Transcript MESA Erste Gedanken

Status MAMI facility
KHUK-workshop , 30.11. 2012
Kurt Aulenbacher
Institut für Kernphysik
Uni Mainz
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Outline
• SFB 1044 and the operation of MAMI
• Prisma and erection of MESA
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MAMI at IKP Mainz
1.6 GeV c.w. polarized beam
150kW beam power
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Operation statistics 2005 – Nov. 2012
average availability for users: 85% !
61%
72%
46%
51%
HDSM-operation
40%
36%
1%
MAMI total (1991 – 2012): 129592 hours of operation
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MAMI at IKP Mainz
Operational highlights 2012:
-A4- ”experiment
PV e-scattering on deuterium@200MeV
- KAOS chicane in high intensity operation
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MAMI beam time in 2012 (until November)
Distribution between the experimental groups
Operation for experiments of SFB 1044 will continue for
(hopefully) many years
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PRISMA
15 June 2012: PRISMA excellence cluster is awarded to JGU
 PRISMA includes construction of innovative particle acclerator
for hadron/particle physics experiments in the 100 MeV range
Mainz Energy recovering Superconducting Accelerator
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MESA at IKP Mainz
High power
beam dump
Experimental
hall
Accessshaft
MESA-hall-2
MESA-hall-1
MAMI/MESA
separation (shielding)
-no new buildings
-MAMI experiments
continue seperatly
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MESA accelerator
project rationale
• Experiments conceivable which require a new & innovative accelerator
• low energy (100-200MeV)  therefore accelerator ‘affordable’
• MAMI acc. team competence represents basis for development
• Project will be attractive for young students and researchers
Make use of innovations in SRF accelerator science:
1. Energy recovery linac (ERL)
2. Recent progress in high gradient-c.w.-SRF
Beam parameter goals in two different modes of operation:
1.) EB-mode External spin-polarized c.w. beam at 200 MeV
(Q2=0.005GeV/c at 30 degree). L>1039 cm-2s-1
2.) ERL-mode: 10mA at 100 MeV with L~1035 cm-2s-1
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MESA-Scheme
KEY:
PS: Photosources: 100keV polarized
(EB, ERL (low charge)),
500keV unpolarized (ERL, high charge)
2ERL
IN: 5 MeV – NC injector
SC: 4 Superconducting cavities
2 3
Energy gain 50 MeV per pass.
1-3 Beam recirculations for EB
Orbit 1 common to ERL and EB,
Orbit 2 could be separate for ERL and EB
PIT
PIT: Pseudo Internal target (ER-experiment)
PV: Parity violation experiment (EB-mode)
DU: 5 MeV beam dump in ERL-mode
Area:22*14m2
MESA-LAYOUT
IN
1
SC
PS
Existing walls: 2-3m thick shielding
RC
DU
to PV-experiment
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EXPERIMENTAL BEAM PARAMETERS:
1.3 GHz c.w.
EB-mode: 150 mA, 200 MeV polarized beam
(liquid Hydrogen target L~1039)
ERL-mode: 10mA, 100 MeV unpolarized beam
(Pseudo-Internal Hydrogen Gas target, L~1035)
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Accelerator Layout
Design by Ralf Eichhorn
(Deutscher Designpreis für Magnethochregallager)
Alternative: Double axis acceleration a la CEBAF:
more compact, but less flexible!
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Accelerator Layout
PIT
P2
V. Bechthold/R. Heine
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ERL-PIT-experiments
20s beam envelope
for en=5mm
beam in
H2
6mm dia
Dublett
V. Tioukine
Dublett
Pump
Assuming target density N=2*1018 atoms/cm-2 (3.2 mg/cm2, 5*10-8 X0)
we have (at I0=10-2 A) luminosity of L= I0/e*N=1.2*1035cm-2s-1
(average) ionization Energy loss: ~ 17eV
 RMS scattering-angle (multiple Coulomb scattering): 10mrad
 single pass beam deterioration is acceptable Note: storage ring:
beam emittance lifetime ~ 10milliseconds (stationary vs. variable background…)
 beam halo & long tails of distribution due to Coulomb scattering have to be studied
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19.09.2012
EB workhorse experiment : PVES at low Q
(P2 experiment within SFB 1044)
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19.09.2012
MESA-beam-parameters stage1/stage-2
Beam Energy ERL/EB [MeV]
105/155 (105/205)
Operating mode
1300 MHz, c.w.
Source type
Photosource d.c. 100keV, polarized
(additional source 200keV, nonpolarized)
Bunch charge EB/ERL [pC]
0.15/0.77 (0.15/7.7)
Norm. Emittance EB/ERL [mm]
0.2/<1 (0.2/<1)
Beam polarization (EB-mode only)
> 0.85
Beam recirculations
2 (3)
Beam power at exp. ERL/EB [kW]
100/22.5 (1000/30)
Total R.f.-power installed [kW]
120 (160)
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MESA- stage1 Timescale
Accelerator basic design: end 2013
Early 2014: ordering SRF
Early 2016 delivery
End 2017 operation
…Thank you!
