The authors would like to thank Matt Reinke and the Alcator C-Mod team for designing, building, and testing HIREXSR. This work was supported by DOE Contract Nos. DE-FC02-99ER54512 and DE-AC02-76CH03073.

<ol>
	<li>Reinke, M. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=X-ray+imaging+crystal+spectroscopy+for+use+in+plasma+transport+research.">X-ray imaging crystal spectroscopy for use in plasma transport research.</a> Rev. Sci. Instrum. 83 (11), 113504 (2012).</li><li>Hill, K. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+a+High+Resolution+X-Ray+Imaging+Crystal+Spectrometer+for+Measurement+of+Ion-Temperature+and+Rotation-Velocity+Profiles+in+Fusion+Energy+Research+Plasmas.">Development of a High Resolution X-Ray Imaging Crystal Spectrometer for Measurement of Ion-Temperature and Rotation-Velocity Profiles in Fusion Energy Research Plasmas.</a> Plasma Fusion Res. 2, 1067-1067 (2007).</li><li>Greenwald, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=20+years+of+research+on+the+Alcator+C-Mod+tokamak.">20 years of research on the Alcator C-Mod tokamak.</a> Phys. Plasmas. 21 (11), 110501 (2014).</li><li>Rice, J. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=X-ray+observations+of+medium+Z+H-+and+He-like+ions+with+satellites+from+C-Mod+tokamak+plasmas.">X-ray observations of medium Z H- and He-like ions with satellites from C-Mod tokamak plasmas.</a> J. Phys. B. 48 (14), 144013 (2015).</li><li>Ince-Cushman, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rotation+studies+in+fusion+plasmas+via+imaging+X-ray+crystal+spectroscopy.">Rotation studies in fusion plasmas via imaging X-ray crystal spectroscopy.</a> Rev. Sci. Instrum. 79, (2008).</li><li>Zachariasen, W. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Theory of X-Ray Diffraction in Crystals. , (2004).</li><li>Johann, H. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Die+Erzeugung+lichtstarker+R&#246;ntgenspektren+mit+Hilfe+von+Konkavkristallen.">Die Erzeugung lichtstarker R&#246;ntgenspektren mit Hilfe von Konkavkristallen.</a> Zeitschrift f&#252;r Physik. 69 (3-4), 185-206 (1931).</li><li>Wang, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calculation+of+the+Johann+error+for+spherically+bent+x-ray+imaging+crystal+spectrometers.">Calculation of the Johann error for spherically bent x-ray imaging crystal spectrometers.</a> Rev. Sci. Instrum. 81 (10), (2010).</li><li>Eikenberry, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PILATUS:+a+two-dimensional+X-ray+detector+for+macromolecular+crystallography.">PILATUS: a two-dimensional X-ray detector for macromolecular crystallography.</a> Nucl. Instr. Meth. Phys. Res. A. 501 (1), 260-266 (2003).</li><li>Howard, N. T., Greenwald, M., Rice, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+impurity+confinement+on+Alcator+C-Mod+using+a+multi-pulse+laser+blow-off+system.">Characterization of impurity confinement on Alcator C-Mod using a multi-pulse laser blow-off system.</a> Rev. Sci. Instrum. 82 (3), 1-6 (2011).</li><li>Rice, J. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non-local+heat+transport,+rotation+reversals+and+up/down+impurity+density+asymmetries+in+Alcator+C-Mod+ohmic+L-mode+plasmas.">Non-local heat transport, rotation reversals and up/down impurity density asymmetries in Alcator C-Mod ohmic L-mode plasmas.</a> Nucl. Fusion. 53, 033004 (2013).</li><li>Reinke, M. L., Podpaly, Y., Gao, C., Science, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Operation and Validation of The HIREXSR Analysis COde MIT-Plasma Science and Fusion Center Alcator C-Mod. , (2013).</li><li>Rosen, A. S., Reinke, M. L., Rice, J. E., Hubbard, A. E., Hughes, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Validation+of+x-ray+line+ratios+for+electron+temperature+determination+in+tokamak+plasmas.">Validation of x-ray line ratios for electron temperature determination in tokamak plasmas.</a> J. Phys. B. 47 (10), 105701 (2014).</li><li>Delgado-Aparicio, L. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In-situ+wavelength+calibration+and+temperature+control+for+the+C-Mod+high-resolution+X-ray+crystal+imaging+spectrometer.">In-situ wavelength calibration and temperature control for the C-Mod high-resolution X-ray crystal imaging spectrometer.</a> Bull. Am. Phys. Soc. 55, (2010).</li></ol>

The authors have nothing to disclose.

