Quantum efficiency (QE), intrinsic emittance, and robustness are the three most important figures of merit for photocathodes, the first two determine the ultimate achievable brightness of an electron beam, and the third one directly correlates with the complications of a beamline design. Nitrogen-incorporated ultrananocrystalline diamond [(N)UNCD] materials are promising candidates for photocathode applications due to their remarkable electron emission performance as well as the moderate vacuum requirement. Two (N)UNCD photocathodes have been characterized in a realistic RF gun environment with the nicely balanced performance of all three figures of merit. The QE of the first (N)UNCD cathode (stored in air for two years before the test) was found to be 3.8 × 10−4 using a 262 nm UV laser and a cathode surface field of 30 MV/m. It was found that the QE of the second (N)UNCD sample (grown days before the test) was nearly the same and, therefore, demonstrates the exceptional environmental tolerance of the material. The intrinsic emittance of (N)UNCD was measured to be 1.00 μm/mm.

The rapidly developing rf photoinjector, capable of producing electron beams of unprecedented brightness, is an enabling tool for many high-impact scientific machines, such as free electron lasers,1 instruments for ultrafast electron diffraction and microscopy,2,3 and Thomson scattering x-ray sources.4 The photocathode is a key component of photoinjectors, as its quantum efficiency (QE) and intrinsic emittance set the ultimate achievable electron beam brightness in the accelerator. The robustness (vacuum tolerance) of the cathode determines the level of complication of the injector design as well as the cathode preparation/transportation system.5–7 Currently, most cathode R&D focuses on metal and semiconductor materials. Popular metal cathodes such as Cu and Nb have relaxed the vacuum requirement of 10−9–10−8 Torr but suffer from a low QE of 10−7–10−5 at UV wavelengths.8–10 Mg is an exception, and a high QE of 10−3 can be achieved.11 However, extra in situ surface cleaning8,11,12 or gun conditioning13 is typically required for metal cathodes due to the formation of oxide layers with air exposure. Semiconductor cathodes such as negative electron affinity (NEA) GaAs and (multi-) alkali antimonide have a high QE of 10−2–10−1 in the visible range but can only be prepared/transported/operated in vacuum better than 10−10 Torr.14–16 Studies are being done on the use of cathode surface coatings/encapsulations17 to prevent the contamination of the vacuum-sensitive semiconductor photocathodes. At room temperature, the current state-of-the-art intrinsic emittance of photocathodes ranges from 0.4–1.2 μm/mm.5–7 

Nitrogen-incorporated ultrananocrystalline diamond [(N)UNCD] is an emerging material that demonstrates balanced performance of QE, intrinsic emittance, and robustness.18,19 It is synthesized by using the chemical vapor deposition (CVD) method and consists of nanostructured sp2- and sp3-bonded carbons. Emitted electrons preferentially originate from the sp2-bonded graphitic grain boundaries.20,21 For UNCD-based materials, the high density (1013/cm2) sp2 grain boundaries22 localized in between the sub-nm-scale (<10 nm) diamond grains provide a higher electron emission probability compared to nanocrystalline diamond (NCD) and microcrystalline diamond (MCD), which have larger diamond grains and relatively low grain boundary densities. Nitrogen incorporation in the plasma during CVD growth of (N)UNCD mostly resides at the grain boundaries with mixed C–N bonding introducing states within the bandgap, which greatly helps for the electrical conduction through the hopping mechanism.23–25 It has been reported that (N)UNCD can be tuned after synthesis via surface hydrogenation treatment to induce negative electron affinity (NEA) through the surface C–H dipole formation.26,27 Using surface termination to significantly enhance the photocathode QE is a possibility that merits further investigation. The intrinsic emittance has recently been measured to be 0.75 ± 0.29 μm/mm with a 261 nm laser28 in a low gradient (0.45 MV/m) DC gun, within the typical range of metal and semiconductor photocathodes under study. Studies on the (N)UNCD material as field emission cathodes have been reported in Refs. 29–31.

