Experimental Techniques Where do we come from, where are we going?

1
Experimental TechniquesWhere do we come
from,where are we going?

• Bernhard A. Mecking
• Jefferson Lab

Gordon Conference on Photonuclear
Reactions August 1 - 6, 2004
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Topics

• Beams
• Targets
• Detectors
• Electronics DAQ
• New facilities
• Trends

I apologize in advance to everybody whose
favorite topic I have left out.
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Technical Progress and Discovery

• Intimate connection between establishing a new
  technical capability and a quantum leap in
  understanding
• General
• field tightly coupled to advances in vacuum and
  surface technology, RF, electronics and
  computing, beam dynamics, simulation
• Specific Examples
• deep-inelastic scattering scaling
  quarks)
• ee- collisions large acceptance
  coverage J/Psi (October 1974)
• polarized beam and target nucleon spin
  structure
• precise data for gN pN tests of Chiral
  PT
• polarization Rosenbluth data for
  Gep/Gmp importance of 2g effects?
• investigation of KN final states penta-quark?

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Experiment Schematics
Data conversion modules
Data acquisition and storage
Detector
Source (pol.)
Accelerator
beam
target (polarized)
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Electron Accelerators

• History
• linear accelerators (HEPL Mark III 1 GeV in
  1950, SLAC 20 GeV in 1967,
• Saclay, MIT, NIKHEF)
• synchrotrons (Bonn 0.5 and 2.5 GeV, Daresbury,
  DESY 6 GeV)
• common features pulsed RF or changing magnetic
  field, limits duty-cycle and
• beam quality
• Present status
• 100 duty-cycle operation using
• low-gradient warm accelerator structures many
  passes (MAMI)
• superconducting accelerator structures few
  passes (CEBAF)
• Future developments
• higher gradients for ee- colliders (cost, not
  duty-cycle important)
• energy recovery for FEL, synchrotron light
  sources, electron beam cooling, etc.
• own community MAMI C, CEBAF 12 GeV upgrade
• electron-ion collider

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MAMI Microtron 3. Stage
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CEBAF Continuous Electron Beam Accelerator
Facility
recirculating arcs
Properties Emax 5.8 GeV Imax 200mA Pe 85
beams 3
accelerating
structures
CHL
RF separators
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Electron Accelerator Beam Quality
Beam Profile in Hall B obtained with dual wire
scanner 10nA to Hall B, 100mA to Hall A
Beam Energy Spread in Hall A Line synchrotron
light interference monitor continuous
non-destructive measurement
dE/E x 10-5
4
s 130mm
2
0
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Electron Accelerators

• History
• linear accelerators (HEPL Mark III 1 GeV in
  1950, SLAC 20 GeV in 1967,
• Saclay, MIT, NIKHEF)
• synchrotrons (Bonn 0.5 and 2.5 GeV, DESY 6 GeV)
• common features pulsed RF or changing magnetic
  field, limits duty-cycle and beam quality
• Present status
• 100 duty-cycle operation using
• low-gradient warm accelerator structures many
  passes (MAMI)
• superconducting accelerator structures few
  passes (CEBAF)
• Future developments
• high gradients for ee- colliders (cost, not
  duty-cycle important)
• energy recovery for FEL, synchrotron light
  sources, electron beam cooling, etc.
• own community MAMI C, CEBAF 12 GeV upgrade
• electron-ion collider?

