1. Traps for antiprotons, electrons and positrons in the 5 T and 1 T magnetic fields
G. Testera & Genoa group
AEGIS main magnetic field (on axis) : from Alexei

2. Traps for antiprotons, electrons and positrons in the 5 T and 1 T magnetic fields
Penning type electric field
2 ztrap: about 6 rtrap
rtrap z
Half length
of the harmonic region:
about 1.6 rtrap
ztrap z
Malmberg type electric field:
2 ztrap>>rtrap

3. The antiproton catching trap used in ATHENA:
r=1.25 cm
Length 35 cm

4. Catching and cooling antiprotons
5 108 electrons
preloaded in the catching trap
Degrader
Solenoid - B =
5 Tesla e -
Antiprotons
Cold electron cloud
[cooled by Synchtrotron Radiation, t ~
0.15s]
a) Degrading
b) Reflecting
99.9% lost
0.1%
E<10kV
c) Trapping
t=0
antiprotons
t=200 ns
c) Cooling
t=several tens s
[through Coulomb interaction]

5. The dimensions of the AEGIS antiproton catching trap
Length of the antiproton catching trap
Antiproton axial energy max : 10 KeV
Velocity v : m/s
AD bunch length t : 200 ns (up to about 500 ns)
L (length of the 10KeV potential well ) : L=0.5 v t= 35 cm
Real trap Length : 40 cm
Trap radius : y
Antiproton cyclotron radius = 2.8 mm (10 KeV)
beam radial size = ? mm
Beam centering
Note: rtrap>> cloud radial size
rtrap =1.5 cm (max 2 cm)
Positron injection??? x

6. Electrons in the antiproton catching traprp
Cold cloud at equilibrium
a=zp/rp zp
Radial size of the plasma
Trap size
Potential well
Number of particles
N=108
Rtrap=2 cm
rp= 1mm
Zp=1.77 cm
V0=200 V
N =5 108
Rtrap=2 cm
rp = 2 mm
Zp = 3 cm
V0 =200 V
change rp with RW
change zp with V0

7. The position of the trap in the 5 T magnet
The region with uniform magnetic field

8. The position of the trap in the 5 T magnet
The region with uniform magnetic field e-
10KV
Movable degrader

9. A movable degrader with few different foils:
in situ optimization of the catching efficiency
ATHENA results
FWHM=10mm
Additional Al thickness mm
Degrading materials in ATHENA:
67 mm silicon beam monitor
25 mm Stainless steel
130 mm Al foil (last degrader)

10. Summary of the parameters of the antiproton catching trap
Electrode voltages : 10 KV on HV1, HV2
V on the others electrode (DAC+ amplifiers)
HV2 connected also to V
HV1, HV2 L=2.5 cm
7 electrodes for Penning trap
11 additional electrodes
1 electrode radially split in 4 sectors
Total : wires (200 V) coaxial cables
2 HV cables (10 KV)
Voltages connected through filters
Voltage rise and fall time: hundreds msec
Fast pulses ( 10 ns rise time, duration about ns) added to some electrodes to dump the particles
Plasma mode detection
RW voltages superimposed to the trap voltages

11. Positron transfer In the e+ accumulator B=0.15-0.2T
The last trap can be Malmberg or Penning (as we like)
e+ cooling : only buffer gas
No significant radiation cooling (B too low)
Radial compression through RW wall during accumulation with gas cooling
Accumulation time : sec
Stop accumulation : gas pump out
3 108 e+
R e+ = max 5 mm
L e+ = 2-3 cm (?)
Temperature: 300K or eV e+
The space charge electric field cancels the applied axial electric field
inside the plasma V
Space charge energy: several tens of eV z

12. e+ transfer from the accumulator in the main magnet
e+ in the accumulator V z V1 V2
Kinetic energy in the flight direction >> velocity spread in the cloud (temperature)
Space time gradient of the accelerating field: optimized to give the “same energy” to all the positrons
Fligtht time << Coulomb explosion time
Energy in the flight direction >> space charge energy
Mirror effect of the magnetic field
e+ energy in the flight direction: several hundreds eV
vflight = m/s (100 eV)
= m/s (1 KeV)

13. e+ catching in the main magnet
5 Tesla region
V3+D
V1= 500 V (example)
Transfer line V3
After catching all the
voltages can be lowered
Only D is important
V2 (=0)
Transfer flight time : few hundreds ns
Positron catching trap : initial L about 30 cm
No antiprotons in trap during e+ transfer
Fast e+ cooling in 5 T magnetic field
Collection of e+ in a shorter trap in the region with high B homogeneity
Compression by RW (several tens sec)
At the same time: catch and cool pbar again

14. The position of the trap in the 5 T magnet
The region with uniform magnetic field e+
Movable degrader out

15. Could we have 10 cm more 5T magnetic field with 10-4 homogeneity?
The solenoid can be longer

16. Summary of the parameters of the positron catching trap
Electrode voltages : 1 KV max added to
V (DAC+amplifiers)
7 electrodes for Penning trap
10 additional electrodes
1 electrode radially split in 4 sectors
Total: (1.2 KV) coaxial cables
(or more, it depends on the length of the magnetic field)
Voltages connected through filters
Voltage rise and fall time: hundreds msec
Fast pulses ( 10 ns rise time, duration about ns) added to some electrodes to dump the particles
Plasma mode detection
RW voltages superimposed to the trap voltages
Entrance electrode: fast pulse

17. Adiabatic transfer Shaping time : 50 msec
Wait at each stage: ms several rotation 5 10 15

18. Single to double particle injection: see last meeting
Pbars lye on axis all the time
Normal “adiabatical” transfer
Positrons have to jump off axis to be shooted on the porous target to form positronium
Diocrotron excitation of the positron plasma
(J. R. Danielson and C. M. Surko Physics of Plasmas 13 (2006), ) 18

19. 100 mK region
10 cm
22.5 cm
Trap radius 2.5 cm (big trap)
0.8 cm (small trap)

22. Particle transfer in the 1 Tesla magnetic field
Transfer length 1m (-40 cm, +60 cm)
About 40 transfer electrodes (l=2.5 cm each)

23. Big radius trap: 17 coaxial cables +- 200 V
Small radius traps pbar manipulation : 10 coaxial cables Volts
e+ manipulation coaxial cables Volts
e+ acceleration toward the target : 5 (or more) cables (3KV?)
pbar cooling and Rydberg accelerator: 25 coaxial cables
+- 50 Volts
1KV for about 100 msec
Additional electrodes after the trap???
MCP+ phosphor screen: can be installed in the place of the grating system
They have to be removed when the grating will be
installed

24. Still preliminary summary of the needed cables:
this is the minimum number….
100 mK 20
50 V 5
3 KV
e+ acceleration (only for few tens ns) 25
50 V-1 KV
1KV only for 100 microsec 4K 17
200 V
big trap before the small ones 40
transfer region 23
1.2 KV
e+ catching 21
pbar catching 2
10 KV

25. Trap mechanics+ electronics & control system
HV pulser
DAC+amplifiers
Fast pulser
Faraday cup amplifiers
MCP+Phosphor+CCD
Plasma mode detection (FPGA based)
RW & plasma manipulation
Labview boards
Assuming to build the electronics : 162 KEuro
Pumps, feedthroughs, vacuum gauges,flanges,movable feedthr. : 90 KEuro