Nuclear Experiment

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W. Udo Schröder, 2011

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Elements of a Generic Nuclear Experiment

A: Study natural radioactivity (cosmic rays, terrestrial active samples)

B: Induce nuclear reactions in accelerator experiments Particle Accelerator produces fast projectile nuclei

Projectile nuclei interact with target nucleiReaction products are

a) collected and measured off line, b) measured on line with radiation detectors

Detector signals are electronically processed

Ion Source Accelerator Target

Detectors

Vacuum ChamberVacuum Beam Transport

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Ionization Process

1. e- impact (gaseous ionization)

• hot cathode arc• discharge in axial magnetic field

(duo-plasmatron)• electron oscillation discharge

(PIG)• radio-frequency electrode-less

discharge (ECR)• electron beam induced discharge

(EBIS)

2. ion impact• charge exchange• sputtering

e-/ion beam

- +q-

discharge

-+q+

Acceleration possible for charged particles ionize neutral atoms

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Electron Cyclotron Resonance (ECR) Source

“Venus”Making an e-/ion plasma

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Overview Accelerator TypesElectrostatic Accelerators

Cascade Van de Graaff V.d.G. Single &Tandemgenerator Accelerator 2-3 stages steady (DC) beam, high quality focusing, energy, currents;

but low energies

Electrodynamic AcceleratorsCyclotrons Synchrotons Linacsconventional, Wideröe, Alvarezsector-focusing pulsed (AC) beam, high energies but lower quality

focusing, energy definition, lower currents

Advanced Technology AcceleratorsNew principles: Collective acceleration, wake-field acceleration

conceptual stage

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Principle of Electrostatic AcceleratorsVan de Graaff, 1929

Operating limitations: 2 MV terminal voltage in air, 18-20 MV in pressure tank with insulating gas (SF6 or gas mixture N2, CO2)

Acceleration tube has equipotential plates connected by resistor chain (R), ramping field down.Typical for a CN:7-8 MV terminal voltage

+

-

R

RR

R

RRR

+

++

+

+

+

++

+

++

++

+

q+

Charger 10 -4C/m2

Corona Points 20kV

+ HV Terminal

Ion Sourc

e

InsulatingAcceleration Tube/wEP plates

Charging Belt/ Pelletron

-Ground Plate

Conducting Sphere

q+

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“Emperor” (MP) Tandem

MP Tandem15 MV

90o Deflection/Analyzing Magnet

Vacuum Beam Line

Ion Source

@Yale, BNL, TUNL, Florida, Seattle,…, Geneseo (small),…many around the world.

Munich University Tandem

Quadrupole Magnet

Pumping Station

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Electrodynamic Accelerators: Cyclotron

Radio Frequencywfield

-+E

Principle of operation of electrodynamic (cyclic) accelerators:Short pulses of low accelerating voltage, apply many times.

Cyclotrons at MIT, Berkeley, MSU, Texas A&M, …., many around the world (Catania, GANIL). Linacs mostly for electrons or protons.Synchrotons and variations for high energy particle physics.

Cyclotron technique:Magnetic holding field, contain particles on circular orbits, apply RF voltage across gaps of 2 half Faraday cages (“D”) shielding most of the orbits.

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Charged Particles in Electromagnetic Fields

0

0

: ( ), ( )

. ,

0 :

,

,

fields electric E magnetic B

particle el charge q velocity v

E F p q v B

p q r B orbit radius r r B

pp q r B equilibrium orbit at rqB

p

Lore

q

mv

Bm

F q E v B

v r

Parti

ntz For

cle

ce

Cyclotron FrequencyB: Magnetic guiding field

vr

Charged particles in electromagnetic fields follow curvilinear trajectories used to guide particles “optically” with magnetic beam transport system

q

B

Independent of velocity or energy

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Electrodynamic Accelerators: Cyclotron

0

Cyclotron Frequencq B same for all vm

y

2

max

2

2

qB

Maximum Ener

m

gy

qKR

A

Relativistic effects: m W = e + moc2 Q: Is there technical compensation ?

