Standard Configurations

The standard configurations for MEC are described below. For Run 19, there are two standard configurations, XRD and PCI. There is additionally a standard platform of beam delivery for short pulse experiments that, while not treated as a standard configuration, will help to ensure experiment feasibility.

Parameter Table

To be considered for scheduling in a standard configuration, users will be required to include a table in the proposal that lists the specific experimental parameters to ensure compatibility with these configurations. If the experimental parameters are not compatible with the standard configurations or if the table of parameters is incomplete, the proposal will be reviewed and considered for scheduling as general user proposal. Please see the table of required parameters. No fundamental changes to the standard configurations will occur, but some details of the configuration may be updated in response to inquiries, so users should recheck the website before submitting your proposal to confirm that you have the latest information. Address any questions to the instrument staff. 

Configuration #1

Standard Configuration #1 for MEC: XRD

Types of Experiments

This configuration of MEC supports diffraction measurements on targets shocked to pressures up to several Mbar, with shocks propagating along the X-ray direction. Four or three ePix10k measure diffraction, with angular range optimized for liquid diffraction at high photon energies (>15 keV). A dual line VISAR diagnostic measures shock break-out to determine pressure. Forward X-ray Thomson scattering (FXTS) is available with the removal of one quad and a reduction in angular coverage; backward X-ray Thomson scattering (BXRTS) is always available at 125o scattering angle.

X-ray Diffraction: ePix10k Configuration and Layout

The base configuration consists of the ns laser drive beams, VISAR, the backward XRTS (optionally) and four ePix10k quad detectors. Fig.1 shows the layout with all of the quads. See XRD platform for a plot of the angular coverage.

Top view XRD configuration

Figure 1. Geometry for XRD standard configuration using two nanosecond, 527nm drive beams.

The lasers hit the sample at an angle of 20° from each side of the x-ray axis. The angle between the target normal and the LCLS x-ray axis is 0° (so that each drive beam is incident at 20°). VISAR is collected normal to the back of the target. 4 Quad detectors are arranged to spatially resolve wide angle scattering from 8 to 72º. BXRTS will be located around 125 degree.

3D view of XRD standard config

Figure 2. 3D view with all four quads.

FXRTS variant:

Quads Q2 can be removed to allow a forward X-ray Thomson scattering diagnostic to be placed. The FXRTS spectrometer will be in the horizontal plane with a fixed scattering angle of 30 degree.

Figure 3 shows the experimental layout with FXRTS. The 3 ePix10k Quads as XRD detectors cover from 8 to 60º.

Top view of XRD configuration FXRTS variantt

Figure 3. Geometry for XRD standard configuration with quad Q2 replaced with a FXRTS spectrometer for high photon energy.

Optical Laser Parameters and Geometry

The full frequency-doubled energy of the MEC LP laser (see Laser Characteristics at MEC; Long pulse laser tab) is delivered to the target with angles of ± 20 deg. in the horizontal plane relative to the X-rays, with the target oriented normal to the X-rays. Both beamlines can be used simultaneously (7 minutes between shots), or staggered (one shot every 3.5 minutes). The 72 mm beams are focused using 250 mm focal length aspheric lenses (F/3.5), and the focal plane of each beam relative to the target can be adjusted from best focus to a ~100 µm spot. MEC uses phase plates generating circular focal spots of 150, 300 and 600 micron by CPP. Phase plates can be manually exchanged during a standard configuration run, requiring a chamber vent. Note that desired pulse shapes and phase plates must be submitted at least 2 months before beamtime.

Configuration #2

Standard Configuration #2 for MEC: PCI

This configuration of MEC supports diffraction and phase contrast imaging (PCI) measurements on targets shocked to pressures up to several Mbar, with shocks propagating perpendicular to the X-ray direction. The new MEC X-ray Imager (MXI), located upstream of the target, focuses the beam to a few 100s of nanometer size before the target, with the ability to shift between three lens sets for different magnification. The expanding X-rays pass through the target and are registered on an X-ray microscope ~4.5 m from TCC. The layout within the chamber is shown in Figure 3. X-ray diffraction is achieved with three out of four ePix10k quads of the XRD platform, covering a range of 8 to 60 degrees. VISAR is also available to measure shock velocity.

PCI standard config

Figure 4. Geometry for MXI standard configurations using two nanosecond, 527nm drive beams in orthogonal beam direction to X-ray beam.  A detector for MXI will be located after the fly-tube, which is ~4.5m away from TCC.


Optical Laser Parameters and Geometry

The full frequency-doubled energy of the MEC LP laser (see Laser Characteristics at MEC; Long pulse laser tab) is delivered to the target with angles of ± 20 deg. in the horizontal plane relative to the target normal, which has an angle of 90 deg. relative to the X-rays. A stair-step target mount design allows for laser and visar access to a target and side-on X-ray imaging of the target. Both beamlines can be used simultaneously (7 minutes between shots), or staggered (one shot every 3.5 minutes). The 72 mm beams are focused using 250 mm focal length aspheric lenses (F/3.5), and the focal plane of each beam relative to the target can be adjusted from best focus to a ~100 µm spot. MEC uses phase plates generating circular focal spots of 150, 300 and 600 micron by CPP. Phase plates can be manually exchanged during a standard configuration run, requiring a chamber vent. Note that desired pulse shapes and phase plates must be submitted at least 2 months before beamtime.

