Development of the Positron Injector for LEPTA Facility

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1 Development of the Positron Injector for LEPTA Facility V.Bykovsky, M.Eseev *, A.Kobets, I.Meshkov, V.Pavlov, R. Pivin, A.Rudakov, G.Trubnikov, S.Yakovenko * - Lomonosov Pomor State Universitet, Arkhangelsk 1 1

2 Contents 1. Positron injector (design and main parameters) 2. Cryogenic source of slow monochromatic positrons 3. Positron trap 4. Status and nearest plans 2

1. Positron injector (design and main parameters) LEPTA Facility Project parameters of the positron beam collector kicker Injection duration energy Injection periodicity Δp/p cooling section

3 1. Positron injector (design and main parameters) LEPTA Facility Project parameters of the positron beam collector kicker Injection duration energy Injection periodicity Δp/p cooling section Helical quadrupole Positron number per pulse 300 ns 2-10 KeV s < *10 8 O-Ps septum e-gun sec=10 8 e + positron trap 22 Na 10 6 e + per sec 10 4 Ps per sec positronium detector 3

1. Positron injector (design and main parameters) (Contnd) LEPTA entrance 8 Positron injector 7 6 4 5 4 3 + 10 kv 1 2 + e e + Isolator tube 11 9 9 10 1 - positron source 22 Na, 2 - radioactive

4 1. Positron injector (design and main parameters) (Contnd) LEPTA entrance 8 Positron injector kv e e + Isolator tube positron source 22 Na, 2 - radioactive protection shield, 3 - vacuum valve, 4 - vacuum chamber for pumping out and diagnostic tools, 5 - positron trap, 6 - vacuum isolator, 7 - positron vacuum channel, 8 - vacuum shutter (fast valve), 9 - ion pump, 10 - turbopump, 11 - LHe vessel. 4

5 1. Positron injector (design and main parameters) (Contnd) Design parameters of the positron injector Length, m Positron injection energy, kev Longitudinal magnetic field, G Longitudinal magnetic field in the trap, G Residual gas pressure, Tor Beam radius, cm Accumulation time, s Injection pulse duration, ns Number of positrons in injection pulse Positron momentum spread 6,

6 2. The cryogenic source of slow monochromatic positrons The cryogenic source. 1-cupper subscribe with isotope 22 Na, 2- cupper cylinder, 3- cryogenic heat exchanger of the cupper cylinder, 4 thermal shield, 5- cryogenic heat exchanger of the thermal shield, 6- nozzles. 6

7 2. The cryogenic source of slow monochromatic positrons (Contnd) The Cryogenic Moderator of Positrons T ~ 5 K Ne 22 Na e + 7

8 2. The cryogenic source of slow monochromatic positrons (Contnd) 8

9 2. The cryogenic source of slow monochromatic positrons (Contnd) Positron Energy Spectrum Moderated positrons Positron yield в + energy spectrum from 22 Na Positron energy (ev) 9

10 2. The cryogenic source of slow monochromatic positrons (Contnd) The stand Positron source 10

11 2. The cryogenic source of slow monochromatic positrons (Contnd) γ-detector γ The slow positron registration scheme Solenoid 2 Partition solenoid 1 Vacuum volume B B МКP B B Cryogenic positron source Fast positrons + - electrostatic analyzer Slow positrons pumping 11

12 2. The cryogenic source of slow monochromatic positrons (Contnd) The elements of registration system 12

13 2. The cryogenic source of slow monochromatic positrons (Contnd) Slow Positron Yield vs Frozen Neon Thickness N/s δ, mkm 13

14 2. The cryogenic source of slow monochromatic positrons (Contnd) Slow Positron Spectrum vs Frozen Neon Thickness dn/de ,00 0,50 1,00 1,50 2,00 2,50 3,00 3,50 4,00 30 mkm ( ) 50 mkm ( ) 90 mkm ( ) 130 mkm ( ) Е,eV 14

15 2. The cryogenic source of slow monochromatic positrons (Contnd) The positron spectrum at the e+ flux of 5.8*10 3 positrons per sec of the average energy of 1.2 ev at the width of 1 ev has been obtained. The moderator efficiency is 1%. 15

16 3. Positron trap Surko Trap eu Area 1 Area 2 Area 3 Pressure, Torr е + N 2 N 2 z 16

3. Positron trap (Contnd) The trap dimensions Electrode Inner diameter (mm) Length (mm) 1 12

17 3. Positron trap (Contnd) The trap dimensions Electrode Inner diameter (mm) Length (mm) Set of electrodes

18 3. Positron trap (Contnd) Assembled positron trap 18

19 3. Positron trap (Contnd) Testing the trap with electrons E-gun e - B I II III IV V VI VII VIII Collector С coll R Dig. oscill. 19

These parameters correspond to the positron beam which we expect from a radioactive source of an activity of 25 mci.

20 3. Positron trap (Contnd) The test electron gun current has been chosen corresponding to dn/dt = 5*10 6 electrons/sec (0.7 pa electron current) of the energy of 50 ev and spectrum width of a few ev. These parameters correspond to the positron beam which we expect from a radioactive source of an activity of 25 mci. Single pass electron beam trough the trap to the collector.trap has been opened in pulse mode Stored electrons extracted to the collector I e (t) dt upper signal, I(t) lower signal, 20

21 3. Positron trap (Contnd) Single pass electron energy spectrum No buffer gas Buffer gas (N 2 ) pressure is optimized dn/duан dn/de 0,70 0,60 0,50 0,40 0,30 0,20 0,10 0, dn/de dn/de Electron energy, ev Еan, В Frank-Hertz peaks appear! Electron energy, ev U ан, В 21

