Workshop on Polarized Electron Sources and Polarimeters

More documents

Recommendations

Info

Status Report of the New Darmstadt Polarized Electron Injector Y. Poltoratska ∗ , R. Barday ∗ , U. Bonnes ∗ , M. Brunken ∗ , C. Eckardt ∗ ,R. Eichhorn ∗ , J. Enders ∗ , C. Heßler ∗ , C. Ingenhaag ∗ , W.F.O. Müller † ,M. Platz ∗ , M. Roth ∗ , B. Steiner † , M. Wagner ∗ and T. Weiland † ∗ Institut für Kernphysik, Technische Universität Darmstadt, Germany † Institut für Theorie Elektromagnetischer Felder, Technische Universität Darmstadt, Germany Abstract. We present the status of the polarized injector for the superconducting Darmstadt electron linear accelerator S-DALINAC. An offline teststand of the source was built to test all components of the S-DALINAC polarized injector SPIN. The new electron source will deliver a 100 keV polarized beam and complement the present thermionic source operating at 250 kV. Results of the beam properties measurements will be introduced and an outlook on the upcoming installation of the new injector at the S-DALINAC will be given. Keywords: S-DALINAC, strained superlattice GaAs, Mott polarimeter, Wien filter PACS: 85.60.Ha, 79.60.-i, 29.27.Hj INTRODUCTION The superconducting Darmstadt electron linear accelerator S-DALINAC [1] is one of very few electron accelerators devoted to nuclear structure physics, including electronscattering experiments. To complement the present scientific programm with the experiments that are focused on the investigation of violation of parity in the nuclei and breakup reactions of light nuclei [2] the new S-DALINAC Polarized injector (SPIN) was designed. It will provide - complementary to the existing 250 kV thermionic electron gun 100 keV polarized beams with polarization of 80 %, a mean current of 60 µA and 3 GHz cw or subharmonic time structure. The concept of the MAMI Gun [3] was used as a starting point for SPIN. To test the new developed polarized electron source independently from the operation of the S-DALINAC, an standalone teststand has been developed. In this contribution we describe the current status of the teststand and present the results of the measurements of the different beam properties. TEST STAND OF THE POLARIZED INJECTOR Figure 1 shows an schematic overview over the teststand of the polarized injector. The electrons are produced at a GaAs cathode by photoemission. As cathode material the strained superlattice crystals [4] are foreseen to achieve high degrees of polarization of more than 80%. Due to the limited space in the accelerator hall a very compact source had to be constructed, and major modifications from the Mainz design were necessary. One spin direction is selected by using circularly polarized light from diode laser system
FIGURE 1. Schematic drawing of the teststand. below the electron source focussed onto the photocathode surface. The photocathode crystal is installed at the front end of a highly polished stainless-steel electrode. The form of the electrode was designed following numerical simulations [5] and deviates from usual Pierce geometry [6]. To extract the electrons from the conduction band of the cathode crystal to the vacuum negative electron affinity (NEA) is needed. Therefore prior to installation into the cathode chamber the cathode is cleaned and activated by depositing thin CsO layer in a separate preparation chamber. With the aid of a load-lock system the photocathode activation can be handled quickly. Afterwards the emitted electrons are accelerated electrostatically to an energy of 100 keV and injected by an alpha magnet into a horizontal beamline, where the beam properties are measured with various diagnostic elements. It is indispensable to create an ultra high vacuum conditions in the gun chamber to prevent a fast degradation of the NEA surface. After bake-out during 12 days at 220 ◦ C an end pressure of < 2 · 10 −11 mbar has been achieved using non-evaporable getter (NEG) and ion-getter pumps. Transverse beam quality The transverse beam properties can be investigated qualitatively by fluorescent screens and quantitatively by a wire scanner [7]. The transverse emittance is determined by measuring of the beam radius for different focussing strengths of a solenoid preceding the wire scanner. The normalized transverse emittance has been determined to εn,x =(0.146 ± 0.037) mm mrad and εn,y =(0.197 ± 0.089) mm mrad, respectively. Time Structure The produced polarized electron beam needs to be modulated with the frequency of the S-DALINAS’s superconducting cavities of 3 GHz for cw operation. This is achieved by modulating a laser diode [8]. The time structure was verified for the laser beam
Page 1 and 2: Workshop on Polari
Page 3 and 4: Surface Analysis of Damaged Superla
Page 5: High Brightness and High Polarizati
Page 9 and 10: To be independent from possible ins
Page 11 and 12: vacuum gauge (AxTRAN X-11,ULVAC). B
Page 13 and 14: In order to research QE degradation
Page 15 and 16: Polarized Photocathode R&D for Futu
Page 17 and 18: charge limitation can be measured.
Page 19 and 20: SUMMARY AND PLANS It is challenging
Page 21 and 22: The most difficult task is to achie
Page 23 and 24: The run with a small laser spot cen
Page 25 and 26: Hydrogen Cleaning of Superlattice P
Page 27 and 28: HABS Prep Load UHV Vessel Ion Pump
