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The Heavy Ion Fusion Science Virtual National Laboratory 1Molvik – HIFS-VNL-PAC – 2006
Art Molvikfor the
Heavy Ion Fusion Science Virtual National Laboratory
Program Advisory Committee ReviewAugust 9-10, 2006
Progress in e-cloud studies in both solenoids and quads
Outline1. Accomplishments2. Why we made progress3. Opportunities on HCX, STX, NDCX,…4. Planning for future
The Heavy Ion Fusion Science Virtual National Laboratory 2Molvik – HIFS-VNL-PAC – 2006
e-
i+haloe-
• ion induced emission from- expelled ions hitting vacuum wall- beam halo scraping
Sources of electron clouds
Primary:
Secondary:
i+ = ion
e- = electron
g = gas
= photon= instability
PositiveIon Beam
Pipe
e-
i+
g
g
• Ionization of - background gas - desorbed gas
• secondary emission from electron-wall collisions
e- e-e-
e-e-
• photo-emission from synchrotron radiation (HEP)
The Heavy Ion Fusion Science Virtual National Laboratory 3Molvik – HIFS-VNL-PAC – 2006
HIFS-VNL has unique tools to study ECE
WARP/POSINST code goes beyond previous state-of-the-art
Parallel 3-D PlC-AMR code with accelerator lattice follows beam self-consistently with gas/electrons generation and evolution
HCX experiment addresses ECE fundamentals relevant to HEP (as well as WDM and HIF)
trapping potential ~2kV with highly instrumented section dedicated to e-cloud studies
Combination of models and experiment unique in the world
unmatched benchmarking capability essential to our credibility ‘Benchmarking’ can include: a. Code debug
b. validate against analytic theory
c. Comparison against codes
d. Verification against experiments
enabled us to attract work on LHC, FNAL-Booster, and ILC problems
The Heavy Ion Fusion Science Virtual National Laboratory 4Molvik – HIFS-VNL-PAC – 2006
(a) (b) (c)CapacitiveProbe (qf4)
Clearing electrodes Suppress
or
Q1 Q2 Q3 Q4
K+ e-
Short experiment => need to deliberately amplify electron effects:
let beam hit end-plate to generate copious electrons which propagate upstream.
End plate
INJECTOR
MATCHINGSECTION
ELECTROSTATICQUADRUPOLES
MAGNETICQUADRUPOLES
1 MeV, 0.18 A, t ≈ 5 s, 6x1012 K+/pulse
HCX is now dedicated to gas/electron effects studies
Retarding Field
Analyser (RFA)
Location of CurrentGas/Electron Experiments
GESD
The Heavy Ion Fusion Science Virtual National Laboratory 5Molvik – HIFS-VNL-PAC – 2006
1.Good test of secondary module - secondary electron emission turned off:
2.run time ~3 days, - without new electron mover and MR, run time would be ~1-2 months!
1.Good test of secondary module - secondary electron emission turned off:
2.run time ~3 days, - without new electron mover and MR, run time would be ~1-2 months!
~6 MHz signal is observed in simulation & experiment
WARP-3DT = 4.65s
Oscillations
Beam ions hit end
plate
(a)
(b)
(c)
e-
0V 0V 0V/+9kV 0V
Q4Q3Q2Q1
200mA K+
200mA K+
Electrons
“Most successful benchmarking result in the world!”
M. Furman
(c)0. 2. time (s) 6.
Simulation Experiment0.
-20.
-40.
I (m
A)
Potential contours
Simulation Experiment
(c)0. 2. time (s) 6.
I (m
A)
0.
-20.
-40.
Electrons bunching
The Heavy Ion Fusion Science Virtual National Laboratory 6Molvik – HIFS-VNL-PAC – 2006
HCX experiment and WARP simulations agree quantitatively on oscillation frequency wavelength amplitude
Array of BPMs in Quad 4 verified simulation resultsBeam Position Monitor (BPM): electrode capacitively coupled to beam
Axial Position (cm) 0 -12 -23.5
Pulsed quad B-dot measurements, 7/9/02
0
1
2
3
4
-20-1001020Axial distance from magnet center (cm)
Quad B (arb. units)
0
100
200
300
400
500
600
-20-15-10-505Axial position from center of magnet (cm)
RMS Power (arb. units)
HCXWARP
FFT 1.9 to 2.9 µs, averaged 1 to 31 MHz, Data 26 January, 2006, Shot 6
The Heavy Ion Fusion Science Virtual National Laboratory 7Molvik – HIFS-VNL-PAC – 2006
Retarding field analyzer (RFA) measures potential on axis = ion-repeller potential
+ beam/e- distr. => f=Ne/Nbeam
First time-dependent measurement of absolute electron cloud density & major discrepancy with simulation
Absolute electron fraction can be inferred from RFA and clearing
electrodesMichel Kireeff Covo, PRL 97,
54801 (2006)
Beam neutralization
B, C, S on
B, C off
S on
B, C, S off
Clear ElectrodeA ~ 7% ~ 25% ~ 89%
RFA (~ 7%) ~ 27% ~ 79%
/RFA
Sim~89%
• Clearing electrodes provide independent measurement of e- density, confirms RFA
• Both RFA and clearing electrodes measure unattenuated transport of electrons through 3 quads whereas WARP finds x0.5 attenuation at each gap.