22 3. Positron trap (Contnd) 50.3 ev e - I II Electron storage studies III IV V VI VII VIII V V -36.1V V V 0 V 30 V 100 V 22

23 3. Positron trap (Contnd) Typical storage functions Electron number, 10^ Filling time, s P=3.4*10^-4Pa P=2.4*10^-4Pa 23

24 3. Positron trap (Contnd) Electron storage equation Data Analysis trap N trap = ε N N trap electron number stored in the trap, ε storage efficiency, τ life - electron life time in the trap. It gives: dn dt N( t) = ε N τ (1 t life e τ ) life τ life Two asymptotes: N( t ) = ε Nt, ε Nτ life, t << τ t life,. At (dn e /dt) entrance = s -1 from the Fig. in the previous slide we find: ε = 0.18, τ life = 12.5 с 24

25 3. Positron trap (Contnd) Rotating Electric Field Method Generator Phase filter (а) B (b) -U(x) (c) One electrode is placed under combined alternative + permanent potentials (Fig.a, b, c). 25

26 3. Positron trap (Contnd) 2,90E+07 Rotating Electric Field Method (Contnd) N 2,70E+07 2,50E+07 2,30E+07 2,10E+07 1,90E+07 1,70E+07 N e 0 0,5 1 1,5 2 2,5 3 3,5 4 A,В Amplitude, V Stored electron number vs amplitude of the rotating field N 4,50E+07 4,00E+07 3,50E+07 N e 3,00E+07 2,50E+07 2,00E+07 1,50E+07 1,00E+07 5,00E+06 0,00E f, f,кгц khz Stored electron number vs frequency of the rotating field Direction of the field rotation opposite to electron drift in crossed B-field and e-field of electron space charge! 26

27 3. Positron trap (Contnd) Rotating Electric Field Method (Contnd) Зависимость числа накопленных электронов от времени накопления 9,00E+07 Stored electron number vs time N 8,00E+07 7,00E+07 6,00E+07 5,00E+07 4,00E+07 3,00E+07 2,00E+07 1,00E+07 0,00E+00 Optimal f rotating = 650 khz, Amplitude = 1 V, ε = 0.4, τ life = 25 s t, сек Pressure distribution and potential are optimized Same + transverse correction field is optimized Same + rotating field is ON and optimized 27

28 3. Positron trap (Contnd) Stored electron number vs time (B=1.2kGs) N 1,80E+08 1,60E+08 1,40E+08 1,20E+08 1,00E+08 8,00E+07 6,00E+07 4,00E+07 2,00E+07 0,00E t, сек τ life 80 s, N max =1,5 10 8, (N 0 = e - /с) 28

3. Positron trap (Contnd) Particle Extraction from The Trap eu, В 90 80 70 60 50 40 30 20 10 0 Potential distribution along the trap axis before extraction (a) and at extraction

29 3. Positron trap (Contnd) Particle Extraction from The Trap eu, В Potential distribution along the trap axis before extraction (a) and at extraction (b) eu, V V (a) coll 1 = 40 C I( t ) dt 35 eu, В Z, L, mm мм L,мм eu, V Extracted bunch duration is about 500 ns Z, mm (b) 29

0 200 400 600 800 1000 1200 1400 1600 1800 2000 3.

30 Positron trap (Contnd) Particle Extraction from The Trap (Contnd) e , ,5 Bz, Гс Ez, kв/см -1-1,5 e Bz Ez -2, , z, мм ALFA, мрад z, мм 30

31 3. Positron trap (Contnd) Particle storage and the space charge limit eu Area 1 Area 2 Area 3 Pressure, Torr е + N 2 N 2 z Estimated bunch intensity when the trap opens: en b ΔU = ln L a N particle number in the bunch, L the bunch length, a, b the radii of the bunch and the tube in the Area 2. For N = , a = 1 mm, b = 15 mm, L = 250 mm we find ΔU = 11.1 V 31

32 3. Positron trap (Contnd) Particle storage and the space charge limit eu Area 1 Area 2 Area 3 Pressure, Torr е + N 2 N 2 z Experimental proves: 1) Leak current was measured and it was found on the electrode in the Area #2! 2) Dynamical control of the Area #2 potential allows us to increase the particle number in the bunch ~ by 2 times! 32

33 4. Status and nearest plans New positron source from South Africa New positron source activity of 25 mci for LEPTA facility has been donated by ithemba LABS (South Africa) 33

34 4. Status and nearest plans The positron injector under assembling 34 Workshop, September 2-7, 2007 Alushta (Crimea, Ukraine)

35 Our great thanks to ithemba Labs and personally to Dr. Lowry Conradie for donation of the e + source that enables us to reach the main goal of the LEPTA project Ps generation in flight. Thank you for attention 35

36 Линия напуска неона в систему Вакуумная система Вакуумметр 4 Дроссель Z Мановакуумметр Мерный объем 3 Редуктор 2 1 Ne Магниторазрядный насос Форвакуумный насос 36

Расчет толщины слоя намороженного замедлителя ε = Эффективность конденсации n (1 Ne = n n V Ne Ne Ne )100 0 0 P Δt atm

37 Расчет толщины слоя намороженного замедлителя ε = Эффективность конденсации n (1 Ne = n n V Ne Ne Ne ) P Δt atm Объем неона, испаряемого в единицу времени V Ne n = P Ne atm n Ne = δpu n ' Ne = ДP 0 U ε = 99,9% T исп (10 мкм) = с 37

Methods for optimization of the dynamics of positrons storage in the Surko trap

Workshop on Beam Cooling and Related Topics COOL 11 1 16 September 011, Alushta, Ukraine Methods for optimization of the dynamics of positrons storage in the Surko trap *М. Есеев, A. Kobets, I. Meshkov,