The data generated by this technique can be used in a wide variety of experimental studies. Ion temperature and toroidal velocity profiles can be used in a wide range of transport studies, including intrinsic self-generated plasma rotation and non-local perturbative effects. Measuring spectra of injected impurities through laser blow-off can also provide important information about the transport of impurities in the plasma, as was done in Howard et al. 201110. At this time, no other plasma diagnostic can provide time and spatially resolved ion profile data from the plasma core1, making X-ray imaging spectroscopy a novel method for probing plasma behavior.
The most critical step in the protocol is the identification of spectral lines in the wavelength region of interest. It is important that the lines being observed are strong to provide good counting statistics, and resolved from both each other and other satellite lines. The relative strength of these lines may change dramatically with different temperatures, and quantum processes like dielectric recombination can have measurable effects.
If the spectral lines are weak, it may be possible to improve their strength by introducing more of the measured impurity. If a different range of wavelengths is of interest, the detectors simply need to be moved along the Rowland circle, as long as the Bragg angle is still between greater than 45&#176; to avoid diverging rays and less than 80&#176; to prevent interference between incoming and reflected photons. The frame rate of the detectors can also be changed to be faster or slower. The detector does not count photons during the readout time, so the fraction of captured photons increases with longer frames, allowing for better statistics in the obtained data.
The spectrometer-reactor interface should be leak tight to 10-9 std cc/sec and capable of sustaining a differential pressure of 1 atm to either side. The beryllium window is the ideal choice for this interface due to its high strength and good X-ray transmission coefficient, which is around 40% for 3.1 keV X-rays. The helium atmosphere maintained within the housing of HIREXSR to reduce X-ray attenuation to around ~1% of incoming rays. The constant pumping ensures that no air is leaking into the housing and contaminating the local atmosphere. These systems should be double-checked for leaks to ensure X-rays make it to the detectors.
A vacuum chamber would be the ideal housing for the spectrometer. However, such a chamber is very expensive and impractical to maintain for such a large spectrometer. Future improvements could focus on using new techniques or recent innovations to create a spectrometer-reactor interface and local atmosphere that minimizes X-ray absorption, or attempt to make current or similar designs cheaper and more viable.
The technique is limited by its temperature requirements, as the plasma needs to be hot enough to ionize the impurity of interest, but cool enough to allow for recombination. In addition, H-like and He-like ionization states are preferred since their spectra are much simpler and easier to characterize. This means it is difficult to get data from the cooler edge of the plasma, and it may require physical reconfiguration of the machine to get useful data from plasmas across the temperature range of the tokamak. Additionally, the technique is somewhat limited by the necessity of running calibration shots due to the thermal expansion of the spectrometer crystal. This could be improved in the future with better temperature controls on the crystal, or other novel calibration techniques.

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line intensity ratios. By using a Johann spectrometer viewing the plasma off-axis, it is possible to construct profiles of plasma parameters such as density, temperature, and velocity inside the plasma with good spatial and time resolution1,2. This manuscript presents the operation of the High Resolution X-ray Crystal Imaging Spectrometer with Spatial Resolution (HIREXSR), a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma.
HIREXSR is deployed on Alcator C-Mod, a tokamak fusion device with a major and minor radius of 0.67 m and 0.22 m respectively. It typically operates with deuterium plasmas lasting ~2 sec with average densities between 0.2-8.0 x 1020 m-3 and central electron temperatures between 1-9 keV3. Under these conditions, medium to high Z impurity elements become highly ionized and radiate in the X-ray range, which HIREXSR measures. Benchmarking atomic code modeling of X-ray spectra obtained from well-diagnosed laboratory plasmas is important to justify use of such spectra to determine plasma parameters when other independent diagnostics are not available4.
Every spectrometer is built for its desired use. Accordingly, a general description about the machine and its related concepts is necessary to fully comprehend these powerful tools5. Bragg reflection occurs when a photon reflects off adjacent layers of a crystal and travels a distance that is a multiple of its wavelength. Figure 1 depicts this phenomenon. This condition is expressed by the equation n&#955; = 2d sin &#952;b, where n is the order of reflection,&#160;&#955; is the wavelength of the photon, d is the separation between adjacent layers of the crystal and &#952;b is the Bragg angle. A one to one correspondence between &#955; and &#952;b indicates that all photons at a specific point of the detector plane travel with the same wavelength. In practice, however, absorption and precision limitations manifest as a deviation from the Bragg angle. This results in only a small range of angles that produce significant constructive interference, represented by a rocking curve6. Figure 2 is an example curve for a calcite crystal.
HIREXSR is a Johann spectrometer with a spherically bent crystal7. Before describing this kind of device, a discussion of a simpler, circular spectrometer is appropriate. This set up consists of a bent crystal that reflects incoming photons at their respective Bragg angles towards an array of single X-ray photon counting pixel detectors. The crystal and the detector lay tangent to the Rowland circle, as displayed in Figure 3. The diameter of the Rowland circle is equal to the radius of curvature of the crystal. All rays from a given point on the circumference to any point on the crystal have the same incident angle with respect to the crystal itself.
In the case of HIREXSR, a spherically bent crystal permits spatial resolution in the meridional plane, illustrated in Figure 4. The meridional focus fm is defined as: fm = Rc sin &#952;b, where Rc is the radius of curvature of the crystal. The sagittal focus fs is defined as: fs = &#8722;fm/cos 2&#952;b. The spatial resolution of the spectrometer &#916;x is given by: <img alt="Equation" src="/files/ftp_upload/54408/54408eq_DELTA_x.jpg" />, where Lcp is the distance between the crystal and the plasma, and d is the height of the crystal. Because the 2-dimensional spacing of the crystal layers is discrete, this must be taken into consideration when choosing a material. Since the detector surfaces are planar, they can only be tangent to the Rowland circle at one point, which consequently gives rise to error since the detected rays are not landing precisely on their corresponding points on the Rowland circle. Physically, this misalignment manifests as a &#34;smearing&#34; of photons of specific energy on the detector. This Johann error is defined as <img alt="Equation" src="/files/ftp_upload/54408/54408eq_delta_xj.jpg" />, where l is the width of the crystal. If the detector pixel width &#948;xp is much larger than the Johann error, then the spectral resolution is independent of it. If they are of comparable size, then the total error can be approximated by <img alt="Equation" src="/files/ftp_upload/54408/54408eq_delta_x_2.jpg" />. The resolving power of the crystal spectrometer is given by: <img alt="Equation" src="/files/ftp_upload/54408/54408eq_lambda0.jpg" />, where <img alt="Equation" src="/files/ftp_upload/54408/54408eq_delta_theta.jpg" />. Instead of placing the detector tangent to a point on the Rowland circle however, in HIREXSR the detector is angled slightly to sacrifice accuracy for spectral range, as shown in Figure 5. This error analysis has been experimentally verified and conforms to expectation8.
There are two crucial parameters to consider when designing a Johann spectrometer. First, the imaging range determines what the spectrometer will be observing. For studying plasmas, it is highly desirable to view its entire cross section in order to distinguish between line shifts caused by poloidal and toroidal rotation. HIREXSR is mounted such that it can view the whole plasma, and is tilted slightly off-axis by &#8764;8&#176; (illustrated in Figure 6) to allow for accurate toroidal measurements. Second, time resolution regulates the minimum time between events that the spectrometer can record. For Alcator C-Mod, desirable values are below 20 msec, shorter than the energy and particle confinement times. The X-ray counting pixel detectors that HIREXSR uses can support a time resolution of 6 to 20 msec or larger9. Table 1 summarizes all of the module specifications.
For perturbative plasma studies, the laser blow-off system on Alcator C-Mod is used to deliver multiple ablations with precise timing10. The laser is a Nd:YAG (neodymium-doped yttrium aluminum garnet) operating at up to 10 Hz. The laser is incident on a remote-controlled optical train as shown in Figure 7 that focuses and steers the beam to the desired location on the slide. Spot sizes of the laser need to be controlled so the injection doesn&#39;t disrupt the plasma. A long focal length (1,146 mm) converging lens is translated along the optical axis via a remote controlled linear stage to allow ablated spot sizes to vary from &#8764;0.5 to 7 mm. Fast beam steering is achieved via a 2D piezoelectric mirror. This piezoelectric system is mounted to an RS232 driven mirror mount capable. In addition to the Nd:YAG laser, a 633 nm diode laser is used to indicate the location of the main (infrared) beam. The beams are made to be collinear through the first mirror.

