alexandr drozhdin march 16, 2005 mi-10 injection

Alexandr Drozhdin

March 16 , 2005

MI-10 Injection

March 15-17, 2005A. Drozhdin - Proton Driver Director's Review 2Fermilab

Outline

• Painting Injection Parameters• Injection Scheme• Results of Simulation• Stripping Efficiency and Beam Loss• Conclusions


Painting injection is required to realize uniform density distributions of the beam in the transverse plane for space charge effect reduction.

Location MI10 straight section Duration 90 turns (1 msec) or 270 turns (3 msec)Repetition rate 0.67 HzAccumulated intensity 1.5e14 ppp Injected beam emittance 1.5 mm-mrad Emittance after painting 40 mm-mradBeam power 143 KW Injection loss (600 µg/cm) 0.005%(nuclear interaction) +0.004%(foil stripping) +0.005%(field stripping)=20 W

Painting injection parameters


aperture with the required emittance. Vertical kicker magnets located in the injection line provide injected beam angle sweeping during injection time.

Painting injection

Painting injection is perfor-med by using fast horizontal and vertical magnets. The closed orbit is moved at the beginning of injection by 21 mm to the graphite stripping foil. Gradual reduction of kicker strength permits “painting'' the injected beam across the accelerator


A stripping foil is located upstream of focusing quadrupole Q102. That is necessary for unstrepped component of the beam separation from the proton beam behind the stripping foil. A septum-magnet is used to separate the circulating beam and

injected H- at the defocusing quadrupole Q101 by 135 mm. Horizontal septum-magnet located behind the stripping foil is used for removal of unstripped beam to the external beam dump.

Painting injection scheme


Horizontal kicker strength and vertical angle of injected beam at the foil (top), horizontal (middle) and vertical (bottom) density distribution of the circulating beam after 90-turn injection.

Circulating beam distribution


Average number of hits upon the stripping foil for each particle is equal to 4.4. This effects pretty high level of nuclear interactions and because of this causes 0.0046% (7 W) of particle loss at injection. Multiple Coulomb scattering in the foil and ionisation loss are negligible small.

The increase of painting injection duration to 270 turns increases an average number of hits upon the stripping foil to 16, that increases foil heating and beam loss at injection.

Particle hits at the foil


The kicker strength drops fast to ~60% of its maximum during 20 turns, and then slowly decreases to 50% during another 70 turns. Stripping foil is located at the exit of kicker number 2, very close to its edge in the fringe field of the magnet. The kicker magnet field is chosen such a way that during injection the magnetic field provide stripping of Stark states hydrogen atoms with principal quantum number n=5 to protons.

Stripping efficiency


This corresponds to kicker maximum field of 0.1T and length of 0.34 m. At these parameters the magnetic field during ~80% of injection cycle is in the range of (0.05-0.06)T. The

probability of H- stripping by magnetic field of kicker magnet during the first turn of injection (B=0.1T) is 0.002. It drops to 0.00005 during five turns (B= 0.08T). This gives

Stripping efficiency

stripping of 5.e-05 of injected beam (7W) of power lost in the injection region. An unstripped part of the beam after interaction with the foil - the H0 states hydrogen atoms - may be stripped to protons by magnetic field of other accelerator elements.


We assumed here that H- atoms pass a distance of (1-2)cm in a fringe field of the kicker magnet number 2. This distance is enough for H0 atoms with n=5 to be stripped. This part goes to circulating beam without changing emittance of the beam. Some part of atoms with n=4 is left unstripped and goes to the beam dump, and, unfortunately, some fraction of them is stripped along the kicker number 3. These protons contribute to the circulating beam halo and cause losses in the collimation system.

Stripping probability of Ho atoms


Experimental Data on H0 yields [*]

[*] Measurement of H(-), H(o), and H(+) yields produced by foil stripping of 800-MeV H(-) ions, M.S.Gulley, P.B.Keating, H.C.Bryant, E.P.MacKerrow, W.A.Miller, D.C.Rislove, S.Cohen, J.B.Donahue, D.H.Fitzgerald, S.C.Frankle, D.J.Funk, R.L.Hutson, R.J.Macek, M.A.Plum, N.G.Stanciu, O.B.van Dyck, C.A.Wilkinson, C.W.Planner, Physical Review A, Volume 53, Number 5, May 1996.

n=1, 2 93.3% n=3 3.6% n=4 1.5% n=5 0.7% n=6 0.3% n>6 0.6%

total 100%

Assuming that fraction of yields of different states n almost does not depend on the foil thickness and energy, one may expect ~97% (n=1, 2 and 3) of the total amount of H(o) to end at the external beam dump, ~1% (n=4) contribute beam halo, and ~2% go to the circulating beam without emittance increase. Foil number 3 is used for a final stripping of atoms (n=1-4) behind the kicker number 3 to reduce field stripping and losses along the extraction magnet and beam line.


No show stoppers have been found at the painting injection system simulations.

Calculated stripping efficiency is 99.5%.

It is shown that all H0 atoms with n>4 are stripped to protons and go to circulating beam without changing emittance of the beam. Atoms with n<5 are left unstripped and end at the beam dump. About 70% of atoms with n=4 are stripped to protons along the injection kicker number 3. These protons contribute the circu-lating beam halo and cause losses (~6 W) in the collimation system.

Magnetic field stripping in the kicker causes 7 W loss.

Nuclear interactions in the foil cause 7 W loss at injection.

CONCLUSIONS

alexandr drozhdin march 16, 2005 mi-10 injection

Documents