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SRF-main accelerator issues
9 cell ‘TESLA’ (E-XFEL) p-mode structure:
Q-curve often measured under not realistic
‘vertical’ conditions…esp. dust particles
& contamination films may
appear during horizontal assembly, accidents
in the vacuum system, etc….
New HIM-building Mainz:
is planned to be equipped with
a Clean room facility &
high pressure (ultrapure) water rinsing
(HPR)
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Problem for high c.w. current
operation: HOM excitation
PHOM~I2B
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A REAL SRF ‘module’
True c.w.-operation SRF facilities: CEBAF, ELBE, S-DALINAC (3GHz)
not: E-XFEL, FLASH, TESLA/ILC.
c.w. requires lowering the Gradient due to power dissipation!
J. Teichert et al. NIMA 557 (2006) 239
Such modules can be ordered from industry. Missing: sufficient higher
order mode damping for I>2-4 mA. Note MESA stage-2
ERL-current is 40mA!  modify after stage-1 or take the risk??
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Injector issues
Pro‘s for normal conducting injector:
• no cryogenic load
• considerably lower cost, established design, e.g. >9mA c.w. without BBU
(HOM excitation strongly suppressed)
• high flexibility: variable beta-design is feasible! probably better beam quality than
existing SRF injectors
GRP: Gun/rotator/
polarimeter (EB-mode)
CBP: Chopper/buncher
Preacc. (g-beta)
HCI: 511keV high bunch
charge injection
(ERL-mode, stage-2)
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2m, 2MeV at PHF=30kW
5MeV
GRP
CBP
HCI
IN
DU
PV
RC
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Back-ups
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Spin polarized source layout
strongly influenced by need of ‘false’ asymmetry control! Afalse <0.2ppb
Spin direction
GUN
f=p/2
Ө
Spin rotation
axis
2.5m
●
f=p/2
DSP
●
f=var
to second part
Systematic electron optical helicity reversal! (similar to JLAB/QWEAK)
Chop.
buncher
from first
part
graded-b
550keV
3m
Injection of 550kV
high charge source
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
tension with desire to have a SHORT injection for high charge  separate 550kV gun
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Spin rotation and source beam energy
 Spin =
V. Tioukine, K.A. NIM A 568 537 (2006)
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1
me 
2
EL
100kV Filter, L=0.3m
operated at 23kV over 2cm gap
not practical to handle filter at 500keV (=2),
… but could probably work at 200keV
(200keV source is able to reach emittance
goal at 7.7pC!)
JLAB development:
A 200keV source is nowadays very
compact - R. Suleiman et al. Proceedings
ERL2011,
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Accelerator Layout
arcs
merger
First Order beam optics for arcs, mergers & combiners
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Summary/Outlook
• MESA: First ERL with particle physics experiments in Europe
• Detailled considerations have begun for all subsystems
• Superconducting Radiofrequency System and it‘s cryogenics
is main cost driver.
• MESA funding is part of ‚PRISMA‘ excellence cluster req
• ERL operation restricted so far to 1mA in order to save costs
for development and cryogenics of high current SRF sections (additional ~ 5 M€)
• Great support from TU-Darmstadt, hope to continue collaboration
• Mainz also collaborates with HZB (Berlin-Pro) &CERN (LHeC)
• Photoinjectors collaborations with HZD (ELBE) and HZB
• main issue now, after funding decision: creating a powerful team!
• good reason to believe that stage-1 can be made operational within 5 years
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Backups
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WHY is source-emittance so important for
ERL-experiments?
20s beam envelope
H2
6mm dia
Dublett
Dublett
Pump
e Norm = 10 m m (or 3.2 p mm * mrad * m e c) (MESA goal)
e Geo =
e Norm
 e Geo (100MeV)
 1
2
Beam diameter
as a function
~ 50nm.
of optical function
b :
r b eam ( z ) = e Geo * b ( z )
2
point z* = 0
in the field free region around symmetry
b ( z ) = b ( z *) 
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 Maximum
z
2
b ( z *)
= b (1  ( z / b ) ) choose : b = 1m
*
beam diameter
*
2
*
 0 . 62 mm over 2 Meters of length
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Emittance requiments
An normalized emittance of 5 mm is the key for successful operation of DM-experiment
With tbunch << taccel we have a lower limit for emittance at the cathode
e min =
q bunch ( E   W )
6 pe 0 E cath mc
2
~  0 . 2 m m @ 7 . 7 pC @ 1 MV / m
( E   W ) ~ 0 . 4 eV (KCsSb),
0 . 1eV (NEA - GaAs)
But: vacuum space charge destroys beam emittance…
Countermeasures:
1.) accelerate with high field to relativistic velocities because Fq~1/2.
a) ERL-d.c guns ~3-6MV/m to 0.25-0.5 MeV
b) SRF gun with 15MV/m to ~ 5 MeV (FZD, future: BERLinPRO).
