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BESIII Collaboration,
M. Ablikim,
M. N. Achasov,
D. J. Ambrose,
F. F. An,
Q. An,
Z. H. An,
J. Z. Bai,
Y. Ban,
J. Becker, [......],
S. H. Zhu,
X. L. Zhu,
X. W. Zhu,
Y. C. Zhu,
Y. M. Zhu,
Y. S. Zhu,
Z. A. Zhu,
J. Zhuang,
B. S. Zou,
J. H. Zou
[show abstract]
[hide abstract]
ABSTRACT: Decays of the chi_{cJ} states (J=0,\ 1,\ 2) to \Lambda \Lambda bar\ pi^{+}
\pi^{-}, including processes with intermediate \Sigma(1385), are studied
through the E1 transition psi'-->\gamma chi_{cJ} using 106 million psi' events
collected with the BESIII detector at BEPCII. This is the first observation of
chi_{cJ} decays to the final state \Lambda\Lambda bar \pi^{+}\pi^{-}. The
branching ratio of the intermediate process chi_{cJ}-->\Sigma(1385)^{+/-}
\bar{\Sigma}(1385)^{-/+} is also measured for the first time, and the results
agree with the theoretical predictions based on the color-octet effect.
07/2012;
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M. Ablikim,
M. N. Achasov,
D. J. Ambrose,
F. F. An,
Q. An,
Z. H. An,
J. Z. Bai,
Y. Ban,
J. Becker,
N. Berger, [......],
S. H. Zhu,
X. L. Zhu,
X. W. Zhu,
Y. M. Zhu,
Y. S. Zhu,
Z. A. Zhu,
J. Zhuang,
B. S. Zou,
J. H. Zou,
J. X. Zuo
[show abstract]
[hide abstract]
ABSTRACT: Based on a data sample of 106×106 ψ′ events collected with the BESIII detector, the decays ψ′→γχc0,2, χc0,2→γγ are studied to determine the two-photon widths of the χc0,2 states. The two-photon decay branching fractions are determined to be B(χc0→γγ)=(2.24±0.19±0.12±0.08)×10-4 and B(χc2→γγ)=(3.21±0.18±0.17±0.13)×10-4. From these, the two-photon widths are determined to be Γγγ(χc0)=(2.33±0.20±0.13±0.17) keV, Γγγ(χc2)=(0.63±0.04±0.04±0.04) keV, and R=Γγγ(χc2)/Γγγ(χc0)=0.271±0.029±0.013±0.027, where the uncertainties are statistical, systematic, and those from the PDG B(ψ′→γχc0,2) and Γ(χc0,2) errors, respectively. The ratio of the two-photon widths for helicity λ=0 and helicity λ=2 components in the decay χc2→γγ is measured for the first time to be f0/2=Γγγλ=0(χc2)/Γγγλ=2(χc2)=0.00±0.02±0.02.
Phys. Rev. D. 06/2012; 85(11).
-
BESIII Collaboration,
M. Ablikim,
M. N. Achasov,
D. J. Ambrose,
F. F. An,
Q. An,
Z. H. An,
J. Z. Bai,
R. B. Ferroli,
Y. Ban, [......],
S. H. Zhu,
X. L. Zhu,
X. W. Zhu,
Y. M. Zhu,
Y. S. Zhu,
Z. A. Zhu,
J. Zhuang,
B. S. Zou,
J. H. Zou,
J. X. Zuo
[show abstract]
[hide abstract]
ABSTRACT: Based on a data sample of 106 M $\psi^{\prime}$ events collected with the
BESIII detector, the decays $\psi^{\prime}\ar\gamma\chi_{c0, 2}$,$\chi_{c0,
2}\ar\gamma\gamma$ are studied to determine the two-photon widths of the
$\chi_{c0, 2}$ states. The two-photon decay branching fractions are determined
to be ${\cal B}(\chi_{c0}\ar\gamma\gamma) = (2.24\pm 0.19\pm 0.12\pm
0.08)\times 10^{-4}$ and ${\cal B}(\chi_{c2}\ar\gamma\gamma) = (3.21\pm 0.18\pm
0.17\pm 0.13)\times 10^{-4}$. From these, the two-photon widths are determined
to be $\Gamma_{\gamma \gamma}(\chi_{c0}) = (2.33\pm0.20\pm0.13\pm0.17)$ keV,
$\Gamma_{\gamma \gamma}(\chi_{c2}) = (0.63\pm0.04\pm0.04\pm0.04)$ keV, and
$\cal R$ $=\Gamma_{\gamma \gamma}(\chi_{c2})/\Gamma_{\gamma
\gamma}(\chi_{c0})=0.271\pm 0.029\pm 0.013\pm 0.027$, where the uncertainties
are statistical, systematic, and those from the PDG ${\cal
B}(\psi^{\prime}\ar\gamma\chi_{c0,2})$ and $\Gamma(\chi_{c0,2})$ errors,
respectively. The ratio of the two-photon widths for helicity $\lambda=0$ and
helicity $\lambda=2$ components in the decay $\chi_{c2}\ar\gamma\gamma$ is
measured for the first time to be $f_{0/2}
=\Gamma^{\lambda=0}_{\gamma\gamma}(\chi_{c2})/\Gamma^{\lambda=2}_{\gamma\gamma}(\chi_{c2})
= 0.00\pm0.02\pm0.02$.
