil heating considerations (3)
Solution of the 3D heat equation with Mathematica for the ESS beam
Fig. 1: Time evolution of the maximum carbon foil temperature at the pulse spot center derived from the 3D PDE (cont. line) and the simplified 1D ODE (dotted line). Both plots differ as the 1D model does not contain the heat conduction effect
Fig. 2: Time evolution of the carbon foil temperature versus the foil height (y dir.). The temperature decreases quite rapidly along the y axis (as along the x axis)
For the beam characteristics of Table 1, both figures show that the foil temperature modulation in the repetitive accumulator filling cycles is quasi stable after the second long cycle, each made of four ms injection pulses (repeated every ms) plus a ms gap (empty injection cycle). Fig. 1 shows that the maximum stripping foil temperature varies between 1032K and 2072K
M.Martini, CERN

17. Linac Pulsing, option if current too high ?
neutrino
neutron
71.4 ms, 14 Hz
35.7 ms
28 Hz
Four Accumulators
Not working!!!
2.86 ms
71.4 ms, 14 Hz
One Accumulator
Lower linac peak current
14.28 ms
70 Hz
2.86 ms
(0.7 * 2) ms, and half the intensity, for example (to mitigate high H- intensity)
How would this option influence the linac ?
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

18. Extraction to 4 targets: Switch-yard
E. Bouquerel
Development for EUROSB
ESSnuSB beam energy is lower
Extraction timing is different (50 Hz -> 70 Hz)
Needs ~ 100 ns gap in Accumulator
Regular gaps in linac beam (chopping)
Extraction from accumulator is included in this work
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

19. Int. gradient last 2 quads
p-beam from Linac
parameter
value
unit
Intensity
p/pulse
Current
62.5 mA
Pulse length
2.86 ms
ex/ey
0.327/0.334
pi.mm.mrad bg
2.966 DE
+- 0.4
MeV
Int. gradient last 2 quads
1.5 T
Aperture
Source: Mamad Eshrakqi,
What will change for H- (simulations have to be done from the source output)
Items to change have been established and injected in the Linac upgrade plans, see for example report from ESS visit by Gerigk and Montesinos
Linac lattice can be found in Optimus folder on the Cloud
We expect the beam conditions at exit from Linac to be available by ESS team (M. Eshraqi)
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

20. Accumulator_Uppsala_Oct_14, E. Wildner
Beam in Accumulator ??
parameter
value
unit
Emittance ( en)
200
pi.mm.mrad
Magnet aperture DE
To be completed!
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

21. Accumulator_Uppsala_Oct_14, E. Wildner
Workplan skeleton 1
We would like to start he work an the planning now to get an idea of the accumulator design, layout and price, to be refined during “Horizon 2020”
The following slides organizes a few ideas (“classical”) about the procedure
Small workforce, but well organized we could achieve a well set goal.
The parts (have to be iterated between them) are
Transferline Linac Accumulator
Injection into accumulator
Extraction
General
Lattice construction
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

22. Accumulator_Uppsala_Oct_14, E. Wildner
Actors
CERN Team
General: Elena
Consulting: Bernhard, Yannis, Brennan, Horst, Frank&Eric, Mamad
Supervision: Bernhard, Elena
Education: Bernhard
Workforce: Horst, Elena…
To some extent we will be able to use CERN competences, for accelerator physics, clearly yes (consulting only, so far).
CERN Core team: Elena, Horst Bernard
Uppsala Team
General: Tord
Consulting:
Supervision:
Education:
Workforce:
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

23. Transfer line Linac-Accumulator
Choose extraction point (energy)
Choose magnet (length, aperture…)
Define transfer line lattice (stripping in magnetic elements )
Debunching (DE and bunching conditions at injection, SC)
Check gaps for accumulator extraction
Elena, Tord, Horst, Bernhard, Brennan, Frank, Mamad
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

24. Injection to Accumulator
Injection optics taken from SNS, to be changed?
Design for foil stripping (optics)?
Stripping efficiency
Injection design (injection elements req.) and emmittance estimations after injection RF
Elena, Horst, Bernhard, UU
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

25. Accumulator_Uppsala_Oct_14, E. Wildner
Construct lattice
Check the lattice with reasonable magnets
Debunching (DE and bunching conditions at injection, SC)
Check gap evolution for accumulator extraction
RF?
Estimate impedances (kickers, bumpers, cavities, instrumentation…)
Stability calculations (collective effects)
Elena, Horst, Bernhard, Frank, UU
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

26. Accumulator_Uppsala_Oct_14, E. Wildner
Extraction
Responsibility of CNRS
Define interface point and beam conditions at this point
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

27. Accumulator_Uppsala_Oct_14, E. Wildner
General
Beam loss and radiation
Controls
Instrumentation
Machine protection
Safety (including access control)
Civil Engineering
Costing
Elena, Tord, Lars Söby ???, Alfredo Ferrari ???, UU and ESS
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

28. Lattice construction steps
Optimize
Circumference
Apertures
Neutron option
Can we define a new lattice in a systematic way
Where to start (circumference)
Magnets (aperture, length, field)
Packing
Injection/Extraction
Characteristics of lattice for very high intensities
Remedies for possible collective effects ?
….etc
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

29. Accumulator_Uppsala_Oct_14, E. Wildner
Lattice construction 2
High intensity / Energy
Gamma transition/Isochonous ring
Lattice types
Phase advance
Symmetry (square??)
Short/long arc
Straights for injection/extraction/RF/instrumentation
RF at injection
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

30. Lattice design, more details 1
by Bernhard
0.) Paper work ...
possible articles / papers to be studied in the field:
PS-Booster Design (Bovet / Reich)
PS-Booster performance (Bovet et al)
Lattice Design of HISTRAP (Oakridge)
Design report of the RCS / Papers on the RCS lattice
(Hanke, Lachaize, Carli)
PHD Miriam Fitterer: She compared different lattices in the context of space charge dominated beam optics & dynamic aperture
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

31. Lattice design, more details 2
1.) Define the geometry of the ring:
check maximum allowed dipole field by lorentz stripping
and also: available space on site
2.) define in first approximation the ring geometry <-->  number of dipoles
three fold (like the RCS e.g.) / four fold / ...
which defines already a bit the tune.
3.) Scale - for the sake of comparison and experience - the space charge problem between the accumulator ring and e.g. the PS-Booster.
4.) Symmetry arguments in the geometry layout
5) do we need dispersion free sections ?
for rf ?
for injection / extraction ?
if so do we maintain (and how) the symmetry ?
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

32. Lattice design, more details 3
6.) Study & chose the focusing structure ...
basic cell layout
doublet / triplet / FoDo
any exotics ?
7.) and then based on this the beam optics.
Do we care about momentum compaction (In think not too much but still...)
Optimisation between beam size determined by beta function / dispersion
Optimisation of the overall beam size to keep the space charge forces limited
Optimisation of the change of the beta function along the lattice (i.e. between QF and QD quadrupoles)
Optimisation of the phase advance --> the tune (See point 2)
8.) tbd
looks like quite some work and in some cases we will have to get used to the tools even (PTC instead or in combination with MAD-X), special space charge tracking codes etc
Clear enough: a lot of work but interesting and not without challenge.
So a pretty nice package.
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner

33. Accumulator_Uppsala_Oct_14, E. Wildner
How to start
Could we start now ?
Who, which lab ?
Person power ?
Timeline and milestones ?
Priorities ?
Meeting plan (CERN Core team every week? 1.5 hours)?
08/10/14
Accumulator_Uppsala_Oct_14, E. Wildner