Extraction from SIS18

(return)

SIS18 can extract beam in single turn mode as well as in slow extraction mode. Typical beam parameters at extraction:

• dp/p: 1-3*10^-3

• maximum rigidity 18.5 Tm (corresponds to 1 GeV/u for Uranium and 4.5 GeV/u for protons)
• fast extraction duration: 1 us, with compression: 200 ns
• slow extraction duration: 10-10000 ms
• typical efficiency expected for resonant extraction: 60%-80% up to rigidity of 14 Tm
• for higher rigidities extraction efficiency drops, mainly because electrostatic spetum is not strong enough.
• emittance at extraction:
  • fast: 30x8 mm*mrad
  • fast with cooling: 5x5 mm*mrad
  • slow: 5*8 mm*mrad
  • Sebastian used for HADES study: ex=1*pi*mm*mrad, ey=4*pi*mm*mrad; these are 2 sigma emittances, ie. ex=pi*(2*sigma)^2/beta (-dispersion contrib) - BTW maybe this is the case for other numbers as well?
  • converting Sebastian's number to 1sigma emittances: ex=ex_Sebastian/(4*pi) = 0.25 mm*mrad, ey=1*mm*mrad
  • preliminary measurement of RMS emittance, on July 4th using GS06DF, slow extraction, assuming optics function as in PSF, gave: 2.5 mm*mrad (H) and 40 mm*mrad (V).

The matching of SIS18 optics with beam line ones is done in intersecion point of the SIS18 straight section with TE-section of HEST beamlines. This point is called PSE. It must be noticed that the beam does not go through this point in reality, as it is smoothly bend by septa magnets already upstream. In MIRKO the difference between the real beam trajectory and the one going through PSE is described in OPSE_REF.MIX file. Currently in MADX this is neglected and the error due to this seems to be negligible.

The OPSE_REF.MIX file describes beam transfer matrix from real, physical PSE point location in SIS18, back to front of septa magnet GS06MU3E (but without taking it into account) another 0.5 meter upstream) and then through GS06MU3E, GS06MU4 and GS06MU5 and again backwards to PSE. Such a beam transport matrix in 4D is:

 [ 0.99645419  1.04532535  0.          0.        ]
 [-0.          0.99645419  0.          0.        ]
 [ 0.          0.          1.          1.04656355]
 [ 0.          0.          0.          1.        ]

Converted to twiss-parameter transport matrix (beta, alpha, gamma), horizontal:

 [ 0.99292095 -2.08323764  1.09270508]
 [ 0.          0.99292095 -1.04161882]
 [ 0.          0.          0.99292095]

and vertical:

 [ 1.         -2.0931271   1.09529526]
 [-0.          1.         -1.04656355]
 [ 0.         -0.          1.        ]

The beam parameters in PSE point of SIS18 are:

The PSE(MADX) was calculated with relativistic beta=1, so dispersions are correct, however the optics did not take into account the active septa, so the orbit deviation (especially horizontal) is underestimated.

The schematic drawing shows the SIS18 extraction region:

The parameters of the magnets:

• GS06MU3E_EDGE1: DIPEDGE,E1= -0.17453293E-01;
• GS06MU3E: SBEND, L= 0.91115323, ANGLE= -0.34906585E-01;
• therefor bending radius = 26.103 m
• DRIFT0016: DRIFT, L= 0.15356565E+01;
• GS06MU4_EDGE1: DIPEDGE,E1= -0.38222711E-01;
• GS06MU4: SBEND, L= 2*0.73667616, ANGLE= 2*-0.38222711E-01;
• therefore bending radius = 19.273 m
• GS06MU4_EDGE2: DIPEDGE,E1= -0.38222711E-01;
• DRIFT0023: DRIFT, L= 0.44848310E+00;
• S06MU5_EDGE1: DIPEDGE,E1= -0.38484510E-01;
• S06MU5: SBEND, L= 2*0.74435236E+00, ANGLE= 2*-0.38484510E-01;
• S06MU5_EDGE2: DIPEDGE,E1= -0.38484510E-01;

the whole section: L=5.85734987 m, angle=0.187797429 rad, therefore averaged bending radius=31.1897 m

The technical drawing of the extraction region:

The scintillating screen GS06DF is before the PSE point where optics files typically start. Here the location of PSE point is approximate.

Electric septum is placed upstream, in section 4. The name of the element is GS04ME1 and currently is 1.5 meter long. Here is the photo:

A new, longer septum is being considered, as this one seems to have not enough strength at maximum rigidity.

Photo of magnetic septum GS06MU3E (from above, beam goes from top of the photo to the bottom):

Photo of vacuum chamber containing GS06DF (from above, beam goes from top of the photo to the bottom):

Photo of the first two dipoles at the extraction line GS06MU4 and GS06MU5 (from above, beam goes from bottom of the photo to the top):

and a photo of GTE1DK1, where the second beam line screen is placed:

The photo of the (old) GTS1MU1 switching dipole (April 2018):

Note that extraction line, down to ventile GTE2VV1T (in front of GTE3MU1 dipole) is beaked before every beam time. It includes GTE2DK4 diagnostic box with special, beakable SEM grid for beam size measurement. It would be good to exchange this grid (together with vaccum chamber) during the 2019 shutdown. Preferable solution is new grid developed for FAIR.