05/2012;
-
BESIII Collaboration,
M. Ablikim,
M. N. Achasov,
D. Alberto,
D. J. Ambrose,
F. F. An,
Q. An,
Z. H. An,
J. Z. Bai,
R. B. Ferroli, [......],
K. J. Zhu,
S. H. Zhu,
X. L. Zhu,
X. W. Zhu,
Y. S. Zhu,
Z. A. Zhu,
J. Zhuang,
B. S. Zou,
J. H. Zou,
J. X. Zuo
[show abstract]
[hide abstract]
ABSTRACT: The mass and width of the lowest lying S-wave spin singlet charmonium state,
the eta_c, are measured using a data sample of 1.06x10^8 psi' decays collected
with the BESIII detector at the BEPCII storage ring. We use a model that
incorporates interference between the signal reaction, psi' -> gamma eta_c, and
a non-resonant radiative background to successfully describe the line shape of
the eta_c. We measure the eta_c mass to be 2984.3 +- 0.6 +- 0.6 MeV/c^2 and the
total width to be 32.0 +- 1.2 +- 1.0 MeV, where the first errors are
statistical and the second are systematic.
11/2011;
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R. Raman,
J-W. Ahn,
J.P. Allain,
R. Andre,
R. Bastasz,
D. Battaglia,
P. Beiersdorfer,
M. Bell,
R. Bell,
E. Belova, [......],
K.L. Wong,
J. Wright,
Z. Xia,
D. Youchison,
G. Yu,
H. Yuh,
L. Zakharov,
D. Zemlyanov,
G. Zimmer,
S.J. Zweben
[show abstract]
[hide abstract]
ABSTRACT: In the last two experimental campaigns, the low aspect ratio NSTX has explored physics issues critical to both toroidal confinement physics and ITER. Experiments have made extensive use of lithium coatings for wall conditioning, correction of non-axisymmetric field errors and control of n = 1 resistive wall modes (RWMs) to produce high-performance neutral-beam heated discharges extending to 1.7 s in duration with non-inductive current fractions up to 0.7. The RWM control coils have been used to trigger repetitive ELMs with high reliability, and they have also contributed to an improved understanding of both neoclassical tearing mode and RWM stabilization physics, including the interplay between rotation and kinetic effects on stability. High harmonic fast wave (HHFW) heating has produced plasmas with central electron temperatures exceeding 6 keV. The HHFW heating was used to show that there was a 20–40% higher power threshold for the L–H transition for helium than for deuterium plasmas. A new diagnostic showed a depletion of the fast-ion density profile over a broad spatial region as a result of toroidicity-induced Alfvén eigenmodes (TAEs) and energetic-particle modes (EPMs) bursts. In addition, it was observed that other modes (e.g. global Alfvén eigenmodes) can trigger TAE and EPM bursts, suggesting that fast ions are redistributed by high-frequency AEs. The momentum pinch velocity determined by a perturbative technique decreased as the collisionality was reduced, although the pinch to diffusion ratio, Vpinch/χ, remained approximately constant. The mechanisms of deuterium retention by graphite and lithium-coated graphite plasma-facing components have been investigated. To reduce divertor heat flux, a novel divertor configuration, the 'snowflake' divertor, was tested in NSTX and many beneficial aspects were found. A reduction in the required central solenoid flux has been realized in NSTX when discharges initiated by coaxial helicity injection were ramped in current using induction. The resulting plasmas have characteristics needed to meet the objectives of the non-inductive start-up and ramp-up program of NSTX.