A first study of (N)UNCD photocathodes in a realistic rf gun environment is reported; this is a key step needed before their routine use in rf photoinjectors.6 Two individual (N)UNCD samples synthesized two years apart have been characterized in an L-band photocathode rf gun, where balanced performance was demonstrated, with a high QE (4.0×104), a competitive intrinsic emittance (1.00 μm/mm), and excellent robustness (no degradation from year-long atmospheric exposure).

The experiment was conducted using an Argonne Cathode Test-stand (ACT)30,32 at the Argonne Wakefield Accelerator (AWA) facility33 (see Fig. 1). The beamline has a single-cell rf gun operated at 1.3 GHz with a detachable cathode. The gun was operated with a 30 MV/m surface field at the photocathode. The normally incident 262 nm laser has a Gaussian longitudinal distribution with a full width at half maximum pulse length of 300 fs and a 2D Gaussian transverse distribution with the size controlled by an iris. Diagnostics in the experiment include a directional waveguide coupler to measure the transmitted and reflected power, a laser power meter, a virtual cathode to align the laser and measure its spot size, and yttrium-aluminum-garnet (YAG) screens to determine the beam spot size. There are an integrating current transformer (ICT) for measuring beam charge and an in-flange button-type beam position monitor (BPM) that can be used for the same purpose. In the experiment, the gun vacuum was maintained at ∼5 ×109 Torr.

FIG. 1.

(a) Layout of the ACT beamline; (b) cross-sectional view of the (N)UNCD photocathode assembly, where ② is the (N)UNCD film with the silicon substrate and the other labeled parts are the holder assembly connected by vented screws; (c) 2D electric-field distribution near the cathode, where ① is the top stainless steel piece that holds the (N)UNCD photocathode in place.

FIG. 1.

(a) Layout of the ACT beamline; (b) cross-sectional view of the (N)UNCD photocathode assembly, where ② is the (N)UNCD film with the silicon substrate and the other labeled parts are the holder assembly connected by vented screws; (c) 2D electric-field distribution near the cathode, where ① is the top stainless steel piece that holds the (N)UNCD photocathode in place.

Close modal

The (N)UNCD photocathodes were prepared on heavily arsenic-doped 500 μm thick silicon substrates using the same synthesis recipe as stated in the paper of Pérez Quintero et al.18 (N)UNCD sample No.1 was stored in air two years between growth and high power testing, whereas sample No. 2 was newly synthesized just a few days before the experiment. Sample No. 1 was identical to that used for our previously reported studies,28 where it was found that the intrinsic emittance is flat with increasing photon energy, unlike the behavior of a typical metal.34 This spectral dependence is likely to be associated with emission from spatially confined states in the graphite regions (where have a low electron effective mass) between the diamond grains. The (N)UNCD film thicknesses were characterized by using an analytical optics methodology based on measured reflectance spectra35 and found to be 129 ± 3 nm and 143 ± 5 nm for the two cathodes, respectively. The film thickness variations of both cathodes were found to be within ∼3 nm. The optical reflection R at the utilized laser wavelength of 262 nm has been measured to be 10%–15% by UV-vis spectrophotometry. The work function was measured using a Kelvin Probe to be 4.3 ± 0.1 eV for both cathodes. The two cathodes were cut into disks with a diameter of 10 mm and held by three stainless steel (SS) pieces as a cathode assembly that fits into the gun; this is illustrated in Fig. 1(b). The field at the cathode center was held at 30 MV/m so as to eliminate rf breakdown on the top SS holder cap [①in Fig. 1(b)]. The estimated field enhancement at the holder rim was a factor of ∼2. The 50° laser injection phase was set for the maximum beam energy (0.76 MeV) in this gradient.