• We are adding diagnostics and a controllable source of electrons (e-gun) to study electron transport and compare with WARP to resolve discrepancy.
The Heavy Ion Fusion Science Virtual National Laboratory 8Molvik – HIFS-VNL-PAC – 2006
Electron effects on beam more accurately simulated
Beam loading in simulation
now uses reconstructed data
from slit-plate measurements
leads to improved agreement
between simulation and
experiment Semi-gaussian load =>
New load from
reconstructed data =>
X'
X X
X'
X'
Low e-
Hi e-
Hi e-
Hi e-
No e-
No e-
The Heavy Ion Fusion Science Virtual National Laboratory 9Molvik – HIFS-VNL-PAC – 2006
Improved model for beam energy and angle of incidence scaling of ion-induced electron yield*
Gas-Electron Source Diagnostic (GESD) measures ion-induced electron yield near grazing incidence
Theoretical
electron
yield
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
82 83 84 85 86 87 88 89
Angle (degrees)
_e
393 keV
305 keV
202 keV
130 keV
50 keV
(a)
K+ on stainless steel
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
82 83 84 85 86 87 88 89
Angle (degrees)
_e
393 keV
305 keV
202 keV
130 keV
50 keV
(b)
Experimenta
l electron
yield
K+ on stainless steel
*Michel Kireeff Covo, PRSTAB 9, 063201 (2006).
Better agreement with data at low-energy (≤400 keV) range where 1/cos() dependency breaks
The Heavy Ion Fusion Science Virtual National Laboratory 10Molvik – HIFS-VNL-PAC – 2006
Intense beam excitation of gas – enabled measuring velocity distribution of desorbed gas
Observation: desorbed gas in beam emits light
View expanding gas cloud from side – f(v0) normal to hole plate [with gated camera or streak camera]
Beam
Gas
Target
Note: Measurement requireshigh line charge density beam
The Heavy Ion Fusion Science Virtual National Laboratory 11Molvik – HIFS-VNL-PAC – 2006
Optical gas measurement has other applications
Velocity distribution of desorbed gas measured
[Further details from Frank Bieniosek]
Future plans:• Absolute calibration to obtain desorption coef. by injecting beam through gas of known pressure
• Then can measure desorption from Non-evaporable Getter (NEG), …[Collaborate with GSI vacuum group]
1.04x10-4 TorrH2
z =3.75 cm
Vertical position
0
100
200
300
400
0 50 100 150 200Axial distance z (Pixel)
Intensity (au)Beam, 5.9x10^-6Torr
Beam+ Hydrogen 1.0x10^-4Torr
Beam+ H2 but 6.3x10^-5TorrTime
The Heavy Ion Fusion Science Virtual National Laboratory 12Molvik – HIFS-VNL-PAC – 2006
Solenoids Electron collectors/ clearing rings
Electron suppressor rings
Coax cable to 1st suppressor ring
Injector
Molvik – 12/21/05
8 cm
65 cm
Insulator
Electron accumulation and effects on beam transport in solenoidal field – commissioning
Short electrodes in solenoids expel or attract electrons, long electrodes collect or emit electrons along solenoidal field lines between magnets.
The Heavy Ion Fusion Science Virtual National Laboratory 13Molvik – HIFS-VNL-PAC – 2006
WARP/POSINST applied outside HIF program
In collaboration with CBP (M. Furman)
LARP funding (started FY06, 0.2 FTE): simulation of e-cloud in LHC
FNAL funding: study of e-cloud in MI upgrade (hiring post-doc)
ILC (with C. Celata, M. Venturini): start work this summer
QuadrupolesDriftsBends
WARP/POSINST-3D - t = 300.5ns
1 LHC FODO cell (~107m) - 5 bunches - periodic BC (04/06)
The Heavy Ion Fusion Science Virtual National Laboratory 14Molvik – HIFS-VNL-PAC – 2006
CERN staff interested in our capabilities
Simulations show tenuous electron clouds (below instability threshold) increase emittance of LHC beam. Request from Frank Zimmermann and Elena Benedetto to
compute initial electron distribution for her simulation starting point, using our self-consistent 3-D code WARP.
