Recap on ELENA machine and challenges, … Topics studied recently (mostly work in progress)
description
Transcript of Recap on ELENA machine and challenges, … Topics studied recently (mostly work in progress)
Status of ELENA –Technical Report, Status of External Contributions
Christian Carli on behalf of the ELENA teams ADUC, 13th June 2012
Recap on ELENA machine and challenges, … Topics studied recently (mostly work in
progress) Lattice and acceptance Bending magnets with very low fields Electron cooling at low energy and equilibrium with
IBS Vacuum system and residual gas interactions Stray Field measurements
Status of external Contributions Summary
Recap on ELENA machine and challenges (Not that) short synchrotron decelerating p-bars
from the AD to very low energy of 100 keV Increase of phase space density by electron
cooling at (two) low energy Weak magnetic field (100 G planned at
present) to limit lattice perturbations Twiss parameter at cooler
D ≈ 1.4 m, bx≈ by ≈ 2 m Challenge for studies:
equilibrium beam parameters with IBSand other blow-up sources, cooler imperfections …
optimization of (lattice) parameters Electron beam potential creates parabolic electron
velocity profile (plotted for 0.5 and 1 mA at 100 keV)
Transfer lines Electrostatic lines proposed: cheap and
magnetic shielding simpler
H- (or other ion) source for commissioning13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
Interaction length reduced to 0.8 m now
Recap on ELENA machine and challenges Direct space charge effects
Additional defocusing due toCoulomb repulsion
Non-linear, depending on positionin bunch
Tune shift and spread (rule of thumb:maximum -0.1 to -0.3 just an indication – true for low periodicity and energy?)
Limits intensity per bunch (or bunch length) Very low energy and, in consequence, low beam rigidity and
magnetic fields Deflection due to ~0.5 G earth magnetic field at 100 keV (beam rigidity
457 Gm): > 1 mrad/m Careful investigations on stray fields to be expected … good closed orbit
control Ratio between magnet gap and curvature radius not (that) small: correct
modeling of magnet entrance/exit
Good field quality of very low field magnets a challenge Instabilities
Possibly despite low intensity with small emittances (momentum spread) and energy
Large direct space charge impedance due to low energy
13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
Anti-
Recap on ELENA machine and challenges Intra Beam Scattering (IBS)
Consider coordinate system movingwith (average velocity of) beam
Still unordered motion of beamparticles
Can be associated with temperature(beam cooling = reduction of thisunordered motion)
IBS: Coulomb scattering between beam particles
ELENA: longitudinal temperature (and relative velocities) small compared to longitudinal ones(longitudinal electron cooling faster than transverse one)
Likely to transfer heat from transverse plane to longitudinal plane Likely the main limitation for equilibrium emittances with electron cooling Several theories exist and give similar results taking into account:
“Dispersion” (describing how beam position depends on (relative) momentum offset) tends to generate horizontal emittance growth due to IBS
Variations of beta-functions (beam sizes) around ring, coupling between transverse planes…13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
s(long. position)
x (t
rans
. pos
ition
)
Lattice and Layout Challenges (usual for low small rings) for lattice design and
optics Many constraints and few “free parameters” (quads)
Suitable working point and sufficient acceptances (small maximum beta function, but also large dynamic aperture with non-linearities)
Long straight with small dispersion for electron cooling .. Modeling of magnets with not that small gaps (compared to bending
radius) Many geometries and lattices studied since last autumn
Square, hexagonal,triangular shape, different quadrupole locations
Baseline lattice (QX≈2.3, QY≈1.3) chosen for further detailed studies
Discussion e.g. on acceptancesand apertures on-going
13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
Pavel Beloshitsky
Lattice and Layout
Integration and mechanical design started (details later in Francois presentation)13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
Francois Butin
and team
Bending magnets with very low fields
Magnets with very low fields(0.35 T to 0.05 T) required Non-linearities due to low
fields a possible issue Was this the limitation for low
energies in other machines? “Dilution”, i.e. mixing of
magnetic steel and non-magnetic (stainless steel laminations)
Higher field in magnetic laminations
Mitigation of non-linearities due to low fields
Many simulations carried out 2D and 3D, static and dynamic
effects, hysteresis effects … C-shape and H magnets …
13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
Daniel Schörling
Inhomogeneity at low field: - Dominated by a gradient - Compensation with quad settings
DB/B 10-4
-10-4
0
~half the field at 100 keV
~1.5 the field at 100 keV
Bending magnets with very low fields
Bending magnet prototype (planned) to verify: Production process of a magnetic yoke
diluted with stainless steel plates. Field quality with chosen steel and
hysteresis Mechanical deformations Wish: test heating during bake-out (NEG
activation) Edge angle and end shim design.
13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
Ratio Magnetic Steel: Stainless
Steel1:2
Magnetic: Non-
Magnetic
Minimum field 0.05 T
Maximum field 0.4 TMagnetic length
(straight) 1.0 mRamp rate 0.4 T/s
Good field region (square)
±30/cos(30°) mm
Local field quality ≤ ±2·10-4 1-B/Bref
Integrated field quality ≤ ±2·10-4 1-∫Bdl/
∫BrefdlTotal gap height 100 mm
Approximate pole width 330 mm
Edge angles 12 deg
Electron cooling at low energy and equilibrium with IBS
Code betacool Developed at JINR, Dubna Models electron cooling,
Intra Beam Scattering (IBS), RF system ….)
Cooling at 100 keV plateau Electron cooling current 0.5 mA Strong blow-up due to IBS limits
final momentum spread Energy spreads expected at experiments
increased by one order of magnitude!!(see presentation by Pavel)
Cooling times around 1 s Final physical rms emittances of
≈0.25 mm and ≈0.17 mm !