Nuclear Fusion 08/2011; 51(9):094011. · 4.09 Impact Factor
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D. A. Gates,
J. Ahn,
J. Allain,
R. Andre,
R. Bastasz,
M. Bell,
R. Bell,
E. Belova,
J. Berkery,
R. Betti, [......],
K. Wong,
J. Wright,
Z. Xia,
X. Xu,
D. Youchison,
G. Yu,
H. Yuh,
L. Zakharov,
D. Zemlyanov,
S. Zweben
[show abstract]
[hide abstract]
ABSTRACT: The mission of the National Spherical Torus Experiment (NSTX) is the demonstration of the physics basis required to extrapolate to the next steps for the spherical torus (ST), such as a plasma facing component test facility (NHTX) or an ST based component test facility (ST-CTF), and to support ITER. Key issues for the ST are transport, and steady state high b operation. To better understand electron transport, a new high-k scattering diagnostic was used extensively to investigate electron gyro-scale fluctuations with varying electron temperature gradient scale length. Results from n = 3 braking studies are consistent with the flow shear dependence of ion transport. New results from electron Bernstein wave emission measurements from plasmas with lithium wall coating applied indicate transmission efficiencies near 70% in H-mode as a result of reduced collisionality. Improved coupling of high harmonic fast-waves has been achieved by reducing the edge density relative to the critical density for surface wave coupling. In order to achieve high bootstrap current fraction, future ST designs envision running at very high elongation. Plasmas have been maintained on NSTX at very low internal inductance li [?] 0.4 with strong shaping (k [?] 2.7, d [?] 0.8) with bN approaching the with-wall b-limit for several energy confinement times. By operating at lower collisionality in this regime, NSTX has achieved record non-inductive current drive fraction fNI [?] 71%. Instabilities driven by super-Alfvenic ions will be an important issue for all burning plasmas, including ITER. Fast ions from NBI on NSTX are super-Alfvenic. Linear toroidal Alfven eigenmode thresholds and appreciable fast ion loss during multi-mode bursts are measured and these results are compared with theory. The impact of n > 1 error fields on stability is an important result for ITER. Resistive wall mode/resonant field amplification feedback combined with n = 3 error field control was used on NSTX to maintain plasma rotation with b above the no-wall limit. Other highlights are results of lithium coating experiments, momentum confinement studies, scrape-off layer width scaling, demonstration of divertor heat load mitigation in strongly shaped plasmas and coupling of coaxial helicity injection plasmas to ohmic heating ramp-up. These results advance the ST towards next step fusion energy devices such as NHTX and ST-CTF.
Nuclear Fusion. 01/2009; 49(10):104016.
-
S.M. Kaye,
M.G. Bell,
R.E. Bell,
S. Bernabei,
J. Bialek,
T. Biewer,
W. Blanchard,
J. Boedo,
C. Bush,
M.D. Carter, [......],
M. Schaffer,
I. Semenov,
K.C. Shaing,
M.A. Shapiro,
K. Shinohara,
P. Sichta, X. Tang,
R. Vero,
D. Walker,
W. Wampler
[show abstract]
[hide abstract]
ABSTRACT: The major objective of the National Spherical Torus Experiment (NSTX) is to understand basic toroidal confinement physics at low aspect ratio and high βT in order to advance the spherical torus (ST) concept. In order to do this, NSTX utilizes up to 7.5 MW of neutral beam injection, up to 6 MW of high harmonic fast waves (HHFWs), and it operates with plasma currents up to 1.5 MA and elongations of up to 2.6 at a toroidal field up to 0.45 T. New facility, and diagnostic and modelling capabilities developed over the past two years have enabled the NSTX research team to make significant progress towards establishing this physics basis for future ST devices. Improvements in plasma control have led to more routine operation at high elongation and high βT (up to ~40%) lasting for many energy confinement times. βT can be limited by either internal or external modes. The installation of an active error field (EF) correction coil pair has expanded the operating regime at low density and has allowed for initial resonant EF amplification experiments. The determination of the confinement and transport properties of NSTX plasmas has benefitted greatly from the implementation of higher spatial resolution kinetic diagnostics. The parametric variation of confinement is similar to that at conventional aspect ratio but with values enhanced relative to those determined from conventional aspect ratio scalings and with a BT dependence. The transport is highly dependent on details of both the flow and magnetic shear. Core turbulence was measured for the first time in an ST through correlation reflectometry. Non-inductive start-up has been explored using PF-only and transient co-axial helicity injection techniques, resulting in up to 140 kA of toroidal current generated by the latter technique. Calculated bootstrap and beam-driven currents have sustained up to 60% of the flat-top plasma current in NBI discharges. Studies of HHFW absorption have indicated parametric decay of the wave and associated edge thermal ion heating. Energetic particle modes, most notably toroidal Alfvén eigenmodes and fishbone-like modes result in fast particle losses, and these instabilities may affect fast ion confinement on devices such as ITER. Finally, a variety of techniques has been developed for fuelling and power and particle control.