SP Standard Platform

Standard beam delivery platform for the MEC SP laser

A standard short pulse laser (SPL) beam delivery is introduced for Run 18 to allow block scheduling and reduce setup time. While not a standard configuration, SPL experiments are encouraged to conform to this beam delivery scheme if possible. In this configuration, the short pulse laser (SPL) beam path delivery geometry, from the entrance port in the target chamber down to the focus position of the final focusing optics, is fixed and cannot be altered. The target sample plan orientation vs the X-ray beam path can be altered but a minimum angle of incidence between the target normal and the laser beam at the final focusing optics is required to be a minimum of 35°. Users may request any standard MEC beamline devices and diagnostics, but the request must be explicitly mentioned in the proposal. For more details, please contact an MEC beamline scientist.

Short pulse laser beam delivery geometry

Delivery of the beam to target from the chamber input consists of a set of 5” dielectric mirrors and a motorized final focusing optics assembly arranged in the target chamber. Fig.5 shows the layout. The input beam in the south-west port of the chamber goes through a chicane to allow for a beam pointing monitoring system which is located in the red shaded area and makes use of a small amount of the beam leaking through the first mirror the short pulse laser encounter in the chamber. This beam pointing monitoring assembly is located outside the chamber and provides shot-to-shot pointing offset. After reflecting off the first motorized mirror (tip and tilt), the SPL beam is then transported with dielectric mirrors down to the Off-Axis parabola (OAP). It has an effective focal length of 330.4 mm and an off axis angle of 35.21°. The clear aperture is 4” and the dielectric coating has a surface figure of λ/22.6 Peak-to-Valley (at 633 nm) over 90% of the clear aperture. The OAP mount is motorized in XYZ (X is lateral, Y is vertical and Z is longitudinal to the input optical laser beam) to allow for less than 5 mm corrections of the position of the optical laser spot. The other mirror mounts are using manual tip/tilts. The preferred target stage sample plan orientation is at 45° vs the LCLS X-ray beam to allow for the use of the Earth as additional radiation protection. Rotating the sample plan is allowed for other geometries as long as:

●      The target holder translation stage do not collide with the final mirror before the OAP

●      The preponderance of accelerated particles originating from the target are travelling south and south-east

The red shaded area indicates a keep-out zone for user diagnostics, while the green shaded area is considered open. A 4” motorized iris is located at the beam entrance of the target chamber short pulse laser port to allow for synchronization between X-rays and SPL. The short pulse laser energy can be checked while the target chamber is pumped down using a vacuum power meter located between this motorized iris and the first dielectric mirror encountered by the SPL.        

 SP standard platform

Figure 5. Geometry for SPL standard beam delivery configurations. The lasers hit the target at an angle of 35° from the target normal. The angle between the target normal and the LCLS x-ray axis is 45°.

Optical Laser Parameters

The MEC fs laser will be delivered to the target as shown in Fig.5. Both compressed and chirped delivery are available. The beam size is 65 mm at the entrance of the target chamber. The laser spot size is about 10 µm FWHM and 40 fs compressed. It delivers up to 1 J on target at a repetition rate is 5 Hz. See the laser characteristics page for more information on the laser parameters.

X-ray Parameters

There are no constraints on the X-ray beam parameters linked to the SPL standard beam delivery.

VISAR

The MEC line VISAR will be available as a diagnostic in configurations #1 and #2 (See Fig.1 and 4). Table 1 lists the etalons available at MEC; alternatively, users can bring their own. Users can take up to 15 test shots with the laser drive beam and VISAR before the start of their X-ray beam time. Visar schematic

Figure 6. Optical schematic of the MEC VISAR system. Two VISAR beds with streak cameras are provided. Etalons for each bed can be chosen from table below, or user can bring their own.

Etalon thickness (mm) Etalon diameter (mm)​
5.072, 5.077, 8.087, 8.096, 11.006,14.999,15.01 ​25
25.036, 25.034, 49.96, 75.04 ​50

Table 1. VISAR etalons available at MEC. All etalons are fused silica. User can bring their own etalons, provided the diameter is either 25 or 50mm. Maximum etalon length that can be supported is 110mm.

Targets

The user provided targets will need to be mounted on target frames that are compatible with the MEC target holder. Please contact an instrument scientist for more information about target mounting. An example target mount design is illustrated in Figure 7.

Target cartridge example

Figure 7. Drawing of the target frames that are compatible with the MEC alignment stage. The targets are mounted on the right side of the side view (on reference plane A). In the side view, the laser comes from the left. Dimensions are in inches. The spacing and size of the target holes may be changed, but all other dimension need to stay unchanged. The chamfer in the front side of the target hole is 60°. (Download detailed drawing)

MEC Instrument Staff

Gilliss Dyer, Bob Nagler, Hae Ja Lee, Eric Galtier, Philip Heimann, Dimitri Khaghani

Laser Contact

Eric Cunningham, Marc Welch

  LCLS proposals are submitted through the User Portal.