The quantum efficiency (QE) of both photocathodes was found by measuring the charge as a function of the laser energy; the results are shown in Fig. 2. The root mean square (rms) size of the laser spot was smaller than 1 mm, and the solenoids were used to eliminate beam loss along the beamline. In the first experiment characterizing cathode No.1, an ICT with a charge sensitivity of 0.08 mV/pC was used for electron detection. In the second experiment characterizing cathode No. 2, the BPM was employed for the charge measurement by calibrating it against the ICT. This improved the charge sensitivity to 15 mV/pC. In the low laser energy region (<12 μJ for No. 1 and <7 μJ for No. 2), the charge is linear with the laser energy, consistent with single-photon emission. Then, in the middle energy region (12–25 μJ for No. 1 and 7–23 μJ for No. 2), the charge grows faster with increasing laser energy; the slopes of the lines for the two cathodes are 1.7 ± 0.12 when data are plotted on a log scale. This could be caused by a partial contribution from multi-photon emission. At higher laser energies, the emitted charge becomes limited by space charge and goes into saturation. The QE was calculated from a linear fit of the low charge regions, as the dashed lines show in Fig. 2. The slopes give a QE of 3.8(±0.06)×10−4 for cathode No. 1 and 4.2(±0.22)×10−4 for cathode No. 2, with the fitting errors of the averaged charges shown in the parentheses. The negligible QE difference demonstrates an excellent robustness of (N)UNCD materials.

FIG. 2.

Beam charge as a function of the incident laser energy for the two (N)UNCD samples. The laser energy value accounts for 92% transmission of the vacuum window and 90% reflection of the mirror. The error bars represent the standard deviation of the measured charge caused by the machine jitter. Inset: zoom-in plot of the low charge region.

FIG. 2.

Beam charge as a function of the incident laser energy for the two (N)UNCD samples. The laser energy value accounts for 92% transmission of the vacuum window and 90% reflection of the mirror. The error bars represent the standard deviation of the measured charge caused by the machine jitter. Inset: zoom-in plot of the low charge region.

Close modal

The QE reported here is two orders of magnitude higher than the value in Ref. 18 (5.3 × 10−6 at 254 nm) where the (N)UNCD film grown on a molybdenum substrate was characterized in a DC setup using a broad-band Hg arc lamp with UV filters. The high QE result here may be in part due to the Schottky effect36 in the rf gun, which reduces the work function by ∼0.2 eV, if we assume that the surface field enhancement factor is 1, since no noticeable dark current has been measured. Another possible factor is the nonequilibrium photoemission that may contribute and could lead to an increase in QE at high laser energy density.37 In the present work, the lowest laser energy density is at the level of 0.1 mJ/cm2, which is at least 10 orders of magnitude higher than that in Ref. 18. The QE of undoped NCD/Si reported by Mazellier et al.38 was ∼10−5 using a 266 nm laser with high laser energy density (0–8 mJ/cm2) and a DC electric field of 17 MV/m. This reported high laser fluence QE of NCD is consistent with our QE value (4 × 10−4), given that electron emission is correlated with the graphite grain boundary densities,20,21 which are higher in UNCD-based samples due to the smaller diamond grain size compared to NCD.

The solenoid scan technique39 has been applied to measure the intrinsic emittance of cathode No. 2, in which the emittance is obtained from a fit of the dependence of the beam spot size on the solenoid strength. The fitted result is the quadrature sum of the intrinsic emittance and growth terms from beamline aberration and space charge. The former emittance growth term was simulated using the ASTRA particle tracking code40 with the real 3D gun field map, and the latter one was not simulated due to the possible uncertainty of the initial emission distribution41 but minimized experimentally. The simulation, which did not include space charge dynamics, shows that noticeable emittance growth starts when the laser rms spot size is larger than 0.5 mm, as shown in Fig. 3. The growth is mainly caused by the transverse electrical field components due to the top piece of the cathode holder, as illustrated in Fig. 1(c).

FIG. 3.

Simulated normalized x and y emittance (cross marks) on YAG3 as a function of the rms laser spot sizes, neglecting the space charge force. The solid line represents the product of the intrinsic emittance per mm with the rms laser size, and the cross marks represent the simulation results for the fitted emittance.

FIG. 3.

Simulated normalized x and y emittance (cross marks) on YAG3 as a function of the rms laser spot sizes, neglecting the space charge force. The solid line represents the product of the intrinsic emittance per mm with the rms laser size, and the cross marks represent the simulation results for the fitted emittance.

