SIS18_HADES_STANDARD optics

(return)

The optics generated initially from MIRKO files present in repository turned out to be rather wrong due to large beta functions and large beam spot on target. This optics has been exchanged, in August 2018, to new optics based on 2012 settings for Au beam (ibhs file HS-197AU-120501-1412-SI-TH-HAD).

The files:

The basic optics plot:

Twiss parameters on target for this optics are not optimized:

Performing simple focusing match on two last quadrupoles, one obtains:

Node_Name            Constraint   Type  Target Value   Final Value      Penalty
---------------------------------------------------------------------------------------
sis18_hades$end:1    betx         4     0.0000E+00     1.45833712E-01   2.12674715E-02
sis18_hades$end:1    bety         4     0.0000E+00     2.16076675E-01   4.66891296E-02

so 10 and 20 cm, for modified settings:

Variable                 Final Value  Initial Value Lower Limit  Upper Limit 
--------------------------------------------------------------------------------
k1l_ghadqt51              4.30659e-01  4.46240e-01  0.00000e+00  6.00000e-01
k1l_ghadqt52             -5.99998e-01 -5.79980e-01 -6.00000e-01  0.00000e+00

Note: the second quadrupole is at the current limit.

The 6-D beam transfer matrix for the new optics is (obtained with MAD-X):

Trajectory Response Matrix

The Trajectory Response Matrix (TRM) is needed for for trajectory correction which is done here by inversing this matrix using Singular Value Decomposition (SVD). It is also needed for error finding algorithm LOCO.

As a simple example, the horizontal trajectory response matrix, obtained with MAD-X (units [m/rad]), this uses only steerers:

The above table is simplified. The internal target of HADES experiment is positioned significantly higher (about 2 meters?) than SIS18 synchrotron, therefore the two last dipoles of the beam line are tilted by about 0.38 rad (22 degrees) in order to bring the beam to this level. This means that the horizontal and vertical TRMs are coupled. The coupling is not very strong but visible in this trajectory response matrix SIS18_HADES_STANDARD_TRMx.txt and trajectory correction matrix SIS18_HADES_STANDARD_TCMx.txt obtained using SVD. Here are the two matrices formatted according to COCO program requirements : SIS18_HADES_STANDARD_TRMx_COCO.txt, SIS18_HADES_STANDARD_TCMx_COCO.txt

Steering knobs

A final focusing knob for standard optics (proposal to be tested, valid within +-2% of k1l):

beta_x = (1849.6 +- 73.7) * k1l_QT51 + (273.8+-56.7) * k1l_QT52 - (645.6+-46.5)

beta_y = (32.56 +- 3.00) * k1l_QT51 + (70.62+-2.31) * k1l_QT52 - (28.07+-1.90)

below is OBSOLETE (to be removed):

This is optics used for Dry Run 4 (January 2018). Optics was generated based on twiss file exported from MIRKO by Sebastan Ratschow. The pion production target is removed (remotely, it remain in vacuum but is no more on the beam path) and the primary ions are transported all the way to the target of the HADES experiment (Hades target).

The beta functions need some investigation. They are showed below:

The horizontal dispersion reaches 100 meters. With dp/p~1E-3, the dispersive contribution to beam size reaches 10 cm! Idea: can this be used to remove off-momentum particles from a spill. Would it improve spill structure?

The files:

This optics gives fault when driving GHADQD21 and 22 magnets.

Beam parameters on target

1. beam spot size
2. beam dispersion

Misalignment study

Due to FAIR works a systematic misalignment of the beamline took place. The SIS18 extraction point got lowered by about 11 mm with respect to values of 2015. The beamline is tilted by about 0.1 mrad from the extraction point to GTH2QD12 magnet, after which the displacement disappears. Such a small deformation of the beamline can be easily corrected by the steerers.

The plot below shows ideal trajectory without displacement (red-zero), trajectory after displacing the machine elements according to the measurements (blue) and correction of the orbit using two steerers: GTE1KY1 (angle=-0.576558 mrad) and GTH2KY1 (angle=90.4734 murad) (green):

The corrector values have beed determined using MADX matching:

// misaligned initial conditions: INITBETA0:  BETA0,
       BETX = 17.29666452, ALFX = -1.818455864, BETY = 6.23424221, ALFY = 0.03280524,
       X    = -0.003400000, Y    = -0.01, PY   = 8E-5,
       DX   = 2.456663071, DPX  = 0.282177284, DY   = -0.001192020176, DPY  = 3.98187E-5;

match, sequence=sis18_hades, beta0=INITBETA0;
         constraint, sequence=sis18_hades, range=gte1ky1/ghaddf4,y=0.0;
         vary, name=k0sl_GTE1KY1, step=1.0e-5;
         vary, name=k0sl_GTH2KY1, step=1.0e-5;
         lmdif, calls=100000, tolerance=1.e-15;
endmatch;

Beam commissioning June 2018

During the beam commissioning on June 26th, the LSA optics was found doubtful. Therefore an old optics was imported from IBHS file from 2014 run, probably this: HS-_14N_-140912-2203-SI-TH-HAD.DAT (tbc). This file was converted to Paramodi Import/Export file: HADES_Paramodi_Import_201806.txt. This, (together with some steerer actions) allowed for getting hits on diamond detector in the HADES cave. Optics image (assuming current HADES sequence without proper description of dipoles):

older investigations

Beam envelope and phase advance from MIRKO (from mid-2017):

The horizontal phase advance reached 550 degrees on target and vertical one about 450 degrees (the exact numbers are in TWISS). The beam is of course focused on the target, what means that the last quadrupoles have higher gradients.

The twiss file (generated with MIRKO) for this optics is here: SH__.twiss