<table><tbody><tr><td>PILATUS 100k Detector System</td><td>DECTRIS</td><td>100k</td><td>Superseded by newer PILATUS3 detectors</td></tr><tr><td>Bragg Crystals</td><td>Kurchaov Institute</td><td>Custom Part</td><td></td></tr><tr><td>CaF&lt;sub&gt;2&lt;/sub&gt; Slides</td><td>LeBow</td><td>Custom Part</td><td></td></tr><tr><td>High Purity Argon</td><td>Airgas</td><td>AR HP300</td><td>Any high purity argon should work</td></tr><tr><td>Be window</td><td>Brush Wellman Electrofusion Products / Motion Hightech</td><td>Custom part</td><td></td></tr></tbody></table>

applying x-ray imaging crystal spectroscopy for use as a high temperature plasma diagnostic

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line intensity ratios. By using a Johann spectrometer viewing the plasma, it is possible to construct profiles of plasma parameters such as density, temperature, and velocity with good spatial and time resolution. However, benchmarking atomic code modeling of X-ray spectra obtained from well-diagnosed laboratory plasmas is important to justify use of such spectra to determine plasma parameters when other independent diagnostics are not available. This manuscript presents the operation of the High Resolution X-ray Crystal Imaging Spectrometer with Spatial Resolution (HIREXSR), a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma. In addition, this manuscript covers a laser blow-off system that can introduce such ions to the plasma with precise timing to allow for perturbative studies of transport in the plasma.