Close modal

During the measurement, the imaging solenoid was used to scan the beam size, and the other solenoids were off. The beam size was measured on a downstream YAG screen [YAG3 in Fig. 1(a)] using a PI-MAX Intensified CCD camera (ICCD).42 The spatial resolution of the camera was ∼32 μm, measured with a standard USAF target. Thirty frames of beam images were saved at each solenoid setting and the beam rms sizes were calculated using the same imaging process as in Ref. 16. Figure 4 illustrates a solenoid scan, using a laser rms spot size of 0.2 mm. The scan yielded normalized emittances per mm of 1.42 ± 0.045 μm/mm and 1.33 ± 0.015 μm/mm in the x and y directions, respectively. The error bar is caused by the beam size variation at fixed solenoid strength due to machine jitter.16 

FIG. 4.

(a) An example solenoid scan showing the beam size as a function of the imaging solenoid strength. The circles are the experimental data, and the error bars are the standard deviation of the beam size across the thirty measurement frames for a specific solenoid setting. The solid lines are fitting results from the solenoid scanning technique.39 (b) An example of the beam image on YAG3 (solenoid field of 0.0323 T). (c) The laser profile taken on the virtual cathode captured using a Blackfly monochrome camera (model: BFLY-PGE-23S6M-C) with a resolution of 20 μm. In (b) and (c), the intensity distribution of each image is projected onto the x and y directions (white curves in figure).

FIG. 4.

(a) An example solenoid scan showing the beam size as a function of the imaging solenoid strength. The circles are the experimental data, and the error bars are the standard deviation of the beam size across the thirty measurement frames for a specific solenoid setting. The solid lines are fitting results from the solenoid scanning technique.39 (b) An example of the beam image on YAG3 (solenoid field of 0.0323 T). (c) The laser profile taken on the virtual cathode captured using a Blackfly monochrome camera (model: BFLY-PGE-23S6M-C) with a resolution of 20 μm. In (b) and (c), the intensity distribution of each image is projected onto the x and y directions (white curves in figure).

Close modal

The emittance was measured over a range of charge levels and laser spot sizes to determine the lowest obtainable value. The emittance was found to be essentially constant for the charge range of 0.08 pC to 1.2 pC (see Fig. 5), so that a contribution to the emittance from space charge forces in this low charge range is negligible. In the low charge region, emittances corresponding to the 0.3 mm and 0.4 mm laser spot sizes were very close to those at 0.2 mm, which agrees with the beam dynamics simulation (Fig. 3) and confirms that the emittance growth term from beamline aberration can be ignored. The intrinsic emittance, found by averaging the measurements in the low charge region including the different laser spot sizes, is found to be 1.00 ± 0.14 μm/mm, in reasonable agreement with the value of 0.75 ± 0.29 μm/mm in our previous study.28 Since emission occurs preferentially from the grain boundaries, the dependence of intrinsic emittance on synthesis parameters (therefore change the sample morphology) might be fruitfully explored.

FIG. 5.

Measured emittance per rms laser size (ε/σ) as a function of bunch charge. Charge values lower than 0.5 pC are derived using the measured QE and the laser energy measured using the power meter. The dotted line indicates the average value of measurements in the low charge region.

FIG. 5.

Measured emittance per rms laser size (ε/σ) as a function of bunch charge. Charge values lower than 0.5 pC are derived using the measured QE and the laser energy measured using the power meter. The dotted line indicates the average value of measurements in the low charge region.

Close modal

To conclude, (N)UNCD photocathodes have been characterized in a rf gun environment. The experiment of two cathodes demonstrated the balanced performance of high QE (4.2 × 10−4), comparable intrinsic emittance (1.00 μm/mm), and excellent robustness (year-long atmospheric exposure and 10−9 Torr operation). The lack of degradation of the photocathode in air is particularly notable and may make these photocathodes an excellent choice for certain applications. Overall, the properties are competitive and make (N)UNCD a promising candidate for high brightness photoinjectors. Future work includes the measurement of the cathode response time, tests with an increased cathode surface field enabled by improved cathode assembly design, characterization of samples with various surface treatments, and additional fundamental research of the emission mechanism.

