HADES

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Introduction

HADES experiment uses two kinds of beams: low intensity heavy ion beam which hits target inside the experiment (called HADES target) or pion beam produced by an interaction of high-intensity ion beam with another target, upstream of the Hades target. This target is called pion production target (stepper motor: GHADET1PS, the traget layout and available positions are explained here: New_Targetleiter_HADET1PS_Feb2011.doc (from Robert Boywitt)). The pion production target is hidden in a bunker for radiation shielding and is remotely controlled. The access to the bunker is only by removing the shielding concrete (there is no door). The following magnets are in the bunker together with pion target: GHADQD21,22,31,32 and GTP1MU1. Because the bunker is not easily accessible, water sensors are installed under the quadrupoles. The control box for these magnets with alarm information is right after entrance to NE-5.

The beamline lies completly within NE-5 zone. The contact persons are: Joachim Stroth, Michael Traxler and Jerzy Pietraszko.

e-mail from W. Koenig via J.Pietraszko:
"The beam spot at the pion production target is much smaller than the Heavy Ion beam spot at the Hades target. It is a MUST to get below 0.5 mm sigma at least vertically and it is NO problem to reach this value. Just needs a strongly defocussed beam in the last quadrupole in front of production target. By the way at Hades target we reached 0.8 mm with Heavy Ions."

There are no specific requirement about the beam shape (circularity).

Beams

For experiments with HADES target a moderate beam intensities (<10⁷ ions/second) are needed. Beam is extracted slowly (spills of about 10 s). The ion type is Au or Ag. Proton beam is a special case. It should be produced in synchrotron with the highest momentum possible (E=4.5 GeV). The protons will be used for strangeness production. Finally, for pion beams, the highest possible primary beam intensities are required. In 2014 it was about 10¹¹ nitrogen ions per spill, which were producing about 4*10⁵ pions.

Optics

There are two main types of optics, depending whether the pion production target is used (pion optics) or not (ion optics):

• SIS18_HADES_STANDARD (ion optics)

• SIS18_HADES_LEGACY (ion optics)

• SIS18_HADES_ENGRUN2018 (ion optics)

• SIS18_HADES_BEAMTIME19 (ion optics)

• SIS18_HADES_SR2018 (alternative ion optics, proposed by S. Ratschow in August 2018)

• SIS18_HADES_SA2018 (alternative ion optics, proposed by S. Appel in October 2018)

• SIS18_HADES_DV2018 (alternative ion optics, proposed by D. Vilsmeier in November 2018)

• SIS18_PION_HADES_STANDARD (pion optics)

Because the HADES experiment is elevated with respect to the beam lines, two of the dipole magnets (GHADMU1 and GHADMU2) are rotated around beam axis. The rotation angle is (+-) 21.57766 degree and the distance between magnets is 18.2765895 meters.

The layout inside HADES Cave, as measured by E.Schwab on Dec 6th, 2018, is the following:

In addition 7 meters behind the target there is a veto detector which ensures that beam is parallel to the detector axis.

Issues

The main issues are:

1. Spill microstructure. During the slow extraction the beam intensity at various timescales is not constant. The spikes, especially at microsecond timescale, lead to loss of significant amount of data by the experiment, because the event pile up, making them useless for many physics measurements.

2. Spill stability. During the spill, which lasts several seconds, the beam spot on target moves. It is show in this slide by J. Pietraszko: hades_spill_stabiliy.pdf. The resonant method of slow extraction was used in this run.

3. Beam losses. Some of the beams, especially for pion program, have very high intensity (10^11/spill). Beam losses lead to raising radiation levels and problems with RP.

Special studies

Several additional studies have been made on this beamline due to its high-inensity beams:

• Beam losses

Photos

TH2 upstream:

TH2 downstream:

HAD1:

HAD2 and HAD3 are inside primary target bunker, HAD4:

Pion production target as seen by camera, aligned in March 2018 (courtesy Joergen Wohlers). In order to see this image one shall:

1. move in the mirror (Spiegelfolie) - device name GHADDFA_P (it is a pneumatic drive which works from Device Control)

2. move in the target itself - device name GHADDE1PS (stepper motor). Currently (August 2018) one cannot drive the target from Device Control. An expert program (/common/usr/sd/bin/ds) must be used. Target positions, in mm, are explained here: New_Targetleiter_HADET1PS_Feb2011.doc.

3. switch on, on the camera board, HADDFA (and switch on the LED, the best in strong light mode). Currently (August 2018) this camera is not available in CUPID.

In the presence of the beam the scintillating screen can be used for beam alingment. In this case the beam goes through the mirror, which is made of thin foil, so it shall not affect the beam significantly. The beam intensity limits for this foil should be investigated, but most likely 10^7 in slow extraction shall not damage it.

Pion production target in the lab (courtesy Bettina Lommel). This target was installed in 2011. From up to down the target bars are: Be 120, Be 120, Be 100, Be 100, Be 80 and Leuchttarget (scintillating screen) 22x33 mm.

Pion production target bunker opened (2016):

HADES detector:

HADES spill monitor: SpillMon_v1.pdf

First results of beam spot on target from November 2018: Beam_quality_hades22_11_2018.pdf

Responsability:

HEST Machine Koordinator responsability starts with... primary target area - HADES responsability.