A representative data sample from the pixel detector for one time bin for the He-like argon spectrum is shown in Figure 17. The spectral lines, bent into an elliptical shape by the spherical crystal, are clearly visible. The top detector has a broken detector panel, and there are some dead pixels scattered across all of the detectors. Data from the broken detector panel should be ignored. Slices from the detector showing the measured spectra and results of the spectral fitting done by THACO over a single chord are shown in Figure 18 and Figure 19. The resulting line-integrated profile data is shown in Figure 20.
An example of an inverted plasma temperature and toroidal velocity profile created by THACO from the He-like argon lines can be seen in Figure 21. The measured ion temperatures from HIREXSR agree with independent diagnostics in other measurement channels1. Using argon, a recycling impurity, allows the ion profiles to be measured over the entire evolution of the plasma. This is critical for transport studies such as in Rice et al. 201311, which study plasma evolution over time scales longer than the impurity confinement time. If the detectors were instead positioned to measure a transient impurity, such as calcium, HIREXSR would provide transient profile data. See Howard et al. 201110 for such a study.
<img alt="Figure 1" src="/files/ftp_upload/54408/54408fig1.jpg" /> 
Figure 1. Illustration of Bragg Reflection. Incoming rays will reflect and constructively interfere based on their angle of incidence and wavelength. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54408/54408fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/54408/54408fig2.jpg" /> 
Figure 2. A Rocking Curve for a Calcite Crystal. The black curve is the best fit to the observed data, while the dotted line is the idealized case where there is no absorption.
<img alt="Figure 3" src="/files/ftp_upload/54408/54408fig3.jpg" /> 
Figure 3. A Johann Spectrometer with a Bent Crystal. Incoming rays incident on the same location on the circumference of the circle have the same angle of incidence on the crystal and end up on the same location on the detector. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54408/54408fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/54408/54408fig4.jpg" /> 
Figure 4. A Johann Spectrometer with a Spherically Bent Crystal. The spherical bending of the crystal allows for spatial resolution along the meridional plane, so spectra are captured along multiple line-averaged chords through the plasma. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54408/54408fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/54408/54408fig5.jpg" /> 
Figure 5. The detector-crystal alignment used in HIREXSR. In HIREXSR, the detector is angled slightly from the standard arrangement to allow for a larger range of wavelengths to be measured. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54408/54408fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/54408/54408fig6.jpg" /> 
Figure 6. Top-down CAD View of HIREXSR. This CAD drawing shows the relative positions of the two detector arrays and the spectrometer crystal to the tokamak vacuum vessel, which contains the plasma. The sightline of the spectrometer is angled slightly off-axis to allow toroidal rotation to be measured through the Doppler shift.
<img alt="Figure 7" src="/files/ftp_upload/54408/54408fig7.jpg" /> 
Figure 7. Layout of Optical System. This figure shows the layout of the optical system for the laser blow-off system from Howard et al.10.
<img alt="Figure 8" src="/files/ftp_upload/54408/54408fig8.jpg" /> 
Figure 8. Fractional Charge State Abundance for Various Noble Gases. This plot shows the fractional charge state abundances for various noble gases in coronal equilibrium. Fully stripped states are in shown with solid lines, H-like with dashed, He-like with dash-dot and Ne-like with dash-dot-dot. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54408/54408fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" src="/files/ftp_upload/54408/54408fig9.jpg" /> 
Figure 9. Ca18+ k/w Brightness Ratios. The measured chord-averaged brightness ratio of the dielectronic satellite k to the resonance line w in He-like Ca18+ (red dots) compared to the theoretical curve (green line).
<img alt="Figure 10" src="/files/ftp_upload/54408/54408fig10.jpg" /> 
Figure 10. Measured He-like Ca18+ Spectrum. The measured He-like Ca18+ (w, x, y, and z) spectrum with satellites (most prominent &#39;4&#39;, &#39;3&#39;, q, r and k) is shown by the dots. A synthetic spectrum calculated with collisional-radiative modeling indicated by the solid line.
<img alt="Figure 11" src="/files/ftp_upload/54408/54408fig11.jpg" /> 
Figure 11. Measured H-like Ar17+ Spectrum. The measured spectrum of the Ar17+ Ly&#945; doublet and nearby satellites (green dots), with synthetic spectrum (red line). Note the overlap between the Mo32+ line and the Ly&#945;2 line.
<img alt="Figure 12" src="/files/ftp_upload/54408/54408fig12.jpg" /> 
Figure 12. Measured He-like Ar16+ Spectrum. Measured X-ray spectra in the vicinity of the Ar16+ w resonance lines. Note the log scale.
<img alt="Figure 13" src="/files/ftp_upload/54408/54408fig13.jpg" /> 
