dynamic nuclear polarization - cern · 2009. 4. 24. · on the other hand, the electron and nuclear...

Dynamic Nuclear Polarization

COMPASS PT- team at CERN:

• K. Kondo,

• N. Doshita,

• J. Koivuniemi,

• F. Gautheron,

• Y. Kisselev

Dynamically Polarized Targets

How the dynamically polarized targets work?

Basic apparatus required and techniques

Recent developments and topics

Elementary consideration S=I=1/2

,

,1( ) tanh( )

2e p

e p

B

Bn nP S I

n n k T

large magnetic

moment of electron

small magnetic

moment of nuclei

B

n+

n-

B=2.5 T

T=1 K

1000e p

One can see that all parameters in this formulae are fixed but the temperature

,e p

are electron and proton

magnetic moments

Dilution refrigerator may cool the nuclear spins down T~0.1 K,

but practice shows that this process takes about 1000 hour due to

excellent isolation of nuclear spins from the lattice!

with MW at with MW at

without Microwave

SS-Reservoir

Cooled down

SS-Reservoir

Heated upThermodynamic

equilibrium

SS Z LT T T 300 400

e ZSS Z

e

TT T

300 400

e ZSS Z

e

TT T

On the other hand, the electron and nuclear spins interact with electromagnetic

irradiation, therefore, to reach lower temperatures, It was elaborated very specific

method called the Dynamic Nuclear Polarization (DNP).

e

exp( )

p

B SS

B

k T

eee

exp( )e

B Z

B

k T

exp( )

p

B SS

B

k T

To realize DNP we need the free electrons in a target material

Free electron spins are induced by electron beam irradiation at about 90 K temperature with the dose of 1016~1017electrons/cm2 which generates

about 1019spins/cm2

Ammonia: NH3, ND3

Lithium Hydrides: 7LiH, 6LiH, 6LiD

6LiD: 6Li=α+ deuteron

30 Jan. 2004 Kaori KONDO, Naogya Univ. 8

THE COMPASS CAVITY FOR OD-MAGNET

Beam line

Cavity 1 Cavity 2 Cavity 3

Thermal screen

Microwave power

Coupling hole

Stainless steel

Silver

waveguides

Copper cavities

Cooling loop

Centering rim

All of cavity elements

provide

a very long use

High magnetic field, low temperature

and microwave irradiation

Polarizing magnet: 2.5T with field uniformity, ~100ppm

Overview of the COMPASS Polarized Targets

First polarization with our new set-up (measured June 14th )

D-butanol

Downstream cellCentral cellUpstream cell

P=-36±2 % in ~ 2-3 hours

NH3

NH3

6LiD

6LiD

Built-up the target polarizations

The typical signal-to-noise for

protons on the display

After the signal accumulation Kaori

receives almost an the free electrons ideal

proton signal

Q-meter circuit for polarization

measurements

Polarization measurements

Summary

• Dynamically Polarized targets have been used in many experiments.

• The techniques are well established although complicated apparatus is needed.

• The targets are still being developed for various applications.