Repeat simulation with WARP, when it can do many turns in LHC.
Jean-Luc Vay invited to speak at CERN Oct. 6, 2006.
Above results may increase interest of CERN management
The Heavy Ion Fusion Science Virtual National Laboratory 15Molvik – HIFS-VNL-PAC – 2006
VNL has capabilities for High-Brightness Studies
Issues
Beam potential
Beam transport
Duration (µs)
Access
HCX
2 kV
Quads
5
Between
quads and
ends
NDCX
STX (Solenoid)
0.4 kV
Solenoids
≤~20
End
NDCX (quads)
0.4 kV
Quads
≤~20
End
Exploit other capabilities such as Paul Trap at PPPL or UMER at Univ. Maryland for testing some slowly-growing phenomena, to supplement our short accelerators.
The Heavy Ion Fusion Science Virtual National Laboratory 16Molvik – HIFS-VNL-PAC – 2006
Expectations for electrons in quadrupoles and solenoids
Transport
Quadrupoles
Solenoids ()
Solenoids ()
Axial flow
Electrons drift
slowly
Electrons flow
freely over
entire length
Electrons flow
freely for 1-
magnet length
Radial flow
Electron flow along B
is slightly impeded by
magnetic gradient
Electron flow
suppressed
Electron flow
suppressed except
between magnetsNot yet clear which is superior for WDM/HIF needs, motivates present STX-ECE experiments
The Heavy Ion Fusion Science Virtual National Laboratory 17Molvik – HIFS-VNL-PAC – 2006
Our present plan for future
WDM/HIFS Continue coordinated experiments and simulation of
electrons and gas effects on HCX magnetic quads in search of complete quantitative agreement – publish areas of agreement and work on areas of disagreement
Beginning solenoid studies, for near-term support of WDM
Study mitigation techniques
HEP implement hybrid (3-D beam though 2-D e- slabs)
“quasi-static” mode to study slow e-cloud driven emittance growth, which is a growing concern for LHC
study e-cloud in ILC, FERMILAB, possibly RHIC develop experiments/diagnostics on HCX/NDCX relevant
to HEP Collaborate with GSI to study beam-induced
desorption from Non-Evaporable Getters (NEG).
The Heavy Ion Fusion Science Virtual National Laboratory 18Molvik – HIFS-VNL-PAC – 2006
Reconvene High-Brightness Planning GroupGoal: What do we need to know to initiate larger HIF facility ~2010 [After NIF ignition and ITER spending-peak]Or – Learn enough to add validated effects into IBEAM systems code& – Apply to near term WDM acceleratorsIssues: E-cloud, gas-cloud (quads vs sols, transport, conditions to
assure non-degraded operation) Halo Beam transport limits Emittance growth Mitigation …Strategy: Benchmark codes over wide parameter range for verified
predictive capability Verify codes with HCX, NDCX, STX, PTSX, UMER… (The Paul Trap
Simulation Experiment and U-Maryland Electron Ring can test effects that occur over 100’s of lattice periods).
Use lists of issues from previous workshops
The Heavy Ion Fusion Science Virtual National Laboratory 19Molvik – HIFS-VNL-PAC – 2006
External recognition of High Brightness program
Significant publications: PRL – Measure electron cloud density PRSTAB – Measure & model e- emission by ion impact POP – e- mover successes
Recognition with invited papers PAC05 2 HB2006 2 HIF06 3 CAARI-06 1 ICAP06 1 DPP05/06 1/1 AVS06 1
Invitations from CERN, FNAL for talks and assistance
The Heavy Ion Fusion Science Virtual National Laboratory 20Molvik – HIFS-VNL-PAC – 2006
BACKUP
Slides
The Heavy Ion Fusion Science Virtual National Laboratory 21Molvik – HIFS-VNL-PAC – 2006
1
WARP-POSINST code suite is unique in four ways
merge of WARP & POSINST
Key: operational; partially implemented (4/28/06)
+ new e-/gas modules
2
+ Adaptive Mesh Refinement
Z
R
concentrates resolution only where it is needed3Speed-up x10-104
beam
quad
e- motion in a quad
+ New e- moverAllows large time step greater than cyclotron period with smooth transition from magnetized to non-magnetized regions
4 Speed-up x10-100