This work was funded by the National Science Foundation (NSF) by Grant No. PHY-1403952 and the Department of Energy (DOE) by Grant No. DE-SC0015479. (N)UNCD synthesis and characterization work at the Center for Nanoscale Materials, Argonne National Laboratory, was performed under proposal No. 63638. The use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The Argonne Wakefield Accelerator Facility (AWA) was supported through the U.S. Department of Energy (DOE), Office of Science under Contract No. DE-AC02-06CH11357. The work at Euclid was supported by DOE SBIR program Grant No. DE-SC0013145. We would like to thank Dr. Lianmin Zheng from Tsinghua University for the suggestions on the emittance measurement.

The data that support the findings of this study are available from the corresponding author upon reasonable request.

1.
P.
Emma
,
R.
Akre
,
J.
Arthur
,
R.
Bionta
,
C.
Bostedt
,
J.
Bozek
,
A.
Brachmann
,
P.
Bucksbaum
,
R.
Coffee
,
F.-J.
Decker
 et al,
Nat. Photonics
4
,
641
(
2010
).
2.
F.
Qi
,
Z.
Ma
,
L.
Zhao
,
Y.
Cheng
,
W.
Jiang
,
C.
Lu
,
T.
Jiang
,
D.
Qian
,
Z.
Wang
,
W.
Zhang
,
P.
Zhu
,
X.
Zou
,
W.
Wan
,
D.
Xiang
, and
J.
Zhang
,
Phys. Rev. Lett.
124
,
134803
(
2020
).
3.
R.
Li
and
P.
Musumeci
,
Phys. Rev. Appl.
2
,
024003
(
2014
).
4.
Y.
Du
,
L.
Yan
,
J.
Hua
,
Q.
Du
,
Z.
Zhang
,
R.
Li
,
H.
Qian
,
W.
Huang
,
H.
Chen
, and
C.
Tang
,
Rev. Sci. Instrum.
84
,
053301
(
2013
).
5.
D.
Dowell
,
I.
Bazarov
,
B.
Dunham
,
K.
Harkay
,
C.
Hernandez-Garcia
,
R.
Legg
,
H.
Padmore
,
T.
Rao
,
J.
Smedley
, and
W.
Wan
,
Nucl. Instrum. Methods Phys. Res. Sect. A
622
,
685
(
2010
).
6.
X.
Wang
,
P.
Musumeci
,
E.
Lessner
, and
J.
Goldstein
, “
Report of the Basic Energy Sciences Workshop on the Future of Electron Sources, September 8–9, 2016
,” USDOE Office of Science (SC), USA,
2016
), https://www.osti.gov/servlets/purl/1616511.
7.
P.
Musumeci
,
J. G.
Navarro
,
J.
Rosenzweig
,
L.
Cultrera
,
I.
Bazarov
,
J.
Maxson
,
S.
Karkare
, and
H.
Padmore
,
Nucl. Instrum. Methods Phys. Res. Sect. A
907
,
209
(
2018
).
8.
D.
Dowell
,
F.
King
,
R.
Kirby
,
J.
Schmerge
, and
J.
Smedley
,
Phys. Rev. Spec. Top.-Accel. Beams
9
,
063502
(
2006
).
9.
J.
Smedley
,
T.
Rao
, and
Q.
Zhao
,
J. Appl. Phys.
98
,
043111
(
2005
).
10.
C. P.
Hauri
,
R.
Ganter
,
F. L.
Pimpec
,
A.
Trisorio
,
C.
Ruchert
, and
H. H.
Braun
,
Phys. Rev. Lett.
