Y. Kisselev PST05 conference 14-17 Nov 05 1

PST05 Conference

Microwave cavity for large COMPASS polarized Microwave cavity for large COMPASS polarized targettarget

By: Y. Kisselev, J. Ball, G. Baum, N. Doshita, F. Gautheron, J. Heckmann,

J. Koivuniemi, K. Kondo, S. Platchkov, A. Magnon, G. Mallot, W. Meyer, • G. Reicherz

COMPASS PT- team at CERN Introduces:

Y. Kisselev PST05 conference 14-17 Nov 05 2

Microwave cavity for the new COMPASS magnetMicrowave cavity for the new COMPASS magnet

Dynamic nuclear polarization under multimode microwave excitation

Spectral structure of a large cylindrical cavity

Design of the coupling hole between feeding waveguide and the cavity

The last release of the three-cells cavity design

Frequency modulation effect

1)

3)

4)

5)

2)

Y. Kisselev PST05 conference 14-17 Nov 05 3

1. To provide resonant excitation of a non-tunable cavity of polarized target with high intensity of a cavity microwave field

2. To provide the best spatial MW-uniformity in the target material

as required for the highest polarization.

The main idea of the presentation:

Solution: use of MW frequency modulated with a bandwidth covering several modes of the cavity

Advantage:

1. Shortened DNP- built up time.

2. Deuteron polarization > 50 %

*V. Bouffard, Y. Roinel, P. Roubeau and A.Abragam.

J. Physique 41 (1980) 1447-1451.

COMPASS, V= 424 cm3 (2004 y)

Time (hour)

D -

Pol

ariz

atio

n (%

)

Irradiated LiD 2.5 Tesla

Bouffard *, V= 0.0125 cm3 (1980 y)

Y. Kisselev PST05 conference 14-17 Nov 05 4

Spectrum of frequency modulated Spectrum of frequency modulated microwave signalmicrowave signal

Frequency bandwidth of FM spectrum

equals to 2·Δωmax/2π 10 MHz

in our example

tCosΔωωω max0ifif

052 .π/Δω max MHz – Frequency deviationMHz – Frequency deviation

5002 πΩ/ Hz – Modulation frequencyHz – Modulation frequency

is the modulation is the modulation indexindex

10000Ω

Δωm max

Ω)t]Sin(ωΩ)t[Sin(ω(m)J

Ω)t]Sin(ωΩ)t[Sin(ω(m)J

tSinω(m)JSinΩinmtSin[ωI

22 002

001

000

Ji(m) – are Bessel functions

m = 1000

Frequency 70 GHz +MHz

Inte

ns

ity

Arb

. U

n.

Y. Kisselev PST05 conference 14-17 Nov 05 5

The number of excited modes The number of excited modes decreases with decreasing decreases with decreasing

cavity diametercavity diameter

22

2103

0

10

Rlp

Mmnf μπ

π 22

2103

0

10

Rlp

Emnf ηπ

π

Electric modesElectric modes Magnetic modesMagnetic modes

Theory for cylindrical cavityTheory for cylindrical cavity

Frequency 70 GHz + MHz

± N

um

ber

of

mo

des

=23 cm, =23 cm, 82 modes, 34 nondegenerate 82 modes, 34 nondegenerate F F 100 MHz/34 100 MHz/34 3 MHz 3 MHz

=15 cm, =15 cm, 61 modes, 34 nondegenerate 61 modes, 34 nondegenerate F F 100 MHz/34 100 MHz/34 3 MHz 3 MHz

Y. Kisselev PST05 conference 14-17 Nov 05 6

MW-ferrite modulator

Preampl.

Display

MW-detector

LF-generator

200 Hz

Microwave sensor for the spectral measurements

The device has linear characteristic within 0.÷ 50 microwatt region

Y. Kisselev PST05 conference 14-17 Nov 05 7

General view of the new microwave cavityGeneral view of the new microwave cavity

Microwave sensor with Microwave sensor with preamplifierpreamplifier

DisplayDisplay

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Position of the whip-antenna in the cavity

The rigid coaxial cable has a considerable attenuation about 10 dB/m or more. The MW energy induced in the NMR coils can

dissipate inside the cable made a parasitic MW-absorption

Y. Kisselev PST05 conference 14-17 Nov 05 9

The experimental mode spectrum of the cylindrical cavitycylindrical cavity

Cylindrical cavity

Important remark: All of the above modes have different intensity therefore

the coupling between feeding waveguide and

a cavity must be inspected

Inte

nsi

ty A

rb. U

n.

F F 10 MHz 10 MHz Spectrum of FM-generator

Frequency 70 GHz + MHz

=23 cm, =23 cm, 36 modes; 36 modes;

F F 100 MHz/36 100 MHz/36 3 3 MHzMHz

Y. Kisselev PST05 conference 14-17 Nov 05 10

Frequency meter MW-receiver

Multimode loadMultimode load

MonomodeMW-transition

MW-generator

Frequency meter MW-receiver

Multimode loadMultimode load

MonomodeMW-transition

MW-generator

reflector

Microwave transmission measuring set-up for multimode load.

It enables the tests of the reflected power

over the frequency band

Y. Kisselev PST05 conference 14-17 Nov 05 11

Finding the shape of coupling holes for the best matching between feeding waveguide and a cavity

70200 MHz

70240

70260

70290

70310

d -matched 8 mm load Matching over the

entire band

Y. Kisselev PST05 conference 14-17 Nov 05 12

The latest version of the three-cells cavity design.

RESUME

NEW COMPASS CAVITY for OD-MAGNET

Beam line

Cavity 1 Cavity 2 Cavity 3

Heat exchanger

Target cell 1 Target cell 2 Target cell 3

2.5 K- thermal screen

Microwave power

Y. Kisselev PST05 conference 14-17 Nov 05 13

Thank You !!!Thank You !!!