Page 29 and 30: FIGURE 4. Comparison of results ach
Page 31 and 32: Heidelberg photoelectron target and
Page 33 and 34: However, it is emphasized here that
Page 35 and 36: Atomic Hydrogen Treatment Atomic hy
Page 37 and 38: Rydberg binding energy. In many cas
Page 39 and 40: the ring dispersion and from fluctu
Page 41 and 42: The valence band splitting ∆Ehh-l
Page 43 and 44: will be achieved by taking the last
Page 45 and 46: A Study of the Activated GaAs Surfa
Page 47 and 48: diffraction (LEED) and auger electr
Page 49 and 50: FIGURE 4. LEED pattern of the GaAs
Page 51 and 52: HIGH POLARIZATION PHOTOEMITTER IMMU
Page 53 and 54: QE (%) 10 9 8 7 6 5 4 3 2 1 650 Cs
Page 55 and 56: Superlattice Photocathode Damage An
Page 57 and 58:
and reactivated between February 11
Page 59 and 60:
Discussion of SIMS data and Compari
Page 61 and 62:
MBE Growth of Graded Structures for
Page 63 and 64:
conduction miniband is higher that
Page 65 and 66:
GRADED ALUMINUM GALLIUM ARSENIDE SU
Page 67 and 68:
Three wafers were grown with differ
Page 69 and 70:
FIGURE 10. Polarization and QE as a
Page 71 and 72:
PHOTOCATHODE WITH NEA SURFACE USING
Page 73 and 74:
FIGURE 2. Dependence of DOS on exci
Page 75 and 76:
High Brightness and high polarizati
Page 77 and 78:
Laser Substrate GaP 355 μm Zoom Bu
Page 79 and 80:
process of NEA-PC with SL layers, o
Page 81 and 82:
FIGURE 1. (a) Band-graded photocath
Page 83 and 84:
Left (a): Homogeneous (HM) layer Ri
Page 85 and 86:
K2CsSb Cathode Development John Sme
Page 87 and 88:
for the potassium deposition. 40nm
Page 89 and 90:
ias of 500V, with 60µA of emitted
Page 91 and 92:
analyzing chamber are used for samp
Page 93 and 94:
spectrum of the film was observed a
Page 95 and 96:
Demo Free Electron Laser (FEL) [1]
Page 97 and 98:
hours, or if the emitter returns at
Page 99 and 100:
neon or argon would have helped pro
Page 101 and 102:
for emittance compensation solenoid
Page 103 and 104:
If one can make electrodes that do
Page 105 and 106:
The last important parameter is cat
Page 107 and 108:
Status of the ALICE Energy Recovery
Page 109 and 110:
TABLE 1. Booster & main linac gradi
Page 111 and 112:
• The beam was fully-characterise
Page 113 and 114:
photocathode. This limitation means
Page 115 and 116:
whilst focusing the heat onto the p
Page 117 and 118:
Development of an electron gun for
Page 119 and 120:
FIGURE 2. Preparation, loading, and
Page 121 and 122:
may help to avoid electric field co
Page 123 and 124:
from its neighbors. The core-to-win
Page 125 and 126:
series connection and the output cu
Page 127 and 128:
Low Emittance Electron Gun for XFEL
Page 129 and 130:
FIGURE 3. Copper cathode and corres
Page 131 and 132:
current in the secondary which oppo
Page 133 and 134:
Equation (2) shows that the effect
Page 135 and 136:
Generally, the equation for the rad
Page 137 and 138:
High-Fidelity RF Gun Simulations wi
Page 139 and 140:
Causal Moving Window The methods us
Page 141 and 142:
(a) y / mm y / mm Transverse Distri
Page 143 and 144:
studies like long term studies of p
Page 145 and 146:
ehavior of the curves is independen
Page 147 and 148:
In Fig. 4 the curve shows an ASTRA
Page 149 and 150:
TABLE 1. RF cavity parameters calcu
Page 151 and 152:
PASSBAND AND ON-AXIS FIELD DISTRIBU
Page 153 and 154:
If the frequency shift on crest is
Page 155 and 156:
In order to increase the quality fa
Page 157 and 158:
THE EXPERIMENT The experimental set
Page 159 and 160:
FIRST COOL-DOWN In the first cool-d
Page 161 and 162:
Non Evaporable Getter (NEG) Pumps:
Page 163 and 164:
Examples of Applications NEG pumps
Page 165 and 166:
isotherms in a controlled and repro
Page 167 and 168:
chemical gettering that results whe
Page 169 and 170:
inside the photogun remains very go
Page 171 and 172:
High Brightness and High Polarizati
Page 173 and 174:
focusing lens is mounted on a trans
Page 175 and 176:
of electron polarization obtained b
Page 177 and 178:
FIGURE 7. Reduced brightness depend
Page 179 and 180:
FIGURE 1. Mott polarimeter with two
Page 181 and 182:
� ��
Page 183 and 184:
Compton Polarimetry at ELSA Wolfgan
Page 185 and 186:
In order to be detected, the Compto
Page 187 and 188:
monitored after the interaction by
Page 189 and 190:
where n + and n - are the counting
Page 191 and 192:
Our test cavity (Figure 3.) consist
Page 193 and 194:
Polarimetry at the Superconducting
Page 195 and 196:
30-130 MEV MØLLER POLARIMETER A 30
Page 197 and 198:
Benchmark studies among own and com
Page 199 and 200:
d2z = ds2 d2x = ds2 eQ eQ 4πε0 m0
Page 201 and 202:
ments of his tracing cord developin
Page 203 and 204:
all requires a slot in the side for
Page 205 and 206:
simulations in GPT show that these
Page 207 and 208:
Polarized Positrons at Jefferson La
Page 209 and 210:
GEANT4 [11]. Using Stokes parameter
Page 211 and 212:
Ultimately, the shower of particles
Page 213 and 214:
It was gratifying to hear about the
Page 215 and 216:
gun/photocathode, and likely repres
Page 217 and 218:
induced emittance growth, especiall
Page 219 and 220:
PESP Workshop Prog
Page 221 and 222:
PESP Posters Posters (17 total) •
Page 223 and 224:
Clendenin, James SLAC National Acce
Page 225 and 226:
McCarter, James Jefferson Lab 12000
Page 227 and 228:
Surles-Law, Ken Jefferson Lab 12050
show all

Workshop on Polarized Electron Sources and Polarimeters

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?