MESA –baseline for ERL-source: 200keV ‘inverted‘ Photogun a la JLAB
(P. A. Adderley et al. PR-ST-AB 13 010101 (2010))
+350keV electrostatic Postaccelerator (reduced Version of famous 2MeV
d.c.-MAMI-A injector)
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SRF-main accelerator issues
9 cell ‘TESLA’ (E-XFEL) p-mode structure:
Q-curve often measured under not realistic
‘vertical’ conditions…esp. dust particles
& contamination films may
appear during horizontal assembly, accidents
in the vacuum system, etc….
New HIM-building Mainz:
is planned to be equipped with
a Clean room facility &
high pressure (ultrapure) water rinsing
(HPR)
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30.11.2012
A REAL SRF ‘module’
True c.w.-operation SRF facilities: CEBAF, ELBE, S-DALINAC (3GHz)
not: E-XFEL, FLASH, TESLA/ILC.
c.w. requires lowering the Gradient due to power dissipation!
J. Teichert et al. NIMA 557 (2006) 239
30.11.2012
Such modules can be ordered from industry. Missing: sufficient higher
order mode damping for I>2-4 mA. Note MESA ERL-current is 40mA!
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Recirculator
• 200 MeV EB could require vertical stacking of 3fold recirculation
• Merger Systems complicated due to limited space
• But Magnets very small (compared to MAMI)
• Beam power (EB) 30kW@200 MeV (ERL) 50kW at 5MeV
•  R.f power needed EB ~ 120kW ERL ~ 140kW
• 1300 MHz R.f. supplied by reliable & stable semiconductor amplifiers (not Klystrons!)
• Experiments are TINY
PV-Experiment
14m
Dark photon-exp.
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405nm Laser
• Advantage of 405 nm: KCsSb QE~30mA/Watt. Cost ~ 3k€/watt (d.c.);
• optimum beam quality: 1mm dia-spot at 1m only with collimation tube!
• electron gun current presently limited by power supply (<3mA)
• Diode is well suited for pulsing at GHz-frequencies , (<40ps at full power)
• Could provide ~1W (40ps, r.f. synchronized) for MESA (1 lifetime ‘overhead’)
 five DVD-player diodes in parallel!
collimation
tube
Laser-out
d.c or
R.f
2cm
€100 purchase from eBay
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Lifetime issue
Milliampere- test experiment with NEA-GaAs
GaAs operation
would be
possible, but
inconvenient
• long lifetime required  KCsSb (unpolarized) photocathode
• lifetime about 100 hours @25mA demonstrated recently at Cornell
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PCA fabrication chamber at Mainz-HIM
PCA-Apparatus
:
•KCsSb technology available at
Mainz
• good results >30mA/Watt
(>10% Q.E)
• evidence for *100 stability
increase with respect to GaAs
(2000 hours at 10mA?)
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DM: Focusing through the PIT
e Norm = 10 m m (or 3.2 p mm * mrad * m e c) (MESA goal)
e Geo =
e Norm
 e Geo (100MeV)
 1
2
as a function
Beam diameter
~ 50nm.
of optical function
b :
r b eam ( z ) = e Geo * b ( z )
2
point z* = 0
in the field free region around symmetry
b ( z ) = b ( z *) 
 Maximum
z
2
b ( z *)
= b (1  ( z / b ) ) choose : b = 1m
*
beam diameter
*
2
*
 0 . 62 mm over 2 Meters of length
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DM: Focusing through the PIT
H2
E0=104MeV
20s beam envelope
6mm dia
Dublett
Pump
Dublett
Assuming target density N=2*1018 atoms/cm-2 (3.2 mg/cm2, 5*10-8 X0)
we have (at I0=10-2 A) luminosity of L= I0/e*N=1.2*1035cm-2s-1
(average) ionization Energy loss: ~ 17eV
 could allow to recuperate more energy than in conventional ERL (2.5MeV).
RMS scattering-angle (multiple Coulomb scattering): 10mrad
 single pass beam deterioration is acceptable Note: storage ring:
beam emittance lifetime ~ 10milliseconds (stationary vs. variable background…)
 beam halo & long tails of distribution due to Coulomb scattering have to be studied
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MESA-experiments-3: Applied physics
High beam power electron beam may be used for:
• ERL-mode: Production of NV-nanodiamonds (e.g. medical markers)
• EB-mode: High brightness source of cold (polarized) positrons
G. Werth et al. :
Appl. Phys. A 33
59 (1984)
Color: NV-centers introduced
in Diamond.
Irradiated at MAMI
for 3 days, 50mA at 14MeV
MESA
can produce
~109 positrons/s
in a beam of <1cm
diameter at 120eV
surface science:
magnetic structures
positronium
production
(J. Tisler et al. ACS NANO 3,7 p.1959 (2009))
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