104
,
234802
(
2010
).
11.
T.
Nakajyo
,
J.
Yang
,
F.
Sakai
, and
Y.
Aoki
,
Jpn. J. Appl. Phys.
42
,
1470
(
2003
).
12.
Q.
Zhao
,
T.
Srinivasan-Rao
, and
M.
Cole
, in
Proceedings of the 2003 Particle Accelerator Conference
(
2003
), Vol.
3
, pp.
2047
2049
.
13.
R.
Akre
,
D.
Dowell
,
P.
Emma
,
J.
Frisch
,
S.
Gilevich
,
G.
Hays
,
P.
Hering
,
R.
Iverson
,
C.
Limborg-Deprey
,
H.
Loos
,
A.
Miahnahri
,
J.
Schmerge
,
J.
Turner
,
J.
Welch
,
W.
White
, and
J.
Wu
,
Phys. Rev. Spec. Top.-Accel. Beams
11
,
030703
(
2008
).
14.
N.
Chanlek
,
J.
Herbert
,
R.
Jones
,
L.
Jones
,
K.
Middleman
, and
B.
Militsyn
,
J. Phys. D
47
,
055110
(
2014
).
15.
T.
Vecchione
,
I.
Ben-Zvi
,
D. H.
Dowell
,
J.
Feng
,
T.
Rao
,
J.
Smedley
,
W.
Wan
, and
H. A.
Padmore
,
Appl. Phys. Lett.
99
,
034103
(
2011
).
16.
L.
Zheng
,
J.
Shao
,
E. E.
Wisniewski
,
J. G.
Power
,
Y.
Du
,
W.
Liu
,
C. E.
Whiteford
,
M.
Conde
,
S.
Doran
,
C.
Jing
 et al,
Phys. Rev. Accel. Beams
23
,
052801
(
2020
).
17.
G.
Wang
,
P.
Yang
,
N. A.
Moody
, and
E. R.
Batista
,
npj 2D Mater. Appl.
2
(
1
),
17
(
2018
).
18.
K. J.
Pérez Quintero
,
S.
Antipov
,
A. V.
Sumant
,
C.
Jing
, and
S. V.
Baryshev
,
Appl. Phys. Lett.
105
,
123103
(
2014
).
19.
A. V.
Sumant
,
S. V.
Baryshev
, and
S. P.
Antipov
, “
Planar field emitters and high efficiency photocathodes based on ultrananocrystalline diamond
,” U.S. Patent No. 9,418,814, issued August 16, 2016, https://patents.justia.com/patent/9418814.
20.
V.
Chatterjee
,
R.
Harniman
,
P. W.
May
, and
P.
Barhai
,
Appl. Phys. Lett.
104
,
171907
(
2014
).
21.
R. L.
Harniman
,
O. J.
Fox
,
W.
Janssen
,
S.
Drijkoningen
,
K.
Haenen
, and
P. W.
May
,
Carbon
94
,
386
(
2015
).
22.
S. V.
Baryshev
,
S.
Antipov
,
J.
Shao
,
C.
Jing
,
K. J.
Pérez Quintero
,
J.
Qiu
,
W.
Liu
,
W.
Gai
,
A. D.
Kanareykin
, and
A. V.
Sumant
,
Appl. Phys. Lett.
105
,
203505
(
2014
).
23.
J.
Birrell
,
J.
Gerbi
,
O.
Auciello
,
J.
Gibson
,
D.
Gruen
, and
J.
Carlisle
,
J. Appl. Phys.
93
,
5606
(
2003
).
24.
R.
Arenal
,
G.
Montagnac
,
P.
Bruno
, and
D.
Gruen
,
Phys. Rev. B
76
,
245316
(
2007
).
25.
S.
Bhattacharyya
,
O.
Auciello
,
J.
Birrell
,
J. A.
Carlisle
,
L. A.
Curtiss
,
A. N.
Goyette
,
D. M.
Gruen
,
A. R.
Krauss
,
J.
Schlueter
,
A.
Sumant
, and
P.
Zapol
,
Appl. Phys. Lett.
79
,
1441
(
2001
).
26.
J. B.
Cui
,
J.
Ristein
, and
L.
Ley
,
Phys. Rev. Lett.
81
,
429