Figure 13. Internal View showing Crystals and Be Window. The beryllium window (a) and crystals (b) are displayed as viewed from within the housing. The Be window is labeled with green, the spherical crystal with red, and the rectangular crystal with purple.
<img alt="Figure 14" src="/files/ftp_upload/54408/54408fig14.jpg" /> 
Figure 14. Internal View Showing Detectors. The three detector array for He-like spectra is shown on the left in (a), and for H-like spectra is shown on the right in (b). The three detectors used for He-like spectra allow for the capture of spectra from the core and edge of the plasma simultaneously.
<img alt="Figure 15" src="/files/ftp_upload/54408/54408fig15.jpg" /> 
Figure 15. Side View of HIREXSR. This diagram illustrates the relative distances of the detectors, crystals, and the tokamak. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54408/54408fig15large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 16" src="/files/ftp_upload/54408/54408fig16.jpg" /> 
Figure 16. Example View of dwscope. This figure shows a screenshot of an instance of dwscope. Line-integrated data from HIREXSR is highlighted by the red box. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54408/54408fig16large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 17" src="/files/ftp_upload/54408/54408fig17.jpg" /> 
Figure 17. Example Detector Output. This figure shows example raw data collected by the detectors over a single time bin for He-like (top, middle) and H-like (bottom) argon spectra. The y-axis corresponds to wavelength, and the x-axis to meridional angle. The spectral lines, bent into an elliptical shape by the spherical crystal, are clearly visible. The top (1x gain) and bottom (2x gain) spectra are from the core, and the middle spectrum (8x gain) is from the edge. The dotted green lines separate different regions for the spectral fitting code. The top detector has a broken detector panel, and there are some dead pixels scattered across all of the detectors. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54408/54408fig17large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 18" src="/files/ftp_upload/54408/54408fig18.jpg" /> 
Figure 18. Example Collected H-like Spectra. Measured line-averaged brightness over the argon H-like spectrum for a single chord and time bin (top, white), corresponding to a single column of pixels in the bottom detector in Figure 17. The removed background is shown in green, and a multi-Gaussian fit is shown in cyan. The total fit composite spectrum is shown by the red line, and the residuals are in the bottom figure. Note the agreement with Figure 11.
<img alt="Figure 19" src="/files/ftp_upload/54408/54408fig19.jpg" /> 
Figure 19. Example Collected He-like Spectra. Measured line-averaged brightness over the argon He-like spectrum for a single chord and time bin (top, white), corresponding to a single column of pixels in the top detector in Figure 17. The removed background is shown in green, and a multi-Gaussian fit is shown in cyan. The total fit composite spectrum is shown by the red line, and the residuals are in the bottom figure.
<img alt="Figure 20" src="/files/ftp_upload/54408/54408fig20.jpg" /> 
Figure 20. Example Line-Integrated Profile. This figure shows an example of the line-integrated data generated by THACO from the results of the line fitting. It needs to be tomographically inverted to return the full profile.
<img alt="Figure 21" src="/files/ftp_upload/54408/54408fig21.jpg" /> 
Figure 21. Example Inverted Plasma Profiles. This figure shows example data that has been inverted by THACO to produce temperature and toroidal rotation profiles. HIREXSR allows for both spatial resolution (along the y-axis) and time resolution (along the x-axis). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54408/54408fig21large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Sensor Type</td>
			<td>Reverse biased silicon diode array</td>
		</tr>
		<tr>
			<td>Sensor Thickness</td>
			<td>320 &#956;m</td>
		</tr>
		<tr>
			<td>Pixel Size</td>
			<td>172 &#956;m &#215; 172 &#956;m</td>
		</tr>
		<tr>
			<td>Format</td>
			<td>487 &#215; 195 = 94,965 pixels</td>
		</tr>
		<tr>
			<td>Area</td>
			<td>83.8 mm &#215; 33.5 mm</td>
		</tr>
		<tr>
			<td>Dynamic Range</td>
			<td>20 bits (1:1,048,576)</td>
		</tr>
		<tr>
			<td>Count Rate Per Pixel</td>
			<td>&#62; 2 &#215; 106 X-rays/sec</td>
		</tr>
		<tr>
			<td>Energy Range</td>
			<td>3-30 keV</td>
		</tr>
		<tr>
			<td>Energy Resolution</td>
			<td>~500 keV</td>
		</tr>
		<tr>
			<td>Adjustable Threshold Range</td>
			<td>2-20 keV</td>
		</tr>
		<tr>
			<td>Readout Time</td>
			<td>2.7 msec</td>
		</tr>
		<tr>
			<td>Maximum Frame Rate</td>
			<td>300 Hz</td>
		</tr>
		<tr>
			<td>Point Spread Function</td>
			<td>1 pixel</td>
		</tr>
		<tr>
			<td>External Trigger/gate</td>
			<td>5 V TTL</td>
		</tr>
		<tr>
			<td>Power Consumption</td>
			<td>15 W</td>
		</tr>
		<tr>
			<td>Dimensions</td>
			<td>275 &#215; 146 &#215; 85 mm</td>
		</tr>
		<tr>
			<td>Weight</td>
			<td>1 kg</td>
		</tr>
	</tbody>
</table>
Table 1. Detector Specifications. This table lists detector specifications relevant to the design of HIREXSR.