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Polarized Electron Sources

• History
• 1977 first parity violation experiment at SLAC
  (e D eX, DIS)
• GaAs photocathode, dye laser, Pe37 (theoretical
  max. of 50)
• rapid polarization reversal via Pockels cell
• experimental asymmetry 6 .10-5 (syst. errors 10x
  smaller)
• Present status
• same technique
• strained GaAs or super-lattice, RF pulsed
  Ti-sapphire laser, Pe85
• systematic errors lt 2 .10-8 (E158 at SLAC)
• polarization measurement at 1 level (Moller
  and Compton scattering)
• Future Developments
• modest push for higher polarization
• smaller systematic errors
• higher current (many mA required for linac-ring
  collider)

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Photon Beams

• History
• bremsstrahlung beams (endpoint, endpoint
  difference)
• tagged bremsstrahlung (first use at Cornell 1953)

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First Use of Tagged Photon Beam
setup
fast (5 nsec) coincidence
Hans Bethe
Boyce McDaniel
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First Use of Tagged Photon Beam
setup
fast (5 nsec) coincidence
Hans Bethe
Boyce McDaniel
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Photon Beams

• History
• bremsstrahlung beams (endpoint, endpoint
  difference)
• tagged bremsstrahlung (first use at Cornell 1953)

• laser backscattering g e g e
  (benefiting from synchrotron light rings)
• Present status
• tagged bremsstrahlung routine with cw beam
  (MAMI, ELSA, CEBAF)
• photon flux 107 - 8/sec, limited by accidentals
  or low-energy background
• laser backscattering routine (HIGS, LEGS, GRAAL,
  LEPS_at_SPring8)
• high polarization at endpoint, tagging required,
  luminosity limited by parasitic operation
• Future developments
• tagged bremsstrahlung beam has reached full
  potential
• luminosity limitation in laser backscattering may
  be helped by continuous injection at full energy
  (ANL, SPring8)

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Laser Backscattering GRAAL at ESRF
variable collimator
interaction region
tagging system
ESRF 6 GeV e
cleaning magnet
Be mirror laser optics
laser intensity, position, and polarization
monitoring
laser
fixed collimator
Performance laser energy 3.53 eV photon
energy (550 1470) MeV resolution 16 MeV
(FWHM) intensity 2.106/sec
Laser hut
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HIgS Photon Source at TUNL

• Principle
• use DUKE 1.2 GeV FEL to produce UV laser light
• laser photons backscatter off subsequent electron
  bunch
• Present capabilities
• mostly lt20 MeV operation due to lifetime
  considerations

injector

1.2 GeV Ring
optical klystron

• Future capabilities
• upgrade underway to allow for full-energy
  injection
• installation of OK-4 optical klystron (capable of
  producing up to 12 eV, mirrors?)
• maximum energy 200 MeV
• maximum flux 108/sec
• energy definition via collimation (no tagging)

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Future Source of High-Energy Photons?

• Method
• collide laser light from FEL with electrons from
  single-turn light source
• Potential
• photon energy (with 12 eV laser)
• 2.4 GeV from 5 GeV ring
• 4.8 GeV from 8 GeV ring
• photon energy resolution lt1
• (collimation, no tagging)
• flux gt 108/sec

FEL
e-gun
dump
dump
SC linac
single-turn synchrotron light source
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H/D Polarized Targets
Electron beams dynamically polarized target
(NH3, butanol) polarize free e at high field
(5T) and low T (1K) use microwave transitions
to transfer e polarization to H or D maximum
luminosity L5.1034cm-2s-1 (for polarized
component) problems nuclear background,
magnet blocking acceptance
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Polarized Solid State Target for CLAS
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H/D Polarized Targets

• Electron beams
• dynamically polarized target (NH3, butanol)
• polarize free e at high field (5T) and low T
  (1K)
• use microwave transitions to transfer e
  polarization to H or D
• maximum luminosity L5.1034cm-2s-1 (for
  polarized component)
• problems nuclear background, magnet blocking
  acceptance
• Photon beams (frozen spin target)
• same substance, same polarizing technique
• but freeze spin at low T (50mK) and lower field
  (0.5T)
• small magnet coil (transparent to particles)
• HD molecule, brute force polarization at 15T and
  10mK
• potential advantage lower dilution due to
  nuclear component
• (first success at LEGS, also in preparation for
  GRAAL)