(
1998
).
27.
T.
Sun
,
F. A. M.
Koeck
,
C.
Zhu
, and
R. J.
Nemanich
,
Appl. Phys. Lett.
99
,
202101
(
2011
).
28.
G.
Chen
,
G.
Adhikari
,
L.
Spentzouris
,
K. K.
Kovi
,
S.
Antipov
,
C.
Jing
,
W. A.
Schroeder
, and
S. V.
Baryshev
,
Appl. Phys. Lett.
114
,
093103
(
2019
).
29.
J.
Qiu
,
S. S.
Baturin
,
K. K.
Kovi
,
O.
Chubenko
,
G.
Chen
,
R.
Konecny
,
S.
Antipov
,
A. V.
Sumant
,
C.
Jing
, and
S. V.
Baryshev
,
IEEE Trans. Electron Devices
65
,
1132
(
2018
).
30.
J.
Shao
,
M.
Schneider
,
G.
Chen
,
T.
Nikhar
,
K. K.
Kovi
,
L.
Spentzouris
,
E.
Wisniewski
,
J.
Power
,
M.
Conde
,
W.
Liu
 et al,
Phys. Rev. Accel. Beams
22
,
123402
(
2019
).
31.
O.
Chubenko
,
S. S.
Baturin
,
K. K.
Kovi
,
A. V.
Sumant
, and
S. V.
Baryshev
,
ACS Appl. Mater. Interfaces
9
,
33229
(
2017
).
32.
J.
Shao
,
J.
Shi
,
S. P.
Antipov
,
S. V.
Baryshev
,
H.
Chen
,
M.
Conde
,
W.
Gai
,
G.
Ha
,
C.
Jing
,
F.
Wang
 et al,
Phys. Rev. Lett.
117
,
084801
(
2016
).
33.
M.
Conde
,
S.
Antipov
,
D.
Doran
,
W.
Gai
,
Q.
Gao
,
G.
Ha
,
C.
Jing
,
W.
Liu
,
N.
Neveu
,
J.
Power
,
J.
Qiu
,
J.
Shao
,
Y.
Wang
,
C.
Whiteford
,
E.
Wisniewski
, and
L.
Zheng
, in
8th International Particle Accelerator Conference (IPAC'17)
, Copenhagen, Denmark, May, 2017 (
JACOW
,
Geneva, Switzerland
,
2017
), pp.
2885
2887
.
34.
D. H.
Dowell
and
J. F.
Schmerge
,
Phys. Rev. Spec. Top.-Accel. Beams
12
,
074201
(
2009
).
35.
G.
Chen
,
L.
Spentzouris
,
K. K.
Kovi
, and
S. V.
Baryshev
,
Surf. Sci. Spectra
27
,
026601
(
2020
).
36.
Z. M.
Yusof
,
M. E.
Conde
, and
W.
Gai
,
Phys. Rev. Lett.
93
,
114801
(
2004
).
37.
J. K.
Bae
,
I.
Bazarov
,
P.
Musumeci
,
S.
Karkare
,
H.
Padmore
, and
J.
Maxson
,
J. Appl. Phys.
124
,
244903
(
2018
).
38.
J.-P.
Mazellier
,
C. D.
Giola
,
P.
Legagneux
,
C.
Hébert
,
E.
Scorsone
,
P.
Bergonzo
, and
S.
Saada
,
J. Vacuum Sci. Technol. B
33
,
03C105
(
2015
).
39.
L.
Zheng
,
J.
Shao
,
Y.
Du
,
J. G.
Power
,
E. E.
Wisniewski
,
W.
Liu
,
C. E.
Whiteford
,
M.
Conde
,
S.
Doran
,
C.
Jing
 et al,
Phys. Rev. Accel. Beams
21
,
122803
(
2018
).
40.
K.
Floettmann
, “
Astra: A space charge tracking algorithm
,” https://www.desy.de/~mpyflo/.
41.
P.-W.
Huang
,
H.
Qian
,
Y.
Chen
,
D.
Filippetto
,
M.
Gross
,
I.
Isaev
,
C.
Koschitzki
,
M.
Krasilnikov
,
S.
Lal
,
X.
Li
 et al,
Phys. Rev. Accel. Beams
23
,
043401
(
2020
).
42.
PI-MAX/PI-MAX2 System, Princeton Instruments,
2004
.