Watch this Scientific Journal Video about Applying X-ray Imaging Crystal Spectroscopy for Use as a High Temperature Plasma Diagnostic at JoVE.com

Applying X-ray Imaging Crystal Spectroscopy for Use as a High Temperature Plasma Diagnostic

X-ray spectra provide a wealth of information on high temperature plasmas. This manuscript presents the operation of a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma.

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line ...

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Nanyang Technological University

Research

JoVE Journal

Engineering

11.3K Views.  Massachusetts Institute of Technology.  X-ray spectra leveren een schat aan informatie over de hoge temperatuur plasma's. Dit manuscript presenteert de werking van een hoge golflengte resolutie ruimtelijk imaging X-ray spectrometer gebruikt om waterstof en helium-achtige ionen van medium atoomnummer elementen in een tokamak plasma te geven. 

Video: Applying X-ray Imaging Crystal Spectroscopy for Use as a High Temperature Plasma Diagnostic

Investigation of Early Plasma Evolution Induced by Ultrashort Laser Pulses

Early plasma is generated owing to high intensity laser irradiation of target and the subsequent target material ionization. Its dynamics plays a significant role in laser-material interaction, especially in the air environment1-11.
Early plasma evolution has been captured through pump-probe shadowgraphy1-3 and interferometry1,4-7. However, the studied time frames and applied laser parameter ranges are limited. For example, direct examinations of plasma front locations and electron number densities within a delay time of 100 picosecond (ps) with respect to the laser pulse peak are still very few, especially for the ultrashort pulse of a duration around 100 femtosecond (fs) and a low power density around 1014 W/cm2. Early plasma generated under these conditions has only been captured recently with high temporal and spatial resolutions12. The detailed setup strategy and procedures of this high precision measurement will be illustrated in this paper. The rationale of the measurement is optical pump-probe shadowgraphy: one ultrashort laser pulse is split to a pump pulse and a probe pulse, while the delay time between them can be adjusted by changing their beam path lengths. The pump pulse ablates the target and generates the early plasma, and the probe pulse propagates through the plasma region and detects the non-uniformity of electron number density. In addition, animations are generated using the calculated results from the simulation model of Ref. 12 to illustrate the plasma formation and evolution with a very high resolution (0.04 ~ 1 ps).
Both the experimental method and the simulation method can be applied to a broad range of time frames and laser parameters. These methods can be used to examine the early plasma generated not only from metals, but also from semiconductors and insulators.

An experimental method to examine the early plasma evolution induced by ultrashort laser pulses is described. Using this method, high quality images of early plasma are obtained with high temporal and spatial resolutions. A novel integrated atomistic model is used to simulate and explain the mechanisms of early plasma.

Early plasma is generated owing to high intensity laser irradiation of target and the subsequent target material ionization. Its dynamics plays a ...

Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures

The physical properties of a material are defined by its electronic structure. Electrons in solids are characterized by energy (&omega;) and momentum (k) and the probability to find them in a particular state with given &omega; and k is described by the spectral function A(k, &omega;). This function can be directly measured in an experiment based on the well-known photoelectric effect, for the explanation of which Albert Einstein received the Nobel Prize back in 1921. In the photoelectric effect the light shone on a surface ejects electrons from the material. According to Einstein, energy conservation allows one to determine the energy of an electron inside the sample, provided the energy of the light photon and kinetic energy of the outgoing photoelectron are known. Momentum conservation makes it also possible to estimate k relating it to the momentum of the photoelectron by measuring the angle at which the photoelectron left the surface. The modern version of this technique is called Angle-Resolved Photoemission Spectroscopy (ARPES) and exploits both conservation laws in order to determine the electronic structure, i.e. energy and momentum of electrons inside the solid. In order to resolve the details crucial for understanding the topical problems of condensed matter physics, three quantities need to be minimized: uncertainty* in photon energy, uncertainty in kinetic energy of photoelectrons and temperature of the sample.
In our approach we combine three recent achievements in the field of synchrotron radiation, surface science and cryogenics. We use synchrotron radiation with tunable photon energy contributing an uncertainty of the order of 1 meV, an electron energy analyzer which detects the kinetic energies with a precision of the order of 1 meV and a He3 cryostat which allows us to keep the temperature of the sample below 1 K. We discuss the exemplary results obtained on single crystals of Sr2RuO4 and some other materials. The electronic structure of this material can be determined with an unprecedented clarity.

The overall goal of this method is to determine the low-energy electronic structure of solids at ultra-low temperatures using Angle-Resolved Photoemission Spectroscopy with synchrotron radiation.

The physical properties of a material are defined by its  electronic structure. Electrons in solids are characterized by energy (&omega;)  and momentum ...

Synthesis and Microdiffraction at Extreme Pressures and Temperatures

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary interiors, design materials with novel properties, understand the mechanical behavior of materials exposed to very high stresses as in explosions or impacts. Synthesis and structural analysis of materials at extreme conditions of pressure and temperature entails remarkable technical challenges. In the laser heated diamond anvil cell (LH-DAC), very high pressure is generated between the tips of two opposing diamond anvils forced against each other; focused infrared laser beams, shined through the diamonds, allow to reach very high temperatures on samples absorbing the laser radiation. When the LH-DAC is installed in a synchrotron beamline that provides extremely brilliant x-ray radiation, the structure of materials under extreme conditions can be probed in situ. LH-DAC samples, although very small, can show highly variable grain size, phase and chemical composition. In order to obtain the high resolution structural analysis and the most comprehensive characterization of a sample, we collect diffraction data in 2D grids and combine powder, single crystal and multigrain diffraction techniques. Representative results obtained in the synthesis of a new iron oxide, Fe4O5 1 will be shown.

The laser heated diamond anvil cell combined with synchrotron micro-diffraction techniques allows researchers to explore the nature and properties of new phases of matter at extreme pressure and temperature (PT) conditions. Heterogeneous samples can be characterized in situ under high pressure by 2D mapping and combined powder, single-crystal and multigrain diffraction approaches.

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary ...

