MEC Standard Configurations Run 17

Types of Experiments

Two variations of the standard configuration are available: the X-ray diffraction variation (XRD) and X-ray Thomson scattering variation (XRTS). A user supplied detector cannot be fielded in either standard configuration. Users may request any standard MEC beamline devices and diagnostics, but the request must be explicitly mentioned in the proposal.

X-ray Diffraction Variation: CSPAD Configuration and Layout

This variation consists of the ns laser drive beams, VISAR, the backward XRTS (optionally) and four CSPADs. Fig.1 shows the layout.

Figure 1. Geometry for XRD standard configurations using two nanosecond, 527nm drive beams. The lasers hit the target 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°). The Backward XRTS looks at a scattering angle of 125°. CSPAD scattering detectors are positioned behind the target, and VISAR is collected normal to the back of the target.


Four CSPAD-560k will be used for the x-ray diffraction measurement, with fixed position. They will cover the scattering angle θ=2θ_b from 20 degrees to 85 degrees. The exact area that is covered is shown in Fig.2.

Figure 2. Scattering angles collected by the various CSPAD in the X-ray diffraction variation. Y-axis is the scattering angle θ=2θB, the x-axis is the azimuthal angle, φ, with θ=90, φ=0 is scattering along the horizontal direction. Black / grey

XRTS Variation: CSPAD Configuration and Layout

This variation consists of the ns drive beams, VISAR, backward XRTS and Forward XRTS, and two out of four of the CSPADs from the XRD configuration. See Fig.3 for the layout. The coverage in θB is unchanged, but coverage in phi is reduced.

Figure 3. Geometry for F-XRTS standard configurations using two nanosecond, 527nm drive beams. Use of the Forward XRTS requires removal one pair of CSPADs. The horizontal angle of the F-XRTS is 25° and the vertical angle of the spectrometer can be changed from 25° to 55°, for a total angle from the x-ray axis of 33° to 59°.

Geometry and Optical Laser Parameters

The MEC ns glass laser will be delivered to the target as shown in Fig.1 and 3. Two beamlines, each containing two multiplexed laser arms. 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 planes relative to the target can be adjusted from best focus to a ~100 µm spot. Optionally, MEC provides phase plates can be used to generate circular focal spots of 100, 200, 300, 350 and 500 micron that can be manually exchanged during a standard configuration run.

Pulse length can vary between 5 ns and 20 ns. Flat top temporal profiles will be available by default; custom profiles can be provided, but must be requested at least 2 months in advance. The total laser energy is dependent on pulse length and profile. For 10ns square pulses the maximum beam energy on target will be 60 J. The arrival time of the optical laser with respect to the x-ray can be changed during the experiment, and is accurate to within 25ps RMS.

X-ray Parameters

X-ray beam operation with be in the standard SASE mode (no seeding) for the X-ray diffraction variation. For the XRTS variation, seeding can be requested. Photon energy and spot size are chosen by users.


The MEC line VISAR will be available as a diagnostic (See Fig.1 and 3). 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.

Figure 4. Optical layout 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.

Read more about VISAR on the VISAR Analysis page


The user provided targets will need to be mounted on target frames that are compatible with the MEC target holder.

Figure 5. 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, and the VISAR beam from the right. Dimensions are in inches. The spacing and size of the target holes may be changed, but all other dimension need to stay unchanged. (Download detailed drawing)

MEC Instrument Staff

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

Laser Contact

Eric Cunningham, Michael Greenberg

Parameter Table

To be considered for scheduling in this 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 configuration 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.