Nuclear Fusion 10/2005; 45(10):S168. · 4.09 Impact Factor
-
E.J. Synakowski,
M.G. Bell,
R.E. Bell,
T. Bigelow,
M. Bitter,
W. Blanchard,
J. Boedo,
C. Bourdelle,
C. Bush,
D.S. Darrow, [......],
B.C. Stratton,
Y. Takase, X. Tang,
R. Vero,
W.R. Wampler,
G.A. Wurden,
X.Q. Xu,
J.G. Yang,
L. Zeng,
W. Zhu
[show abstract]
[hide abstract]
ABSTRACT: A major research goal of the national spherical torus experiment is establishing long-pulse, high beta, high confinement operation and its physics basis. This research has been enabled by facility capabilities developed during 2001 and 2002, including neutral beam (up to 7 MW) and high harmonic fast wave (HHFW) heating (up to 6 MW), toroidal fields up to 6 kG, plasma currents up to 1.5 MA, flexible shape control, and wall preparation techniques. These capabilities have enabled the generation of plasmas with of up to 35%. Normalized beta values often exceed the no-wall limit, and studies suggest that passive wall mode stabilization enables this for H mode plasmas with broad pressure profiles. The viability of long, high bootstrap current fraction operations has been established for ELMing H mode plasmas with toroidal beta values in excess of 15% and sustained for several current relaxation times. Improvements in wall conditioning and fuelling are likely contributing to a reduction in H mode power thresholds. Electron thermal conduction is the dominant thermal loss channel in auxiliary heated plasmas examined thus far. HHFW effectively heats electrons, and its acceleration of fast beam ions has been observed. Evidence for HHFW current drive is obtained by comparision of the loop voltage evolution in plasmas with matched density and temperature profiles but varying phases of launched HHFW waves. Studies of emissions from electron Bernstein waves indicate a density scale length dependence of their transmission across the upper hybrid resonance near the plasma edge that is consistent with theoretical predictions. A peak heat flux to the divertor targets of 10 MW m−2 has been measured in the H mode, with large asymmetries being observed in the power deposition between the inner and outer strike points. Non-inductive plasma startup studies have focused on coaxial helicity injection. With this technique, toroidal currents up to 400 kA have been driven, and studies to assess flux closure and coupling to other current drive techniques have begun.