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a stable and continuous operation of the plasma is possible and the plasma torch can be used for many different applications. On one hand, the hot (3,600 K gas temperature) plasma can be used for chemical processes and on the other hand the cold afterglow (temperatures down to almost RT) can be applied for surface processes. For example chemical syntheses are interesting volume processes. Here the microwave plasma torch can be used for the decomposition of waste gases which are harmful and contribute to the global warming but are needed as etching gases in growing industry sectors like the semiconductor branch. Another application is the dissociation of CO2. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 to CO and O2. The CO can be further processed to gaseous or liquid higher hydrocarbons thereby providing chemical storage of the energy, synthetic fuels or platform chemicals for the chemical industry. Applications of the afterglow of the plasma torch are the treatment of surfaces to increase the adhesion of lacquer, glue or paint, and the sterilization or decontamination of different kind of surfaces. The movie will explain how to ignite the plasma solely by microwave power without any additional igniters, e.g., electric sparks. The microwave plasma torch is based on a combination of two resonators &#8212; a coaxial one which provides the ignition of the plasma and a cylindrical one which guarantees a continuous and stable operation of the plasma after ignition. The plasma can be operated in a long microwave transparent tube for volume processes or shaped by orifices for surface treatment purposes.

This movie shows how an atmospheric plasma torch can be ignited by microwaves with no additional igniters and provides a stable and continuous plasma operation suitable for plenty of applications.

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a ...

Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron

Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution for future high-speed reentry missions. But despite the advancements made since Apollo, heat flux prediction remains an imperfect science and engineers resort to safety factors to determine the TPS thickness. This goes at the expense of embarked payload, hampering, for example, sample return missions. 
Ground testing in plasma wind-tunnels is currently the only affordable possibility for both material qualification and validation of material response codes. The subsonic 1.2MW Inductively Coupled Plasmatron facility at the von Karman Institute for Fluid Dynamics is able to reproduce a wide range of reentry environments. This protocol describes a procedure for the study of the gas/surface interaction on ablative materials in high enthalpy flows and presents sample results of a non-pyrolyzing, ablating carbon fiber precursor. With this publication, the authors envisage the definition of a standard procedure, facilitating comparison with other laboratories and contributing to ongoing efforts to improve heat shield reliability and reduce design uncertainties.
The described core techniques are non-intrusive methods to track the material recession with a high-speed camera along with the chemistry in the reactive boundary layer, probed by emission spectroscopy. Although optical emission spectroscopy is limited to line-of-sight measurements and is further constrained to electronically excited atoms and molecules, its simplicity and broad applicability still make it the technique of choice for analysis of the reactive boundary layer. Recession of the ablating sample further requires that the distance of the measurement location with respect to the surface is known at all times during the experiment. Calibration of the optical system of the applied three spectrometers allowed quantitative comparison. At the fiber scale, results from a post-test microscopy analysis are presented.

Development of new ablative materials and their numerical modeling requires extensive experimental investigation. This protocol describes procedures for material response characterization in plasma flows with the core techniques being non-intrusive methods to track the material recession along with the chemistry in the reactive boundary layer by emission spectroscopy.

Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution ...

High-resolution Thermal Micro-imaging Using Europium Chelate Luminescent Coatings

Micro-electronic devices often undergo significant self-heating when biased to their typical operating conditions. This paper describes a convenient optical micro-imaging technique which can be used to map and quantify such behavior. Europium thenoyltrifluoroacetonate (EuTFC) has a 612 nm luminescence line whose activation efficiency drops strongly with increasing temperature, due to T-dependent interactions between the Eu3+ ion and the organic chelating compound. This material may be readily coated on to a sample surface by thermal sublimation in vacuum. When the coating is excited with ultraviolet light (337 nm) an optical micro-image of the 612 nm luminescent response can be converted directly into a map of the sample surface temperature. This technique offers spatial resolution limited only by the microscope optics (about 1 micron) and time resolution limited by the speed of the camera employed. It offers the additional advantages of only requiring comparatively simple and non-specialized equipment, and giving a quantitative probe of sample temperature.

Europium thenoyltrifluoroacetonate (EuTFC) has an optical luminescence line at 612 nm, whose activation efficiency decreases strongly with temperature. If a sample coated with a thin film of this material is micro-imaged, the 612 nm luminescent response intensity may be converted into a direct map of sample surface temperature.

Micro-electronic devices often undergo significant self-heating when biased to their typical operating conditions. This paper describes a convenient ...

High Pressure Single Crystal Diffraction at PX^2

In this report we describe detailed procedures for carrying out single crystal X-ray diffraction experiments with a diamond anvil cell (DAC) at the GSECARS 13-BM-C beamline at the Advanced Photon Source. The DAC program at 13-BM-C is part of the Partnership for Extreme Xtallography (PX^2) project. BX-90 type DACs with conical-type diamond anvils and backing plates are recommended for these experiments. The sample chamber should be loaded with noble gas to maintain a hydrostatic pressure environment. The sample is aligned to the rotation center of the diffraction goniometer. The MARCCD area detector is calibrated with a powder diffraction pattern from LaB6. The sample diffraction peaks are analyzed with the ATREX software program, and are then indexed with the RSV software program. RSV is used to refine the UB matrix of the single crystal, and with this information and the peak prediction function, more diffraction peaks can be located. Representative single crystal diffraction data from an omphacite (Ca0.51Na0.48)(Mg0.44Al0.44Fe2+0.14Fe3+0.02)Si2O6 sample were collected. Analysis of the data gave a monoclinic lattice with P2/n space group at 0.35 GPa, and the lattice parameters were found to be: a = 9.496 &#177;0.006 &#197;, b = 8.761 &#177;0.004 &#197;, c = 5.248 &#177;0.001 &#197;, &#946; = 105.06 &#177;0.03&#186;, &#945; = &#947; = 90&#186;.

