Development of polarized target for nuclear fusion experiments. ÇlÇÅÇìÇÅÇç

Transcription

1 Development of polarized target for nuclear fusion experiments ÇlÇÅÇìÇÅÇç Department of Applied Physics Faculty of Engineering Miyazaki University 9th International Workshop on Polarized Solid Targets and Techniques

2 Contents 1. Introduction 2. The thin film CD 2 Target 3. Polarized Target System 4. Determination of target polarization 5. The Test using the CD 2 Target 6. Summary & Out Look

3 1. Introduction We perform an experiment of which purpose is the measurement of the spin dependent cross sections in a nuclear fusion reaction, D(d, p)t, using a polarized deuteron beam (20MeV) and target at the Tandem Van de Graaff Accelerator Center, University of Tsukuba in Japan. It aims at verification of the proposal of Princeton & BNL group(1982) saying that cross sections of nuclear fusion reactions increase or decrease when incidence particles and target particles are polarized parallel or anti-parallel to each other. The cross sections in nuclear fusion reactions in double polarization are measured for the first time in the world. Nagoya University and Miyazaki University took charge of the development of the polarized target system for this experiment.

4 2. The thin film CD 2 Target < Low Energy Experiment > ÅThe energy loss is very large. Å The incidence particles stop in the target. Å The target heat up by energy loss. ( The polarization of the target decreases!!! ) The target must be shaped to be a thin film.

5 The Deuterated polyethylene (CD 2 ) Target Coil for NMR (300Å500 nh) 8 mm É5 mm 30Å50 Ém 8 mm Å300 Ém The target was equipped at the tip of an Insert.

6 The technique of inducing paramagnetic center Method 1 : diffusion TEMPO (2,2,6,6-Tetra-Methyl-Piperidine-1-Oxil) Method 2 : Irradiation 7 MeV electron CD 2 foil located in liquid nitrogen bath Method 1 Method 2 Polarization [%] Deuteron Polarization 11Å Polarization [%] Deuteron Polarization 17 Å Temperature : Å 500 mk Magnetic field : 2.5 Tesla TEMPO density [/cm3] electron density [electron/cm2] Higher polarization can be obtained by irradiation. The world record : Å30 % (by Bochum-Nagoya) However it is difficult to handle at room temp.!

7 How to make thin film Target PTFE Coating Gap (30Ém, 10Ém)

8 How to make thin film Target CD 2 powder (Euriso-top:E077P) PTFE sheet (thickness 100Ém) Åheat up 160Åé4hours CD 2 sheet 8mmÅ8mm, thicknesså4 0 60Ém A hole (É5mm) is made in a sheet A PTFE sheet is put in a hole Åpress Å heat up 160Åé2hours remove PTFE sheets thickness 500ÉmÅ3 0 50Ém(center) TEMPO dope Å heat up 80Åé10hours spin density:3å [spins/cm 3 ] The thin film CD 2 Target NMR coil (É7mm, Å500nH)

9 3. Polarized Target System Tandem Accelerator Center, University of Tsukuba

10 Cryostat

11 Mixing Chamber

12 The performance of a Cryostat The minimum attainment temperature Å250 mk The time taken from 300K to 1K Å18 hour The amount of consumption of Liq. 4 He 5 Ü/hour 6 The flow of 3 He Å@ 1.5 Å 2 Ü/min < Cooling Power > E d = 20 MeV current Ç na CD 2 50Ém Heat input :0.2 mw liquid He 1 mm Heat Heat input input :0.3 :0.7 mw mw Mylar 25ÉmÅ2 When beam intensity is 1nA, MÇ can maintain Total about Heat input 300 :1.2 mk.! mw 5 4 Cooling Power [mw] MC temp. [mk]

13 Super Conducting Magnet VCR 1/ 2" 4He out l et VCR 1/ 4" 4He inlet 4He out l et 4He i nl et 6 2 top view A A' 5. 0 Deuteron beam A? ]A' mm 100 mm Central magnetic field : 2.5 T Uniformity (A sphere with a diameter of 5mm) ÉB/B : 10-4 Diameter of Bore : É 30 mm Diameter of Outer : É100 mm Gap : 5mm Dead angle : 15 Å 3 Current at 2.5 T : 81.1 A Deviation angle of deuteron (20MeV) : 8

14 4. Determination of target polarization Çe need the target polarization in the reaction point. We determine the exact target polarization using the method of the asymmetry of yield. Reaction of D ( d, d) D ( :32.5 o ) MAX A y Unpolarized deuteron beam θ SSD P t arget = 1 3iT 11 Polarized Target ( θ ) N N L pol L pol SSD ( θ ) N ( θ ) + N R pol R pol ( θ ) ( θ )

15 Set up of Detector Faraday cup D beam Detector ÉE-E SSD counter telescope Å 4 Å polarimatorå2 Å Scattered particle target Thickness 100 Ém + 3 mm. Solid angle 2 msr. The angle which can be measured ±70

16 5. The Test using the CD 2 Target scattering angleåf= 32.5 magnetic field ÅB = 0 Inside of MC Åwithout Liq.He channel channel

17 The spectrum of deuteron É=32.5 ÇcÅiÇÑÅ counts 12 ÇbÅiÇÑ 12 Ç 16 ÇnÅiÇÑ 16 Ç channel

18 The spectrum of proton É=32.5 ÇgÅiÇÑÅ counts ÇcÅiÇÑÅ 16 ÇnÅiÇÑ 16 Ç 12 ÇbÅiÇÑ 13 Ç channel

19 Polarization of thin film Target Temperature Å0.8 [K] Magnetic field Å2.5 [T] Micro wave Å70.03 [MHz] Voltage [mv] Density of unpaired electrons ÅTEMPOÅ Å2.9Å10 19 [ spin/cm 3 ] The signal of NMR which enhanced polarization Frequency [MHz] 16.5 (1000 sweep)

20 Polarization by the method using the asymmetry of yield non-pol. pol. total P = 2/A y Å(R-1)/(R+1) target polarization R = N left /N right A y ~ Polarization 9.6 ±2.6 % run No.

21 6. Summary & Out Look Summary We developed polarized target for low energy experiment using CD2 foil. The PT system is installed in the Tandem Accelerator Center, University of Tsukuba, and It is testing now. When deuteron beam of 20MeV was bombarded at the target by the beam intensity of 1nA. We obtained about Å10% of the target polarization. Out Look The PT system is going to be improved and made stability more. We are going to measure exact target polarization. We are going to measure of the spin dependent cross section in a nuclear fusion reaction.

22 Collaborators Izuru DAITO a, Naoaki HORIKAWA d, Takeo HASEGAWA b, Yoshihiro TAGISHI c, Takahiro IWATA e, Mitsutaka Yamaguchi c, Takuya SHINBA c, Naoko YOSHIMARU c, Norihiro OKUMURA c, Tomohiro KOBAYASHI, Takaya INAGAKI, Yoshikazu TAZIMA f, Satoshi ISHII f a Research Center for Nuclear Physics, Osaka University b Faculty of Engineering, Miyazaki University c Institute of Physics, University of Tsukuba d College of Engineering, Chubu University e Faculty of Science, Yamagata University f Tandem Accelerator Center, University of Tsukuba

23 Polarization by the method using the asymmetry of NMR signal 2003/09/ r = I I P = r 2 r 1 + r I I =10 ± 4%