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Bonn Frozen Spin Target
Setup for GDH experiment at MAMI tagged photon
beam
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Bonn Frozen Spin Target (GDH Experiment at MAMI)
Improvement of polarization of deuterated butanol
during 2003 running period
(based on detailed ESR studies of different
materials at U. of Bochum)
Butanol with titryl radical (chemically doped)
Butanol with porphyrexid (radiation doped)
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Polarized 3He Targets

• Physics interests
• few-body structure
• good approximation for polarized free n (Pn87
  and Pp2.7 ), requires corrections for
  nuclear effects
• Standard technique
• optical pumping of Rb vapor, followed by
  polarization transfer to 3He through
  spin-exchange collisions
• target polarization measured by EPR/NMR
• Performance
• 40cm long target (10atm, Ie12mA)
• luminosity 2.1036cm-2s-1
• average polarization 42

Hall A 3He target
25 Gauss

• Latest development
• optical pumping of Rb/K mixture

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Particle Detection Focusing Magnetic
Spectrometers

• advantage
• high momentum resolution possible
• (due to point-to-point imaging from target _gt
  detector)
• detectors far away from target (behind magnetic
  channel)
• - insensitive to background
• - can operate at very high luminosity
• disadvantage
• coverage in solid angle and momentum range is
  limited
• examples
• 3-spectrometer setup at MAMI
• Hall A HRS at JLab

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MAMI 3-Spectrometer Setup
A B C
configuration QSDD D QSDD
pmax MeV/c 665 810 490
DW msr 28 5.6 28
Qmin 18 7 18
Dp/p 20 15 25
all magnet coils resistive
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HRS 4GeV/c Spectrometer Pair in Hall A
DW 7 msr dp/p 10-4 Dp/p 10-1
all magnet coils super-conducting
detector hut
Q
optical bench
target
D
Q
Q
beam
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Particle Detection Large Acceptance Detectors

• advantage large coverage in solid angle and
  momentum range possible for
• - multi-particle final states
• - luminosity limited (photon tagging,
  polarized target)
• disadvantage resolution and luminosity limited,
  large of channels ()
• examples
• optimized for photon detection
• SASY (BNL LEGS)
• LAGRANGE (GRAAL)
• Crystal Barrel (ELSA)
• Crystal Ball (MAMI)
• optimized for charged particle detection
• HERMES (HERA)
• LEPS (SPring-8)
• CLAS (CEBAF)

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LAGRANGE at GRAAL
scintillator barrel
liquid hydrogen target
cylindrical wire chambers
photon beam
BGO calorimeter
lead/ scintillator sandwich
Components 480 BGO crystals (21Xo) with PMT
readout, Q-coverage 25o - 155o wire chambers
for charged particle tracking forward TOF and
photon detection in lead/scintillator sandwich
detector
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Crystal Barrel at ELSA
CB prior service at LEAR
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Crystal Ball - TAPS Combination

• Crystal Ball
• central detector
• 672 NaI crystals
• 80 MHz FADC electronics (collaboration with CMS)
• TAPS
• forward detector
• 528 BaF2 crystals with veto counters
• particle ID via fast/slow scintillation light
• First experiments
• D magnetic moment from gp ppog
• rare h-decays

CB
TAPS
CB prior service at SPEAR, DORIS, BNL
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Crystal Ball at MAMI
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LEPS at SPring-8
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CLAS in Maintenance Position
Operating conditions (e-scattering luminosity 1034
cm-2s-1 hadronic rate 106/sec Moller e
rate 109/sec e-trigger Cer. calorimeter event
size 5 kBytes trigger rate 4,000/sec data
transfer rate 20 Mbytes/sec
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Electronic Instrumentation

• History
• 1950s modules in crates lab (CalTech) or
  proprietary company (EGG) standards
• 1960s NIM standard (mechanical and electrical,
  no bus specified)
• 1970s CAMAC standard (bus system, limited
  success for industrial control)
• 1978 FASTBUS standard (high channel density,
  no industrial use)
• 1981 VME standard (flexible, many industrial
  applications)