Nuclear Fusion 12/2003; 43(12):1653. · 4.09 Impact Factor
-
M. Ono,
M. G. Bell,
R. E. Bell,
T. Bigelow,
M. Bitter,
W. Blanchard,
J. Boedo,
C. Bourdelle,
C. Bush,
W. Choe, [......],
J. Robinson,
P. Roney,
K. Shaing,
S. Shiraiwa,
P. Sichta,
D. Stotler,
B. C. Stratton,
R. Vero,
W. R. Wampler,
G. A. Wurden
[show abstract]
[hide abstract]
ABSTRACT: Research on the spherical torus (or spherical tokamak) (ST) is being pursued to explore the scientific benefits of modifying the field line structure from that in more moderate aspect ratio devices, such as the conventional tokamak. The ST experiments are being conducted in various US research facilities including the MA-class National Spherical Torus Experiment (NSTX) at Princeton, and three medium sized ST research facilities: PEGASUS at University of Wisconsin, HIT-II at University of Washington, and CDX-U at Princeton. In the context of the fusion energy development path being formulated in the US, an ST-based Component Test Facility (CTF) and, ultimately a Demo device, are being discussed. For these, it is essential to develop high performance, steady-state operational scenarios. The relevant scientific issues are energy confinement, MHD stability at high beta (), non-inductive sustainment, Ohmic-solenoid-free start-up, and power and particle handling. In the confinement area, the NSTX experiments have shown that the confinement can be up to 50% better than the ITER-98-pby2 H-mode scaling, consistent with the requirements for an ST-based CTF and Demo. In NSTX, CTF-relevant average toroidal beta values beta(T) of up to 35% with a near unity central beta(T) have been obtained. NSTX will be exploring advanced regimes where beta(T) up to 40% can be sustained through active stabilization of resistive wall modes. To date, the most successful technique for non-inductive sustainment in NSTX is the high beta poloidal regime, where discharges with a high non-inductive fraction (similar to60% bootstrap current+NBI current drive) were sustained over the resistive skin time. Research on radio-frequency (RF) based heating and current drive utilizing high harmonic fast wave and electron Bernstein wave is also pursued on NSTX, PEGASUS, and CDX-U. For non-inductive start-up, the coaxial helicity injection, developed in HIT/HIT-II, has been adopted on NSTX to test the method up to I-p similar to 500 kA. In parallel, start-up using a RF current drive and only external poloidal field coils are being developed on NSTX. The area of power and particle handling is expected to be challenging because of the higher power density expected in the ST relative to that in conventional aspect-ratio tokamaks. Due to its promise for power and particle handling, liquid lithium is being studied in CDX-U as a potential plasma-facing surface for a fusion reactor.
Plasma Physics and Controlled Fusion. 45:A335-A350.
-
E. J. Synakowski,
M. G. Bell,
R. E. Bell,
T. Bigelow,
M. Bitter,
W. Blanchard,
J. Boedo,
C. Bourdelle,
C. Bush,
D. S. Darrow, [......],
B. C. Stratton,
Y. Takase, X. Tang,
R. Vero,
W. R. Wampler,
G. A. Wurden,
X. Q. Xu,
J. G. Yang,
L. Zeng,
W. Zhu
[show abstract]
[hide abstract]
ABSTRACT: A major research goal of the national spherical torus experiment is establishing long-pulse, high beta, high confinement operation and its physics basis. This research has been enabled by facility capabilities developed during 2001 and 2002, including neutral beam (up to 7 MW) and high harmonic fast wave (HHFW) heating (up to 6 MW), toroidal fields up to 6 kG, plasma currents up to 1.5 MA, flexible shape control, and wall preparation techniques. These capabilities have enabled the generation of plasmas with beta(T) equivalent to
/(B-T0(2)/2mu(0)) of up to 35%. Normalized beta values often exceed the no-wall limit, and studies suggest that passive wall mode stabilization enables this for H mode plasmas with broad pressure profiles. The viability of long, high bootstrap current fraction operations has been established for ELMing H mode plasmas with toroidal beta values in excess of 15% and sustained for several current relaxation times. Improvements in wall conditioning and fuelling are likely contributing to a reduction in H mode power thresholds. Electron thermal conduction is the dominant thermal loss channel in auxiliary heated plasmas examined thus far. HHFW effectively heats electrons, and its acceleration of fast beam ions has been observed. Evidence for HHFW current drive is obtained by comparision of the loop voltage evolution in plasmas with matched density and temperature profiles but varying phases of launched HHFW waves. Studies of emissions from electron Bernstein waves indicate a density scale length dependence of their transmission across the upper hybrid resonance near the plasma edge that is consistent with theoretical predictions. A peak heat flux to the divertor targets of 10 MW m(-2) has been measured in the H-mode, with large asymmetries being observed in the power deposition between the inner and outer strike points. Non-inductive plasma startup studies have focused on coaxial helicity injection. With this technique, toroidal currents up to 400 kA have been driven, and studies to assess flux closure and coupling to other current drive techniques have begun.
Nuclear Fusion. 43(12):1653-1664.
-
M. Ono,
M. G. Bell,
R. E. Bell,
S. Bernabei,
J. M. Bialek,
T. Bigelow,
M. Bitter,
T. M. Biewer,
W. Blanchard,
J. Boedo, [......],
M. Schaffer,
P. Sichta, X. Tang,
J. Timberlake,
M. Wade,
W. R. Wampler,
Z. Wang,
R. Woolley,
G. A. Wurden,
X. Xu
Transactions of the Institute of Electrical Engineers of Japan, Part A. 125-A(11).
