Presentation on theme: "Source Outlook High polarization strained-layer photocathodes were activated in both electron guns during the summer shutdown, with usual QE (0.2% at 850."— Presentation transcript:
Source Outlook High polarization strained-layer photocathodes were activated in both electron guns during the summer shutdown, with usual QE (0.2% at 850 nm). We have been running during the Fall months using PGun2 with beam polarization between 75-80%. We will re- measure the QE from PGun3 prior to the holiday shutdown and may start with PGun3 in January. The 499 MHz Ti:Sapphire laser for HAPPEx2 is due at the end of January. As with the G0 laser, once it is delivered we will test it in the lab before tunnel installation.
Plans for next year… We would like to install the Ti:Sap laser during the February/March shutdown. Hall C has agreed to use the laser for a 100 A un-polarized beam experiment (E01-002), which we could do at either a low- or high- polarization laser wavelength. Alternatively, we could install the HAPPEx2 laser for the GDH experiment, however, with limited opportunity at high current.
Experience with the G0 Ti:Sapphire laser Ti:Sapphire lasers requires more care and maintenance than the diode lasers. Typically, once per week the laser requires either cleaning or re-alignment. Otherwise, it has performed very well. The 499 MHz HAPPEx2 laser should be easier to maintain simply because of the shorter cavity length (alignment sensitivity and mirror surfaces are both reduced). The G0 laser intensity noise at 30 Hz can be as large at ppm and as small as ppm. We think this is alignment dependent and we are presently investigating this by implementing a computer readback of the laser noise from its controller. This readback is included in the HAPPEx2 laser controller.
Parity Quality Feedback An intensity device (Pockels cell attenuator) and position device (piezoelectric mirror) are located in the Hall A laser path. Devices common to all of the users are still available (polarization Pockels cell, insertable half-waveplate, rotatable half-waveplate). The hardware and software controls for these devices via EPICS are ready for the spin experiments and for testing starting in G0 continues through early February so parity testing with the common devices needs to be coordinated between the users. We plan to use the parity lock server for feedback for Spin Duality and GDH. Hall A parity can evaluate its performance. If it is shown to be unsatisfactory we can work toward direct hardware control of the parity devices from Hall A.
Parity Feedback Status The parity feedback devices were qualified for G0 in September. The intensity and position noise at 30 Hz were first measured. Next, the rotatable half-waveplate was aligned without any feedback. At the optimal orientation the HC asymmetries near the source were measured to be < 250 ppm for intensity and < 200 nm for transverse position.
For HC intensity control we can employ a double-feedback approach; one device which provides rapid and small corrections (5 min & < 100 ppm) and another device which provides a slower, drift correction (shifts & ~500 ppm). Intensity Characterization
We want to take advantage of adiabatic position damping from the source to end-stations. We hope to meet G0 and HAPPEx2 HC position asymmetry specs without position feedback. However, we have installed an independent PZT mirror in the Hall A laser path. We measured the correlated intensity modulation to be 50 ppm/V near the source and 250 ppm/V after the chopper, resulting from aperture interception. Position Characterization
Meeting G0 specs has been tough: poor transmission at the G0 repetition rate no adiabatic damping irreproducible calibration results (machine vs. laser ?) We have added a G0 pick-off quadrant photodiode to compare the laser and electron beams for HC intensity, position, and noise. During December, with Hall A off, well gain much more data at the injector, and now at the laser table, to decouple the source from the accelerator for easier diagnosis. Keep in mind, running 100 A, 499 MHz beam will ease many of the beam transport issues compared to that of 40 A, 31 MHz beam. Continued parity testing