• Trends
• number of industrial suppliers going down
• reasons
• custom solutions needed for high-density
  on-detector electronics
• large size collaborations (e.g. LHC) have enough
  expertise
• large projects provide financial incentive for
  detector-specific developments

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Data Acquisition (a personal experience)
Tagged photon beam operation at the Bonn 500 MeV
Synchrotron time mid 1970s duty-cycle 3 bunc
h separation 6 nsec tagged beam
intensity 105/sec magnetic spectrometer DW100
msr data rate 1/10 sec on-line
computer Nova memory (16 bit) 32kB
core clock speed 1.5 MHz
500 MeV Synchrotron
20-channel Internal tagging system
radiator
B
magnetic spectrometer
Improvement factors expected 100 duty-cycle
30 2 nsec bunch separation 3 4p
spectrometer 100 overall 10,000
How to handle 1000 events per second??
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Development of Raw Data Volume
source Ian Bird
Moores law for CPU power
,
,
GByte/year
,
,
,
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New Facilities

• HIgS
• MAMI Upgrade
• CEBAF 12 GeV Upgrade
• e-ion Collider

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MAMI Upgrade Program

• add double-sided microton HDSM to increase energy
  to 1.5 GeV
• first beam in 2005

• add experimental equipment
• Crystal Ball
• Kaon Spectrometer

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Properties Emax 12 GeV Imax 80mA beams 3

• Upgrade Experimental Equipment
• Glue-X detector in new Hall D
• MAD spectrometer in Hall A
• upgraded CLAS in Hall B
• SHMS spectrometer in Hall C

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Hall D GlueX Detector
barrel calorimeter central ToF
cylindrical drift chambers
forward drift chambers
lead-glass calorimeter
tagged photon beam
SC solenoid (LASS, MEGA)
forward time-of-flight
Target
vertex detector
Cerenkov
2 meters
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Medium Acceptance Device Spectrometer in Hall A

• Technology
• 2 SC magnets
• 120cm circular aperture
• cosQcos2Q windings
• 6 Tesla max. field

• Properties
• DW 30 msr
• Pmax 7 GeV/c
• Dp/p 30
• dp/p 5.10-3

HRS
MAD
DQ
detector package
DQ
target
support structure
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Upgraded CLAS (CLAS)
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Future Facility Electron-Ion Collider?

• Physics motivation
• study processes at high c.m.s energy and low x
  10-(3-4)
• especially gluon distribution functions
• Technical challenges
• high luminosity (high bunch charge, electron beam
  cooling)
• polarization control for both beams
• Technical approaches
• eRHIC
• add 10 GeV e-ring to 250 GeV RHIC, L1033cm-2s-1
• ELIC
• add 30-150 GeV p-ring to 3-7 GeV single-turn
  CEBAF, L1033-35cm-2s-1
• could also recirculate 5 GeV to get 25 GeV for
  fixed target experiments

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ELIC Electron-Light Ion Collider Layout
Ion linac and pre-booster
Electron cooling
-
-
booster
IR
IR
IR
IR
Snake
Snake
Solenoid
Solenoid
3-7 GeV electrons
30-150 GeV light ions
3
-
7 GeV
electrons
30
-
150 GeV light ions
Electron Injector
CEBAF with Energy Recovery
CEBAF with Energy Recovery
Beam Dump
Beam dump
from Lia Merminga at EIC Workshop, JLab
03/15/2004
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Future Trends

• Experiments coverage , polarization observables
  , accuracy
• Accelerators energy , helicity correlated
  effects , dedicated collider?
• Detectors
• focusing magnetic spectrometers energy ,
  acceptance , resolution
• large acceptance spectrometers luminosity
• 
  balance between charged and
  neutrals
• 
  cooperation with HEP
• Electronics/DAQ
• local intelligence
• DAQ rates
• on-line analysis