-+E

Electrodynamic linear (LINAC) or cyclic accelerators(cyclotrons,synchrotons)

Cyclotrons at MIT, Berkeley, MSU, Texas A&M, …., many around the world (Catania, GANIL)

Acceleration, if wfield = w0

Equilibrium orbit r: p = qBr maximum pmax = qBR

Radio Frequencywfield

R

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Injection and Acceleration

Transfer to accelerator

Acceleration

Injection (axial)

Ion trajectory (cyclic)

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Linear AcceleratorsWideröe 1928, Alvarez 1946 Linear trajectory, no deflection

magnet, no radiative losses

Hollow drift tubes, E-field-free interior, contain magn. focusing elements. Accelerating gap between 2 drift tubes on different el. potentialU(t) = U0.sin (wt) 10MHz-3GHzon all gaps alternating E fieldswitch polarity while particle is hidden.

0

2 22( ):

n

Match drift tube length toTL c

qUAfter gap n n velocitym

Phase conditions may change during acceleration, particle speed. Q: Is continuous operation possible without loss of particles?

q+

RF Power Supply

+ +-Ln-1 Ln Ln+1

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Phase Stability

ideally synchronous particle passes gaps at tn=ts+nT

Passage time (at gaps): t= / ,f w encountering U(t) ~ U0sin(wt)

Phase angle of particle: f = fs+ w·(t-ts),

force F=qU0/(gap length L)

2

2

:

22

2

cos 0

0

f

f

ff f f f

f f

ss s

s

Fddt p

d differential equationdt

Stability analysis: Stable oscillations about synchronous phase occur for cosfs > 0, fs < 900 inject during first quarter cycle!

U(t) DE

tNominalts =fs/w

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CERN PS Proton Linac

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Secondary-Beam Facilities

2 principles:A) Isotope Separator On Line

Dump intense beam into very thick production target, extract volatile reaction products, study radiochemistry or reaccelerate to induce reactions in 2nd target (requires long life times: ms)GANIL-SPIRAL, EURISOL, RIA, TAMU,….

B) Fragmentation in Flight Induce fragmentation/spallation reactions in thick production

target, select reaction products for experimentation: reactions in 2nd target

GSI, RIKEN, MSU, Catania, (RIA)

G. Raciti, 2005

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ISOLDE Facility at CERN

Primary proton beam CERN-SPS

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Secondary-Beam Accelerator

Radiochemical goal (high-T chemistry, surface physics, metallurgy): produce ion beam with isotopes of only one element

Ion Source

Low-energy LINAC

Mass Separator

X1+

High Charge

Primary target: oven at 7000C – 20000C, bombarded with beams from 2 CERN accelerators (SC, PS).

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RIA: A New Secondary-Beam Facility

One of 2 draft designs : MSU/NSCL proposal

Superconducting-RF driver linear accelerator ( 400 kW) All beams up to uranium 200 MeV/nucleon, lighter ions with increasing energy (protons at 600 MeV/nucleon)

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Secondary Beam Production

Bombard a Be target with 1.6-GeV 58Ni projectiles from SCC LNS Catania

Particle Identification Matrix DE x EDE

DEE

Particle

Target

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ISOLDE Mass Separators

High Resolution SeparatorM 5000 30000MD

General Purpose Separator

calculated

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Secondary ISOLDE Beams

Yellow: produced by ISOLDEn-rich, n-rich

Sn: A = 108 -142 low energy

O: A = 19 -22 low energy

Source: CERN/ISOLDE

ISOLDE accepts beams from several CERN accelerators (SC, PS)

Nuclear Experiment

Documents

udo schrder

nuclear reactions

nuclear experimentelements

generic nuclear experimenta

particles optical

magnetic holding field

pulsed ac beam

ramping field