In this report, we describe detailed procedures for carrying out single crystal X-ray diffraction experiments with a diamond anvil cell at the GSECARS 13-BM-C beamline at the Advanced Photon Source. ATREX and RSV programs are used to analyze the data.

In this report we describe detailed procedures for carrying out single crystal X-ray diffraction experiments with a diamond anvil cell (DAC) at the ...

Chemistry

Non-equilibrium Microwave Plasma for Efficient High Temperature Chemistry

A flowing microwave plasma based methodology for converting electric energy into internal and/or translational modes of stable molecules with the purpose of efficiently driving non-equilibrium chemistry is discussed. The advantage of a flowing plasma reactor is that continuous chemical processes can be driven with the flexibility of startup times in the seconds timescale. The plasma approach is generically suitable for conversion/activation of stable molecules such as CO2, N2 and CH4. Here the reduction of CO2 to CO is used as a model system: the complementary diagnostics illustrate how a baseline thermodynamic equilibrium conversion can be exceeded by the intrinsic non-equilibrium from high vibrational excitation. Laser (Rayleigh) scattering is used to measure the reactor temperature and Fourier Transform Infrared Spectroscopy (FTIR) to characterize in situ internal (vibrational) excitation as well as the effluent composition to monitor conversion and selectivity.

This article describes a flowing microwave reactor that is used to drive efficient non-equilibrium chemistry for the application of conversion/activation of stable molecules such as CO2, N2 and CH4. The goal of the procedure described here is to measure the in situ gas temperature and gas conversion.

A flowing microwave plasma based methodology for converting electric energy into internal and/or translational modes of stable molecules with the purpose ...

An Atmospheric Pressure Plasma Setup to Investigate the Reactive Species Formation

Non-thermal atmospheric pressure (&#39;cold&#39;) plasmas have received increased attention in recent years due to their significant biomedical potential. The reactions of cold plasma with the surrounding atmosphere yield a variety of reactive species, which can define its effectiveness. While efficient development of cold plasma therapy requires kinetic models, model benchmarking needs empirical data. Experimental studies of the source of reactive species detected in aqueous solutions exposed to plasma are still scarce. Biomedical plasma is often operated with He or Ar feed gas, and a specific interest lies in investigation of the reactive species generated by plasma with various gas admixtures (O2, N2, air, H2O vapor, etc.) Such investigations are very complex due to difficulties in controlling the ambient atmosphere in contact with the plasma effluent. In this work, we addressed common issues of &#39;high&#39; voltage kHz frequency driven plasma jet experimental studies. A reactor was developed allowing the exclusion of ambient atmosphere from the plasma-liquid system. The system thus comprised the feed gas with admixtures and the components of the liquid sample. This controlled atmosphere allowed the investigation of the source of the reactive oxygen species induced in aqueous solutions by He-water vapor plasma. The use of isotopically labelled water allowed distinguishing between the species originating in the gas phase and those formed in the liquid. The plasma equipment was contained inside a Faraday cage to eliminate possible influence of any external field. The setup is versatile and can aid in further understanding the cold plasma-liquid interactions chemistry.

An experimental setup was created for the helium-operated kHz frequency plasma jet. The setup includes a cage for the plasma power supply and jet and an in-house built reactor to monitor plasma-induced reactive species without the interference of the ambient atmosphere.

Non-thermal atmospheric pressure (&#39;cold&#39;) plasmas have received increased attention in recent years due to their significant biomedical potential. ...

Spark Plasma Sintering Apparatus Used for the Formation of Strontium Titanate Bicrystals

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with one twist grain boundary. This apparatus utilizes high uniaxial pressure and a pulsed direct current for rapid consolidation of material. Diffusion bonding of strontium titanate bicrystals without fracture, in a spark plasma sintering apparatus, is possible at high pressures due to the unusual temperature dependent plasticity behavior of strontium titanate. We demonstrate a method for the successful formation of bicrystals at accelerated time scales and lower temperatures in a spark plasma sintering apparatus compared to bicrystals formed by conventional diffusion bonding parameters. Bond quality was verified by scanning electron microscopy. A clean and atomically abrupt interface containing no secondary phases was observed using transmission electron microscopy techniques. Local changes in bonding across the boundary was characterized by simultaneous scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy.

A viable technique for the formation of strontium titanate bicrystals at high pressure and fast heating rate via the spark plasma sintering apparatus is developed.

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with ...

Applying X-ray Imaging Crystal Spectroscopy for Use as a High Temperature Plasma Diagnostic

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