13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
A. Smirnov (JINR), P.Beloshitsky,G.Tranquille, M.Martini
RMS emittances and rel. momentum spread
Capture after electron cooling RF capture after switching off
cooler Sufficiently slowly to avoid
non-adiabaticities Sufficiently fast to avoid
(longitudinal)blow-up due to IBS
Four bunches with 0.6 107 pbars each
Characteristics for experiments(with VRF,h=4 ≈ 500 V) Rms bunch length: ≈0.25 m Rms energy spread: ≈0.5 keV
(impact on experiments & design of lines!)
13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
A.Smirnov (JINR), S.Hancock,
P.Beloshitsky, G.Tranquille, M.Martini
RMS emittances and rel. momentum spread
0 0.01 0.02 0.03 0.04 0.05 0.060.01
0.11
10100
1000
reference time, sec
RF
Vol
tage
, V
Required RF voltageunder discussion
(could be less than 500 V)
Vacuum system and rest gas interactions
Very first simulations of pressures around the ring Only H2 desorption with 1.203 10-12 Torr l s-1 cm-2 (realistic for baked
machine everywhere) Some pressure variations since H2 not pumped efficiently by NEGs
(assumed in the whole ring) Next (more realistic simulations for gas compositions and more realistic
hardware): Realistic gas loads for
heavier molecules Injection/ejection
equipments Transfer lines
(differential pumpingclose to ring)
Electron cooler Final apertures
(smaller aperturesreduce conductance)
13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
10-1
2 Tor
r2.
53.
5
Position along a sector between bends
R.Kersevan
Vacuum system and rest gas interactions
Very low pressure and velocity at 100 keV Most p-bars do not interact with rest gas
molecules (black): in average ~40 s between interactions!
Nuclear interactions (red): very rare Large angle scattering outside acceptance
(orange): large cross section due to low energy (losses slow due to low pressure and velocity)
Small angle scattering (blue): several deflections of one p-bar at 100
keV very unlikely Rms angles (and blow-up) strongly
overestimated if p-bars undergoing large angle scattering angles are taken into account
13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
NucleusElectrons
Stray field measurements in the AD hall
Motivation: Beam at very low energy in not that short machine sensitive to stray field Make sure that stray fields in the hall are not too strong
First - preliminary for the moment - selected results Earth magnetic field dominates at the position of future ELENA ring (few
locations with higher and lower fields understood and not an issue) …. Excellent news for ELENA ring
Stronger fields a few meters from an experimental solenoid (AEGIS) .. Watch out for lines
13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
General field levelBVERTICAL ≈ 35 mT
BHORIZONTAL ≈ 30 mT
Scaffolding structure behind kicker spools:
150 mT (70 mT @ 0.2 m)
Field at AD ring concrete shielding blocks:|B|≈ 10 mT
No gross time dependence observed
M. Buzio
Beam Transfers and Lines
Studies on beam transfers (injection/ejection, lines) underway (see presentation tomorrow by W.Bartmann and G.Vanbavinckhove) Extraction channels Geometry of lines Optics Design Test triplet (by and at
ASACUSA)
13th June 2012 ELENA Status C.Carli on behalf of the ELENA teamASACUSA triplet (Courtesy: D.Barna, M.Hori and T.Koichi)
W. Bartmann, G.Vanbavinckhove many contributions from ASACUSA
Status of external Contributions
13th June 2012 ELENA Status C.Carli on behalf of the ELENA team
Univ. Tokyo and MPQ-MPI: - 2 MCHF (possibly electron cooler) - 7 FTE (identified, electrostatic transfer lines and devices) Cockcroft Institute & Univ’s and Swansea University: - Costing of the order of 500 kGBP has been applied by U Liverpool, - A proposal has been submitted for work : this would cover 2 Postdocs, some PhD students
and equipment; the overall funding requested is about 1 M€; a decision is expected until June. Denmark: - Applied for the money for bends and quadrupoles (Danfysik), possibly funding for a postdoc IKP-FZ Julich: - Several aspects of the source have been discussed in meeting on 27th of March in Juelich - Work has started and will be again discussed tomorrow afternoon: substantial development
work is required to make such a source operational for ELENA commissioning. Many interfaces to be clarified (vacuum with differential pumping, design of lines, integration, infrastructure …).
Univ. Brescia: 50 kEuros (to be transferred after ADUC) RIKEN (new since last ADUC)
- Compensation solenoids for electron cooler- Manpower (student)
TRIUMF: Help for design of electrostatic transfer lines Hemholtz Institute Mainz: Construction of supports Manne-Siegmann: Help with ELENA commissioning Berkeley: DOE does not (yet) support – MoU not signed, but discussion not yet abandoned! CEA-IRFU Saclay-SIGMAPHI: only prototypes are interesting for them – did not sign MoU, but
still discussions
Summary/Status Studies on-going on several technical issues
Better understanding of limitations at low energy Intra Beam Scattering (IBS) seems the dominant limitation for
ELENA Expect larger energy spreads at the experiments
Still many studies work in progress …. and some studies to be started (e.g. instabilities, IBS on ramps ….)
Status Aim: Technical Design Report (TDR) to be ready in autumn For other milestones and more details on some topics
(parameter, new building, experimental zones …) see presentations by Stephan, Pavel, François and Wolfgang
Memory of Understanding of collaboration signed this morning On track for first ELENA physics at the beginning of 2017
Thanks To everybody who helped with the preparation of this presentation For your attention13th June 2012 ELENA Status C.Carli on behalf of the ELENA team