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

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

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

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]

The dimensions of the AEGIS antiproton catching trap Length of the antiproton catching trap Antiproton axial energy max : 10 KeV Velocity v : 1.4 106 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

Electrons in the antiproton catching trap rp 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

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

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

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)

Summary of the parameters of the antiproton catching trap Electrode voltages : 10 KV on HV1, HV2 + - 200 V on the others electrode (DAC+ amplifiers) HV2 connected also to +-200 V HV1, HV2 L=2.5 cm 7 electrodes for Penning trap 11 additional electrodes 1 electrode radially split in 4 sectors Total : 21 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 100-200 ns) added to some electrodes to dump the particles Plasma mode detection RW voltages superimposed to the trap voltages

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 : 300-500 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

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 = 6 106 m/s (100 eV) = 1.9 107 m/s (1 KeV)

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

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

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

Summary of the parameters of the positron catching trap Electrode voltages : 1 KV max added to + - 200 V (DAC+amplifiers) 7 electrodes for Penning trap 10 additional electrodes 1 electrode radially split in 4 sectors Total: 23 (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 100-200 ns) added to some electrodes to dump the particles Plasma mode detection RW voltages superimposed to the trap voltages Entrance electrode: fast pulse

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

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), 123502) 18

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

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

Big radius trap: 17 coaxial cables +- 200 V Small radius traps pbar manipulation : 10 coaxial cables +- 50 Volts e+ manipulation 10 coaxial cables +- 50 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

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

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